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diff --git a/intl/icu/source/common/umutex.h b/intl/icu/source/common/umutex.h
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+// © 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
+
+#ifndef __wasi__
+#include <atomic>
+#include <condition_variable>
+#include <mutex>
+#endif
+
+#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+// Support for including an alternate implementation of atomic & mutex operations has been withdrawn.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
+
+#ifndef __wasi__
+
+// 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
+
+#endif
+
+U_NAMESPACE_BEGIN
+
+/****************************************************************************
+ *
+ *   Low Level Atomic Operations, ICU wrappers for.
+ *
+ ****************************************************************************/
+
+#ifndef __wasi__
+
+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;
+}
+
+#else
+
+typedef int32_t u_atomic_int32_t;
+#define ATOMIC_INT32_T_INITIALIZER(val) val
+
+inline int32_t umtx_loadAcquire(u_atomic_int32_t &var) {
+    return var;
+}
+
+inline void umtx_storeRelease(u_atomic_int32_t &var, int32_t val) {
+    var = val;
+}
+
+inline int32_t umtx_atomic_inc(u_atomic_int32_t *var) {
+    return ++(*var);
+}
+
+inline int32_t umtx_atomic_dec(u_atomic_int32_t *var) {
+    return --(*var);
+}
+
+#endif
+
+/*************************************************************************************************
+ *
+ *  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() {
+#ifndef __wasi__
+        std::mutex *m = fMutex.load(std::memory_order_acquire);
+        if (m == nullptr) { m = getMutex(); }
+        m->lock();
+#endif
+    }
+    void unlock() {
+#ifndef __wasi__
+        fMutex.load(std::memory_order_relaxed)->unlock();
+#endif
+    }
+
+    static void cleanup();
+
+private:
+#ifndef __wasi__
+    alignas(std::mutex) char fStorage[sizeof(std::mutex)] {};
+    std::atomic<std::mutex *> fMutex { nullptr };
+#endif
+
+    /** 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.
+     */
+#ifndef __wasi__
+    std::mutex *getMutex();
+#endif
+};
+
+
+/* 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*/