中央调度中心，目标C，阻塞问题

Question

我有以下方法

+ (NSString*)getMeMyString
{
   NSString *result;
   dispatch_async(dispatch_get_main_queue(), ^{
        result = [ClassNotThreadSafe getString];
    });
   return result;
}

我怎么能使块做它的工作同步，使它不返回结果之前，它被检索?

Answer 1

您正在调用dispatch_async，它异步调度您的块。如果您的目标是阻塞主线程，请尝试使用dispatch_sync或dispatch_main。

+ (NSString*)getMeMyString
{
   __block NSString *result;
   dispatch_sync(dispatch_get_main_queue(), ^{
        result = [ClassNotThreadSafe getString];
    });
   return result;
}

中央调度参考

Answer 2

使用dispatch_sync而不是dispatch_async -那么当前线程将被阻塞，直到阻塞在主线程上完成执行。

Answer 3

既然你想在不同的线程上执行方法并获得返回值，为什么不使用NSInvocation呢?

SEL theSelector;
NSMethodSignature *aSignature;
NSInvocation *anInvocation;
theSelector = @selector(getString);
aSignature = [ClassNotThreadSafe instanceMethodSignatureForSelector:theSelector];
anInvocation = [NSInvocation invocationWithMethodSignature:aSignature];
[anInvocation setSelector:theSelector];
NSString *result;
[anInvocation performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:YES];
[anInvocation getReturnValue:result];