Re: [ECOS] Condition Variables recap

[Jonathan Larmour <jlarmour at redhat dot com>]

"Trenton D. Adams" wrote:
> 
>   > > WHY DO WE REQUIRE THE WHILE LOOP? ANY WAY THE
>   > > CYG_COND_WAIT CANNOT PROCEED BEFORE IT OBTAINS THE
>   > > MUTEX AND BROADCAST FROM THE PRODUCER AND OTHER
>   > > THREADS?
>   >
>   > Two threads waiting on the condition may be woken up. They won't run
> at
>   > the
>   > same time since only one can have the mutex locked, but when the
> second
>   > one
>   > runs, the condition will not be true any more.
>   >
> 
> Does this mean that during cyg_cond_wait () an internal variable is set
> to FALSE?

No, the state of the condition variable doesn't necessarily reflect the
_actual_ state of the condition, that's why you have to retest.

>  If so, then the next thread to continue inside it's
> cyg_cond_wait () will simply return because the condition variable is no
> longer valid?

It will lock the mutex though - as all cyg_cond_wait()'s must do on return,
so it won't block immediately.

>   > > ALSO COULD ANYONE EXPLAIN - WHAT IS THE VARIABLE IN
>   > > THE WHILE LOOP. WHAT DOES IT TEST?
>   >
>   > The condition you are waiting for...
>   >
> 
> The condition_not_true statement must contain a variable that I make for
> testing whether the loop should continue or not, and I would set this
> variable to true after one of the consumer threads finished using the
> resource!  Correct?

Generally the condition is more like  "is there data available to read" and
so on.

Jifl
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