- (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) {
if ([keyPath isEqualToString:NSStringFromSelector(@selector(dataTasks))]) {
tasks = dataTasks;
} else if ([keyPath isEqualToString:NSStringFromSelector(@selector(uploadTasks))]) {
tasks = uploadTasks;
} else if ([keyPath isEqualToString:NSStringFromSelector(@selector(downloadTasks))]) {
tasks = downloadTasks;
} else if ([keyPath isEqualToString:NSStringFromSelector(@selector(tasks))]) {
tasks = [@[dataTasks, uploadTasks, downloadTasks] valueForKeyPath:@"@unionOfArrays.self"];
}
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
return tasks;
}
这段代码是AFNeting中对dispatch_semaphore_t的使用，给了我很大的启发。之前对执行耗时的block，在需要返回操作时，会crash。通过加锁设计可以解决先后的问题。
