···
From: Philippe Hausler via swift-corelibs-dev
To: Mamatha Busi <mamabusi@in.ibm.com>
Cc: swift-corelibs-dev@swift.org
Date: 05/06/2016 09:43 AM
Subject: Re: [swift-corelibs-dev] Setting property
"maxConcurrentOperationCount = 1" of NSOperation fails to
execute operations using OpenSource Foundation.
Sent by: swift-corelibs-dev-bounces@swift.org
I have a feeling this is associated with the changes for IUO types that
recently landed. I am very worried that this actually could happen on
Darwin targets as well. Perhaps it is the swift overlay for dispatch that
is correcting the failure on Darwin and the dispatch on Linux is missing
that annotation. Worth looking into.
Sent from my iPhone
On May 6, 2016, at 12:16 AM, Mamatha Busi <mamabusi@in.ibm.com> wrote:
@ Philippe: Your right. Converting the 'attr' to an optional did do
the job of creating a serial queue successfully. Thanks for that. I
will create a PR for this.
But this makes me think as to why until now, this was not caught by
the compiler itself?
Regards
Mamatha
----- Original message -----
From: phausler@apple.com
To: Mamatha Busi/India/IBM@IBMIN
Cc: swift-corelibs-dev <swift-corelibs-dev@swift.org>
Subject: Re: [swift-corelibs-dev] Setting property
"maxConcurrentOperationCount = 1" of NSOperation fails to execute
operations using OpenSource Foundation.
Date: Thu, May 5, 2016 10:54 PM
Hmm that seems unfortunate. I wonder if the serial creation is due
to an unwrapped optional? var attr: dispatch_queue_attr_t? instead
might do the trick… or alternatively we could just let the
underlying queue be concurrent all the time and enforce the max ops
via making the semaphore always instantiated (in the case of max ops
being 1) and initializing it to 1 to gate the operations.
On May 5, 2016, at 1:15 AM, Mamatha Busi via swift-corelibs-dev <swift-corelibs-dev@swift.org> wrote:
Hello
Code snippet:
———————————————————————
let operation1 : NSBlockOperation = NSBlockOperation
(block: {
sleep(1)
print("Opertion1")
})
let operation2 : NSBlockOperation = NSBlockOperation
(block: {
sleep(1)
print("Opertion2”)
})
var operations = [NSOperation]()
operations.append(operation1)
operations.append(operation2)
let queue = NSOperationQueue()
queue.maxConcurrentOperationCount = 1
queue.addOperations(operations, waitUntilFinished:
true)
————————————————————————
The above code snippet of adding operations to an operation
queue and executing with the property
‘maxConcurrentOperationCount = 1’ fails while executing the
above with the OpenSource Foundation and libDispatch of MAC
inside Xcode.
The error I am seeing is:
fatal error: unexpectedly found nil while unwrapping an
Optional value
Stack trace points to: attr = DISPATCH_QUEUE_SERIAL
which implies that the libDispatch macro is coming as nil
during the creation of the serial queue using libDispatch in
the file NSOperationQueue
The same test-case passes on OSx.
When I do not restrict the serial operation i.e. I remove ‘
queue.maxConcurrentOperationCount = 1’ , test case executes
successfully.
Setting it to a different value other than 1 also causes no
problems.
Am I doing something wrong with the API. If I set the property
‘ queue.maxConcurrentOperationCount = 1’ after adding
operations to the queue, then the problem does not occur. But
then this restricts me to control the operation execution to
be serial. So, I expect the above snippet to work on
OpenSource as well. Any thoughts on this?
Thank you.
Regards
Mamatha
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