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In-Reply-To: <1110262256.6900.118.camel@desk.home>
Subject: Re: starvation in pthread_once?
To: Ross Johnson <rpj@callisto.canberra.edu.au>
Cc: Pthreads-Win32 list <pthreads-win32@sources.redhat.com>
Message-ID: <OF60172FE4.0D25A226-ONC1256FBE.00337955-C1256FBE.0035CF09@de.ibm.com>
From: Alexander Terekhov <TEREKHOV@de.ibm.com>
Date: Tue, 08 Mar 2005 09:49:00 -0000
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[... pthread_once() and cancelation ...]

> Should one or more waiting threads get woken up and made to
> re-compete to run the init routine?

Yes. As for the rest, what you need here is DCSI-TLS or DCSI-MBR
(acquire/release memory barriers are needed on both Itanic and
XBOX NEXT... and, apart from hardware memory model, compiler
shall respect acquire/release semantics on IA-32 as well). For
serialization simply use a named mutex associated with address
of control variable and process id (to minimize contention).

DCSI-TLS: (__declspec(thread) for control variable; DLL issues
aside for a moment)

  if (!once_control) {
    named_mutex::guard guard(&once_control);
    if (!once_control) {
      <init>
      once_control = true;
    }
  }

DCSI-MBR: (atomic<> for control variable)

  if (!once_control.load(msync::acq)) {
    named_mutex::guard guard(&once_control);
    if (!once_control.load(msync::none)) {
      <init>
      once_control.store(true, msync::rel);
    }
  }

regards,
alexander.