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#if !defined(_EVENT_DISABLE_THREAD_SUPPORT) || defined(_EVENT_IN_DOXYGEN)
#define EVTHREAD_LOCK_API_VERSION 1
/**
@name Types of locks
锁类型
其实这里包含第三种锁类型，即 0 值代表 普通锁
@{*/
/** 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. */
// 递归锁类型是指，该锁可以在同一个线程中被获取多次；其他线程无法分配该锁，直到
// 持有该锁的线程对其解锁相同数量的次数
#define EVTHREAD_LOCKTYPE_RECURSIVE 1
/* A read-write lock is one that allows multiple simultaneous readers, but
* where any one writer excludes all other writers and readers. */
#define EVTHREAD_LOCKTYPE_READWRITE 2
/**@}*/
/** This structure describes the interface a threading library uses for
* locking. It's used to tell evthread_set_lock_callbacks() how to use
* locking on this platform.
*/
// 线程锁操作函数指针结构体
// 该结构用于告知 evthread_set_lock_callbacks() 在当前平台上如何使用锁
struct evthread_lock_callbacks {
/** The current version of the locking API. Set this to
* EVTHREAD_LOCK_API_VERSION */
int lock_api_version;
/** Which kinds of locks does this version of the locking API
* support? A bitfield of EVTHREAD_LOCKTYPE_RECURSIVE and
* EVTHREAD_LOCKTYPE_READWRITE.
*
* (Note that RECURSIVE locks are currently mandatory, and
* READWRITE locks are not currently used.)
**/
unsigned supported_locktypes;
/** Function to allocate and initialize new lock of type 'locktype'.
* Returns NULL on failure. */
void *(*alloc)(unsigned locktype);
/** Function to release all storage held in 'lock', which was created
* with type 'locktype'. */
void (*free)(void *lock, unsigned locktype);
/** Acquire an already-allocated lock at 'lock' with mode 'mode'.
* Returns 0 on success, and nonzero on failure. */
// 以 'mode' 模式持有由 'lock' 指向的已经分配的锁；0 为获取成功，非零为失败
int (*lock)(unsigned mode, void *lock);
/** Release a lock at 'lock' using mode 'mode'. Returns 0 on success,
* and nonzero on failure. */
int (*unlock)(unsigned mode, void *lock);
};
/** 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_set_lock_callbacks(const struct evthread_lock_callbacks *);
...
#if (defined(WIN32) && !defined(_EVENT_DISABLE_THREAD_SUPPORT)) || defined(_EVENT_IN_DOXYGEN)
/** Sets up Libevent for use with Windows builtin locking and thread ID
functions. Unavailable if Libevent is not built for Windows.
@return 0 on success, -1 on failure. */
int evthread_use_windows_threads(void); // windows 上的锁使能
/**
Defined if Libevent was built with support for evthread_use_windows_threads()
*/
#define EVTHREAD_USE_WINDOWS_THREADS_IMPLEMENTED 1
#endif
#if defined(_EVENT_HAVE_PTHREADS) || defined(_EVENT_IN_DOXYGEN)
/** 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.
令 libevent 可以使用 pthread 锁和相应的获取线程 id 的函数
如果构建 libevent 时候不支持 pthread 则无法使用该函数
使用时要求链接 libevent_pthreads 库和 libevent 库
@return 0 on success, -1 on failure. */
int evthread_use_pthreads(void); // linux 上的锁使能
/** Defined if Libevent was built with support for evthread_use_pthreads() */
#define EVTHREAD_USE_PTHREADS_IMPLEMENTED 1
#endif
/** 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.
**/
void evthread_enable_lock_debuging(void);
#endif /* _EVENT_DISABLE_THREAD_SUPPORT */
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