我应该与self同步还是与method参数同步? [英] Should I synchronize with self or with the method argument?

问题描述

在这样的方法中，它们是否可以同步(即self或thing)?

In a method like this, which do synchronize (i.e. self or thing)?

- (BOOL)deleteThing:(MSThing *)thing error:(NSError **)error
{
    @synchronized(self)  {
        if (!thing) {
            return YES;
        }

        NSString *fileName = [[self thingDirectory] stringByAppendingPathComponent:thing.cacheInstanceName];

        if (![[NSFileManager defaultManager] fileExistsAtPath:fileName]) {
        //...

===或===

- (BOOL)deleteThing:(MSThing *)thing error:(NSError **)error
{
    @synchronized(thing)  {
        if (!thing) {
            return YES;
        }

        NSString *fileName = [[self thingDirectory] stringByAppendingPathComponent:thing.cacheInstanceName];

        if (![[NSFileManager defaultManager] fileExistsAtPath:fileName]) {
        //...

推荐答案

在第一种情况下，

@synchronized(self)  { ... }

代码不会被两个线程同时在同一方法上调用同时执行 实例(self).如果代码访问或修改实例，这可能就是您想要的 以线程不安全的方式.

the code will not be executed simultaneously by two threads calling the method on the same instance (self). This is probably what you want if the code accesses or modifies the instance in a thread-unsafe way.

在第二种情况下，

@synchronized(thing)  { ... }

代码不会被两个线程同时调用的方法同时执行 相同的参数(thing).

the code will not be executed simultaneously by two threads calling the method with the same argument (thing).

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