evthread(3)

NAME
evthread -

Functions for multi-threaded applications using Libevent.

SYNOPSIS

#include <event2/thread.h>
#include <event2/event-config.h>

  Data Structures
struct evthread_condition_callbacks
This structure describes the interface a threading library uses for condition variables.
struct evthread_lock_callbacks
This structure describes the interface a threading library uses for locking.

  Macros
#define EVTHREAD_CONDITION_API_VERSION 1
#define EVTHREAD_LOCK_API_VERSION 1
#define EVTHREAD_USE_PTHREADS_IMPLEMENTED 1
Defined if Libevent was built with support for evthread_use_pthreads()
#define EVTHREAD_USE_WINDOWS_THREADS_IMPLEMENTED 1
Defined if Libevent was built with support for evthread_use_windows_threads()

Flags passed to lock functions
#define EVTHREAD_WRITE 0x04
A flag passed to a locking callback when the lock was allocated as a read-write lock, and we want to acquire or release the lock for writing.
#define EVTHREAD_READ 0x08
A flag passed to a locking callback when the lock was allocated as a read-write lock, and we want to acquire or release the lock for reading.
#define EVTHREAD_TRY 0x10
A flag passed to a locking callback when we don't want to block waiting for the lock; if we can't get the lock immediately, we will instead return nonzero from the locking callback.

Types of locks
#define EVTHREAD_LOCKTYPE_RECURSIVE 1
A recursive lock is one that can be acquired multiple times at once by the same thread.
#define EVTHREAD_LOCKTYPE_READWRITE 2

  Functions
void evthread_enable_lock_debuging (void)
Enable debugging wrappers around the current lock callbacks.
int evthread_make_base_notifiable (struct event_base *base)
Make sure it's safe to tell an event base to wake up from another thread or a signal handler.
int evthread_set_condition_callbacks (const struct evthread_condition_callbacks *)
Sets a group of functions that Libevent should use for condition variables.
void evthread_set_id_callback (unsigned long(*id_fn)(void))
Sets the function for determining the thread id.
int evthread_set_lock_callbacks (const struct evthread_lock_callbacks *)
Sets a group of functions that Libevent should use for locking.
int evthread_use_pthreads (void)
Sets up Libevent for use with Pthreads locking and thread ID functions.
int evthread_use_windows_threads (void)
Sets up Libevent for use with Windows builtin locking and thread ID functions.

Detailed Description

Functions for multi-threaded applications using Libevent. When using a multi-threaded application in which multiple threads add and delete events from a single event base, Libevent needs to lock its data structures.

Like the memory-management function hooks, all of the threading functions must be set up before an event_base is created if you want the base to use them.

Most programs will either be using Windows threads or Posix threads. You can configure Libevent to use one of these event_use_windows_threads() or event_use_pthreads() respectively. If you're using another threading library, you'll need to configure threading functions manually using evthread_set_lock_callbacks() and evthread_set_condition_callbacks().

Macro Definition Documentation

  #define EVTHREAD_LOCKTYPE_RECURSIVE 1

A recursive lock is one that can be acquired multiple times at once by the same thread. No other process can allocate the lock until the thread that has been holding it has unlocked it as many times as it locked it.

  #define EVTHREAD_READ 0x08

A flag passed to a locking callback when the lock was allocated as a read-write lock, and we want to acquire or release the lock for reading.

  #define EVTHREAD_TRY 0x10

A flag passed to a locking callback when we don't want to block waiting for the lock; if we can't get the lock immediately, we will instead return nonzero from the locking callback.

  #define EVTHREAD_WRITE 0x04

A flag passed to a locking callback when the lock was allocated as a read-write lock, and we want to acquire or release the lock for writing.

Function Documentation

  void evthread_enable_lock_debuging (void)

Enable debugging wrappers around the current lock callbacks. If Libevent makes one of several common locking errors, exit with an assertion failure.

If you're going to call this function, you must do so before any locks are allocated.

  int evthread_make_base_notifiable (struct event_base *base)

Make sure it's safe to tell an event base to wake up from another thread or a signal handler. Returns:
    0 on success, -1 on failure.

  int evthread_set_condition_callbacks (const struct evthread_condition_callbacks *)

Sets a group of functions that Libevent should use for condition variables. For full information on the required callback API, see the documentation for the individual members of evthread_condition_callbacks.

Note that if you're using Windows or the Pthreads threading library, you probably shouldn't call this function; instead, use evthread_use_windows_threads() or evthread_use_pthreads() if you can.

  void evthread_set_id_callback (unsigned long(*)(void)id_fn)

Sets the function for determining the thread id. Parameters:
    base the event base for which to set the id function
    id_fn the identify function Libevent should invoke to determine the identity of a thread.

  int evthread_set_lock_callbacks (const struct evthread_lock_callbacks *)

Sets a group of functions that Libevent should use for locking. For full information on the required callback API, see the documentation for the individual members of evthread_lock_callbacks.

Note that if you're using Windows or the Pthreads threading library, you probably shouldn't call this function; instead, use evthread_use_windows_threads() or evthread_use_posix_threads() if you can.

  int evthread_use_pthreads (void)

Sets up Libevent for use with Pthreads locking and thread ID functions. Unavailable if Libevent is not build for use with pthreads. Requires libraries to link against Libevent_pthreads as well as Libevent.

Returns:
    0 on success, -1 on failure.

  int evthread_use_windows_threads (void)

Sets up Libevent for use with Windows builtin locking and thread ID functions. Unavailable if Libevent is not built for Windows.

Returns:
    0 on success, -1 on failure.

Author

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