CODEWITHSUNDEEP
c#.netmultithreadingconcurrencythread-safety
Chengting
Chengting

Reputation: 355

Update a bool value being used by a thread without lock protection

I want to know, if trying to update a boolean value being used by a thread is guaranteed to be successful, without any lock protection.

like the following case: there wont be any problem for Stop() to change the boolean member of m_ThreadActive, while threadproc is running?

private bool m_ThreadActive = true;

public void threadproc
{
    while (m_ThreadActive)
    {
    ...
    }
}

public void Stop()
{
   m_ThreadActive = false;
}

Upvotes: 1

Views: 624

Answers (1)

Matthew Watson
Matthew Watson

Reputation: 109587

It is theoretically possible that the compiler could optimise the loop in such a way that the loop variable always remains true.

To ensure that can't happen, use a Volatile.Read():

while (Volatile.Read(ref ThreadActive))

If you don't have a version of .Net which supports Volatile.Read() you could declare m_ThreadActive as volatile:

private volatile bool m_ThreadActive = true;

Or, better, use Thread.MemoryBarrier():

while (ThreadActive)
{
    Thread.MemoryBarrier();
    // ...
}

See my answer here for a program that demonstrates a requirement for volatile, Volatile.Read() or Thread.MemoryBarrier() for it to work correctly.

For more information on why the use of the volatile keyword can be a bit suspect, see this article from Eric Lippert.

Upvotes: 6

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