iOS·宏封装线程锁小技巧

#define Lock() dispatch_semaphore_wait(self->_lock, DISPATCH_TIME_FOREVER)
#define Unlock() dispatch_semaphore_signal(self->_lock)

- (NSInteger)totalCount {
    Lock();
    int count = [_kv getItemsCount];
    Unlock();
    return count;
}

- (int)getItemsCount {
    return [self _dbGetTotalItemCount];
}

#define LOCK(...) dispatch_semaphore_wait(self->_lock, DISPATCH_TIME_FOREVER); \
__VA_ARGS__; \
dispatch_semaphore_signal(self->_lock);

#define LOCK_VIEW(...) dispatch_semaphore_wait(view->_lock, DISPATCH_TIME_FOREVER); \
__VA_ARGS__; \
dispatch_semaphore_signal(view->_lock);

- (void)didReceiveMemoryWarning:(NSNotification *)notification {
    [_requestQueue cancelAllOperations];
    [_requestQueue addOperationWithBlock: ^{
        _incrBufferCount = -60 - (int)(arc4random() % 120); // about 1~3 seconds to grow back..
        NSNumber *next = @((_curIndex + 1) % _totalFrameCount);
        LOCK(
             NSArray * keys = _buffer.allKeys;
             for (NSNumber * key in keys) {
                 if (![key isEqualToNumber:next]) { // keep the next frame for smoothly animation
                     [_buffer removeObjectForKey:key];
                 }
             }
        )//LOCK
    }];
}