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steipete/PSPDFEnvironment.m

Last active March 26, 2019 09:39
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PSPDFApplicationIsTerminating - detect application termination on iOS and macOS. License: MIT. Taken out of the commercial PSPDFKit PDF SDK. http://pspdfkit.com
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PSPDFEnvironment.m
static _Atomic(BOOL) _applicationWillTerminate = NO;
__attribute__((constructor)) static void PSPDFInstallAppWillTerminateHandler(void) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[NSNotificationCenter.defaultCenter addObserverForName:UIApplicationWillTerminateNotification object:nil queue:nil usingBlock:^(NSNotification *note) {
_applicationWillTerminate = YES;
PSPDFLogWarning(@"Application shutdown event detected.");
}];
});
}
PSPDF_EXTERN BOOL PSPDFApplicationIsTerminating(void) {
return _applicationWillTerminate;
}
@LeoNatan
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LeoNatan commented Dec 11, 2018 •
edited

The worst that can happen by specifying sequentially consistent is a performance penalty. The worst that can happen when you specify a more relaxed ordering than you meant to have is that your code is subtly wrong. Worst of all, if you test it on a strongly ordered architecture such as x86, it's likely to work — and then subtly fail when you port it to something like ARM.

Ouch! TIL indeed!
Thanks!

@LeoNatan
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LeoNatan commented Dec 11, 2018 •
edited

I got confused for a second. It's been a while since I used atomic_fetch_add/atomic_fetch_sub. Is the default relax order relaxed?

If I understand correctly, what I really want is memory_order_seq_cst, which is then the order that is used by _Atomic(XXX), which also has a nicer syntax.

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