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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// Support for including an alternate implementation of mutexes has been withdrawn.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;
}
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