Re: waiting for more than one cond in pThread question

[Keith Willis <keith at bytebrothers dot co dot uk>]

On Wed, 03 Apr 2002 10:15:03 +1000, Ross Johnson
<rpj@ise.canberra.edu.au> wrote:

>Keith Willis wrote:
>> 
>> OK, how about you associate one mutex/condvar with the _set_ of
>> predicate conditions[1], and do something like:
>> 
>> ============================================================
>> pthread_mutex_lock(&mutex);
>> while (predicate_one == FALSE && predicate_two == FALSE)
>> {
>>         pthread_cond_wait(&condvar, &mutex);
>> }
>> pthread_unlock_mutex(&mutex);
>> 
>> if (predicate_one == TRUE)
>>         do_something();
>> else if (predicate_two == TRUE)
>>         do_something_else();
>> else
>>         something_horrible_happened();
>> ============================================================
>> 
>
>... except you need to unlock the mutex after you've finished
>using or copying the predicate values locally, otherwise
>you've got a race condition.

So, something more like this might do the trick?

============================================================
pthread_mutex_lock(&mutex);
while (predicate_one == FALSE && predicate_two == FALSE)
{
    pthread_cond_wait(&condvar, &mutex);
}

if (predicate_one == TRUE)
{
    pthread_unlock_mutex(&mutex);
    do_something();
}
else if (predicate_two == TRUE)
{
    pthread_unlock_mutex(&mutex);
    do_something_else();
}
else
{
    pthread_unlock_mutex(&mutex);
    something_horrible_happened();
}
============================================================

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