Is this the proper way to use a Mutex Semaphore to protect a resource?

I have two threads that call this function.  It seems to me that it is
possible that the first thread can be pre-empted before completing, then
a second thread calls this function and completes it before the first
function has returned a value.

ULONG  someFn()
{

  request.MutexSem();

  ULONG rc = 0;

  rc = something;

  str = somethingtoo;  // this also needs protecting because str is
                       // used in another function that is also
                       // called by two or more threads.

  release.MutexSem();

  return rc;  // A calling thread is pre-empted here before returning rc.

              // A second threads comes along and completes the
              // function before the first thread has finished,
              // thus causing rc to contain invalid data.
              // Is this possible?
}


Phil Crown
pcrown{at}airmail.net
http://web2.airmail.net/pcrown/

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