dispatch_async Nested Block

Question

I am using dispatch_async method to execute task in main queue. But it causing retain cycle:

Following is the code snippet:

self.test = ^{
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"%@", self);
        });
   };

I am not able to get properly why it is creating retain cycle. As My controller does not have ownership of dispatch_async block.

Property test retains the closure and the closure contains a reference to self It doesn't matter that that reference is itself in a block — Paulw11
– Paulw11, Commented May 16, 2017 at 12:32

koen · Accepted Answer · 2017-05-16 12:40:01Z

1

Try using weakSelf:

__weak typeof(self) weakSelf = self;

self.test = ^{
    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"%@", weakSelf);
    });
};

edited May 16, 2017 at 12:40

answered May 16, 2017 at 12:32

koen

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1 Comment

newacct Over a year ago

but then self could get deallocated between the running of the outer block and the (asynchronous) running of the inner block, which may not be what he wants

newacct · Accepted Answer · 2017-05-18 01:28:13Z

0

If you don't want the outer block to retain self, but want the inner block to be able to keep self alive once dispatched, maybe something like this:

typeof(self) __weak weakSelf = self;
self.test = ^{
    typeof(self) strongSelf = weakSelf;
    if (strongSelf) {
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"%@", strongSelf);
        });
    }
};

answered May 18, 2017 at 1:28

newacct

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