GStreamer 1.0 Core Reference Manual: GstPoll

## GstPoll GstPoll — Keep track of file descriptors and make it possible to wait on them in a cancelable way |

## Functions

gboolean | gst_poll_add_fd ()
gboolean | gst_poll_fd_can_read ()
gboolean | gst_poll_fd_can_write ()
gboolean | gst_poll_fd_ctl_read ()
gboolean | gst_poll_fd_ctl_write ()
gboolean | gst_poll_fd_has_closed ()
gboolean | gst_poll_fd_has_error ()
void | gst_poll_fd_ignored ()
void | gst_poll_fd_init ()
void | gst_poll_free ()
GstPoll * | gst_poll_new ()
GstPoll * | gst_poll_new_timer ()
void | gst_poll_get_read_gpollfd ()
gboolean | gst_poll_remove_fd ()
void | gst_poll_restart ()
gboolean | gst_poll_set_controllable ()
void | gst_poll_set_flushing ()
gint | gst_poll_wait ()
gboolean | gst_poll_read_control ()
gboolean | gst_poll_write_control ()

## Types and Values

| GstPoll
| GstPollFD
#define | GST_POLL_FD_INIT

## Object Hierarchy

## Includes

    #include <gst/gst.h>

## Description

A GstPoll keeps track of file descriptors much like fd_set (used with `select()`) or a struct pollfd array (used with `poll()`). Once created with `gst_poll_new()`, the set can be used to wait for file descriptors to be readable and/or writable. It is possible to make this wait be controlled by specifying `TRUE` for the `controllable` flag when creating the set (or later calling `gst_poll_set_controllable()`).

New file descriptors are added to the set using `gst_poll_add_fd()`, and removed using `gst_poll_remove_fd()`. Controlling which file descriptors should be waited for to become readable and/or writable are done using `gst_poll_fd_ctl_read()` and `gst_poll_fd_ctl_write()`.

Use `gst_poll_wait()` to wait for the file descriptors to actually become readable and/or writable, or to timeout if no file descriptor is available in time. The wait can be controlled by calling `gst_poll_restart()` and `gst_poll_set_flushing()`.

Once the file descriptor set has been waited for, one can use `gst_poll_fd_has_closed()` to see if the file descriptor has been closed, `gst_poll_fd_has_error()` to see if it has generated an error, `gst_poll_fd_can_read()` to see if it is possible to read from the file descriptor, and `gst_poll_fd_can_write()` to see if it is possible to write to it.

## Functions

### gst_poll_add_fd ()

    gboolean
    gst_poll_add_fd (GstPoll *set,
                     GstPollFD *fd);

Add a file descriptor to the file descriptor set.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |

#### Returns

`TRUE` if the file descriptor was successfully added to the set.

### gst_poll_fd_can_read ()

    gboolean
    gst_poll_fd_can_read (const GstPoll *set,
                          GstPollFD *fd);

Check if `fd` in `set` has data to be read.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |

#### Returns

`TRUE` if the descriptor has data to be read.

### gst_poll_fd_can_write ()

    gboolean
    gst_poll_fd_can_write (const GstPoll *set,
                           GstPollFD *fd);

Check if `fd` in `set` can be used for writing.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |

#### Returns

`TRUE` if the descriptor can be used for writing.

### gst_poll_fd_ctl_read ()

    gboolean
    gst_poll_fd_ctl_read (GstPoll *set,
                          GstPollFD *fd,
                          gboolean active);

Control whether the descriptor `fd` in `set` will be monitored for readability.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |
active | a new status. |

#### Returns

`TRUE` if the descriptor was successfully updated.

### gst_poll_fd_ctl_write ()

    gboolean
    gst_poll_fd_ctl_write (GstPoll *set,
                           GstPollFD *fd,
                           gboolean active);

Control whether the descriptor `fd` in `set` will be monitored for writability.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |
active | a new status. |

#### Returns

`TRUE` if the descriptor was successfully updated.

### gst_poll_fd_has_closed ()

    gboolean
    gst_poll_fd_has_closed (const GstPoll *set,
                            GstPollFD *fd);

Check if `fd` in `set` has closed the connection.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |

#### Returns

`TRUE` if the connection was closed.

### gst_poll_fd_has_error ()

    gboolean
    gst_poll_fd_has_error (const GstPoll *set,
                           GstPollFD *fd);

Check if `fd` in `set` has an error.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |

#### Returns

`TRUE` if the descriptor has an error.

### gst_poll_fd_ignored ()

    void
    gst_poll_fd_ignored (GstPoll *set,
                         GstPollFD *fd);

Mark `fd` as ignored so that the next call to `gst_poll_wait()` will yield the same result for `fd` as last time. This function must be called if no operation (read/write/recv/send/etc.) will be performed on `fd` before the next call to `gst_poll_wait()`.

The reason why this is needed is because the underlying implementation might not allow querying the fd more than once between calls to one of the re-enabling operations.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |

### gst_poll_fd_init ()

    void
    gst_poll_fd_init (GstPollFD *fd);

Initializes `fd` . Alternatively you can initialize it with GST_POLL_FD_INIT.

#### Parameters

fd | a GstPollFD |

### gst_poll_free ()

    void
    gst_poll_free (GstPoll *set);

Free a file descriptor set.

#### Parameters

set | a file descriptor set. | [transfer full]

### gst_poll_new ()

    GstPoll *
    gst_poll_new (gboolean controllable);

Create a new file descriptor set. If `controllable` , it is possible to restart or flush a call to `gst_poll_wait()` with `gst_poll_restart()` and `gst_poll_set_flushing()` respectively.

Free-function: gst_poll_free

#### Parameters

controllable | whether it should be possible to control a wait. |

#### Returns

a new GstPoll, or `NULL` in case of an error. Free with `gst_poll_free()`.

[transfer full]

### gst_poll_new_timer ()

    GstPoll *
    gst_poll_new_timer (void);

Create a new poll object that can be used for scheduling cancellable timeouts.

A timeout is performed with `gst_poll_wait()`. Multiple timeouts can be performed from different threads.

Free-function: gst_poll_free

#### Returns

a new GstPoll, or `NULL` in case of an error. Free with `gst_poll_free()`.

[transfer full]

### gst_poll_get_read_gpollfd ()

    void
    gst_poll_get_read_gpollfd (GstPoll *set,
                               GPollFD *fd);

Get a GPollFD for the reading part of the control socket. This is useful when integrating with a GSource and GMainLoop.

#### Parameters

set | a GstPoll |
fd | a GPollFD |

### gst_poll_remove_fd ()

    gboolean
    gst_poll_remove_fd (GstPoll *set,
                        GstPollFD *fd);

Remove a file descriptor from the file descriptor set.

#### Parameters

set | a file descriptor set. |
fd | a file descriptor. |

#### Returns

`TRUE` if the file descriptor was successfully removed from the set.

### gst_poll_restart ()

    void
    gst_poll_restart (GstPoll *set);

Restart any `gst_poll_wait()` that is in progress. This function is typically used after adding or removing descriptors to `set` .

If `set` is not controllable, then this call will have no effect.

#### Parameters

set | a GstPoll. |

### gst_poll_set_controllable ()

    gboolean
    gst_poll_set_controllable (GstPoll *set,
                               gboolean controllable);

When `controllable` is `TRUE`, this function ensures that future calls to `gst_poll_wait()` will be affected by `gst_poll_restart()` and `gst_poll_set_flushing()`.

#### Parameters

set | a GstPoll. |
controllable | new controllable state. |

#### Returns

`TRUE` if the controllability of `set` could be updated.

### gst_poll_set_flushing ()

    void
    gst_poll_set_flushing (GstPoll *set,
                           gboolean flushing);

When `flushing` is `TRUE`, this function ensures that current and future calls to `gst_poll_wait()` will return -1, with errno set to EBUSY.

Unsetting the flushing state will restore normal operation of `set` .

#### Parameters

set | a GstPoll. |
flushing | new flushing state. |

### gst_poll_wait ()

    gint
    gst_poll_wait (GstPoll *set,
                   GstClockTime timeout);

Wait for activity on the file descriptors in `set` . This function waits up to the specified `timeout` . A timeout of GST_CLOCK_TIME_NONE waits forever.

For GstPoll objects created with `gst_poll_new()`, this function can only be called from a single thread at a time. If called from multiple threads, -1 will be returned with errno set to EPERM.

This is not true for timer GstPoll objects created with `gst_poll_new_timer()`, where it is allowed to have multiple threads waiting simultaneously.

#### Parameters

set | a GstPoll. |
timeout | a timeout in nanoseconds. |

#### Returns

The number of GstPollFD in `set` that have activity or 0 when no activity was detected after `timeout` . If an error occurs, -1 is returned and errno is set.

### gst_poll_read_control ()

    gboolean
    gst_poll_read_control (GstPoll *set);

Read a byte from the control socket of the controllable `set` . This function is mostly useful for timer GstPoll objects created with `gst_poll_new_timer()`.

#### Parameters

set | a GstPoll. |

#### Returns

`TRUE` on success. `FALSE` when `set` is not controllable or when there was no byte to read.

### gst_poll_write_control ()

    gboolean
    gst_poll_write_control (GstPoll *set);

Write a byte to the control socket of the controllable `set` . This function is mostly useful for timer GstPoll objects created with `gst_poll_new_timer()`.

It will make any current and future `gst_poll_wait()` function return with 1, meaning the control socket is set. After an equal amount of calls to `gst_poll_read_control()` have been performed, calls to `gst_poll_wait()` will block again until their timeout expired.

#### Parameters

set | a GstPoll. |

#### Returns

`TRUE` on success. `FALSE` when `set` is not controllable or when the byte could not be written.

## Types and Values

### GstPoll

    typedef struct _GstPoll GstPoll;

A set of file/network descriptors.

### GstPollFD

    typedef struct {
      int fd;
    } GstPollFD;

A file descriptor object.

#### Members

int `fd`; | a file descriptor |

### GST_POLL_FD_INIT

    #define GST_POLL_FD_INIT  { -1, -1 }

A GstPollFD must be initialized with this macro, before it can be used. This macro can used be to initialize a variable, but it cannot be assigned to a variable. In that case you have to use `gst_poll_fd_init()`.