[ILUG] Asynchronous thread ipc

[Bryan O'Donoghue]

case 1.

[blob of logic thread:1 does some stuff has some information which is shared 
between (n) threads]
|
|
Time
|
|
[blob of logic_2 thread:2 needs to know about stuff in blob of logic 1]

case 2.

Sometimes blob of logic 1 can happen *after* blob of logic 2.


For case 2 a simple pthread_cond_time/dwait should suffice.
For case 1, the asynchronous nature of the synchronisation violates that logic, 
so that

[blob of logic1 thread:1 pthread_cond_broadcast(something);]
|
|
[blob of logic2 pthread_cond_wait(something) : blocks forever]

Which is bad.

Right now I'm having thread 1, wait for thread 2 to become ready, which also is 
bad.

[blob 1 : can be here pthread_cond_wait(something);]
|
time
|
[blob of logic 2 (thread_read==false){ nanosleep(for a while); } else { 
pthread_cond_broadcast(something);]
|
|
time
|
[or blob of logic 1 can be here pthread_cond_wait]

My other thinking is to try using a named pipe, have blob of logic 2 send some 
data onto the pipe and go about it's merry way, where blob of logic 1, does a 
select() on a shared file descriptor looking for a state change.

I haven't tried that before, but, I think it should work, however, I'd rather 
not have the overhead of running a select on a shared fd on a named pipe, if a 
manipulation of a pthread condition would allow for asynchronous signalling.

It would be highly cool if I didn't have to do polling in thread (n) for a 
state change and could just rely on an asynchronous condition.

Am I barking up the wrong tree on that and is polling in one thread or another 
unavoidable?

Trinkets/sweets to somebody who can find a non-polling solution

-- 
Bryan O'Donoghue
Embedded Software Engineer

Europlex Technologies Ltd
Clonshaugh Business & Technology Park
Dublin 17
Ireland

T:+353 (0) 1 2500500
F:+353 (0) 1 2500590
E:bryano at euoplex.ie
W:www.europlex.ie