Is it worth broadening out the discussion to other sorts of named objects?  Named Pipes particularly spring to my mind...

The main reason why I requested this enhancement was to ensure that multiple processes can read/write a shared memory segment without corrupting that data in it.

To ensure the same shared semaphores came to mind. Each shared memory segment, can have a corresponding shared semaphore.

I don't think using named pipes would be a good way to ensure the same. Although, if you think otherwise please suggest so.

I also thought keeping a semphore inside the shared memory segment would be much cleaner and easier to do, but unfortunately macos has deprecated sem_t.

Other ways include storing an integer in the shared memory segment, which could be altered via atomic operations, this integer can be used as a counting semaphore.

Python uses the following atomic operations to implement GIL, which can also be used above.

https://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Atomic-Builtins.html

Also, the reason for asking named shared semaphore's was that they already exist in python library, but they are cleaned up, as soon as the process which created them dies. 

Since, macos has deprecated sem_t, the Semaphore in multiprocessor.synchronize uses SemLock class which in turn uses named semaphores, the only issue is that these semaphores are erased as soon as the process which created them dies.

Therefore, I thought it would be much easier to provide a public API to use named semaphores, since they are already implemented, after a few changes of course.

On 09-Jun-2020, at 10:32 PM, Rhodri James <rhodri@kynesim.co.uk> wrote:

On 09/06/2020 17:16, Vinay Sharma wrote:
Hi,
I posted this here because a core Developer (Tal Einat), asked me to, although I am not sure what is the protocol from here. Does this enhancement request look reasonable ?
If yes, I would love to open a PR.
If not, any suggestions, feedback is very welcome.

I've been thinking about this for a couple of days now, and I think for what little it's worth my answer is mostly yes.  You're basically asking for Named Semaphores, which are a perfectly sensible thing to want for inter-program communications.  I hesitate only because I'm more used to thinking about these things in terms of message-passing protocols, but that's no reason to reject your request.  My only bit of bikeshedding is that they ought to be a different class to the basic Semaphore to make it clear they have a different scope.

Is it worth broadening out the discussion to other sorts of named objects?  Named Pipes particularly spring to my mind...

--
Rhodri James *-* Kynesim Ltd
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