aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/icu/common/umutex.h
blob: 1b8332409c6dda72c4f09dbe5a88218d9a8bfdf0 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
**********************************************************************
*   Copyright (C) 1997-2015, International Business Machines
*   Corporation and others.  All Rights Reserved.
**********************************************************************
*
* File UMUTEX.H
*
* Modification History:
*
*   Date        Name        Description
*   04/02/97  aliu        Creation.
*   04/07/99  srl         rewrite - C interface, multiple mutices
*   05/13/99  stephen     Changed to umutex (from cmutex)
******************************************************************************
*/

#ifndef UMUTEX_H
#define UMUTEX_H

#include <atomic>
#include <condition_variable>
#include <mutex>
#include <type_traits>

#include "unicode/utypes.h"
#include "unicode/uclean.h"
#include "unicode/uobject.h"

#include "putilimp.h"

#if defined(U_USER_ATOMICS_H) || defined(U_USER_MUTEX_H)
// Support for including an alternate implementation of atomic & mutex operations has been withdrawn.
// See issue ICU-20185.
#error U_USER_ATOMICS and U_USER_MUTEX_H are not supported
#endif

// Export an explicit template instantiation of std::atomic<int32_t>. 
// When building DLLs for Windows this is required as it is used as a data member of the exported SharedObject class.
// See digitlst.h, pluralaffix.h, datefmt.h, and others for similar examples.
//
// Similar story for std::atomic<std::mutex *>, and the exported UMutex class.
#if U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN && !defined(U_IN_DOXYGEN)
#if defined(__clang__) || defined(_MSC_VER)
  #if defined(__clang__)
    // Suppress the warning that the explicit instantiation after explicit specialization has no effect.
    #pragma clang diagnostic push
    #pragma clang diagnostic ignored "-Winstantiation-after-specialization"
  #endif
template struct U_COMMON_API std::atomic<int32_t>;
template struct U_COMMON_API std::atomic<std::mutex *>;
  #if defined(__clang__)
    #pragma clang diagnostic pop
  #endif
#elif defined(__GNUC__)
// For GCC this class is already exported/visible, so no need for U_COMMON_API.
template struct std::atomic<int32_t>;
template struct std::atomic<std::mutex *>;
#endif
#endif


U_NAMESPACE_BEGIN

/****************************************************************************
 *
 *   Low Level Atomic Operations, ICU wrappers for.
 *
 ****************************************************************************/

typedef std::atomic<int32_t> u_atomic_int32_t;

inline int32_t umtx_loadAcquire(u_atomic_int32_t &var) {
    return var.load(std::memory_order_acquire);
}

inline void umtx_storeRelease(u_atomic_int32_t &var, int32_t val) {
    var.store(val, std::memory_order_release);
}

inline int32_t umtx_atomic_inc(u_atomic_int32_t *var) {
    return var->fetch_add(1) + 1;
}

inline int32_t umtx_atomic_dec(u_atomic_int32_t *var) {
    return var->fetch_sub(1) - 1;
}


/*************************************************************************************************
 *
 *  UInitOnce Definitions.
 *
 *************************************************************************************************/

struct U_COMMON_API UInitOnce {
    u_atomic_int32_t   fState {0};
    UErrorCode       fErrCode {U_ZERO_ERROR};
    void reset() {fState = 0;}
    UBool isReset() {return umtx_loadAcquire(fState) == 0;}
// Note: isReset() is used by service registration code.
//                 Thread safety of this usage needs review.
};

U_COMMON_API UBool U_EXPORT2 umtx_initImplPreInit(UInitOnce &);
U_COMMON_API void  U_EXPORT2 umtx_initImplPostInit(UInitOnce &);

template<class T> void umtx_initOnce(UInitOnce &uio, T *obj, void (U_CALLCONV T::*fp)()) {
    if (umtx_loadAcquire(uio.fState) == 2) {
        return;
    }
    if (umtx_initImplPreInit(uio)) {
        (obj->*fp)();
        umtx_initImplPostInit(uio);
    }
}


// umtx_initOnce variant for plain functions, or static class functions.
//               No context parameter.
inline void umtx_initOnce(UInitOnce &uio, void (U_CALLCONV *fp)()) {
    if (umtx_loadAcquire(uio.fState) == 2) {
        return;
    }
    if (umtx_initImplPreInit(uio)) {
        (*fp)();
        umtx_initImplPostInit(uio);
    }
}

// umtx_initOnce variant for plain functions, or static class functions.
//               With ErrorCode, No context parameter.
inline void umtx_initOnce(UInitOnce &uio, void (U_CALLCONV *fp)(UErrorCode &), UErrorCode &errCode) {
    if (U_FAILURE(errCode)) {
        return;
    }
    if (umtx_loadAcquire(uio.fState) != 2 && umtx_initImplPreInit(uio)) {
        // We run the initialization.
        (*fp)(errCode);
        uio.fErrCode = errCode;
        umtx_initImplPostInit(uio);
    } else {
        // Someone else already ran the initialization.
        if (U_FAILURE(uio.fErrCode)) {
            errCode = uio.fErrCode;
        }
    }
}

// umtx_initOnce variant for plain functions, or static class functions,
//               with a context parameter.
template<class T> void umtx_initOnce(UInitOnce &uio, void (U_CALLCONV *fp)(T), T context) {
    if (umtx_loadAcquire(uio.fState) == 2) {
        return;
    }
    if (umtx_initImplPreInit(uio)) {
        (*fp)(context);
        umtx_initImplPostInit(uio);
    }
}

// umtx_initOnce variant for plain functions, or static class functions,
//               with a context parameter and an error code.
template<class T> void umtx_initOnce(UInitOnce &uio, void (U_CALLCONV *fp)(T, UErrorCode &), T context, UErrorCode &errCode) {
    if (U_FAILURE(errCode)) {
        return;
    }
    if (umtx_loadAcquire(uio.fState) != 2 && umtx_initImplPreInit(uio)) {
        // We run the initialization.
        (*fp)(context, errCode);
        uio.fErrCode = errCode;
        umtx_initImplPostInit(uio);
    } else {
        // Someone else already ran the initialization.
        if (U_FAILURE(uio.fErrCode)) {
            errCode = uio.fErrCode;
        }
    }
}

// UMutex should be constexpr-constructible, so that no initialization code
// is run during startup.
// This works on all C++ libraries except MS VS before VS2019.
#if (defined(_CPPLIB_VER) && !defined(_MSVC_STL_VERSION)) || \
    (defined(_MSVC_STL_VERSION) && _MSVC_STL_VERSION < 142)
    // (VS std lib older than VS2017) || (VS std lib version < VS2019)
#   define UMUTEX_CONSTEXPR
#else
#   define UMUTEX_CONSTEXPR constexpr
#endif

/**
 * UMutex - ICU Mutex class.
 *
 * This is the preferred Mutex class for use within ICU implementation code.
 * It is a thin wrapper over C++ std::mutex, with these additions:
 *    - Static instances are safe, not triggering static construction or destruction,
 *      and the associated order of construction or destruction issues.
 *    - Plumbed into u_cleanup() for destructing the underlying std::mutex,
 *      which frees any OS level resources they may be holding.
 *
 * Limitations:
 *    - Static or global instances only. Cannot be heap allocated. Cannot appear as a
 *      member of another class.
 *    - No condition variables or other advanced features. If needed, you will need to use
 *      std::mutex and std::condition_variable directly. For an example, see unifiedcache.cpp
 *
 * Typical Usage:
 *    static UMutex myMutex;
 *
 *    {
 *       Mutex lock(myMutex);
 *       ...    // Do stuff that is protected by myMutex;
 *    }         // myMutex is released when lock goes out of scope.
 */

class U_COMMON_API UMutex {
public:
    UMUTEX_CONSTEXPR UMutex() {}
    ~UMutex() = default;

    UMutex(const UMutex &other) = delete;
    UMutex &operator =(const UMutex &other) = delete;
    void *operator new(size_t) = delete;

    // requirements for C++ BasicLockable, allows UMutex to work with std::lock_guard
    void lock() {
        std::mutex *m = fMutex.load(std::memory_order_acquire);
        if (m == nullptr) { m = getMutex(); }
        m->lock();
    }
    void unlock() { fMutex.load(std::memory_order_relaxed)->unlock(); }

    static void cleanup();

private:
    alignas(std::mutex) char fStorage[sizeof(std::mutex)] {};
    std::atomic<std::mutex *> fMutex { nullptr };

    /** All initialized UMutexes are kept in a linked list, so that they can be found,
     * and the underlying std::mutex destructed, by u_cleanup().
     */
    UMutex *fListLink { nullptr };
    static UMutex *gListHead;

    /** Out-of-line function to lazily initialize a UMutex on first use.
     * Initial fast check is inline, in lock().  The returned value may never
     * be nullptr.
     */
    std::mutex *getMutex();
};


/* Lock a mutex.
 * @param mutex The given mutex to be locked.  Pass NULL to specify
 *              the global ICU mutex.  Recursive locks are an error
 *              and may cause a deadlock on some platforms.
 */
U_CAPI void U_EXPORT2 umtx_lock(UMutex* mutex);

/* Unlock a mutex.
 * @param mutex The given mutex to be unlocked.  Pass NULL to specify
 *              the global ICU mutex.
 */
U_CAPI void U_EXPORT2 umtx_unlock (UMutex* mutex);


U_NAMESPACE_END

#endif /* UMUTEX_H */
/*eof*/