How do you get the current count from CSemaphore?

I am trying to debug a multi-thr开发者_开发技巧eaded program that uses CSemaphore to limit the size of a buffer.

How do you get the current value of the semaphore counter from this class? It doesn't seem to be directly accessed from any of its members, and I can't seem to find any functions that will give me it either.

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You're not supposed to care - this is a semaphore, not thread-shared counter.

That said, you might abuse the ReleaseSemaphore API's lpPreviousCount output parameter

BOOL WINAPI ReleaseSemaphore(
  __in       HANDLE hSemaphore,
  __in       LONG lReleaseCount,
  __out_opt  LPLONG lpPreviousCount
);

The idea:

CSemaphore &mySemaphore = /*initialized from somewhere*/;

HANDLE hsem = (HANDLE) mySemaphore; // http://msdn.microsoft.com/en-us/library/f5zcch25.aspx
LONG peeked_count;
::ReleaseSemaphore(hsem, 1 /*can't be 0, sorry!*/, &peeked_count);

Note that unfortunately you'll have to actually release the semaphore (lReleaseCount must be >0)

---

That is not easily possible. If you really want to do that, all I can think of doing is to try to lock the semaphore manually as many times as possible, until the locking fails, with 0 time-out, and unlocking immediately after that. You will also have to remember the max count. E.g., untested code:

int max_count = 5;
CSemaphore sem (max_count, max_count);
/*...*/
int count = 0;
while (sem.Lock (0))
  ++count;
for (int i = 0; i != count; ++i)
  sem.Unlock(count);
std::cout << "the lock count is " << (max_count - count);

EDIT:

After seeing sehe's solution, I think a better solution would be combination of both:

int max_count = 5;
CSemaphore sem (max_count, max_count);
if (sem.Lock(0))
{
  LONG peeked_count;
  ::ReleaseSemaphore(hsem, 1 /*can't be 0, sorry!*/, &peeked_count);
  /* peeked_count has the count */
}
else
{
  /* I do not think it is safe to release the semaphore even if just for debugging. */
  /* max_count has the count */
}