1

I'm using the code below to initialise 4 thread with the same method so that each one can perform the same process but on a separate file.

for (int i = 0; i < 4; i++)
{
    Thread newProcessThread = new Thread(ThreadProcessFile)
    {
        Priority = ThreadPriority.BelowNormal,
        IsBackground = true
    };
    newProcessThread.Start();
}

Inside the ThreadProcessFile method, it starts like this so each thread knows what is its ID is. _threadInitCount is declared in the same class.

int threadID = _threadInitCount;
_threadInitCount += 1;

However, I'm getting a weird behaviour where a number might be missed or duplicated. e.g. the first thread might have an ID of 1 and not 0 or 2 will be missing from the set of four threads.

Can anyone explain this behaviour or advise on a better way of doing this?

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2
  • 1
    Use Interlocked.Increment for shared variable Commented Jan 18, 2018 at 7:43
  • 2
    Use Parallel.For instead, it's easier. Commented Jan 18, 2018 at 7:45

1 Answer 1

Reset to default
2

Each thread already has an unique ID assigned to it. You can access it with

Thread.CurrentThread.ManagedThreadId

property.

The reason you get duplicated/missing numbers is that a context switch might occur at every moment. Imagine, for instance, that your threads get executed one-by-one line-by-line. The first thread assigns its threadID variable to _threadInitCount, which is 0. Then the second does the same, its threadID is 0 too. Then the third gets its threadID=0 and so on. Then the first thread turns on again to increase _threadInitCount to 1, then the second increases it to 2 and so on.

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