Test of RAII-style Objective-C class. See: http://stackoverflow.com/questions/19551973/will-this-raii-style-objective-c-class-work

RAII-style Objective-C class

$ cat locktest.m
#import <Foundation/Foundation.h>

@interface Locker : NSObject {
    NSRecursiveLock *_lock;
}
- (void)setLock:(NSRecursiveLock *)lock;
@end

@implementation Locker

- (void)setLock:(NSRecursiveLock *)lock {
    if (_lock) {
        NSLog(@"%p unlocking %p", self, _lock);
        [_lock unlock];
    }
    _lock = lock;
    if (_lock) {
        NSLog(@"%p locking %p", self, _lock);
        [_lock lock];
    }
}

- (void)dealloc {
    NSLog(@"%p dealloc", self);
    self.lock = nil;
}
@end

@interface TestObject : NSObject {
    NSRecursiveLock *_lock;
}

- (void)foo;
- (void)bar;

@end

@implementation TestObject

- (id)init {
    self = [super init];
    if (self) {
        _lock = [[NSRecursiveLock alloc] init];
    }
    return self;
}

- (void)foo {
    Locker *locker = [[Locker alloc] init];
    locker.lock = _lock;

    NSLog(@"foo in");
    [NSThread sleepForTimeInterval:10.0];
    NSLog(@"foo out");
}

- (void)bar {
    Locker *locker = [[Locker alloc] init];
    locker.lock = _lock;

    NSLog(@"bar in");
    [NSThread sleepForTimeInterval:10.0];
    NSLog(@"bar out");
}

@end

int main(int argc, const char **argv) {
    @autoreleasepool {
        TestObject *testObj = [[TestObject alloc] init];
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            [testObj foo];
        });
        [testObj bar];
    }
    return 0;
}

$ clang -o locktest locktest.m -fobjc-arc -framework Foundation
$ ./locktest
2013-10-24 10:59:21.659 locktest[17027:1603] 0x7fe24ae00050 locking 0x7fe24ac0ad90
2013-10-24 10:59:21.659 locktest[17027:707] 0x7fe24ac0af10 locking 0x7fe24ac0ad90
2013-10-24 10:59:21.660 locktest[17027:1603] foo in
2013-10-24 10:59:31.661 locktest[17027:1603] foo out
2013-10-24 10:59:31.662 locktest[17027:1603] 0x7fe24ae00050 dealloc
2013-10-24 10:59:31.662 locktest[17027:1603] 0x7fe24ae00050 unlocking 0x7fe24ac0ad90
2013-10-24 10:59:31.662 locktest[17027:707] bar in
2013-10-24 10:59:41.664 locktest[17027:707] bar out
2013-10-24 10:59:41.664 locktest[17027:707] 0x7fe24ac0af10 dealloc
2013-10-24 10:59:41.664 locktest[17027:707] 0x7fe24ac0af10 unlocking 0x7fe24ac0ad90

i wouldnt count on this. i had instances where the objects are released much later. seems the auto release pools are popped kinda randomly, like in a gc...