GCD头文件里那些像dispatch_async_f后面带 f 的函数是干嘛的？
我们先来看看源文件中有哪些后面带 f 的函数：
/*!
* @function dispatch_async_f
*
* @abstract
* Submits a function for asynchronous execution on a dispatch queue.
*
* @discussion
* See dispatch_async() for details.
*
* @param queue
* The target dispatch queue to which the function is submitted.
* The system will hold a reference on the target queue until the function
* has returned.
* The result of passing NULL in this parameter is undefined.
*
* @param context
* The application-defined context parameter to pass to the function.
*
* @param work
* The application-defined function to invoke on the target queue. The first
* parameter passed to this function is the context provided to
* dispatch_async_f().
* The result of passing NULL in this parameter is undefined.
*/
API_AVAILABLE(macos(10.6), ios(4.0))
DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
void
dispatch_async_f(dispatch_queue_t queue,
void *_Nullable context,
dispatch_function_t work);
/*!
* @function dispatch_sync_f
*
* @abstract
* Submits a function for synchronous execution on a dispatch queue.
*
* @discussion
* See dispatch_sync() for details.
*
* @param queue
* The target dispatch queue to which the function is submitted.
* The result of passing NULL in this parameter is undefined.
*
* @param context
* The application-defined context parameter to pass to the function.
*
* @param work
* The application-defined function to invoke on the target queue. The first
* parameter passed to this function is the context provided to
* dispatch_sync_f().
* The result of passing NULL in this parameter is undefined.
*/
API_AVAILABLE(macos(10.6), ios(4.0))
DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
void
dispatch_sync_f(dispatch_queue_t queue,
void *_Nullable context,
dispatch_function_t work);
/*!
* @function dispatch_barrier_async_f
*
* @abstract
* Submits a barrier function for asynchronous execution on a dispatch queue.
*
* @discussion
* Submits a function to a dispatch queue like dispatch_async_f(), but marks
* that function as a barrier (relevant only on DISPATCH_QUEUE_CONCURRENT
* queues).
*
* See dispatch_async_f() for details.
*
* @param queue
* The target dispatch queue to which the function is submitted.
* The system will hold a reference on the target queue until the function
* has returned.
* The result of passing NULL in this parameter is undefined.
*
* @param context
* The application-defined context parameter to pass to the function.
*
* @param work
* The application-defined function to invoke on the target queue. The first
* parameter passed to this function is the context provided to
* dispatch_barrier_async_f().
* The result of passing NULL in this parameter is undefined.
*/
API_AVAILABLE(macos(10.7), ios(4.3))
DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
void
dispatch_barrier_async_f(dispatch_queue_t queue,
void *_Nullable context,
dispatch_function_t work);
/*!
* @function dispatch_barrier_sync_f
*
* @abstract
* Submits a barrier function for synchronous execution on a dispatch queue.
*
* @discussion
* Submits a function to a dispatch queue like dispatch_sync_f(), but marks that
* fuction as a barrier (relevant only on DISPATCH_QUEUE_CONCURRENT queues).
*
* See dispatch_sync_f() for details.
*
* @param queue
* The target dispatch queue to which the function is submitted.
* The result of passing NULL in this parameter is undefined.
*
* @param context
* The application-defined context parameter to pass to the function.
*
* @param work
* The application-defined function to invoke on the target queue. The first
* parameter passed to this function is the context provided to
* dispatch_barrier_sync_f().
* The result of passing NULL in this parameter is undefined.
*/
API_AVAILABLE(macos(10.7), ios(4.3))
DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
void
dispatch_barrier_sync_f(dispatch_queue_t queue,
void *_Nullable context,
dispatch_function_t work);
group.h中的相关函数
/*!
* @function dispatch_group_async_f
*
* @abstract
* Submits a function to a dispatch queue and associates the block with the
* given dispatch group.
*
* @discussion
* See dispatch_group_async() for details.
*
* @param group
* A dispatch group to associate with the submitted function.
* The result of passing NULL in this parameter is undefined.
*
* @param queue
* The dispatch queue to which the function will be submitted for asynchronous
* invocation.
*
* @param context
* The application-defined context parameter to pass to the function.
*
* @param work
* The application-defined function to invoke on the target queue. The first
* parameter passed to this function is the context provided to
* dispatch_group_async_f().
*/
API_AVAILABLE(macos(10.6), ios(4.0))
DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL2 DISPATCH_NONNULL4
DISPATCH_NOTHROW
void
dispatch_group_async_f(dispatch_group_t group,
dispatch_queue_t queue,
void *_Nullable context,
dispatch_function_t work);
/*!
* @function dispatch_group_notify_f
*
* @abstract
* Schedule a function to be submitted to a queue when all the blocks
* associated with a group have completed.
*
* @discussion
* See dispatch_group_notify() for details.
*
* @param group
* The dispatch group to observe.
* The result of passing NULL in this parameter is undefined.
*
* @param context
* The application-defined context parameter to pass to the function.
*
* @param work
* The application-defined function to invoke on the target queue. The first
* parameter passed to this function is the context provided to
* dispatch_group_notify_f().
*/
API_AVAILABLE(macos(10.6), ios(4.0))
DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL2 DISPATCH_NONNULL4
DISPATCH_NOTHROW
void
dispatch_group_notify_f(dispatch_group_t group,
dispatch_queue_t queue,
void *_Nullable context,
dispatch_function_t work);
就拿这几个有代表性的函数当做例子吧。
这些函数有一个特点，去掉后面的 _f 就是我们平时常用的GCD以block回调的方式处理多线程的函数。而加上了这个 _f 之后它们会变成什么鬼呢？
看看官方文档中的解释，以 dispatch_async_f 为例：
/*!
* @function dispatch_async_f
*
* @abstract
* Submits a function for asynchronous execution on a dispatch queue.
*
* @discussion
* See dispatch_async() for details.
*
* @param queue
* The target dispatch queue to which the function is submitted.
* The system will hold a reference on the target queue until the function
* has returned.
* The result of passing NULL in this parameter is undefined.
*
* @param context
* The application-defined context parameter to pass to the function.
*
* @param work
* The application-defined function to invoke on the target queue. The first
* parameter passed to this function is the context provided to
* dispatch_async_f().
* The result of passing NULL in this parameter is undefined.
*/
文档中 @abstract 摘要部分写到:
Submits a function for asynchronous execution on a dispatch queue.
就是说“提交一个在分派队列上异步执行的函数”。再看 @discussion 部分：
See dispatch_async() for details.
哈哈，让我们到 dispatch_async() 去找更多的细节。接下来再看 @param context：
The application-defined context parameter to pass to the function.
要传递给函数的应用程序定义的上下文参数，也就是我们自定义的要传给执行函数的参数。最后看看 @param work ：
The application-defined function to invoke on the target queue. The first parameter passed to this function is the context provided to dispatch_async_f().
The result of passing NULL in this parameter is undefined.
要在目标队列上调用的自定义函数。传入到函数的第一个参数是提供给 dispatch_async_f() 函数的上下文参数。如果这个参数传NULL，那么结果是未定义的。
综上所述，我们其实已经可以看得出这些函数是干嘛的了。就是以函数执行具体任务的方式替代GCD以Block执行具体任务的方式。
下面我 给出两个具体代码案例，仅供参考！
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_async_f(dispatch_get_main_queue(), (void *)123, (void *)async_func);
dispatch_sync_f(dispatch_get_global_queue(0, DISPATCH_QUEUE_PRIORITY_DEFAULT), (void *)456, (void *)sync_func);
}
void async_func(int param) {
printf("我是给async添加的C语言函数：%d",param);
printf("\n");
}
void sync_func(int param) {
printf("我是给sync添加的C语言函数：%d",param);
printf("\n");
}
控制台：
ok，写这篇博客就是为了记录一下当初的好奇心，为什么会有很多CGD函数有个后面带 _f 的版本，算是一篇笔记了。