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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
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Date: Thu, 13 Oct 2011 12:54:38 +0200
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Cc: pjd@freebsd.org
Subject: incorrect use of pidfile(3)
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I looked at some of the programs that use pidfile(3) in base, and they
pretty much all get it wrong.  Consider these two scenarios:

1) common case

    process A                           process B

    main()
      pidfile_open() -> success
      perform_initialization()
      daemon()
        pidfile_write() -> success
        perform_work()                  main()
                                          pidfile_open() -> EEXIST
                                          exit()

2) very unlikely but still possible case

    process A                           process B

    main()
      pidfile_open() -> success         main()
      perform_initialization()            pidfile_open() -> EAGAIN
      daemon()                            perform_initialization()
        pidfile_write() -> success        daemon()
        perform_work()                      perform_work()

The problem is that most of them (at least the ones I checked) ignore a
pidfile_open() failure unless errno =3D=3D EEXIST.

How do we fix this?  My suggestion is to loop until pidfile_open()
succeeds or errno !=3D EAGAIN.  Does anyone have any objections to that
approach?

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no