为什么在此示例中线程连接的行为有所不同？

Question

更新的问题更通用:

我有以下代码.当您交换线程[i] .Join()的位置时,您会得到不同的输出.

static void ThreadedWorker(int startIndex, int endIndex)
{
    Console.WriteLine("Working from results[ " + startIndex +"] to results["+endIndex+"]");
}

static void Main(string[] args)
{
    int threadCount = System.Environment.ProcessorCount;
    int calculationCount = 500; //the number of array elements we'd be iterating over if we were doing our work
    int threadDataChunkSize = calculationCount / threadCount;
    if (threadDataChunkSize < 1) threadDataChunkSize = 1; //just in case we have loads of threads

    Thread[] threads = new Thread[threadCount];
    for (int i = 0; i < threadCount; i++)
    {
        threads[i] = new Thread(() => ThreadedWorker(threadDataChunkSize * i, threadDataChunkSize*(i+1)));
        threads[i].Start();
        //threads[i].Join(); //****Uncomment for correct behaviour****
    }

    for (int i = 0; i < threadCount; i++)
    {
        //threads[i].Join(); //****Uncomment for incorrect behaviour****
    }

    Console.WriteLine("breakhere");
}

当Join()在第一个循环中,创建顺序行为时,您将获得输出

Working from results[ 0] to results[125]
Working from results[ 125] to results[250]
Working from results[ 250] to results[375]
Working from results[ 375] to results[500]

当Join()在第二个循环中,创建并行行为时,您将得到非确定性输出,如:

Working from results[ 375] to results[500]
Working from results[ 375] to results[500]
Working from results[ 500] to results[625]
Working from results[ 500] to results[625] (i is sometimes more than it should ever be!)

我怀疑lambda表达式会以某种方式导致问题.希望这个改述也表明这不是一个错误的计算错误,或其他滥用我的阵列!

---

最初的问题不太通用,并使用startIndex和endIndex来迭代执行工作的字节数组.我将其描述ThreadedWorker为"不工作",因为它似乎有时更新结果数组,有时不会.它现在似乎被调用,但startindex和endindex被破坏了.

Answer 1

Join在启动它之前,在启动下一个线程之前,每个线程的第一个代码.

因此,所有线程按顺序运行.

第二个代码立即运行所有线程,然后立即运行所有线程Join.

因此,线程在完全相同的数据上并发运行.

第二个代码可能无法正常工作,因为您的代码或数据不是线程安全的.