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diff --git a/thirdparty/icu4c/common/umutex.cpp b/thirdparty/icu4c/common/umutex.cpp
new file mode 100644
index 0000000000..ccbee9960a
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+++ b/thirdparty/icu4c/common/umutex.cpp
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+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+******************************************************************************
+*
+*   Copyright (C) 1997-2016, International Business Machines
+*   Corporation and others.  All Rights Reserved.
+*
+******************************************************************************
+*
+* File umutex.cpp
+*
+* Modification History:
+*
+*   Date        Name        Description
+*   04/02/97    aliu        Creation.
+*   04/07/99    srl         updated
+*   05/13/99    stephen     Changed to umutex (from cmutex).
+*   11/22/99    aliu        Make non-global mutex autoinitialize [j151]
+******************************************************************************
+*/
+
+#include "umutex.h"
+
+#include "unicode/utypes.h"
+#include "uassert.h"
+#include "ucln_cmn.h"
+#include "cmemory.h"
+
+U_NAMESPACE_BEGIN
+
+
+#if defined(U_USER_MUTEX_CPP)
+// Support for including an alternate implementation of mutexes has been withdrawn.
+// See issue ICU-20185.
+#error U_USER_MUTEX_CPP not supported
+#endif
+
+
+/*************************************************************************************************
+ *
+ *  ICU Mutex wrappers.
+ *
+ *************************************************************************************************/
+
+namespace {
+std::mutex *initMutex;
+std::condition_variable *initCondition;
+
+// The ICU global mutex.
+// Used when ICU implementation code passes nullptr for the mutex pointer.
+UMutex globalMutex;
+
+std::once_flag initFlag;
+std::once_flag *pInitFlag = &initFlag;
+
+}  // Anonymous namespace
+
+U_CDECL_BEGIN
+static UBool U_CALLCONV umtx_cleanup() {
+    initMutex->~mutex();
+    initCondition->~condition_variable();
+    UMutex::cleanup();
+
+    // Reset the once_flag, by destructing it and creating a fresh one in its place.
+    // Do not use this trick anywhere else in ICU; use umtx_initOnce, not std::call_once().
+    pInitFlag->~once_flag();
+    pInitFlag = new(&initFlag) std::once_flag();
+    return true;
+}
+
+static void U_CALLCONV umtx_init() {
+    initMutex = STATIC_NEW(std::mutex);
+    initCondition = STATIC_NEW(std::condition_variable);
+    ucln_common_registerCleanup(UCLN_COMMON_MUTEX, umtx_cleanup);
+}
+U_CDECL_END
+
+
+std::mutex *UMutex::getMutex() {
+    std::mutex *retPtr = fMutex.load(std::memory_order_acquire);
+    if (retPtr == nullptr) {
+        std::call_once(*pInitFlag, umtx_init);
+        std::lock_guard<std::mutex> guard(*initMutex);
+        retPtr = fMutex.load(std::memory_order_acquire);
+        if (retPtr == nullptr) {
+            fMutex = new(fStorage) std::mutex();
+            retPtr = fMutex;
+            fListLink = gListHead;
+            gListHead = this;
+        }
+    }
+    U_ASSERT(retPtr != nullptr);
+    return retPtr;
+}
+
+UMutex *UMutex::gListHead = nullptr;
+
+void UMutex::cleanup() {
+    UMutex *next = nullptr;
+    for (UMutex *m = gListHead; m != nullptr; m = next) {
+        (*m->fMutex).~mutex();
+        m->fMutex = nullptr;
+        next = m->fListLink;
+        m->fListLink = nullptr;
+    }
+    gListHead = nullptr;
+}
+
+
+U_CAPI void  U_EXPORT2
+umtx_lock(UMutex *mutex) {
+    if (mutex == nullptr) {
+        mutex = &globalMutex;
+    }
+    mutex->lock();
+}
+
+
+U_CAPI void  U_EXPORT2
+umtx_unlock(UMutex* mutex)
+{
+    if (mutex == nullptr) {
+        mutex = &globalMutex;
+    }
+    mutex->unlock();
+}
+
+
+/*************************************************************************************************
+ *
+ *  UInitOnce Implementation
+ *
+ *************************************************************************************************/
+
+// This function is called when a test of a UInitOnce::fState reveals that
+//   initialization has not completed, that we either need to call the init
+//   function on this thread, or wait for some other thread to complete.
+//
+// The actual call to the init function is made inline by template code
+//   that knows the C++ types involved. This function returns true if
+//   the caller needs to call the Init function.
+//
+U_COMMON_API UBool U_EXPORT2
+umtx_initImplPreInit(UInitOnce &uio) {
+    std::call_once(*pInitFlag, umtx_init);
+    std::unique_lock<std::mutex> lock(*initMutex);
+    if (umtx_loadAcquire(uio.fState) == 0) {
+        umtx_storeRelease(uio.fState, 1);
+        return true;      // Caller will next call the init function.
+    } else {
+        while (umtx_loadAcquire(uio.fState) == 1) {
+            // Another thread is currently running the initialization.
+            // Wait until it completes.
+            initCondition->wait(lock);
+        }
+        U_ASSERT(uio.fState == 2);
+        return false;
+    }
+}
+
+
+// This function is called by the thread that ran an initialization function,
+// just after completing the function.
+//   Some threads may be waiting on the condition, requiring the broadcast wakeup.
+//   Some threads may be racing to test the fState variable outside of the mutex,
+//   requiring the use of store/release when changing its value.
+
+U_COMMON_API void U_EXPORT2
+umtx_initImplPostInit(UInitOnce &uio) {
+    {
+        std::unique_lock<std::mutex> lock(*initMutex);
+        umtx_storeRelease(uio.fState, 2);
+    }
+    initCondition->notify_all();
+}
+
+U_NAMESPACE_END
+
+/*************************************************************************************************
+ *
+ *  Deprecated functions for setting user mutexes.
+ *
+ *************************************************************************************************/
+
+U_DEPRECATED void U_EXPORT2
+u_setMutexFunctions(const void * /*context */, UMtxInitFn *, UMtxFn *,
+                    UMtxFn *,  UMtxFn *, UErrorCode *status) {
+    if (U_SUCCESS(*status)) {
+        *status = U_UNSUPPORTED_ERROR;
+    }
+    return;
+}
+
+
+
+U_DEPRECATED void U_EXPORT2
+u_setAtomicIncDecFunctions(const void * /*context */, UMtxAtomicFn *, UMtxAtomicFn *,
+                           UErrorCode *status) {
+    if (U_SUCCESS(*status)) {
+        *status = U_UNSUPPORTED_ERROR;
+    }
+    return;
+}