c++ - Statement reordering with locks -

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Here are some C ++ code which is accessed from multiple threads in parallel. There is an important section in it: 

  lock.Acquire (); Current_id = shared_id; // Less amount of other code shared_id = (shared_id + 1)% max_id; Lock.Release (); // do something with current_id

The class of lock variable is wrapped around the POSIX mutation implementation. Due to module operations, it is not possible to use nuclear operations.

Is it possible that a GCC compiler with the O3 flag optimizes the code so that the current_id's assignment can be transferred before lock?

It is possible to compile from O3!

Make a function call the compiler until the function is marked as pure using function-attributes.

Mutex functions are not pure, so they are perfectly safe to use with O3.


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