Horton

Re: Back-patch use of unnamed POSIX semaphores for Linux?

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: pgsql-hackers@postgreSQL.org
Date: 2016-12-07T14:38:10Z
Lists: pgsql-hackers 
Peter Eisentraut <peter.eisentraut@2ndquadrant.com> writes:
> On 12/6/16 9:53 PM, Tom Lane wrote:
>> I think we should give serious consideration to back-patching commit
>> ecb0d20a9, which changed the default semaphore type to unnamed-POSIX
>> on Linux.

> Even with that change, dynamic shared memory is still vulnerable to be
> removed.

Really?  I thought we concluded that it is safe because it is detectably
attached to running processes.  The trouble with SysV semaphores is that
they lack any such attachment, so systemd is left to guess whether they
are still in use.

			regards, tom lane

Commits

  1. Make the different Unix-y semaphore implementations ABI-compatible.

  2. Use unnamed POSIX semaphores, if available, on Linux and FreeBSD.