CODEWITHSUNDEEP
c++cwindowswinapisynchronization
T.T.T.
T.T.T.

Reputation: 34523

Does a mutex still need to be released if it times-out?

Using the WaitForSingleObject Function.

If the function is called and times out, does it still need to release the mutex?

i.e. should ReleaseMutex be in position 1. or 2. if the five seconds elapse? 

WaitForSingleObject(5 second time out)
{
  //access shared resource

  //1. - ReleaseMutex() here?
}
  //2. - ReleaseMutex() here?

Upvotes: 4

Views: 436

Answers (3)

John
John

Reputation: 5635

You only need to release the mutex if you got ownership. Note that there are 4 possible return values, in 2 cases you get ownership, and in 2 you do not.

WAIT_ABANDONED - you got ownership and need to release the mutex, but the previous owner terminated without explicitly releasing the mutext so shared state may be inconsistent.

WAIT_OBJECT_0 - you got the ownership. You need to release the mutext.

WAIT_TIMEOUT - the mutext was not released for the duration of timeout

WAIT_FAILED - usually due to a bug in your code (i.e. invalid handle).

Upvotes: 2

Amardeep AC9MF
Amardeep AC9MF

Reputation: 19034

Your case #1 is correct. If you time out on that call, it means the resource was not acquired and you should not attempt to release it.

Upvotes: 2

Anthony Williams
Anthony Williams

Reputation: 68561

No. If the call to WaitForSingleObject times out then you have not acquired the mutex, so should not release it.

i.e. you only need ReleaseMutex at position 1.

Upvotes: 6

Related Questions