Test and conditionally update a long using Interlocked

Is there a neat way to do this using the Interlocked class? Or should I just use lock { }?

My specific use case is that I have multiple threads that compute a long value, and compare it to a shared "Maximum" value, replacing the shared value开发者_Python百科 only if the local value is larger.

Try the Interlocked.CompareExchange method. I haven't tried, but something like this seems logical to me:

long localMax = Interlocked.Read(ref max);
while (value > localMax) {
  Interlocked.CompareExchange(ref max, value, localMax);
  localMax = Interlocked.Read(ref max);
}

As usual, stress test your code to try to catch concurrency issues.

So long as the value of your shared field only ever increases then you could do something like this with a combination of Read and CompareExchange.

long sharedVal = Interlocked.Read(ref _sharedField);
while (localVal > sharedVal)
{
    long temp = Interlocked.CompareExchange(ref _sharedField, localVal, sharedVal);
    sharedVal = (temp == sharedVal) ? localVal : temp;
}

However, I would go for a plain lock in this situation: using Interlocked like this is less readable than a lock block and has the potential for much poorer performance too.