141 lines
4.7 KiB
C++
141 lines
4.7 KiB
C++
/*
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*******************************************************************************
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*
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* Copyright (C) 2008-2011, International Business Machines
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* Corporation and others. All Rights Reserved.
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*
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*******************************************************************************
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* file name: mutex.cpp
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* encoding: US-ASCII
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* tab size: 8 (not used)
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* indentation:4
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*/
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#include "unicode/utypes.h"
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#include "mutex.h"
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#include "uassert.h"
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U_NAMESPACE_BEGIN
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void *SimpleSingleton::getInstance(InstantiatorFn *instantiator, const void *context,
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void *&duplicate,
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UErrorCode &errorCode) {
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duplicate=NULL;
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if(U_FAILURE(errorCode)) {
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return NULL;
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}
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// TODO: With atomicops.h: void *instance = (void*)Acquire_Load(&fInstance);
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// and remove UMTX_ACQUIRE_BARRIER below.
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void *instance=ANNOTATE_UNPROTECTED_READ(fInstance);
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UMTX_ACQUIRE_BARRIER;
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ANNOTATE_HAPPENS_AFTER(&fInstance);
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if(instance!=NULL) {
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return instance;
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}
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// Attempt to create the instance.
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// If a race occurs, then the losing thread will assign its new instance
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// to the "duplicate" parameter, and the caller deletes it.
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instance=instantiator(context, errorCode);
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UMTX_RELEASE_BARRIER; // Release-barrier before fInstance=instance;
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Mutex mutex;
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if(fInstance==NULL && U_SUCCESS(errorCode)) {
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U_ASSERT(instance!=NULL);
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ANNOTATE_HAPPENS_BEFORE(&fInstance);
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// TODO: With atomicops.h: Release_Store(&fInstance, (AtomicWord)instance);
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// and remove UMTX_RELEASE_BARRIER above.
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fInstance=instance;
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} else {
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duplicate=instance;
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}
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return fInstance;
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}
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/*
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* Three states:
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*
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* Initial state: Instance creation not attempted yet.
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* fInstance=NULL && U_SUCCESS(fErrorCode)
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*
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* Instance creation succeeded:
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* fInstance!=NULL && U_SUCCESS(fErrorCode)
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*
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* Instance creation failed:
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* fInstance=NULL && U_FAILURE(fErrorCode)
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* We will not attempt again to create the instance.
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*
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* fInstance changes at most once.
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* fErrorCode changes at most twice (intial->failed->succeeded).
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*/
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void *TriStateSingleton::getInstance(InstantiatorFn *instantiator, const void *context,
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void *&duplicate,
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UErrorCode &errorCode) {
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duplicate=NULL;
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if(U_FAILURE(errorCode)) {
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return NULL;
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}
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// TODO: With atomicops.h: void *instance = (void*)Acquire_Load(&fInstance);
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// and remove UMTX_ACQUIRE_BARRIER below.
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void *instance=ANNOTATE_UNPROTECTED_READ(fInstance);
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UMTX_ACQUIRE_BARRIER;
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ANNOTATE_HAPPENS_AFTER(&fInstance);
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if(instance!=NULL) {
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// instance was created
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return instance;
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}
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// The read access to fErrorCode is thread-unsafe, but harmless because
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// at worst multiple threads race to each create a new instance,
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// and all losing threads delete their duplicates.
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UErrorCode localErrorCode=ANNOTATE_UNPROTECTED_READ(fErrorCode);
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if(U_FAILURE(localErrorCode)) {
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// instance creation failed
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errorCode=localErrorCode;
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return NULL;
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}
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// First attempt to create the instance.
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// If a race occurs, then the losing thread will assign its new instance
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// to the "duplicate" parameter, and the caller deletes it.
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instance=instantiator(context, errorCode);
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UMTX_RELEASE_BARRIER; // Release-barrier before fInstance=instance;
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Mutex mutex;
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if(fInstance==NULL && U_SUCCESS(errorCode)) {
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// instance creation newly succeeded
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U_ASSERT(instance!=NULL);
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ANNOTATE_HAPPENS_BEFORE(&fInstance);
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// TODO: With atomicops.h: Release_Store(&fInstance, (AtomicWord)instance);
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// and remove UMTX_RELEASE_BARRIER above.
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fInstance=instance;
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// Set fErrorCode on the off-chance that a previous instance creation failed.
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fErrorCode=errorCode;
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// Completed state transition: initial->succeeded, or failed->succeeded.
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} else {
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// Record a duplicate if we lost the race, or
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// if we got an instance but its creation failed anyway.
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duplicate=instance;
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if(fInstance==NULL && U_SUCCESS(fErrorCode) && U_FAILURE(errorCode)) {
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// instance creation newly failed
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fErrorCode=errorCode;
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// Completed state transition: initial->failed.
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}
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}
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return fInstance;
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}
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void TriStateSingleton::reset() {
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fInstance=NULL;
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fErrorCode=U_ZERO_ERROR;
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}
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#if UCONFIG_NO_SERVICE
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/* If UCONFIG_NO_SERVICE, then there is no invocation of Mutex elsewhere in
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common, so add one here to force an export */
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static Mutex *aMutex = 0;
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/* UCONFIG_NO_SERVICE */
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#endif
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U_NAMESPACE_END
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