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1 /* Copyright (C) 2002-2017 Free Software Foundation, Inc.
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2 Contributed by Zack Weinberg <zack@codesourcery.com>
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3
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4 This file is part of GCC.
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5
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6 GCC is free software; you can redistribute it and/or modify it under
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7 the terms of the GNU General Public License as published by the Free
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8 Software Foundation; either version 3, or (at your option) any later
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9 version.
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10
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11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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14 for more details.
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15
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16 Under Section 7 of GPL version 3, you are granted additional
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17 permissions described in the GCC Runtime Library Exception, version
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18 3.1, as published by the Free Software Foundation.
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19
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20 You should have received a copy of the GNU General Public License and
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21 a copy of the GCC Runtime Library Exception along with this program;
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22 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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23 <http://www.gnu.org/licenses/>. */
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24
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25 /* Threads compatibility routines for libgcc2 for VxWorks.
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26 These are out-of-line routines called from gthr-vxworks.h. */
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27
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28 #include "tconfig.h"
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29 #include "tsystem.h"
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30 #include "gthr.h"
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31
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32 #if defined(__GTHREADS)
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33 #include <vxWorks.h>
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34 #ifndef __RTP__
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35 #include <vxLib.h>
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36 #endif
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37 #include <taskLib.h>
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38 #ifndef __RTP__
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39 #include <taskHookLib.h>
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40 #else
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41 # include <errno.h>
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42 #endif
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43
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44 /* Init-once operation.
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45
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46 This would be a clone of the implementation from gthr-solaris.h,
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47 except that we have a bootstrap problem - the whole point of this
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48 exercise is to prevent double initialization, but if two threads
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49 are racing with each other, once->mutex is liable to be initialized
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50 by both. Then each thread will lock its own mutex, and proceed to
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51 call the initialization routine.
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52
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53 So instead we use a bare atomic primitive (vxTas()) to handle
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54 mutual exclusion. Threads losing the race then busy-wait, calling
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55 taskDelay() to yield the processor, until the initialization is
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56 completed. Inefficient, but reliable. */
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57
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58 int
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59 __gthread_once (__gthread_once_t *guard, void (*func)(void))
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60 {
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61 if (guard->done)
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62 return 0;
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63
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64 #ifdef __RTP__
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65 __gthread_lock_library ();
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66 #else
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67 while (!vxTas ((void *)&guard->busy))
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68 {
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69 #ifdef __PPC__
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70 /* This can happen on powerpc, which is using all 32 bits
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71 of the gthread_once_t structure. */
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72 if (guard->done)
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73 return 0;
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74 #endif
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75 taskDelay (1);
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76 }
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77 #endif
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78
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79 /* Only one thread at a time gets here. Check ->done again, then
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80 go ahead and call func() if no one has done it yet. */
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81 if (!guard->done)
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82 {
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83 func ();
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84 guard->done = 1;
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85 }
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86
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87 #ifdef __RTP__
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88 __gthread_unlock_library ();
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89 #else
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90 guard->busy = 0;
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91 #endif
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92 return 0;
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93 }
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94
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95 #endif /* __GTHREADS */
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