1/* Return the internal lock used by mbrtowc and mbrtoc32.
2   Copyright (C) 2019-2020 Free Software Foundation, Inc.
3
4   This program is free software: you can redistribute it and/or modify
5   it under the terms of the GNU General Public License as published by
6   the Free Software Foundation; either version 3 of the License, or
7   (at your option) any later version.
8
9   This program 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 General Public License for more details.
13
14   You should have received a copy of the GNU 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>, 2019-2020.  */
18
19#include <config.h>
20
21/* When it is known that the gl_get_mbtowc_lock function is defined
22   by a dependency library, it should not be defined here.  */
23#if OMIT_MBTOWC_LOCK
24
25/* This declaration is solely to ensure that after preprocessing
26   this file is never empty.  */
27typedef int dummy;
28
29#else
30
31/* This file defines the internal lock used by mbrtowc and mbrtoc32.
32   It is a separate compilation unit, so that only one copy of it is
33   present when linking statically.  */
34
35/* Prohibit renaming this symbol.  */
36# undef gl_get_mbtowc_lock
37
38/* Macro for exporting a symbol (function, not variable) defined in this file,
39   when compiled into a shared library.  */
40# ifndef DLL_EXPORTED
41#  if HAVE_VISIBILITY
42  /* Override the effect of the compiler option '-fvisibility=hidden'.  */
43#   define DLL_EXPORTED __attribute__((__visibility__("default")))
44#  elif defined _WIN32 || defined __CYGWIN__
45#   define DLL_EXPORTED __declspec(dllexport)
46#  else
47#   define DLL_EXPORTED
48#  endif
49# endif
50
51# if defined _WIN32 && !defined __CYGWIN__
52
53#  define WIN32_LEAN_AND_MEAN  /* avoid including junk */
54#  include <windows.h>
55
56#  include "windows-initguard.h"
57
58/* The return type is a 'CRITICAL_SECTION *', not a 'glwthread_mutex_t *',
59   because the latter is not guaranteed to be a stable ABI in the future.  */
60
61/* Make sure the function gets exported from DLLs.  */
62DLL_EXPORTED CRITICAL_SECTION *gl_get_mbtowc_lock (void);
63
64static glwthread_initguard_t guard = GLWTHREAD_INITGUARD_INIT;
65static CRITICAL_SECTION lock;
66
67/* Returns the internal lock used by mbrtowc and mbrtoc32.  */
68CRITICAL_SECTION *
69gl_get_mbtowc_lock (void)
70{
71  if (!guard.done)
72    {
73      if (InterlockedIncrement (&guard.started) == 0)
74        {
75          /* This thread is the first one to need the lock.  Initialize it.  */
76          InitializeCriticalSection (&lock);
77          guard.done = 1;
78        }
79      else
80        {
81          /* Don't let guard.started grow and wrap around.  */
82          InterlockedDecrement (&guard.started);
83          /* Yield the CPU while waiting for another thread to finish
84             initializing this mutex.  */
85          while (!guard.done)
86            Sleep (0);
87        }
88    }
89  return &lock;
90}
91
92# elif HAVE_PTHREAD_API
93
94#  include <pthread.h>
95
96static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
97
98/* Make sure the function gets exported from shared libraries.  */
99DLL_EXPORTED pthread_mutex_t *gl_get_mbtowc_lock (void);
100
101/* Returns the internal lock used by mbrtowc and mbrtoc32.  */
102pthread_mutex_t *
103gl_get_mbtowc_lock (void)
104{
105  return &mutex;
106}
107
108# elif HAVE_THREADS_H
109
110#  include <threads.h>
111#  include <stdlib.h>
112
113static int volatile init_needed = 1;
114static once_flag init_once = ONCE_FLAG_INIT;
115static mtx_t mutex;
116
117static void
118atomic_init (void)
119{
120  if (mtx_init (&mutex, mtx_plain) != thrd_success)
121    abort ();
122  init_needed = 0;
123}
124
125/* Make sure the function gets exported from shared libraries.  */
126DLL_EXPORTED mtx_t *gl_get_mbtowc_lock (void);
127
128/* Returns the internal lock used by mbrtowc and mbrtoc32.  */
129mtx_t *
130gl_get_mbtowc_lock (void)
131{
132  if (init_needed)
133    call_once (&init_once, atomic_init);
134  return &mutex;
135}
136
137# endif
138
139# if (defined _WIN32 || defined __CYGWIN__) && !defined _MSC_VER
140/* Make sure the '__declspec(dllimport)' in mbrtowc.c and mbrtoc32.c does not
141   cause a link failure when no DLLs are involved.  */
142#  if defined _WIN64 || defined _LP64
143#   define IMP(x) __imp_##x
144#  else
145#   define IMP(x) _imp__##x
146#  endif
147void * IMP(gl_get_mbtowc_lock) = &gl_get_mbtowc_lock;
148# endif
149
150#endif
151