I execute the following code in a subclass of NSOperationQueue:
if (error) {
NSLog(@"Cancelling all operations due to error") ;
[self cancelAllOperations] ;
}
NSLog(@"#1 Remaining operations in %p:\n%@", self, [self operations]) ;
NSLog(@"#2 Remaining operations in %p:\n%@", self, [self operations]) ;
The console result:
2010-03-31 14:06:11.581 TestApp[10342:7d0f] Cancelling all operations due to
error
2010-03-31 14:06:11.583 TestApp[10342:7d0f] #1 Remaining operations in
0x1a38e6a0:
(
<NSInvocationOperation: 0x1a38d740>,
SSYOperation 0x1a38d7e0 selector=saveDocument,
<NSInvocationOperation: 0x1a386510>,
SSYOperation 0x1a3a5510 selector=terminateWork,
<NSInvocationOperation: 0x1a385f20>
)
2010-03-31 14:06:11.584 TestApp[10342:7d0f] #2 Remaining operations in
0x1a38e6a0:
(
<NSInvocationOperation: 0x1a38d740>
)
So you see in NSLog #1 there are 5 operations in the queue. This is expected,
because although the documentation for -cancelAllOperations is a little vague,
it does not say that it *removes* any operations from the queue.
But what happens in NSLog #2? All operations are gone except the first one.
All of a sudden!
Big thanks to anyone who can offer any clues on this.
Jerry Krinock
P.S. The above code is executing on a secondary thread. Is that a possible
issue? NSOperationQueue is not listed as a thread-safe class in the Threading
Programming Guide. But in the class documentation it says "It is safe to use a
single NSOperationQueue object from multiple threads without creating
additional locks to synchronize access to that object." I tried running the
above code with performSelectorOnMainThread wrappers, but got a deadlock I
can't explain either. (Sample shows mach_msg_trap.)
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