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* Copyright (C) 1997-2008, International Business Machines
* Corporation and others. All Rights Reserved.
* 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 "unicode/utypes.h"
#include "unicode/uclean.h"
/* APP_NO_THREADS is an old symbol. We'll honour it if present. */
# define ICU_USE_THREADS 0
* Allows thread support (use of mutexes) to be compiled out of ICU.
* Default: use threads.
* Even with thread support compiled out, applications may override the
* (empty) mutex implementation with the u_setMutexFunctions() functions.
# define ICU_USE_THREADS 1
* By default assume that we are on a machine with a weak memory model,
* and the double check lock won't work reliably.
* Encapsulates a safe check of an expression
* for use with double-checked lazy inititialization.
* On CPUs with weak memory models, this must use memory fence instructions
* or mutexes.
* The expression must involve only a _single_ variable, typically
* a possibly null pointer or a boolean that indicates whether some service
* is initialized or not.
* The setting of the variable involved in the test must be the last step of
* the initialization process.
* @internal
#define UMTX_CHECK(pMutex, expression, result) \
#define UMTX_CHECK(pMutex, expression, result) \
umtx_lock(pMutex); \
(result)=(expression); \
* Code within ICU that accesses shared static or global data should
* instantiate a Mutex object while doing so. The unnamed global mutex
* is used throughout ICU, so keep locking short and sweet.
* For example:
* void Function(int arg1, int arg2)
* {
* static Object* foo; // Shared read-write object
* umtx_lock(NULL); // Lock the ICU global mutex
* foo->Method();
* umtx_unlock(NULL);
* }
* an alternative C++ mutex API is defined in the file common/mutex.h
/* 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 ( UMTX* mutex );
/* Unlock a mutex. Pass in NULL if you want the single global
* @param mutex The given mutex to be unlocked. Pass NULL to specify
* the global ICU mutex.
U_CAPI void U_EXPORT2 umtx_unlock ( UMTX* mutex );
/* Initialize a mutex. Use it this way:
umtx_init( &aMutex );
* ICU Mutexes do not need explicit initialization before use. Use of this
* function is not necessary.
* Initialization of an already initialized mutex has no effect, and is safe to do.
* Initialization of mutexes is thread safe. Two threads can concurrently
* initialize the same mutex without causing problems.
* @param mutex The given mutex to be initialized
U_CAPI void U_EXPORT2 umtx_init ( UMTX* mutex );
/* Destroy a mutex. This will free the resources of a mutex.
* Use it this way:
* umtx_destroy( &aMutex );
* Destroying an already destroyed mutex has no effect, and causes no problems.
* This function is not thread safe. Two threads must not attempt to concurrently
* destroy the same mutex.
* @param mutex The given mutex to be destroyed.
U_CAPI void U_EXPORT2 umtx_destroy( UMTX *mutex );
* Atomic Increment and Decrement of an int32_t value.
* Return Values:
* If the result of the operation is zero, the return zero.
* If the result of the operation is not zero, the sign of returned value
* is the same as the sign of the result, but the returned value itself may
* be different from the result of the operation.
U_CAPI int32_t U_EXPORT2 umtx_atomic_inc(int32_t *);
U_CAPI int32_t U_EXPORT2 umtx_atomic_dec(int32_t *);
#endif /*_CMUTEX*/