[ILUG] Asynchronous thread ipc

[Bryan O'Donoghue]

> I'm not sure I understand: is the problem that thread 1 might update twice
> and at least one of threads 2 to n might miss a transition?

The problem is that thread 2: can send data before or after thread 1 has 
executed. A race condition I guess you'd call it.

The pthread_cond_wait/broadcast logic assumes thread 1 to be in a wait state 
for thread 2, to signal it and wake it up.

This is no good if thread 2 is finished it's execution before thread 1 has put 
itself into a wait state.

So either thread 2, polls a shared variable to await thread 1, being in a sleep 
state (naff and ineffecient) or thread 1, I guess does a similar sort of 
polling on a shared file descriptor which I'm hoping will allow me not to have 
to block in the signalling thread.

The real problem is that I'm trying to replace a Windows IOCompletion blob of 
logic with a pthread solution (GNU points++;), but, the Windows IOCompletion 
ports are asynchronous, whereas the pthread_condition/broadcast sets of logic 
aren't.

Basically I'm going to introduce latency into the application by polling a 
shared state variable/descriptor. I'd like to avoid that if at all possible.

Bod

-- 
Bryan O'Donoghue
Embedded Software Engineer

Europlex Technologies Ltd
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