On Apr 15, 2016, at 4:34 AM, Tamas Nagy <tamas.lov.n...@gmail.com> wrote:
>
> I have an ongoing project where I’m using a CFMessagePort some sort of IPC
> communication. The CFMessagePort has a callback, something like this:
>
> static CFDataRef Callback(CFMessagePortRef port,
> SInt32 messageID,
> CFDataRef data,
> void *info)
> {
> return CFBridgingRetain([NSArchiver
> archivedDataWithRootObject:[(__bridge AppDelegate *)info getParameters]]);
> }
>
> The Callback runs on the main queue, it has been setup with
> CFMessagePortSetDispatchQueue(localPort, dispatch_get_main_queue());
>
> The interesting part is, and I don’t know why is this happening,
> CFBridgingRetain does not leak memory here - checked out with Instruments,
> also let the app run for a couple of hours, and memory usage does not
> increased (check out in Activity Monitor). Should not that CFBridgingRetain
> leak memory in this example, since I’m retaining a CF object and not
> releasing it by CFRelease?
No, there's no leak.
Traditionally, memory management in Core Foundation does not use an autorelease
mechanism. (There is now a CFAutorelease() function, but that doesn't play
into the Core Foundation memory management conventions.) So, if a function
needs to return a new or otherwise untracked object, what are its options? It
can't release it before it returns it. It may not get an opportunity to
release it "some time later". It has to return ownership to the caller.
The caller of your callback is expecting to receiving ownership and takes
responsibility for releasing the object it receives. In fact, the
documentation for CFMessagePortCallBack says, "The system releases the returned
CFData object."
<https://developer.apple.com/library/mac/documentation/CoreFoundation/Reference/CFMessagePortRef/#//apple_ref/c/tdef/CFMessagePortCallBack>
So, your code is doing the right thing.
Regards,
Ken
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