GCD in AFNetworking 的使用
AFURLSessionManager 网络连接的 session 管理
创建同步队列
static dispatch_queue_t url_session_manager_creation_queue() {
static dispatch_queue_t af_url_session_manager_creation_queue;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
af_url_session_manager_creation_queue = dispatch_queue_create("com.alamofire.networking.session.manager.creation", DISPATCH_QUEUE_SERIAL);
});
return af_url_session_manager_creation_queue;
}
保证单线程执行session 在iOS8 之前，如果有相同的taskId 会清除之前的，引起bug，引入条件判断，8之前，同步队列处理。
static void url_session_manager_create_task_safely(dispatch_block_t _Nonnull block) {
if (block != NULL) {
if (NSFoundationVersionNumber < NSFoundationVersionNumber_With_Fixed_5871104061079552_bug) {
// Fix of bug
// Open Radar:http://openradar.appspot.com/radar?id=5871104061079552 (status: Fixed in iOS8)
// Issue about:https://github.com/AFNetworking/AFNetworking/issues/2093
dispatch_sync(url_session_manager_creation_queue(), block);
} else {
block();
}
}
}
创建并行队列
static dispatch_queue_t url_session_manager_processing_queue() {
static dispatch_queue_t af_url_session_manager_processing_queue;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
af_url_session_manager_processing_queue = dispatch_queue_create("com.alamofire.networking.session.manager.processing", DISPATCH_QUEUE_CONCURRENT);
});
return af_url_session_manager_processing_queue;
}
创建group
static dispatch_group_t url_session_manager_completion_group() {
static dispatch_group_t af_url_session_manager_completion_group;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
af_url_session_manager_completion_group = dispatch_group_create();
});
return af_url_session_manager_completion_group;
}
处理dispatch group group组，采用默认，或者用户设置的 completionQueue or main queue 中来完成任务， 完成之后，在主线程发送通知
- (void)URLSession:(__unused NSURLSession *)session
task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error
{
...
if (error) {
...
dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
if (self.completionHandler) {
self.completionHandler(task.response, responseObject, error);
}
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
});
});
} else {
dispatch_async(url_session_manager_processing_queue(), ^{
...
dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
if (self.completionHandler) {
self.completionHandler(task.response, responseObject, serializationError);
}
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
});
});
});
}
}
主线程发通知
- (void)taskDidResume:(NSNotification *)notification {
NSURLSessionTask *task = notification.object;
if ([task respondsToSelector:@selector(taskDescription)]) {
if ([task.taskDescription isEqualToString:self.taskDescriptionForSessionTasks]) {
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidResumeNotification object:task];
});
}
}
}
- (void)taskDidSuspend:(NSNotification *)notification {
NSURLSessionTask *task = notification.object;
if ([task respondsToSelector:@selector(taskDescription)]) {
if ([task.taskDescription isEqualToString:self.taskDescriptionForSessionTasks]) {
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidSuspendNotification object:task];
});
}
}
}
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session {
if (self.didFinishEventsForBackgroundURLSession) {
dispatch_async(dispatch_get_main_queue(), ^{
self.didFinishEventsForBackgroundURLSession(session);
});
}
}
dispatch_semaphore信号量当lock 使用，串行等待 异步执行完毕 getTasksWithCompletionHandler 异步方法
- (NSArray *)tasksForKeyPath:(NSString *)keyPath {
__block NSArray *tasks = nil;
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
[self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
...// 异步执行
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
return tasks;
}
url_session_manager_create_task_safely 串行创建，保证taskId 唯一
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject, NSError * _Nullable error))completionHandler {
__block NSURLSessionDataTask *dataTask = nil;
url_session_manager_create_task_safely(^{
dataTask = [self.session dataTaskWithRequest:request];// 有对应的 taskid，避免多线程执行时，taskId 相同
});
...
return dataTask;
}
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request
fromFile:(NSURL *)fileURL
progress:(void (^)(NSProgress *uploadProgress)) uploadProgressBlock
completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{
__block NSURLSessionUploadTask *uploadTask = nil;
url_session_manager_create_task_safely(^{
uploadTask = [self.session uploadTaskWithRequest:request fromFile:fileURL];
... // 保证，多线程情况下，创建taskId 唯一
});
if (uploadTask) {
[self addDelegateForUploadTask:uploadTask
progress:uploadProgressBlock
completionHandler:completionHandler];
}
return uploadTask;
}
- (NSURLSessionUploadTask *)uploadTaskWithStreamedRequest:(NSURLRequest *)request
progress:(void (^)(NSProgress *uploadProgress)) uploadProgressBlock
completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{
__block NSURLSessionUploadTask *uploadTask = nil;
url_session_manager_create_task_safely(^{
// 保证，多线程情况下，创建taskId 唯一
uploadTask = [self.session uploadTaskWithStreamedRequest:request];
});
[self addDelegateForUploadTask:uploadTask progress:uploadProgressBlock completionHandler:completionHandler];
return uploadTask;
}
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request
progress:(void (^)(NSProgress *downloadProgress)) downloadProgressBlock
destination:(NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
completionHandler:(void (^)(NSURLResponse *response, NSURL *filePath, NSError *error))completionHandler
{
__block NSURLSessionDownloadTask *downloadTask = nil;
url_session_manager_create_task_safely(^{
// 保证，多线程情况下，创建taskId 唯一
downloadTask = [self.session downloadTaskWithRequest:request];
});
[self addDelegateForDownloadTask:downloadTask progress:downloadProgressBlock destination:destination completionHandler:completionHandler];
return downloadTask;
}
总结：
- 串行队列，可以保证线程安全，如 url_session_manager_create_task_safely 的使用
- group组的使用, group 关联的 block 执行完毕之后，给出回调，主要目的监听执行完毕
- dispatch_semphore_t 可以当作 锁🔒 使
- 对于通知，保证明确到主线程，最好自己明确要做什么
补充：
// create group
dispatch_group_t dispatch_group_create(void);
// 自动 entry， leave group
dispatch_group_async(dispatch_group_t group,
dispatch_queue_t queue,
dispatch_block_t block);
// 收到
dispatch_group_enter(dispatch_group_t group);
dispatch_group_leave(dispatch_group_t group);
// 同步等待, all block complete
dispatch_group_wait(dispatch_group_t group, dispatch_time_t timeout);
// async 等待 all block complete
dispatch_group_notify(dispatch_group_t group,
dispatch_queue_t queue,
dispatch_block_t block);
扩展：
// 实现跟 dispatch_semaphore_t 差不多的功能
dispatch_queue_t queue = dispatch_queue_create("test.01", DISPATCH_QUEUE_SERIAL);
dispatch_group_t group = dispatch_group_create();
NSLog(@"1");
dispatch_group_async(group, queue, ^{
NSLog(@"4 %@", NSThread.currentThread);
});
NSLog(@"2");
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
NSLog(@"3");
// 下面的将造成死锁， 都是主线程等待
dispatch_group_t group = dispatch_group_create();
NSLog(@"1");
dispatch_group_async(group, dispatch_get_main_queue(), ^{
NSLog(@"4 %@", NSThread.currentThread);
});
NSLog(@"2");
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
NSLog(@"3");
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