iOS之《Effective Objective-C 2.0》读书笔记（41）

第41条：多用派发队列，少用同步锁

问题由来：如果有多个线程要执行同一份代码，那么有时候可能会出问题，这种情况下，通常要使用锁／GCD来实现某种同步机制

方法一：同步块

- (void)synchronizedMethod
{
@synchronized (self) {
//Safe
}
}

方法二：使用NSLock对象

_lock = [[NSLock alloc]init];

- (void)synchronizedMethod
{
[_lock lock];
//Safe
[_lock unlock];
}

方法三：串行同步队列

dispatch_queue_t _syncQueue = dispatch_queue_create("com.effective-c.syncQueue", NULL);

-(NSString*) someString {
__block NSString* localSomething;
dispatch_sync(_syncQueue,^{
localSomeString = _someString;
});
return localSomeString
}
-(void) setSomeString:(NSString*) someString{
dispatch_sync(_syncQueue,^{
_someString = someString;
});
}

方法四：并发队列

dispatch_queue_t _concurrentQueue = dispatch_queue_create("com.read-write.queue", DISPATCH_QUEUE_CONCURRENT);

-(NSString*) someString {
__block NSString* localSomething;
dispatch_async(_concurrentQueue,^{
localSomeString = _someString;
});
return localSomeString
}
-(void) setSomeString:(NSString*) someString{
dispatch_barrier_sync(_concurrentQueue,^{  // 栅栏
_someString = someString;
});
}