X Session Management Library

X Consortium Standard

Ralph Mor

X Consortium

X Version 11, Release 7.7

Version 1.0

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Table of Contents

1. Overview of Session Management
2. The Session Management Library
3. Understanding SMlib's Dependence on ICE
4. Header Files and Library Name
5. Session Management Client (Smc) Functions

    Connecting to the Session Manager

        The Save Yourself Callback
        The Die Callback
        The Save Complete Callback
        The Shutdown Cancelled Callback

    Closing the Connection
    Modifying Callbacks
    Setting, Deleting, and Retrieving Session Management Properties
    Interacting With the User
    Requesting a Save Yourself
    Requesting a Save Yourself Phase 2
    Completing a Save Yourself
    Using Smc Informational Functions
    Error Handling

6. Session Management Server (Sms) Functions

    Initializing the Library

        The Register Client Callback
        The Interact Request Callback
        The Interact Done Callback
        The Save Yourself Request Callback
        The Save Yourself Phase 2 Request Callback
        The Save Yourself Done Callback
        The Connection Closed Callback
        The Set Properties Callback
        The Delete Properties Callback
        The Get Properties Callback

    Registering the Client
    Sending a Save Yourself Message
    Sending a Save Yourself Phase 2 Message
    Sending an Interact Message
    Sending a Save Complete Message
    Sending a Die Message
    Cancelling a Shutdown
    Returning Properties
    Pinging a Client
    Cleaning Up After a Client Disconnects
    Using Sms Informational Functions
    Error Handling

7. Session Management Properties
8. Freeing Data
9. Authentication of Clients
10. Working in a Multi-Threaded Environment
11. Acknowledgements

Chapter 1. Overview of Session Management

The purpose of the X Session Management Protocol (XSMP) is to provide a uniform
mechanism for users to save and restore their sessions. A session is a group of
clients, each of which has a particular state. The session is controlled by a
network service called the session manager. The session manager issues commands
to its clients on behalf of the user. These commands may cause clients to save
their state or to terminate. It is expected that the client will save its state
in such a way that the client can be restarted at a later time and resume its
operation as if it had never been terminated. A client's state might include
information about the file currently being edited, the current position of the
insertion point within the file, or the start of an uncommitted transaction.
The means by which clients are restarted is unspecified by this protocol.

For purposes of this protocol, a client of the session manager is defined as a
connection to the session manager. A client is typically, though not
necessarily, a process running an application program connected to an X
display. However, a client may be connected to more than one X display or not
be connected to any X displays at all.

Chapter 2. The Session Management Library

The Session Management Library (SMlib) is a low-level "C" language interface to
XSMP. It is expected that higher level toolkits, such as Xt, will hide many of
the details of session management from clients. Higher level toolkits might
also be developed for session managers to use, but no such effort is currently
under way.

SMlib has two parts to it:

  • One set of functions for clients that want to be part of a session

  • One set of functions for session managers to call

Some applications will use both sets of functions and act as nested session
managers. That is, they will be both a session manager and a client of another
session. An example is a mail program that could start a text editor for
editing the text of a mail message. The mail program is part of a regular
session and, at the same time, is also acting as a session manager to the
editor.

Clients initialize by connecting to the session manager and obtaining a
client-ID that uniquely identifies them in the session. The session manager
maintains a list of properties for each client in the session. These properties
describe the client's environment and, most importantly, describe how the
client can be restarted (via an SmRestartCommand). Clients are expected to save
their state in such a way as to allow multiple instantiations of themselves to
be managed independently. For example, clients may use their client-ID as part
of a filename in which to store the state for a particular instantiation. The
client-ID should be saved as part of the SmRestartCommand so that the client
will retain the same ID after it is restarted.

Once the client initializes itself with the session manager, it must be ready
to respond to messages from the session manager. For example, it might be asked
to save its state or to terminate. In the case of a shutdown, the session
manager might give each client a chance to interact with the user and cancel
the shutdown.

Chapter 3. Understanding SMlib's Dependence on ICE

The X Session Management Protocol is layered on top of the Inter-Client
Exchange (ICE) Protocol. The ICE protocol is designed to multiplex several
protocols over a single connection. As a result, working with SMlib requires a
little knowledge of how the ICE library works.

The ICE library utilizes callbacks to process messages. When a client detects
that there is data to read on an ICE connection, it should call the
IceProcessMessages function. IceProcessMessages will read the message header
and look at the major opcode in order to determine which protocol the message
was intended for. The appropriate protocol library will then be triggered to
unpack the message and hand it off to the client via a callback.

The main point to be aware of is that an application using SMlib must have some
code that detects when there is data to read on an ICE connection. This can be
done via a select call on the file descriptor for the ICE connection, but more
typically, XtAppAddInput will be used to register a callback that will invoke
IceProcessMessages each time there is data to read on the ICE connection.

To further complicate things, knowing which file descriptors to call select on
requires an understanding of how ICE connections are created. On the client
side, a call must be made to SmcOpenConnection in order to open a connection
with a session manager. SmcOpenConnection will internally makea call into
IceOpenConnection which will, in turn, determine if an ICE connection already
exists between the client and session manager. Most likely, a connection will
not already exist and a new ICE connection will be created. The main point to
be aware of is that, on the client side, it is not obvious when ICE connections
get created or destroyed, because connections are shared when possible. To deal
with this, the ICE library lets the application register watch procedures that
will be invoked each time an ICE connection is opened or closed. These watch
procedures could be used to add or remove ICE file descriptors from the list of
descriptors to call select on.

On the session manager side, things work a bit differently. The session manager
has complete control over the creation of ICE connections. The session manager
has to first call IceListenForConnections in order to start listening for
connections from clients. Once a connection attempt is detected,
IceAcceptConnection must be called, and the session manager can simply add the
new ICE file descriptor to the list of descriptors to call select on.

For further information on the library functions related to ICE connections,
see the “Inter-Client Exchange Library” standard.

Chapter 4. Header Files and Library Name

Applications (both session managers and clients) should include the header file
<X11/SM/SMlib.h>. This header file defines all of the SMlib data structures and
function prototypes. SMlib.h includes the header file <X11/SM/SM.h>, which
defines all of the SMlib constants.

Because SMlib is dependent on ICE, applications should link against SMlib and
ICElib by using “-lSM -lICE”.

Chapter 5. Session Management Client (Smc) Functions

Table of Contents

Connecting to the Session Manager

    The Save Yourself Callback
    The Die Callback
    The Save Complete Callback
    The Shutdown Cancelled Callback

Closing the Connection
Modifying Callbacks
Setting, Deleting, and Retrieving Session Management Properties
Interacting With the User
Requesting a Save Yourself
Requesting a Save Yourself Phase 2
Completing a Save Yourself
Using Smc Informational Functions
Error Handling

This section discusses how Session Management clients:

  • Connect to the Session Manager

  • Close the connection

  • Modify callbacks

  • Set, delete, and retrieve Session Manager properties

  • Interact with the user

  • Request a “Save Yourself”

  • Request a “Save Yourself Phase 2”

  • Complete a “Save Yourself”

  • Use Smc informational functions

  • Handle Errors

Connecting to the Session Manager

To open a connection with a session manager, use SmcOpenConnection

SmcConn SmcOpenConnection(char *network_ids_list, SmPointer context, int
xsmp_major_rev, int xsmp_minor_rev, unsigned long mask, SmcCallbacks
*callbacks, char *previous_id, char **client_id_ret, int error_length, char
*error_string_ret);

network_ids_list Specifies the network ID(s) of the session manager.

context          A pointer to an opaque object or NULL. Used to determine if an
                 ICE connection can be shared (see below).

xsmp_major_rev   The highest major version of the XSMP the application
                 supports.

xsmp_minor_rev   The highest minor version of the XSMP the application supports
                 (for the specified xsmp_major_rev).

mask             A mask indicating which callbacks to register.

callbacks        The callbacks to register. These callbacks are used to respond
                 to messages from the session manager.

previous_id      The client ID from the previous session.

client_id_ret    The client ID for the current session is returned.

error_length     Length of the error_string_ret argument passed in.

                 Returns a null-terminated error message, if any. The
error_string_ret error_string_ret argument points to user supplied memory. No
                 more than error_length bytes are used.

The network_ids_list argument is a null-terminated string containing a list of
network IDs for the session manager, separated by commas. If network_ids_list
is NULL, the value of the SESSION_MANAGER environment variable will be used.
Each network ID has the following format:

tcp/<hostname>:<portnumber>  or
decnet/<hostname>::<objname> or
local/<hostname>:<path>       

An attempt will be made to use the first network ID. If that fails, an attempt
will be made using the second network ID, and so on.

After the connection is established, SmcOpenConnection registers the client
with the session manager. If the client is being restarted from a previous
session, previous_id should contain a null terminated string representing the
client ID from the previous session. If the client is first joining the
session, previous_id should be set to NULL. If previous_id is specified but is
determined to be invalid by the session manager, SMlib will re-register the
client with previous_id set to NULL.

If SmcOpenConnection succeeds, it returns an opaque connection pointer of type
SmcConn and the client_id_ret argument contains the client ID to be used for
this session. The client_id_ret should be freed with a call to free when no
longer needed. On failure, SmcOpenConnection returns NULL, and the reason for
failure is returned in error_string_ret.

Note that SMlib uses the ICE protocol to establish a connection with the
session manager. If an ICE connection already exists between the client and
session manager, it might be possible for the same ICE connection to be used
for session management.

The context argument indicates how willing the client is to share the ICE
connection with other protocols. If context is NULL, then the caller is always
willing to share the connection. If context is not NULL, then the caller is not
willing to use a previously opened ICE connection that has a different non-NULL
context associated with it.

As previously discussed (section 3, “Understanding SMlib's Dependence on ICE”),
the client will have to keep track of when ICE connections are created or
destroyed (using IceAddConnectionWatch and IceRemoveConnectionWatch and will
have to call IceProcessMessages each time a select shows that there is data to
read on an ICE connection. For further information, see the “Inter-Client
Exchange Library” standard.

The callbacks argument contains a set of callbacks used to respond to session
manager events. The mask argument specifies which callbacks are set. All of the
callbacks specified in this version of SMlib are mandatory. The mask argument
is necessary in order to maintain backwards compatibility in future versions of
the library.

The following values may be ORed together to obtain a mask value:

SmcSaveYourselfProcMask
SmcDieProcMask
SmcSaveCompleteProcMask
SmcShutdownCancelledProcMask

For each callback, the client can register a pointer to client data. When SMlib
invokes the callback, it will pass the client data pointer.

typedef struct {

        struct {
                SmcSaveYourselfProc callback;
                SmPointer client_data;
        } save_yourself;

        struct {
                SmcDieProc callback;
                SmPointer client_data;
        } die;

        struct {
                SmcSaveCompleteProc callback;
                SmPointer client_data;
        } save_complete;

        struct {
                SmcShutdownCancelledProc callback;
                SmPointer client_data;
        } shutdown_cancelled;

} SmcCallbacks;

The Save Yourself Callback

The Save Yourself callback is of type SmcSaveYourselfProc

typedef void (*SaveYourselfProc)(SmcConn smc_conn, SmPointer client_data, int
save_type, Bool shutdown, int interact_style, Bool fast);

smc_conn       The session management connection object.

client_data    Client data specified when the callback was registered.

save_type      Specifies the type of information that should be saved.

shut_down      Specifies if a shutdown is taking place.

interact_style The type of interaction allowed with the user.

fast           if True, then client should save its state as quickly as
               possible.

The session manager sends a “Save Yourself” message to a client either to
checkpoint it or just before termination so that it can save its state. The
client responds with zero or more calls to SmcSetProperties to update the
properties indicating how to restart the client. When all the properties have
been set, the client calls SmcSaveYourselfDone

If interact_style is SmInteractStyleNone the client must not interact with the
user while saving state. If interact_style is SmInteractStyleErrors the client
may interact with the user only if an error condition arises. If interact_style
is SmInteractStyleAny then the client may interact with the user for any
purpose. Because only one client can interact with the user at a time, the
client must call SmcInteractRequest and wait for an “Interact” message from the
session manager. When the client is done interacting with the user, it calls
SmcInteractDone The client may only call SmcInteractRequest after it receives a
“Save Yourself” message and before it calls SmcSaveYourselfDone

If save_type is SmSaveLocal the client must update the properties to reflect
its current state. Specifically, it should save enough information to restore
the state as seen by the user of this client. It should not affect the state as
seen by other users. If save_type is SmSaveGlobal the user wants the client to
commit all of its data to permanent, globally accessible storage. If save_type
is SmSaveBoth the client should do both of these (it should first commit the
data to permanent storage before updating its properties).

Some examples are as follows:

  • If a word processor were sent a “Save Yourself” with a type of SmSaveLocal
    it could create a temporary file that included the current contents of the
    file, the location of the cursor, and other aspects of the current editing
    session. It would then update its SmRestartCommand property with enough
    information to find this temporary file.

  • If a word processor were sent a “Save Yourself” with a type of SmSaveGlobal
    it would simply save the currently edited file.

  • If a word processor were sent a “Save Yourself” with a type of SmSaveBoth
    it would first save the currently edited file. It would then create a
    temporary file with information such as the current position of the cursor
    and what file is being edited. Finally, it would update its 
    SmRestartCommand property with enough information to find the temporary
    file.

The shutdown argument specifies whether the system is being shut down. The
interaction is different depending on whether or not shutdown is set. If not
shutting down, the client should save its state and wait for a “Save Complete”
message. If shutting down, the client must save state and then prevent
interaction until it receives either a “Die” or a “Shutdown Cancelled.”

The fast argument specifies that the client should save its state as quickly as
possible. For example, if the session manager knows that power is about to
fail, it would set fast to True.

The Die Callback

The Die callback is of type SmcDieProc

typedef void (*SmcDieProc)(SmcConn smc_conn, SmPointer client_data);

smc_conn    The session management connection object.

client_data Client data specified when the callback was registered.

The session manager sends a “Die” message to a client when it wants it to die.
The client should respond by calling SmcCloseConnection. A session manager that
behaves properly will send a “Save Yourself” message before the “Die” message.

The Save Complete Callback

The Save Complete callback is of type SmcSaveCompleteProc

typedef void (*SmcSaveCompleteProc)(SmcConn smc_conn, SmPointer client_data);

smc_conn    The session management connection object.

client_data Client data specified when the callback was registered.

The Shutdown Cancelled Callback

The Shutdown Cancelled callback is of type SmcShutdownCancelledProc

typedef void (*SmcShutdownCancelledProc)(SmcConn smc_conn, SmPointer
client_data);

smc_conn    The session management connection object.

client_data Client data specified when the callback was registered.

The session manager sends a “Shutdown Cancelled” message when the user
cancelled the shutdown during an interaction (see section 5.5, “Interacting
With the User”). The client can now continue as if the shutdown had never
happened. If the client has not called SmcSaveYourselfDone yet, it can either
abort the save and then call SmcSaveYourselfDone with the success argument set
to False or it can continue with the save and then call SmcSaveYourselfDone
with the success argument set to reflect the outcome of the save.

Closing the Connection

To close a connection with a session manager, use SmcCloseConnection

SmcCloseStatus SmcCloseConnection(SmcConn smc_conn, int count, char
**reason_msgs);

smc_conn    The session management connection object.

count       The number of reasons for closing the connection.

reason_msgs The reasons for closing the connection.

The reason_msgs argument will most likely be NULL if resignation is expected by
the client. Otherwise, it contains a list of null-terminated Compound Text
strings representing the reason for termination. The session manager should
display these reason messages to the user.

Note that SMlib used the ICE protocol to establish a connection with the
session manager, and various protocols other than session management may be
active on the ICE connection. When SmcCloseConnection is called, the ICE
connection will be closed only if all protocols have been shutdown on the
connection. Check the ICElib standard for IceAddConnectionWatch and
IceRemoveConnectionWatch to learn how to set up a callback to be invoked each
time an ICE connection is opened or closed. Typically this callback adds/
removes the ICE file descriptor from the list of active descriptors to call
select on (or calls XtAppAddInput or XtRemoveInput).

SmcCloseConnection returns one of the following values:

  • SmcClosedNow - the ICE connection was closed at this time, the watch
    procedures were invoked, and the connection was freed.

  • SmcClosedASAP - an IO error had occurred on the connection, but
    SmcCloseConnection is being called within a nested IceProcessMessages The
    watch procedures have been invoked at this time, but the connection will be
    freed as soon as possible (when the nesting level reaches zero and
    IceProcessMessages returns a status of IceProcessMessagesConnectionClosed

  • SmcConnectionInUse - the connection was not closed at this time, because it
    is being used by other active protocols.

Modifying Callbacks

To modify callbacks set up in SmcOpenConnection use SmcModifyCallbacks

void SmcModifyCallbacks(SmcConn smc_conn, unsigned long mask, SmcCallbacks
*callbacks);

smc_conn  The session management connection object.

mask      A mask indicating which callbacks to modify.

callbacks The new callbacks.

When specifying a value for the mask argument, the following values may be ORed
together:

SmcSaveYourselfProcMask
SmcDieProcMask
SmcSaveCompleteProcMask
SmcShutdownCancelledProcMask

Setting, Deleting, and Retrieving Session Management Properties

To set session management properties for this client, use SmcSetProperties

void SmcSetProperties(SmcConn smc_conn, int num_props, SmProp **props);

smc_conn  The session management connection object.

num_props The number of properties.

props     The list of properties to set.

The properties are specified as an array of property pointers. Previously set
property values may be over-written using the SmcSetProperties function. Note
that the session manager is not expected to restore property values when the
session is restarted. Because of this, clients should not try to use the
session manager as a database for storing application specific state.

For a description of session management properties and the SmProp structure,
see section 7, “Session Management Properties.”

To delete properties previously set by the client, use SmcDeleteProperties

void SmcDeleteProperties(SmcConn smc_conn, int num_props, char **prop_names);

smc_conn   The session management connection object.

num_props  The number of properties.

prop_names The list of properties to set.

To get properties previously stored by the client, use SmcGetProperties

Status SmcGetProperties(SmcConn smc_conn, SmcPropReplyProc prop_reply_proc,
SmPointer client_data);

smc_conn        The session management connection object.

prop_reply_proc The callback to be invoked when the properties reply comes
                back.

client_data     This pointer to client data will be passed to the
                SmcPropReplyProc callback.

The return value of SmcGetProperties is zero for failure and a positive value
for success.

Note that the library does not block until the properties reply comes back.
Rather, a callback of type SmcPropReplyProc is invoked when the data is ready.

typedef void (*SmcPropReplyProc)(SmcConn smc_conn, SmPointer client_data, int
num_props, SmProp **props);

smc_conn    The session management connection object.

client_data This pointer to client data will be passed to the SmcPropReplyProc
            callback.

num_props   The number of properties returned.

props       The list of properties returned.

To free each property, use SmFreeProperty (see section 8, “Freeing Data”). To
free the actual array of pointers, use free

Interacting With the User

After receiving a “Save Yourself” message with an interact_style of
SmInteractStyleErrors or SmInteractStyleAny the client may choose to interact
with the user. Because only one client can interact with the user at a time,
the client must call SmcInteractRequest and wait for an “Interact” message from
the session manager.

Status SmcInteractRequest(SmcConn smc_conn, int dialog_type, SmcInteractProc
interact_proc, SmPointer client_data);

smc_conn      The session management connection object.

dialog_type   The type of dialog the client wishes to present to the user.

interact_proc The callback to be invoked when the “Interact” message arrives
              from the session manager.

client_data   This pointer to client data will be passed to the SmcInteractProc
              callback when the “Interact” message arrives.

The return value of SmcInteractRequest is zero for failure and a positive value
for success.

The dialog_type argument specifies either SmDialogError indicating that the
client wants to start an error dialog, or SmDialogNormal meaning that the
client wishes to start a nonerror dialog.

Note that if a shutdown is in progress, the user may have the option of
cancelling the shutdown. If the shutdown is cancelled, the clients that have
not interacted yet with the user will receive a “Shutdown Cancelled” message
instead of the “Interact” message.

The SmcInteractProc callback will be invoked when the “Interact” message
arrives from the session manager.

typedef void (*SmcInteractProc)(SmcConn smc_conn, SmPointer client_data);

smc_conn    The session management connection object.

client_data Client data specified when the callback was registered.

After interacting with the user (in response to an “Interact” message), you
should call SmcInteractDone

void SmcInteractDone(SmcConn smc_conn, Bool cancel_shutdown);

smc_conn        The session management connection object.

cancel_shutdown If True, indicates that the user requests that the entire
                shutdown be cancelled.

The cancel_shutdown argument may only be True if the corresponding “Save
Yourself” specified True for shutdown and SmInteractStyleErrors or
SmInteractStyleAny for the interact_style.

Requesting a Save Yourself

To request a checkpoint from the session manager, use SmcRequestSaveYourself

void SmcRequestSaveYourself(SmcConn smc_conn, int save_type, Bool shutdown, int
interact_style, Bool fast, Bool global);

smc_conn       The session management connection object.

save_type      Specifies the type of information that should be saved.

shutdown       Specifies if a shutdown is taking place.

interact_style The type of interaction allowed with the user.

fast           If True the client should save its state as quickly as possible.

global         Controls who gets the “Save Yourself.”

The save_type, shutdown, interact_style, and fast arguments are discussed in
more detail in section 5.1.1, “The Save Yourself Callback.”

If global is set to True then the resulting “Save Yourself” should be sent to
all clients in the session. For example, a vendor of a Uninterruptible Power
Supply (UPS) might include a Session Management client that would monitor the
status of the UPS and generate a fast shutdown if the power is about to be
lost.

If global is set to False then the “Save Yourself” should only be sent to the
client that requested it.

Requesting a Save Yourself Phase 2

In response to a “Save Yourself”, the client may request to be informed when
all the other clients are quiescent so that it can save their state. To do so,
use SmcRequestSaveYourselfPhase2

Status SmcRequestSaveYourselfPhase2(SmcConn smc_conn, SmcSaveYourselfPhase2Proc
save_yourself_phase2_proc, SmPointer client_data);

smc_conn              The session management connection object.

save_type_phase2_proc The callback to be invoked when the “Save Yourself Phase
                      2” message arrives from the session manager.

                      This pointer to client data will be passed to the
client_data           SmcSaveYourselfPhase2Proc callback when the “Save
                      Yourself Phase 2” message arrives.

The return value of SmcRequestSaveYourselfPhase2 is zero for failure and a
positive value for success.

This request is needed by clients that manage other clients (for example,
window managers, workspace managers, and so on). The manager must make sure
that all of the clients that are being managed are in an idle state so that
their state can be saved.

Completing a Save Yourself

After saving state in response to a “Save Yourself” message, you should call
SmcSaveYourselfDone

void SmcSaveYourselfDone(SmcConn smc_conn, Bool success);

smc_conn The session management connection object.

success  If True the “Save Yourself” operation was completed successfully.

Before calling SmcSaveYourselfDone the client must have set each required
property at least once since the client registered with the session manager.

Using Smc Informational Functions

int SmcProtocolVersion(SmcConn smc_conn);

SmcProtocolVersion returns the major version of the session management protocol
associated with this session.

int SmcProtocolRevision(SmcConn smc_conn);

SmcProtocolRevision returns the minor version of the session management
protocol associated with this session.

char *SmcVendor(SmcConn smc_conn);

SmcVendor returns a string that provides some identification of the owner of
the session manager. The string should be freed with a call to free

char *SmcRelease(SmcConn smc_conn);

SmcRelease returns a string that provides the release number of the session
manager. The string should be freed with a call to free

char *SmcClientID(SmcConn smc_conn);

SmcClientID returns a null-terminated string for the client ID associated with
this connection. This information was also returned in SmcOpenConnection (it is
provided here for convenience). Call free on this pointer when the client ID is
no longer needed.

IceConn SmcGetIceConnection(SmcConn smc_conn);

SmcGetIceConnection returns the ICE connection object associated with this
session management connection object. The ICE connection object can be used to
get some additional information about the connection. Some of the more useful
functions which can be used on the IceConn are IceConnectionNumber,
IceConnectionString, IceLastSentSequenceNumber, IceLastReceivedSequenceNumber,
and IcePing. For further information, see the “Inter-Client Exchange Library”
standard.

Error Handling

If the client receives an unexpected protocol error from the session manager,
an error handler is invoked by SMlib. A default error handler exists that
simply prints the error message to stderr and exits if the severity of the
error is fatal. The client can change this error handler by calling the
SmcSetErrorHandler function.

SmcErrorHandler SmcSetErrorHandler(SmcErrorHandler handler);

The error handler. You should pass NULL to restore the default handler.

SmcSetErrorHandler returns the previous error handler.

The SmcErrorHandler has the following type:

typedef void (*SmcErrorHandler)(SmcConn smc_conn, Bool swap, int
offending_minor_opcode, unsigned long offending_sequence_num, int error_class,
int severity, IcePointer values);

smc_conn               The session management connection object.

swap                   A flag that indicates if the specified values need byte
                       swapping.

offending_minor_opcode The minor opcode of the offending message.

offending_sequence_num The sequence number of the offending message.

error_class            The error class of the offending message.

severity               IceCanContinue, IceFatalToProtocol, or
                       IceFatalToConnection

values                 Any additional error values specific to the minor opcode
                       and class.

Note that this error handler is invoked for protocol related errors. To install
an error handler to be invoked when an IO error occurs, use
IceSetIOErrorHandler For further information, see the “Inter-Client Exchange
Library” standard.

Chapter 6. Session Management Server (Sms) Functions

Table of Contents

Initializing the Library

    The Register Client Callback
    The Interact Request Callback
    The Interact Done Callback
    The Save Yourself Request Callback
    The Save Yourself Phase 2 Request Callback
    The Save Yourself Done Callback
    The Connection Closed Callback
    The Set Properties Callback
    The Delete Properties Callback
    The Get Properties Callback

Registering the Client
Sending a Save Yourself Message
Sending a Save Yourself Phase 2 Message
Sending an Interact Message
Sending a Save Complete Message
Sending a Die Message
Cancelling a Shutdown
Returning Properties
Pinging a Client
Cleaning Up After a Client Disconnects
Using Sms Informational Functions
Error Handling

This section discusses how Session Management servers:

  • Initialize the library

  • Register the client

  • Send a “Save Yourself” message

  • Send a “Save Yourself Phase 2” message

  • Send an “Interact” message

  • Send a “Save Complete” message

  • Send a “Die” message

  • Cancel a shutdown

  • Return properties

  • Ping a client

  • Clean up after a client disconnects

  • Use Sms informational functions

  • Handle errors

Initializing the Library

SmsInitialize is the first SMlib function that should be called by a session
manager. It provides information about the session manager and registers a
callback that will be invoked each time a new client connects to the session
manager.

Status SmsInitialize(const char *vendor, const char *release, SmsNewClientProc
new_client_proc, SmPointer manager_data, IceHostBasedAuthProc
host_based_auth_proc, int error_length, char *error_string_ret);

vendor               A string specifying the session manager vendor.

release              A string specifying the session manager release number.

new_client_proc      Callback to be invoked each time a new client connects to
                     the session manager.

manager_data         When the SmsNewClientProc callback is invoked, this
                     pointer to manager data will be passed.

host_based_auth_proc Host based authentication callback.

error_length         Length of the error_string_ret argument passed in.

                     Returns a null-terminated error message, if any. The
error_string_ret     error_string_ret points to user supplied memory. No more
                     than error_length bytes are used.

After the SmsInitialize function is called, the session manager should call the
IceListenForConnections function to listen for new connections. Afterwards,
each time a client connects, the session manager should call
IceAcceptConnection

See section 9, “Authentication of Clients,” for more details on authentication
(including host based authentication). Also see the “Inter-Client Exchange
Library” standard for further details on listening for and accepting ICE
connections.

Each time a new client connects to the session manager, the SmsNewClientProc
callback is invoked. The session manager obtains a new opaque connection object
that it should use for all future interaction with the client. At this time,
the session manager must also register a set of callbacks to respond to the
different messages that the client might send.

typedef Status (*SmsNewClientProc)(SmsConn sms_conn, SmPointer manager_data,
unsigned long *mask_ret, SmsCallbacks *callbacks_ret, char
**failure_reason_ret);

sms_conn           A new opaque connection object.

manager_data       Manager data specified when the callback was registered.

mask_ret           On return, indicates which callbacks were set by the session
                   manager.

callbacks_ret      On return, contains the callbacks registered by the session
                   manager.

failure_reason_ret Failure reason returned.

If a failure occurs, the SmsNewClientProc should return a zero status as well
as allocate and return a failure reason string in failure_reason_ret. SMlib
will be responsible for freeing this memory.

The session manager must register a set of callbacks to respond to client
events. The mask_ret argument specifies which callbacks are set. All of the
callbacks specified in this version of SMlib are mandatory. The mask_ret
argument is necessary in order to maintain backwards compatibility in future
versions of the library.

The following values may be ORed together to obtain a mask value:

SmsRegisterClientProcMask
SmsInteractRequestProcMask
SmsInteractDoneProcMask
SmsSaveYourselfRequestProcMask
SmsSaveYourselfP2RequestProcMask
SmsSaveYourselfDoneProcMask
SmsCloseConnectionProcMask
SmsSetPropertiesProcMask
SmsDeletePropertiesProcMask
SmsGetPropertiesProcMask

For each callback, the session manager can register a pointer to manager data
specific to that callback. This pointer will be passed to the callback when it
is invoked by SMlib.

typedef struct {
        struct {
                SmsRegisterClientProc callback;
                SmPointer manager_data;
        } register_client;

        struct {
                SmsInteractRequestProc callback;
                SmPointer manager_data;
        } interact_request;

        struct {
                SmsInteractDoneProc callback;
                SmPointer manager_data;
        } interact_done;

        struct {
                SmsSaveYourselfRequestProc callback;
                SmPointer manager_data;
        } save_yourself_request;

        struct {
                SmsSaveYourselfPhase2RequestProc callback;
                SmPointer manager_data;
        } save_yourself_phase2_request;

        struct {
                SmsSaveYourselfDoneProc callback;
                SmPointer manager_data;
        } save_yourself_done;

        struct {
                SmsCloseConnectionProc callback;
                SmPointer manager_data;
        } close_connection;

        struct {
                SmsSetPropertiesProc callback;
                SmPointer manager_data;
        } set_properties;

        struct {
                SmsDeletePropertiesProc callback;
                SmPointer manager_data;
        } delete_properties;

        struct {
                SmsGetPropertiesProc callback;
                SmPointer manager_data;
        } get_properties;

} SmsCallbacks;

The Register Client Callback

The Register Client callback is the first callback that will be invoked after
the client connects to the session manager. Its type is SmsRegisterClientProc

typedef Status (*SmsRegisterClientProc)(SmsConn sms_conn, SmPointer
manager_data, char *previous_id);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

previous_id  The client ID from the previous session.

Before any further interaction takes place with the client, the client must be
registered with the session manager.

If the client is being restarted from a previous session, previous_id will
contain a null-terminated string representing the client ID from the previous
session. Call free on the previous_id pointer when it is no longer needed. If
the client is first joining the session, previous_id will be NULL.

If previous_id is invalid, the session manager should not register the client
at this time. This callback should return a status of zero, which will cause an
error message to be sent to the client. The client should re-register with
previous_id set to NULL.

Otherwise, the session manager should register the client with a unique client
ID by calling the SmsRegisterClientReply function (to be discussed shortly),
and the SmsRegisterClientProc callback should return a status of one.

The Interact Request Callback

The Interact Request callback is of type SmsInteractRequestProc

typedef void (*SmsInteractRequestProc)(SmsConn sms_conn, SmPointer
manager_data, int dialog_type);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

dialog_type  The type of dialog the client wishes to present to the user.

When a client receives a “Save Yourself” message with an interact_style of
SmInteractStyleErrors or SmInteractStyleAny the client may choose to interact
with the user. Because only one client can interact with the user at a time,
the client must request to interact with the user. The session manager should
keep a queue of all clients wishing to interact. It should send an “Interact”
message to one client at a time and wait for an “Interact Done” message before
continuing with the next client.

The dialog_type argument specifies either SmDialogError indicating that the
client wants to start an error dialog, or SmDialogNormal meaning that the
client wishes to start a nonerror dialog.

If a shutdown is in progress, the user may have the option of cancelling the
shutdown. If the shutdown is cancelled (specified in the “Interact Done”
message), the session manager should send a “Shutdown Cancelled” message to
each client that requested to interact.

The Interact Done Callback

When the client is done interacting with the user, the SmsInteractDoneProc
callback will be invoked.

typedef void (*SmsInteractDoneProc)(SmsConn sms_conn, SmPointer manager_data,
Bool cancel_shutdown);

sms_conn        The session management connection object.

manager_data    Manager data specified when the callback was registered.

cancel_shutdown Specifies if the user requests that the entire shutdown be
                cancelled.

Note that the shutdown can be cancelled only if the corresponding “Save
Yourself” specified True for shutdown and SmInteractStyleErrors or
SmInteractStyleAny for the interact_style.

The Save Yourself Request Callback

The Save Yourself Request callback is of type SmsSaveYourselfRequestProc

typedef void (*SaveYourselfRequestProc)(SmsConn sms_conn, SmPointer
manager_data, int save_type, Bool shutdown, int interact_style, Bool fast, Bool
global);

sms_conn       The session management connection object.

manager_data   Manager data specified when the callback was registered.

save_type      Specifies the type of information that should be saved.

shutdown       Specifies if a shutdown is taking place.

interact_style The type of interaction allowed with the user.

fast           If True the client should save its state as quickly as possible.

global         Controls who gets the “Save Yourself.”

The Save Yourself Request prompts the session manager to initiate a checkpoint
or shutdown. For information on the save_type, shutdown, interact_style, and
fast arguments, see section 6.3, “Sending a Save Yourself Message.”

If global is set to True then the resulting “Save Yourself” should be sent to
all applications. If global is set to False then the “Save Yourself” should
only be sent to the client that requested it.

The Save Yourself Phase 2 Request Callback

The Save Yourself Phase 2 Request callback is of type
SmsSaveYourselfPhase2RequestProc

typedef void (*SmsSaveYourselfPhase2RequestProc)(SmsConn sms_conn, SmPointer
manager_data);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

This request is sent by clients that manage other clients (for example, window
managers, workspace managers, and so on). Such managers must make sure that all
of the clients that are being managed are in an idle state so that their state
can be saved.

The Save Yourself Done Callback

When the client is done saving its state in response to a “Save Yourself”
message, the SmsSaveYourselfDoneProc will be invoked.

typedef void (*SaveYourselfDoneProc)(SmsConn sms_conn, SmPointer manager_data,
Bool success);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

success      If True the Save Yourself operation was completed successfully.

Before the “Save Yourself Done” was sent, the client must have set each
required property at least once since it registered with the session manager.

The Connection Closed Callback

If the client properly terminates (that is, it calls SmcCloseConnection, the
SmsCloseConnectionProc callback is invoked.

typedef void (*SmsCloseConnectionProc)(SmsConn sms_conn, SmPointer
manager_data, int count, char **reason_msgs);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

count        The number of reason messages.

reason_msgs  The reasons for closing the connection.

The reason_msgs argument will most likely be NULL and the count argument zero
(0) if resignation is expected by the user. Otherwise, it contains a list of
null-terminated Compound Text strings representing the reason for termination.
The session manager should display these reason messages to the user.

Call SmFreeReasons to free the reason messages. For further information, see
section 8, “Freeing Data”

The Set Properties Callback

When the client sets session management properties, the SmsSetPropertiesProc
callback will be invoked.

typedef void (*SmsSetPropertiesProc)(SmsConn sms_conn, SmPointer manager_data,
int num_props, SmProp **props);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

num_props    The number of properties.

props        The list of properties to set.

The properties are specified as an array of property pointers. For a
description of session management properties and the SmProp structure, see
section 7, “Session Management Properties.”

Previously set property values may be over-written. Some properties have
predefined semantics. The session manager is required to store nonpredefined
properties.

To free each property, use SmFreeProperty. For further information, see section
8, “Freeing Data” You should free the actual array of pointers with a call to
free

The Delete Properties Callback

When the client deletes session management properties, the
SmsDeletePropertiesProc callback will be invoked.

typedef void (*SmsDeletePropertiesProc)(SmsConn sms_conn, SmPointer
manager_data, int num_props, char **prop_names);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

num_props    The number of properties.

prop_names   The list of properties to delete.

The properties are specified as an array of strings. For a description of
session management properties and the SmProp structure, see section 7, “Session
Management Properties.”

The Get Properties Callback

The SmsGetPropertiesProc callback is invoked when the client wants to retrieve
properties it set.

typedef void (*SmsGetPropertiesProc)(SmsConn sms_conn, SmPointer manager_data);

sms_conn     The session management connection object.

manager_data Manager data specified when the callback was registered.

The session manager should respond by calling SmsReturnProperties. All of the
properties set for this client should be returned.

Registering the Client

To register a client (in response to a SmsRegisterClientProc callback), use
SmsRegisterClientReply.

Status SmsRegisterClientReply(SmsConn sms_conn, char *client_id);

sms_conn  The session management connection object.

client_id A null-terminated string representing a unique client ID.

The return value of SmsRegisterClientReply is zero for failure and a positive
value for success. Failure will occur if SMlib can not allocate memory to hold
a copy of the client ID for it's own internal needs.

If a non-NULL previous_id was specified when the client registered itself,
client_id should be identical to previous_id.

Otherwise, client_id should be a unique ID freshly generated by the session
manager. In addition, the session manager should send a “Save Yourself” message
with type = Local, shutdown = False, interact-style = None, and fast = False
immediately after registering the client.

Note that once a client ID has been assigned to the client, the client keeps
this ID indefinitely. If the client is terminated and restarted, it will be
reassigned the same ID. It is desirable to be able to pass client IDs around
from machine to machine, from user to user, and from session manager to session
manager, while retaining the identity of the client. This, combined with the
indefinite persistence of client IDs, means that client IDs need to be globally
unique.

You should call the SmsGenerateClientID function to generate a globally unique
client ID.

char *SmsGenerateClientID(SmsConn sms_conn);

sms_conn The session management connection object.

NULL will be returned if the ID could not be generated. Otherwise, the return
value of the function is the client ID. It should be freed with a call to free
when no longer needed.

Sending a Save Yourself Message

To send a “Save Yourself” to a client, use SmsSaveYourself.

void SmsSaveYourself(SmsConn sms_conn, int save_type, Bool shutdown, int
interact_style, Bool fast);

sms_conn       The session management connection object.

save_type      Specifies the type of information that should be saved.

shutdown       Specifies if a shutdown is taking place.

interact_style The type of interaction allowed with the user.

fast           If True the client should save its state as quickly as possible.

The session manager sends a “Save Yourself” message to a client either to
checkpoint it or just before termination so that it can save its state. The
client responds with zero or more “Set Properties” messages to update the
properties indicating how to restart the client. When all the properties have
been set, the client sends a “Save Yourself Done” message.

If interact_style is SmInteractStyleNone the client must not interact with the
user while saving state. If interact_style is SmInteractStyleErrors the client
may interact with the user only if an error condition arises. If interact_style
is SmInteractStyleAny then the client may interact with the user for any
purpose. The client must send an “Interact Request” message and wait for an
“Interact” message from the session manager before it can interact with the
user. When the client is done interacting with the user, it should send an
“Interact Done” message. The “Interact Request” message can be sent any time
after a “Save Yourself” and before a “Save Yourself Done.”

If save_type is SmSaveLocal the client must update the properties to reflect
its current state. Specifically, it should save enough information to restore
the state as seen by the user of this client. It should not affect the state as
seen by other users. If save_type is SmSaveGlobal the user wants the client to
commit all of its data to permanent, globally accessible storage. If save_type
is SmSaveBoth the client should do both of these (it should first commit the
data to permanent storage before updating its properties).

The shutdown argument specifies whether the session is being shut down. The
interaction is different depending on whether or not shutdown is set. If not
shutting down, then the client can save and resume normal operation. If
shutting down, the client must save and then must prevent interaction until it
receives either a “Die” or a “Shutdown Cancelled,” because anything the user
does after the save will be lost.

The fast argument specifies that the client should save its state as quickly as
possible. For example, if the session manager knows that power is about to
fail, it should set fast to True.

Sending a Save Yourself Phase 2 Message

In order to send a “Save Yourself Phase 2” message to a client, use
SmsSaveYourselfPhase2

void SmsSaveYourselfPhase2(SmsConn sms_conn);

sms_conn The session management connection object.

The session manager sends this message to a client that has previously sent a
“Save Yourself Phase 2 Request” message. This message informs the client that
all other clients are in a fixed state and this client can save state that is
associated with other clients.

Sending an Interact Message

To send an “Interact” message to a client, use SmsInteract.

void SmsInteract(SmsConn sms_conn);

sms_conn The session management connection object.

The “Interact” message grants the client the privilege of interacting with the
user. When the client is done interacting with the user, it must send an
“Interact Done” message to the session manager.

Sending a Save Complete Message

To send a “Save Complete” message to a client, use SmsSaveComplete.

void SmsSaveComplete(SmsConn sms_conn);

sms_conn The session management connection object.

The session manager sends this message when it is done with a checkpoint. The
client is then free to change its state.

Sending a Die Message

To send a “Die” message to a client, use SmsDie.

void SmsDie(SmsConn sms_conn);

sms_conn The session management connection object.

Before the session manager terminates, it should wait for a “Connection Closed”
message from each client that it sent a “Die” message to, timing out
appropriately.

Cancelling a Shutdown

To cancel a shutdown, use SmsShutdownCancelled.

void SmsShutdownCancelled(SmsConn sms_conn);

sms_conn The session management connection object.

The client can now continue as if the shutdown had never happened. If the
client has not sent a “Save Yourself Done” message yet, it can either abort the
save and send a “Save Yourself Done” with the success argument set to False or
it can continue with the save and send a “Save Yourself Done” with the success
argument set to reflect the outcome of the save.

Returning Properties

In response to a “Get Properties” message, the session manager should call
SmsReturnProperties.

void SmsReturnProperties(SmsConn sms_conn, int num_props, SmProp **props);

sms_conn  The session management connection object.

num_props The number of properties.

props     The list of properties to return to the client.

The properties are returned as an array of property pointers. For a description
of session management properties and the SmProp structure, see section 7,
“Session Management Properties.”

Pinging a Client

To check that a client is still alive, you should use the IcePing function
provided by the ICE library. To do so, the ICE connection must be obtained
using the SmsGetIceConnection (see section 6.12, “Using Sms Informational
Functions”).

void IcePing(IceConn ice_conn, IcePingReplyProc ping_reply_proc, IcePointer
client_data);

ice_conn        A valid ICE connection object.

ping_reply_proc The callback to invoke when the Ping reply arrives.

client_data     This pointer will be passed to the IcePingReplyProc callback.

When the Ping reply is ready (if ever), the IcePingReplyProc callback will be
invoked. A session manager should have some sort of timeout period, after which
it assumes the client has unexpectedly died.

typedef void (*IcePingReplyProc)(IceConn ice_conn, IcePointer client_data);

ice_conn    A valid ICE connection object.

client_data The client data specified in the call to IcePing

Cleaning Up After a Client Disconnects

When the session manager receives a “Connection Closed” message or otherwise
detects that the client aborted the connection, it should call the SmsCleanUp
function in order to free up the connection object.

void SmsCleanUp(SmsConn sms_conn);

sms_conn The session management connection object.

Using Sms Informational Functions

int SmsProtocolVersion(SmsConn sms_conn);

SmsProtocolVersion returns the major version of the session management protocol
associated with this session.

int SmsProtocolRevision(SmsConn sms_conn);

SmsProtocolRevision returns the minor version of the session management
protocol associated with this session.

char *SmsClientID(SmsConn sms_conn);

SmsClientID returns a null-terminated string for the client ID associated with
this connection. You should call free on this pointer when the client ID is no
longer needed.

To obtain the host name of a client, use SmsClientHostName. This host name will
be needed to restart the client.

char *SmsClientHostName(SmsConn sms_conn);

The string returned is of the form protocol/hostname, where protocol is one of
{tcp, decnet, local}. You should call free on the string returned when it is no
longer needed.

IceConn SmsGetIceConnection(SmsConn sms_conn);

SmsGetIceConnection returns the ICE connection object associated with this
session management connection object. The ICE connection object can be used to
get some additional information about the connection. Some of the more useful
functions which can be used on the IceConn are IceConnectionNumber and
IceLastSequenceNumber. For further information, see the “Inter-Client Exchange
Library” standard.

Error Handling

If the session manager receives an unexpected protocol error from a client, an
error handler is invoked by SMlib. A default error handler exists which simply
prints the error message (it does not exit). The session manager can change
this error handler by calling SmsSetErrorHandler.

SmsErrorHandler SmsSetErrorHandler(SmsErrorHandler handler);

The error handler. You should pass NULL to restore the default handler.

SmsSetErrorHandler returns the previous error handler. The SmsErrorHandler has
the following type:

typedef void (*SmsErrorHandler)(SmsConn sms_conn, Bool swap, int
offending_minor_opcode, unsigned long offending_sequence_num, int error_class,
int severity, IcePointer values);

sms_conn               The session management connection object.

swap                   A flag which indicates if the specified values need byte
                       swapping.

offending_minor_opcode The minor opcode of the offending message.

offending_sequence_num The sequence number of the offending message.

error_class            The error class of the offending message.

severity               IceCanContinue, IceFatalToProtocol, or
                       IceFatalToConnection

values                 Any additional error values specific to the minor opcode
                       and class.

Note that this error handler is invoked for protocol related errors. To install
an error handler to be invoked when an IO error occurs, use
IceSetIOErrorHandler. For further information, see the “Inter-Client Exchange
Library” standard.

Chapter 7. Session Management Properties

Each property is defined by the SmProp structure:

typedef struct {
        char *name;     /* name of property */
        char *type;     /* type of property */
        int num_vals;   /* number of values */
        SmPropValue *vals;      /* the list of values */
} SmProp;

typedef struct {
        int length;     /* the length of the value */
        SmPointer value;        /* the value */
} SmPropValue;

The X Session Management Protocol defines a list of predefined properties,
several of which are required to be set by the client. The following table
specifies the predefined properties and indicates which ones are required. Each
property has a type associated with it.

A type of SmCARD8 indicates that there is a single 1-byte value. A type of 
SmARRAY8 indicates that there is a single array of bytes. A type of 
SmLISTofARRAY8 indicates that there is a list of array of bytes.

┌──────────────────┬───────────┬──────────────┬────────┐
│Name              │Type       │POSIX Type    │Required│
├──────────────────┼───────────┼──────────────┼────────┤
│SmCloneCommand    │OS-specific│SmLISTofARRAY8│Yes     │
├──────────────────┼───────────┼──────────────┼────────┤
│SmCurrentDirectory│OS-specific│SmARRAY8      │No      │
├──────────────────┼───────────┼──────────────┼────────┤
│SmDiscardCommand  │OS-specific│SmLISTofARRAY8│No*     │
├──────────────────┼───────────┼──────────────┼────────┤
│SmEnvironment     │OS-specific│SmLISTofARRAY8│No      │
├──────────────────┼───────────┼──────────────┼────────┤
│SmProcessID       │OS-specific│SmARRAY8      │No      │
├──────────────────┼───────────┼──────────────┼────────┤
│SmProgram         │OS-specific│SmARRAY8      │Yes     │
├──────────────────┼───────────┼──────────────┼────────┤
│SmRestartCommand  │OS-specific│SmLISTofARRAY8│Yes     │
├──────────────────┼───────────┼──────────────┼────────┤
│SmResignCommand   │OS-specific│SmLISTofARRAY8│No      │
├──────────────────┼───────────┼──────────────┼────────┤
│SmRestartStyleHint│SmCARD8    │SmCARD8       │No      │
├──────────────────┼───────────┼──────────────┼────────┤
│SmShutdownCommand │OS-specific│SmLISTofARRAY8│No      │
├──────────────────┼───────────┼──────────────┼────────┤
│SmUserID          │SmARRAY8   │SmARRAY8      │Yes     │
└──────────────────┴───────────┴──────────────┴────────┘

* Required if any state is stored in an external repository (for example, state
file).

  • SmCloneCommand

    This is like the SmRestartCommand, except it restarts a copy of the
    application. The only difference is that the application does not supply
    its client ID at register time. On POSIX systems, this should be of type 
    SmLISTofARRAY8.

  • SmCurrentDirectory

    On POSIX-based systems, this specifies the value of the current directory
    that needs to be set up prior to starting the SmProgram and should of type 
    SmARRAY8.

  • SmDiscardCommand

    The discard command contains a command that when delivered to the host that
    the client is running on (determined from the connection), will cause it to
    discard any information about the current state. If this command is not
    specified, the Session Manager will assume that all of the client's state
    is encoded in the SmRestartCommand. On POSIX systems, the type should be 
    SmLISTofARRAY8.

  • SmEnvironment

    On POSIX based systems, this will be of type SmLISTofARRAY8, where the 
    ARRAY8s alternate between environment variable name and environment
    variable value.

  • SmProcessID

    This specifies an OS-specific identifier for the process. On POSIX systems,
    this should contain the return value of getpid turned into a Latin-1
    (decimal) string.

  • SmProgram

    This is the name of the program that is running. On POSIX systems, this
    should be first parameter passed to execve and should be of type SmARRAY8.

  • SmRestartCommand

    The restart command contains a command that, when delivered to the host
    that the client is running on (determined from the connection), will cause
    the client to restart in its current state. On POSIX-based systems, this is
    of type SmLISTofARRAY8, and each of the elements in the array represents an
    element in the argv array. This restart command should ensure that the
    client restarts with the specified client-ID.

  • SmResignCommand

    A client that sets the SmRestartStyleHint to SmRestartAnyway uses this
    property to specify a command that undoes the effect of the client and
    removes any saved state. As an example, consider a user that runs xmodmap
    which registers with the Session Manager, sets SmRestartStyleHint to
    SmRestartAnyway, and then terminates. To allow the Session Manager (at the
    user's request) to undo this, xmodmap would register a SmResignCommand that
    undoes the effects of the xmodmap.

  • SmRestartStyleHint

    If the SmRestartStyleHint is present, it will contain the style of
    restarting the client prefers. If this style is not specified,
    SmRestartIfRunning is assumed. The possible values are as follows:

    ┌─────────────────────┬─────┐
    │Name                 │Value│
    ├─────────────────────┼─────┤
    │SmRestartIfRunning   │0    │
    ├─────────────────────┼─────┤
    │SmRestartAnyway      │1    │
    ├─────────────────────┼─────┤
    │SmRestartImmediately │2    │
    ├─────────────────────┼─────┤
    │SmRestartNever       │3    │
    └─────────────────────┴─────┘

    The SmRestartIfRunning style is used in the usual case. The client should
    be restarted in the next session if it was running at the end of the
    current session.

    The SmRestartAnyway style is used to tell the Session Manager that the
    application should be restarted in the next session even if it exits before
    the current session is terminated. It should be noted that this is only a
    hint and the Session Manager will follow the policies specified by its
    users in determining what applications to restart.

    A client that uses SmRestartAnyway should also set the SmResignCommand and 
    SmShutdownCommand properties to commands that undo the state of the client
    after it exits.

    The SmRestartImmediately style is like SmRestartAnyway, but, in addition,
    the client is meant to run continuously. If the client exits, the Session
    Manager should try to restart it in the current session.

    SmRestartNever style specifies that the client does not wish to be
    restarted in the next session.

  • SmShutdownCommand

    This command is executed at shutdown time to clean up after a client that
    is no longer running but retained its state by setting SmRestartStyleHint
    to SmRestartAnyway. The client must not remove any saved state as the
    client is still part of the session. As an example, consider a client that
    turns on a camera at start up time. This client then exits. At session
    shutdown, the user wants the camera turned off. This client would set the 
    SmRestartStyleHint to SmRestartAnyway and would register a 
    SmShutdownCommand that would turn off the camera.

  • SmUserID

    Specifies the user ID. On POSIX-based systems, this will contain the user's
    name (the pw_name member of struct passwd).

Chapter 8. Freeing Data

To free an individual property, use SmFreeProperty

void SmFreeProperty(SmProp *prop);

prop The property to free.

To free the reason strings from the SmsCloseConnectionProc callback, use
SmFreeReasons

void SmFreeReasons(int count, char **reasons);

count   The number of reason strings.

reasons The list of reason strings to free.

Chapter 9. Authentication of Clients

As stated earlier, the session management protocol is layered on top of ICE.
Authentication occurs at two levels in the ICE protocol:

  • The first is when an ICE connection is opened.

  • The second is when a Protocol Setup occurs on an ICE connection.

The authentication methods that are available are implementation-dependent
(that is., dependent on the ICElib and SMlib implementations in use). For
further information, see the “Inter-Client Exchange Library” standard.

Chapter 10. Working in a Multi-Threaded Environment

To declare that multiple threads in an application will be using SMlib (or any
other library layered on top of ICElib), you should call IceInitThreads. For
further information, see the “Inter-Client Exchange Library” standard.

Chapter 11. Acknowledgements

Thanks to the following people for their participation in the X Session
Management design: Jordan Brown, Ellis Cohen, Donna Converse, Stephen Gildea,
Vania Joloboff, Stuart Marks, Bob Scheifler, Ralph Swick, and Mike Wexler.

