ios - 写入流 iOS 时的自旋锁(仅在模拟器上)

Question

每当我将应用程序发送到后台时，我都会收到旋转锁定错误。这是最小化应用程序时的代码:

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    if (savedResults || savedSchedule || watchingClasses || professors) {
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *docDir = [paths objectAtIndex:0];
        NSString *fullPath = [docDir stringByAppendingFormat:@"/%@", kFileName];
        NSMutableArray *array = [NSMutableArray arrayWithCapacity:4];
        if (!savedResults)  {
            [array addObject:[NSNull null]];
        }else {
            [array addObject:savedResults];
        }
        if (!savedSchedule) {
            [array addObject:[NSNull null]];
        }else {
            [array addObject:savedSchedule];
        }
        if (!watchingClasses) {
            [array addObject:[NSNull null]];
        }else {
            [array addObject:watchingClasses];
        }
        if (!serverAnnouncements) {
            [array addObject:[NSNull null]];
        }else {
            [array addObject:serverAnnouncements];

        }if (!professors) {
            [array addObject:[NSNull null]];
        }else {
            [array addObject:professors];
        }
        [NSKeyedArchiver archiveRootObject:[array copy] toFile:fullPath];
    }
        //close connection
    if (outputStream) {
        if ([outputStream hasSpaceAvailable]) {
            dispatch_queue_t task = dispatch_queue_create("Close Connection", nil);
            NSString *str = @"_CLOSE_CONNECTION*\n";
            NSData *dataToSend = [[NSData alloc] initWithData:[str dataUsingEncoding:NSUTF8StringEncoding]];
            dispatch_async(task, ^{
                [outputStream write:[dataToSend bytes] maxLength:[dataToSend length]];
            });
        }
    }
    [inputStream close];
    [outputStream close];
    inputStream = nil;
    outputStream = nil;
    [inputStream removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [outputStream removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    initializedSocket = NO;

    [FlurryAds setAdDelegate:nil];
}

我在 ouputStream 写入方法上收到 EXC_BAD_ACCESS。我还附上了屏幕截图。

Answer 1

看起来像一个悬空指针。

该流在 ivar 中被引用，因此您的分派(dispatch) block 仅保留 self，而不是 self->outputStream。当您在分派(dispatch) block 后立即清除 ivar 时，对它的唯一强引用就会消失，并且流在仍在使用时会被释放，从而导致崩溃。

为了避免这个问题，请确保您的 block 通过使用本地范围的变量而不是 ivar 来维护对流的强引用:

NSOutputStream *os = self->outputStream;
dispatch_async
(
    ...,
    ^ {
        [os write:...];
    }
);

注意，在这里为这一个 block 创建调度队列是没有意义的；你应该只使用全局队列。