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Asked: 2026-05-13T13:33:27+00:00

I have a counter variable which will be accessed by multiple threads which will

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I have a counter variable which will be accessed by multiple threads which will increment/decrement it. It should not be updated by multiple threads at the same time.

I know that you can create a mutex object which has to be obtained before the variable in question can be changed. A critical section in this case is not appropriate because there are more than 1 function which can change the variable in question.

Is there another I can do this without using the mutex? Using a mutex does have a performance penalty (see http://www.codeguru.com/forum/showthread.php?t=333192). I believe that in Java, there is a key word you can use in the variable declaration to accomplish that (is it called “synchronized”?), but is there such a thing in C++ at all?

I know that volatile is not the keyword I am looking for.

Thank you very much.

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1 Answer

  1. Editorial Team

    Most processors have ‘atomic‘ increment and decrement instructions – in a large part, they are how mutexes are implemented at a machine level.

    You can access these atomic instructions in your own code. Windows provides the InterlockedIncrement() function, and glib provides equivalents. In x86 assembly language, you can use LOCK CMPXCHG and kin directly.

    C++ does not know anything about these concepts – you must use them yourself; there are no magic keywords for thread safety in C++.

    See Atomic Instruction

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