linux-kernel - Re: WaitForMultipleObjects/etc. In Kernel

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Message-ID: <52EC297B.7080909@ladisch.de>
Date:	Fri, 31 Jan 2014 23:53:47 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Network Nut <sillystack@...il.com>
CC:	"'Austin S. Hemmelgarn'" <ahferroin7@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: WaitForMultipleObjects/etc. In Kernel

Network Nut wrote:
>> Assuming that you're porting to mainline distributions (and not embedded
>> devices), named SHM segments are accessible (providing the accessing
>> process has correct permissions) under /dev/shm.  You just need to make
>> sure that you create the segment with the right permissions for the
>> other processes to access it.
>
> I already know how to do named shared memory between two processes. I only included that to describe my overall problem.
>
> The problem that I am having is how I can make three totally-independent processes interact:
>
> 1. M is a master process that creates a semaphore.
> 2. P1 is a process that operates against the semaphore.
> 3. P2 is a process that operates against the semaphore.
> 4. It is not permissible that M be responsible for launching P1 or P2.
> 5.  The semaphore, one way or another, must allow itself to be specified as one of the synchronization primitives in epoll_wait()

This general problem descripton does not say anything more than your first
mail.

Use eventfd.  To share it, use a Unix domain socket created by M.  (This
socket must be created at a well-known path.  shm_open() works similarly,
but that it creates a file in a RAM disk and mmap()s it is just an
implementation detail.)


Regards,
Clemens
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