Objective-C的NSMutableArray是否是线程安全的？ [英] Is Objective-C's NSMutableArray thread-safe?

问题描述

我一直试图解决这个崩溃已近一周了。应用程序崩溃，没有任何异常或堆栈跟踪。在僵尸模式下运行仪器时，应用程序不会以任何方式崩溃。

I've been trying to fix this crash for almost a week. The application crashes without any exception or stack-trace. The application does not crash in any way while running through instruments in zombie mode.

我有一个在不同线程上调用的方法。
修复崩溃的解决方案是替换

I have a method that gets called on a different thread. The solution that fixed the crash was replacing

[self.mutableArray removeAllObjects];

with

dispatch_async(dispatch_get_main_queue(), ^{
    [self.searchResult removeAllObjects];
});

我认为这可能是一个时间问题，所以我尝试同步它，但它仍然崩溃：

I thought it might be a timing issue, so I tried to synchronize it, but it still crashed:

@synchronized(self)
{
    [self.searchResult removeAllObjects];
}

这是代码

- (void)populateItems
{
   // Cancel if already exists  
   [self.searchThread cancel];

   self.searchThread = [[NSThread alloc] initWithTarget:self
                                               selector:@selector(populateItemsinBackground)
                                                 object:nil];

    [self.searchThread start];
}


- (void)populateItemsinBackground
{
    @autoreleasepool
    {
        if ([[NSThread currentThread] isCancelled])
            [NSThread exit];

        [self.mutableArray removeAllObjects];

        // Populate data here into mutable array

        for (loop here)
        {
            if ([[NSThread currentThread] isCancelled])
                [NSThread exit];

            // Add items to mutableArray
        }
    }
}

NSMutableArray的这个问题是不是线程安全的？

Is this problem with NSMutableArray not being thread-safe?

推荐答案

否。

它不是线程安全的，如果你需要从另一个线程修改你的可变数组，你应该使用 NSLock 来确保一切顺利计划：

It is not thread safe and if you need to modify your mutable array from another thread you should use NSLock to ensure everything goes as planned:

NSLock *arrayLock = [[NSLock alloc] init];

[...] 

[arrayLock lock]; // NSMutableArray isn't thread-safe
[myMutableArray addObject:@"something"];
[myMutableArray removeObjectAtIndex:5];
[arrayLock unlock];

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