Objective C 线程中线程变量的生命周期

Question

我有一个 NSOperation，在其 -main 方法中使用 [NSThread detachNewThreadSelector:@selector(aMethod:) toTarget:self withObject:anArgument];

aObject （我的实例变量NSOperation 子类）是对 -main 方法内返回的自动释放数组的对象的弱引用...

-(void)main {

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSArray *clients = [group produceClients]; // clients array is an autorelease instance
    self->aObject = [clients objectAtIndex:3]; // a weak reference, Lets say at index three!

    [NSThread detachNewThreadSelector:@selector(aMethod:) 
                             toTarget:self 
                           withObject:@"I use this for another thing"];

    // Do other things here that may take some time

    [pool release];
}

-(void)aMethod:(NSString*)aStr {

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    // aStr object is reserved for another functionality
    // I know that I could pass a NSDictionary with a number of entries, which would be
    // retained by `detachNewThreadSelector` but then ... 
    // I wouldn't have to ask this question ! :)

    // Do several things with aObject, which is a weak reference as described above.
    NSLog(@"%@", [self->aObject.id]);
    // Is it safe ?

    [pool release];
}

我知道 NSThread 的 detachNewThreadSelector 方法保留 self 和withObject:anArgument，但是 aObject 会发生什么？是否确定在执行分离线程 (aMethod:) 期间会存在？ Self 被 detachNewThreadSelector 保留，这是否意味着主线程的池将被延迟释放，因为它被保留，因此 clients 将存在，因此 >aObject 会存在吗？
或者 -main (NSOperation) 线程将在 -aMethod (NSThread) 完成之前完成执行并释放，因此在那里使用 aObject 是不安全的？

真正的问题是：当从线程内部调用 [NSThread detachNewThreadSelector:@selector(aMethod:) ...toTarget:self ...] 时，最后一个线程是否以它的方式保留自动释放的实例（clients 数组）可以安全地在 aMethod (self->aObject) 中使用（可以说通过弱引用）？

Answer 1

你的方法似乎非常不稳定，但我不是多线程专家，所以我可能是错的。您的客户端数组位于主自动释放池中，您不能保证它会等到您的 aMethod 线程完成耗尽。怎么样：

-(void)main {

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    [NSThread detachNewThreadSelector:@selector(aMethod:) 
                             toTarget:self 
                           withObject:@"I use this for another thing"];

    [pool release];
}

-(void)aMethod:(NSString*)aStr {

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSArray *clients = [group produceClients]; // clients array is an autorelease instance
    self->aObject = [clients objectAtIndex:3]; // a weak reference, Lets say at index three!

    [pool release];
}

通过这种方法，您的客户端数组位于线程的自动释放池中。