Alfred Perlstein wrote:
> Ok, any of you guys have a copy of the standards documents that
> describe the sem_* API?
>
> I have a question...
>
> What are the semantics of the sem_init when pshared is set to true?
The sem_init() function is used to initialise the unnamed
semaphore referred to by sem. The value of the initialised
semaphore is value. Following a successful call to sem_init(),
the semaphore may be used in subsequent calls to sem_wait(),
sem_trywait(), sem_post(), and sem_destroy(). This semaphore
remains usable until the semaphore is destroyed.
If the pshared argument has a non-zero value, then the
semaphore is shared between processes; in this case, any
process that can access the semaphore sem can use sem for
performing sem_wait(), sem_trywait(), sem_post(), and
sem_destroy() operations.
Only sem itself may be used for performing synchronisation.
The result of referring to copies of sem in calls to
sem_wait(), sem_trywait(), sem_post(), and sem_destroy(), is
undefined.
If the pshared argument is zero, then the semaphore is shared
between threads of the process; any thread in this process can
use sem for performing sem_wait(), sem_trywait(), sem_post(),
and sem_destroy() operations. The use of the semaphore by
threads other than those created in the same process is
undefined.
Attempting to initialise an already initialised semaphore
results in undefined behaviour.
> Like, if the process that created the semaphore exits, then what?
The use of the semaphore by threads other than those created
in the same process is undefined.
> Is it only valid for the life of the process that did the sem_init?
The use of the semaphore by threads other than those created
in the same process is undefined.
8-).
-- Terry
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