gl/setlocale-lock.c

   1 /* Return the internal lock used by setlocale_null_r.
   2    Copyright (C) 2019-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2019.  */
  18
  19 #include <config.h>
  20
  21 /* The option '--disable-threads' explicitly requests no locking.  */
  22 /* When it is known that the gl_get_setlocale_null_lock function is defined
  23    by a dependency library, it should not be defined here.  */
  24 #if AVOID_ANY_THREADS || OMIT_SETLOCALE_LOCK
  25
  26 /* This declaration is solely to ensure that after preprocessing
  27    this file is never empty.  */
  28 typedef int dummy;
  29
  30 #else
  31
  32 /* This file defines the internal lock used by setlocale_null_r.
  33    It is a separate compilation unit, so that only one copy of it is
  34    present when linking statically.  */
  35
  36 /* Prohibit renaming this symbol.  */
  37 # undef gl_get_setlocale_null_lock
  38
  39 /* Macro for exporting a symbol (function, not variable) defined in this file,
  40    when compiled into a shared library.  */
  41 # ifndef SHLIB_EXPORTED
  42 #  if HAVE_VISIBILITY
  43   /* Override the effect of the compiler option '-fvisibility=hidden'.  */
  44 #   define SHLIB_EXPORTED __attribute__((__visibility__("default")))
  45 #  elif defined _WIN32 || defined __CYGWIN__
  46 #   define SHLIB_EXPORTED __declspec(dllexport)
  47 #  else
  48 #   define SHLIB_EXPORTED
  49 #  endif
  50 # endif
  51
  52 # if defined _WIN32 && !defined __CYGWIN__
  53
  54 #  define WIN32_LEAN_AND_MEAN  /* avoid including junk */
  55 #  include <windows.h>
  56
  57 #  include "windows-initguard.h"
  58
  59 /* The return type is a 'CRITICAL_SECTION *', not a 'glwthread_mutex_t *',
  60    because the latter is not guaranteed to be a stable ABI in the future.  */
  61
  62 /* Make sure the function gets exported from DLLs.  */
  63 SHLIB_EXPORTED CRITICAL_SECTION *gl_get_setlocale_null_lock (void);
  64
  65 static glwthread_initguard_t guard = GLWTHREAD_INITGUARD_INIT;
  66 static CRITICAL_SECTION lock;
  67
  68 /* Returns the internal lock used by setlocale_null_r.  */
  69 CRITICAL_SECTION *
  70 gl_get_setlocale_null_lock (void)
  71 {
  72   if (!guard.done)
  73     {
  74       if (InterlockedIncrement (&guard.started) == 0)
  75         {
  76           /* This thread is the first one to need the lock.  Initialize it.  */
  77           InitializeCriticalSection (&lock);
  78           guard.done = 1;
  79         }
  80       else
  81         {
  82           /* Don't let guard.started grow and wrap around.  */
  83           InterlockedDecrement (&guard.started);
  84           /* Yield the CPU while waiting for another thread to finish
  85              initializing this mutex.  */
  86           while (!guard.done)
  87             Sleep (0);
  88         }
  89     }
  90   return &lock;
  91 }
  92
  93 # elif HAVE_PTHREAD_API
  94
  95 #  include <pthread.h>
  96
  97 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
  98
  99 /* Make sure the function gets exported from shared libraries.  */
 100 SHLIB_EXPORTED pthread_mutex_t *gl_get_setlocale_null_lock (void);
 101
 102 /* Returns the internal lock used by setlocale_null_r.  */
 103 pthread_mutex_t *
 104 gl_get_setlocale_null_lock (void)
 105 {
 106   return &mutex;
 107 }
 108
 109 # elif HAVE_THREADS_H
 110
 111 #  include <threads.h>
 112 #  include <stdlib.h>
 113
 114 static int volatile init_needed = 1;
 115 static once_flag init_once = ONCE_FLAG_INIT;
 116 static mtx_t mutex;
 117
 118 static void
 119 atomic_init (void)
 120 {
 121   if (mtx_init (&mutex, mtx_plain) != thrd_success)
 122     abort ();
 123   init_needed = 0;
 124 }
 125
 126 /* Make sure the function gets exported from shared libraries.  */
 127 SHLIB_EXPORTED mtx_t *gl_get_setlocale_null_lock (void);
 128
 129 /* Returns the internal lock used by setlocale_null_r.  */
 130 mtx_t *
 131 gl_get_setlocale_null_lock (void)
 132 {
 133   if (init_needed)
 134     call_once (&init_once, atomic_init);
 135   return &mutex;
 136 }
 137
 138 # endif
 139
 140 # if (defined _WIN32 || defined __CYGWIN__) && !defined _MSC_VER
 141 /* Make sure the '__declspec(dllimport)' in setlocale_null.c does not cause
 142    a link failure when no DLLs are involved.  */
 143 #  if defined _WIN64 || defined _LP64
 144 #   define IMP(x) __imp_##x
 145 #  else
 146 #   define IMP(x) _imp__##x
 147 #  endif
 148 void * IMP(gl_get_setlocale_null_lock) = &gl_get_setlocale_null_lock;
 149 # endif
 150
 151 #endif