On 31 May 2012, at 17:14, Scott A Andrew wrote:
> My guess is that you are crashing because kMyVLFContext is not an objective C
> object. According to the Apple documentation
> (https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocThreading.html#//apple_ref/doc/uid/TP30001163-CH19-SW1):
>
> The @synchronized() directive takes as its only argument any Objective-C
> object, including self. This object is known as a mutual exclusion semaphore
> or mutex. It allows a thread to lock a section of code to prevent its use by
> other threads. You should use separate semaphores to protect different
> critical sections of a program. It’s safest to create all the mutual
> exclusion objects before the application becomes multithreaded, to avoid race
> conditions.
>
> My guess is that ARC is trying to do a bit of memory management on your
> context pointer and the calls it expects aren't there.
Ok, that seems to make sense. At any rate, changing kMyVLFContext to a more
regular style (an NSString) seems to fix the issue.
static NSString *kMyVLFContext = @"kMyVLFContext";
Thanks,
António
> Scott
>
> On May 31, 2012, at 8:47 AM, Antonio Nunes wrote:
>
>> I have a function that looks essentially like this:
>>
>> static void *kMyVLFContext = &kMyVLFContext;
>> Boolean myFunction(CFURLRef path)
>> {
>> CFDictionaryRef myDictionary = NULL;
>>
>> @synchronized(kMyVLFContext) {
>> … work …
>> }
>>
>> return myDictionary != NULL;
>> }
>>
>> This function works fine with manual memory management. After compiling with
>> ARC though, a crash occurs on line "@synchronized(kMyVLFContext) {". I
>> wouldn't think this should be affected by ARC at all. Any hints as to what
>> might be afoot here, or is it more likely something else, earlier on is
>> causing a failure here (e.g. stomping kMyVLFContext)?
>>
>> Removing the lock causes the function to return successfully, but may of
>> course cause issues on occasions when the function is called from several
>> threads at once.
>>
>> -António
>>
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