一对一执行跨线程功能

Question

I have some special functions in my project, they will execute cross many threads, such as childContext perform block or AFNetwork response block:

(void)my_function {
    dispatch_async(dispatch_get_main_queue(), ^{
        NSManagedObjectContext *childContext = [[[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType] autorelease];
        childContext.parentContext = self.managedObjectContext;
        [childContext performBlock:^{
            [self.operationManager POST:URL parameters:nil block:^(AFHTTPRequestOperation *operation, id responseObject) {
                //Do something
                [childContext performBlock:^{
                    //Do something
                }];
            }];
        }];
    });
}

Now I want to execute them one by one (including all blocks in function). After reading a couple of other answers, some of the Apple documentation, I get some answers:

1. NSRecursiveLock

I can add NSRecursiveLock for each function, but the issue is that I can't lock/unlock cross thread.

(void)my_function {
    [MyLock lock];    // Lock here
    dispatch_async(dispatch_get_main_queue(), ^{
        NSManagedObjectContext *childContext = [[[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType] autorelease];
        childContext.parentContext = self.managedObjectContext;
        [childContext performBlock:^{
            [self.operationManager POST:URL parameters:nil block:^(AFHTTPRequestOperation *operation, id responseObject) {
                //Do something
                [childContext performBlock:^{
                    //Do something
                    [MyLock unlock];    //Unlock here
                }];
            }];
        }];
    });
}

2. NSOperation

I can add each function to NSOperationQueue as a NSOperation, and set concurrent operation number to 1, but the issue is that I can't make sure the code in block has been executed even the NSOperation finishes successfully.

3. @synchronized

I can add @synchronized, but has same issue as NSOperation

Answer 1

My suggestion is using NSOperationQueue and Asynchronous NSOperation .

You can make sure operation execute one by one in two ways

• addDependency:
• Set maxConcurrentOperationCount to 1

With Asynchronous NSOperation ,it is you to decide when this Operation is done.

For example

-(void)my_function {
dispatch_async(dispatch_get_main_queue(), ^{
    NSManagedObjectContext *childContext = [[[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType] autorelease];
    childContext.parentContext = self.managedObjectContext;
    [childContext performBlock:^{
        [self.operationManager POST:URL parameters:nil block:^(AFHTTPRequestOperation *operation, id responseObject) {
            //Do something
            [childContext performBlock:^{
                //Do something
                //Only mark this NSOperation is done when all task of this function is finished.
            }];
        }];
    }];
});
}

How to make an Asynchronous NSOperation ,This is what I usually do,you can also refer it in the document.

1. Keep two property

    @interface AsyncOperation (){ BOOL finished; BOOL executing; } 

2. Use these two property to manage Operation state

    -(BOOL)isFinished{ return finished; } -(BOOL)isExecuting{ return executing; } 

   3.Mark Operation start

Note:start function is called on the thread the Operation created

    -(void)start{
    if ([self isCancelled])
    {
       // Must move the operation to the finished state if it is canceled.
        [self willChangeValueForKey:@"isFinished"];
        finished = NO;
        [self didChangeValueForKey:@"isFinished"];
        return;
    }  

     // If the operation is not canceled, begin executing the task.
    [self willChangeValueForKey:@"isExecuting"];
    [NSThread detachNewThreadSelector:@selector(main) toTarget:self    withObject:nil];
    executing = YES;
    [self didChangeValueForKey:@"isExecuting"];
    }

4. Mark Operation is done

I use this function

    -(void)setOperationFinished{
       [self willChangeValueForKey:@"isFinished"];
       [self willChangeValueForKey:@"isExecuting"];
       executing = NO;
       finished = YES;
       [self didChangeValueForKey:@"isExecuting"];
       [self didChangeValueForKey:@"isFinished"]; 
    }