'Why is HANDLE event object assumed valid in thread function?

Why is HANDLE event object(synchronization object which is created by CreateEvent function) in winapi assumed to be valid in thread function?

From multithreading example to microsoft docs code examples, this event object is passed to WaitForSingleObject function without any protection.

I've been doing the same. And today, I just reached to the thought that how can I deal with this "branch" safe, in such a sense like branch coverage in code perspective.

In the strict sense, this event object is shared along multiple threads, at least in the thread which calls SetEvent and in the thread which Calls WaitForSingleObject.

Therefore, it has to be classified as a type of shared resource. Then, all shared resources must be protected by "lock", such as mutex or critical section.

Also, it is possible to deliberately call CloseHandle after SetEvent while thread is alive, which will lead to passing closed event handle to WaitForSingleObject in thread function. (maybe the event object won't be deleted due to deferred deletion)

Acquiring lock and calling WaitForSingleObject in thread function, and trying to acquire lock in other thread in order to call SetEvent would definitely lead to deadlock.

[EDIT]

Maybe I misled my point by mentioning "assumed" and particular code example. I wonder how to do thread safe validity check for HANDLE event object, treating HANDLE as variable.

c++multithreadingwinapilockingshared-resource


Solution 1:[1]

According to Synchronizing Execution of Multiple Threads, There are a number of objects whose handles can be used to synchronize multiple threads. These objects include:

  • Console input buffers
  • Events
  • Mutexes
  • Processes
  • Semaphores
  • Threads
  • Timers

The state of each of these objects is either signaled or not signaled.(atomic)

For handle concerned, WaitForSingleObject function say If this handle is closed while the wait is still pending, the function's behavior is undefined.
For an invalid handle, It's programmer's responsibility to troubleshoot where the handle becomes invalid(BUG).

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Source: Stack Overflow

Solution Source
Solution 1

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