libgcc/config/vxlib.c

   1 /* Copyright (C) 2002, 2003, 2004, 2005, 2009 Free Software Foundation, Inc.
   2    Contributed by Zack Weinberg <zack@codesourcery.com>
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 Under Section 7 of GPL version 3, you are granted additional
  17 permissions described in the GCC Runtime Library Exception, version
  18 3.1, as published by the Free Software Foundation.
  19
  20 You should have received a copy of the GNU General Public License and
  21 a copy of the GCC Runtime Library Exception along with this program;
  22 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 <http://www.gnu.org/licenses/>.  */
  24
  25 /* Threads compatibility routines for libgcc2 for VxWorks.
  26    These are out-of-line routines called from gthr-vxworks.h.  */
  27
  28 #include "tconfig.h"
  29 #include "tsystem.h"
  30 #include "gthr.h"
  31
  32 #if defined(__GTHREADS)
  33 #include <vxWorks.h>
  34 #ifndef __RTP__
  35 #include <vxLib.h>
  36 #endif
  37 #include <taskLib.h>
  38 #ifndef __RTP__
  39 #include <taskHookLib.h>
  40 #else
  41 # include <errno.h>
  42 #endif
  43
  44 /* Init-once operation.
  45
  46    This would be a clone of the implementation from gthr-solaris.h,
  47    except that we have a bootstrap problem - the whole point of this
  48    exercise is to prevent double initialization, but if two threads
  49    are racing with each other, once->mutex is liable to be initialized
  50    by both.  Then each thread will lock its own mutex, and proceed to
  51    call the initialization routine.
  52
  53    So instead we use a bare atomic primitive (vxTas()) to handle
  54    mutual exclusion.  Threads losing the race then busy-wait, calling
  55    taskDelay() to yield the processor, until the initialization is
  56    completed.  Inefficient, but reliable.  */
  57
  58 int
  59 __gthread_once (__gthread_once_t *guard, void (*func)(void))
  60 {
  61   if (guard->done)
  62     return 0;
  63
  64 #ifdef __RTP__
  65   __gthread_lock_library ();
  66 #else
  67   while (!vxTas ((void *)&guard->busy))
  68     {
  69 #ifdef __PPC__
  70       /* This can happen on powerpc, which is using all 32 bits
  71          of the gthread_once_t structure.  */
  72       if (guard->done)
  73         return;
  74 #endif
  75       taskDelay (1);
  76     }
  77 #endif
  78
  79   /* Only one thread at a time gets here.  Check ->done again, then
  80      go ahead and call func() if no one has done it yet.  */
  81   if (!guard->done)
  82     {
  83       func ();
  84       guard->done = 1;
  85     }
  86
  87 #ifdef __RTP__
  88   __gthread_unlock_library ();
  89 #else
  90   guard->busy = 0;
  91 #endif
  92   return 0;
  93 }
  94
  95 #endif /* __GTHREADS */