Did he run ikegami's code?

Of course I did. What else do you think triggered my reaction to it?

Can you please explain, how exactly does it hang?

The best I've been able to conclude is that the signal is simply not seen by the waiters; because of the crude and sloppy emulation.

But even in *nix, cond_vars are known to be unreliable with waits spuriously returning even when no thread has signalled; and signals being missed if there are no waiters waiting at the exact moment of the signal. Edge-triggered semantics.

The best analogy I've seen for it is: playing phone tag in the days before voicemail and answering machines. Unless the recipient of the call is sat waiting by the phone when it rings; the call goes completely unnoticed.

The unlock-and-block part of cond_wait() is atomic; hence, by the time another thread acquires the lock, this first thread is guaranteed to be in a waiting state.

Spurious signals cannot cause a deadlock either — the test condition is lock-protected and can only proceed when other thread has entered cond_wait() (with the cond variable set to the satisfaction of the first thread).

The unlock-and-block part of cond_wait() is atomic; hence, by the time another thread acquires the lock, this first thread is guaranteed to be in a waiting state.

But if the signalling thread signals before the other thread(s) reach the wait(); that signal can be lost.

• lost signals.
• signals getting lost
• Lost wakeups in pthreads
• Lost signals - slow conditions
• a) spurious wakeups. b) lost signals; c) broadcast deadlock d) unfairness
• In our approach we use Petri nets to represent the key elements of interactions among threads to identify potential problems such as race conditions, lost signals, and deadlocks. A tool called C2Petri has been developed which converts C-Pthreads programs to the equivalent Petri net model. This tool helps verification of Pthread-based programs.
• Hundreds more...

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In the absence of evidence, opinion is indistinguishable from prejudice.