完成块?嵌入在同步工作流程中的异步流程 [英] Completion Blocks ? Asynchronous processes embedded in synchronous workflow

问题描述

长时间潜伏，第一次海报.我对Objective-C相对较新，因此如果我问一些简单的问题，我深表歉意.我的Google&堆栈溢出-fu让我失望了，所以我想也许有人可以帮忙.

Long time lurker, first time poster. I'm relatively new to objective-C so my apologies if I'm asking something fairly simple. My google & stack overflow-fu has let me down here, so I figured somebody could maybe help.

我有一个同步进程，该进程连续执行三个函数-称为A-> B-> C，在其中执行任务A，然后依次执行B和C.

I have a synchronous process executing, say, three functions in a row - call it A -> B-> C , where task A executes, followed by B, followed by C.

现在，B涉及一个异步过程，该过程具有委托回调以完成操作.但是B必须在执行C之前完成，因此我需要某种机制，使得在B完成之前不会触发C.我想必须为此问题设计一个通用的设计模式?

Now, B involves an asynchronous process with a delegate callback for completion. But B must complete before C is executed, so I need some mechanism such that C is not triggered before B has finished. I imagine there must be a common design pattern for this problem?

最初的解决方案是-

执行A
执行B
一会儿(！B完成){}
执行C

execute A
execute B
while (!B finished) {}
execute C

...但这似乎真是la脚.

...but this seems really lame.

我怀疑我可以用某种障碍来做到这一点，但是对于我一生，我只是想不通.有人可以帮忙吗?

I suspect I can do this with some kind of block, but for the life of me I just can't figure it out. Could anyone help?

感谢任何帮助！

纪尧姆

推荐答案

感谢所有退款-很抱歉没有尽快回复.我现在以与建议稍有不同的方式解决了这个问题:

Thanks for all the feeback - apologies for not responding sooner. I've now resolved this in a slightly different way to the suggestions:

首先，我将NSObject扩展为具有以下方法-

Firstly, I extended NSObject to have the following method -

#import "NSObject+LTExtensions.h"

@implementation NSObject (Testing)

- (void) performSelectorWithBlock: (SEL) selector withSemaphore:(dispatch_semaphore_t)semaphore
{
  [self performSelector:selector]; // This selector should complete the semaphore
  dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
  dispatch_release(semaphore);
}

@end

这使我可以通过选择器执行一个块.当该块执行时，在其上执行的线程将等待，直到特定的分派信号量发出继续执行信号的信号为止.

This allows me to execute a block via a selector. When the block executes, the thread on which it is executed will wait until signaled to proceed by a specific dispatch semaphore.

接下来我们可以做的是:

What we can then do is as follows:

• 致电A
• 创建调度信号并定义执行B的选择器
• 调用上面定义的方法以执行B并等待选择器完成
• B完成后(通过委托回调)，它向调度信号通知挂起等待状态
• 然后我执行C

所以我们有

A
B -> Asynchronous with delegate callback
C 

这是实现上述内容的简单示例

Here's a simple example of how the above is implemented

-(void) methodA {

  // ... do something

  // Assign your semaphore (this is a dispatch_semaphore_t)
  self.semaphore = dispatch_semaphore_create(0);
  [self performSelectorWithBlock:@selector(methodB) withSemaphore:semaphore];
  [self methodC];
}

-(void) methodB {
  // ... do whatever needs to be done asynchronously
  CFRunLoopRun();
}

-(void) methodBDelegateCallBack {
  // This is called when B completes

  // Signal completion
  dispatch_semaphore_signal(self.semaphore);
  CFRunLoopStop(CFRunLoopGetCurrent());
}

-(void) methodC {
 ...
}

工作得很好，没有任何问题(但是我是Obj C的新手，所以我的方法可能存在明显的问题).

Works very well without any issues (but I am new to Obj C, so there may be glaring issues with my approach).

这篇关于完成块?嵌入在同步工作流程中的异步流程的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！