Windows Event implementation in Linux using conditional variables?

Question

I am trying to implement very simple Windows events in Linux. Only for my scenario - 3 threads, 1 main and 2 secondary. Each of secondary threads raise 1 event by SetEvent a

Answer 1

Basing this on the description of WaitForSingleObject

The WaitForSingleObject function checks the current state of the specified object. If the object's state is nonsignaled, the calling thread enters the wait state until the object is signaled or the time-out interval elapses.

The difference between that behavior and the code is that the code will always wait on the condition variable, as it does not check a predicate. This introduces synchronization issues between the pthread_condt_timewait and pthread_cond_signal calls.

The general idiom for signalling a condition variable is:

lock mutex
set predicate
unlock mutex
signal condition variable

And when waiting for a condition variable:

lock mutex
while ( !predicate )
{ 
  wait on condition variable
}
unlock mutex

Based on what is trying to be accomplished, a separate bool could be used as a predicate for each Event. By introducing a predicate, WaitForSingleObject should only wait on the condition variable if the Event has not been signaled. The code would look similar to the following:

bool SetEvent (mutex, condition)
{
    pthread_mutex_lock(mutex);                 // lock mutex
    bool& signalled = find_signal(condition);  // find predicate
    signalled = true;                          // set predicate
    pthread_mutex_unlock(mutex);               // unlock mutex
    pthread_cond_signal(condition);            // signal condition variable
}

int WaitForSingleObject(mutex, condition, timeout)
{
    pthread_mutex_lock(mutex);                         // lock mutex
    bool& signalled = find_signal(condition);          // find predicate
    while (!signalled)
    {
      pthread_cond_timedwait(condition, mutex, timeout);
    }
    signalled = false;                                 // reset predicate
    pthread_mutex_unlock(mutex);                       // unlock mutex
}