wget2: Implementation of multi-threading basic functionality

| wget2 2.2.1

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Implementation of multi-threading basic functionality

## Data Structures
struct | wget_thread_st
struct | wget_thread_mutex_st
struct | wget_thread_cond_st

## Functions
int | wget_thread_mutex_init (wget_thread_mutex *mutex)
int | wget_thread_mutex_destroy (wget_thread_mutex *mutex)
void | wget_thread_mutex_lock (wget_thread_mutex mutex)
void | wget_thread_mutex_unlock (wget_thread_mutex mutex)
int | wget_thread_cond_init (wget_thread_cond *cond)
int | wget_thread_cond_destroy (wget_thread_cond *cond)
int | wget_thread_cond_signal (wget_thread_cond cond)
int | wget_thread_cond_wait (wget_thread_cond cond, wget_thread_mutex mutex, long long ms)
int | wget_thread_start (wget_thread *thread, void *(*start_routine)(void *), void *arg, WGET_GCC_UNUSED int flags)
int | wget_thread_cancel (WGET_GCC_UNUSED wget_thread thread)
int | wget_thread_kill (WGET_GCC_UNUSED wget_thread thread, WGET_GCC_UNUSED int sig)
int | wget_thread_join (wget_thread *thread)
wget_thread_id | wget_thread_self (void)
bool | wget_thread_support (void)

## Detailed Description

This is a wrapper around Gnulib's glthread functionality.

It currently supports Posix threads (pthreads), GNU Pth threads, Solaris threads and Windows threads.

## Function Documentation

## ◆ wget_thread_mutex_init()

int wget_thread_mutex_init | ( | wget_thread_mutex * | mutex | ) |

Parameters

  [in,out] | mutex | The mutex to initialize

Returns
  0 on success, non-zero on failure

Initializes the `mutex`.

After usage, a call to wget_thread_mutex_destroy() frees the allocated resources.

## ◆ wget_thread_mutex_destroy()

int wget_thread_mutex_destroy | ( | wget_thread_mutex * | mutex | ) |

Parameters

  [in,out] | mutex | The mutex to destroy

Returns
  0 on success, non-zero on failure

Free's the `mutex` and it's resources.

After calling this function, the `mutex` cannot be used any more.

## ◆ wget_thread_mutex_lock()

void wget_thread_mutex_lock | ( | wget_thread_mutex | mutex | ) |

Parameters

  [in] | mutex | The mutex to be locked

Creates a lock on the `mutex`.

To unlock the `mutex`, call wget_thread_mutex_unlock().

## ◆ wget_thread_mutex_unlock()

void wget_thread_mutex_unlock | ( | wget_thread_mutex | mutex | ) |

Parameters

  [in] | mutex | The mutex to be unlocked

Unlocks the `mutex`.

## ◆ wget_thread_cond_init()

int wget_thread_cond_init | ( | wget_thread_cond * | cond | ) |

Parameters

  [in,out] | cond | The conditional to initialize

Returns
  0 on success, non-zero on failure

Initializes the conditional `cond`.

After usage, a call to wget_thread_cond_destroy() frees the allocated resources.

## ◆ wget_thread_cond_destroy()

int wget_thread_cond_destroy | ( | wget_thread_cond * | cond | ) |

Parameters

  [in,out] | cond | The conditional to destroy

Returns
  0 on success, non-zero on failure

Free's the conditional `cond` and it's resources.

After calling this function, `cond` cannot be used any more.

## ◆ wget_thread_cond_signal()

int wget_thread_cond_signal | ( | wget_thread_cond | cond | ) |

Parameters

  [in] | cond | The conditional to signal a condition

Returns
  0 on success, non-zero on failure

Wakes up one (random) thread that waits on the conditional.

## ◆ wget_thread_cond_wait()

int wget_thread_cond_wait | ( | wget_thread_cond | cond,
|  | wget_thread_mutex | mutex,
|  | long long | ms )

Parameters

  [in] | cond | The conditional to wait for
  [in] | mutex | The mutex needed for thread-safety
  [in] | ms | The wait timeout in milliseconds

Returns
  0 on success, non-zero on failure

Waits for a condition with a max. timeout of `ms` milliseconds.

To wait forever use a timeout lower or equal then 0.

## ◆ wget_thread_start()

int wget_thread_start | ( | wget_thread * | thread,
|  | void *(* | start_routine )(void *),
|  | void * | arg,
|  | WGET_GCC_UNUSED int | flags )

Parameters

  [out] | thread | The thread variable to be initialized
  [in] | start_routine | The thread function to start
  [in] | arg | The argument given to `start_routine`
  [in] | flags | Currently unused

Returns
  0 on success, non-zero on failure

Start `start_routine` as own thread with argument `arg`.

## ◆ wget_thread_cancel()

int wget_thread_cancel | ( | WGET_GCC_UNUSED wget_thread | thread | ) |

Parameters

  [in] | thread | Thread to cancel

Returns
  0 on success, non-zero on failure

Currently a no-op function, since it's not portable.

## ◆ wget_thread_kill()

int wget_thread_kill | ( | WGET_GCC_UNUSED wget_thread | thread,
|  | WGET_GCC_UNUSED int | sig )

Parameters

  [in] | thread | Thread to send the signal to
  [in] | sig | Signal to send

Returns
  0 on success, non-zero on failure

Currently a no-op function, since it's not portable.

## ◆ wget_thread_join()

int wget_thread_join | ( | wget_thread * | thread | ) |

Parameters

  [in] | thread | Thread to wait for

Returns
  0 on success, non-zero on failure

Wait until the `thread` has been stopped.

This function just waits - to stop a thread you have take your own measurements.

## ◆ wget_thread_self()

wget_thread_id wget_thread_self | ( | void |  | ) |

Returns
  The thread id of the caller.

## ◆ wget_thread_support()

bool wget_thread_support | ( | void |  | ) |

Returns
  Whether libwget supports multi-threading on this platform or not.