1 /* 2 ********************************************************************** 3 * Copyright (C) 1997-2006, International Business Machines 4 * Corporation and others. All Rights Reserved. 5 ********************************************************************** 6 * 7 * File UMUTEX.H 8 * 9 * Modification History: 10 * 11 * Date Name Description 12 * 04/02/97 aliu Creation. 13 * 04/07/99 srl rewrite - C interface, multiple mutices 14 * 05/13/99 stephen Changed to umutex (from cmutex) 15 ****************************************************************************** 16 */ 17 18 #ifndef UMUTEX_H 19 #define UMUTEX_H 20 21 #include "unicode/utypes.h" 22 #include "unicode/uclean.h" 23 24 25 /* APP_NO_THREADS is an old symbol. We'll honour it if present. */ 26 #ifdef APP_NO_THREADS 27 # define ICU_USE_THREADS 0 28 #endif 29 30 /* ICU_USE_THREADS 31 * 32 * Allows thread support (use of mutexes) to be compiled out of ICU. 33 * Default: use threads. 34 * Even with thread support compiled out, applications may override the 35 * (empty) mutex implementation with the u_setMutexFunctions() functions. 36 */ 37 #ifndef ICU_USE_THREADS 38 # define ICU_USE_THREADS 1 39 #endif 40 41 /** 42 * By default assume that we are on a machine with a weak memory model, 43 * and the double check lock won't work reliably. 44 */ 45 #if !defined(UMTX_STRONG_MEMORY_MODEL) 46 #define UMTX_STRONG_MEMORY_MODEL 0 47 #endif 48 49 /** 50 * \def UMTX_CHECK 51 * Encapsulates a safe check for an expression (usually a condition) 52 * for lazy variable inititialization. 53 * On CPUs with weak memory models, this must use memory fence instructions 54 * or mutexes. 55 * @internal 56 */ 57 #if UMTX_STRONG_MEMORY_MODEL 58 59 #define UMTX_CHECK(pMutex, expression, result) \ 60 (result)=(expression) 61 62 #else 63 64 #define UMTX_CHECK(pMutex, expression, result) \ 65 umtx_lock(pMutex); \ 66 (result)=(expression); \ 67 umtx_unlock(pMutex) 68 69 #endif 70 71 /* 72 * Code within ICU that accesses shared static or global data should 73 * instantiate a Mutex object while doing so. The unnamed global mutex 74 * is used throughout ICU, so keep locking short and sweet. 75 * 76 * For example: 77 * 78 * void Function(int arg1, int arg2) 79 * { 80 * static Object* foo; // Shared read-write object 81 * umtx_lock(NULL); // Lock the ICU global mutex 82 * foo->Method(); 83 * umtx_unlock(NULL); 84 * } 85 * 86 * an alternative C++ mutex API is defined in the file common/mutex.h 87 */ 88 89 /* Lock a mutex. 90 * @param mutex The given mutex to be locked. Pass NULL to specify 91 * the global ICU mutex. Recursive locks are an error 92 * and may cause a deadlock on some platforms. 93 */ 94 U_CAPI void U_EXPORT2 umtx_lock ( UMTX* mutex ); 95 96 /* Unlock a mutex. Pass in NULL if you want the single global 97 mutex. 98 * @param mutex The given mutex to be unlocked. Pass NULL to specify 99 * the global ICU mutex. 100 */ 101 U_CAPI void U_EXPORT2 umtx_unlock ( UMTX* mutex ); 102 103 /* Initialize a mutex. Use it this way: 104 umtx_init( &aMutex ); 105 * ICU Mutexes do not need explicit initialization before use. Use of this 106 * function is not necessary. 107 * Initialization of an already initialized mutex has no effect, and is safe to do. 108 * Initialization of mutexes is thread safe. Two threads can concurrently 109 * initialize the same mutex without causing problems. 110 * @param mutex The given mutex to be initialized 111 */ 112 U_CAPI void U_EXPORT2 umtx_init ( UMTX* mutex ); 113 114 /* Destroy a mutex. This will free the resources of a mutex. 115 * Use it this way: 116 * umtx_destroy( &aMutex ); 117 * Destroying an already destroyed mutex has no effect, and causes no problems. 118 * This function is not thread safe. Two threads must not attempt to concurrently 119 * destroy the same mutex. 120 * @param mutex The given mutex to be destroyed. 121 */ 122 U_CAPI void U_EXPORT2 umtx_destroy( UMTX *mutex ); 123 124 125 126 /* 127 * Atomic Increment and Decrement of an int32_t value. 128 * 129 * Return Values: 130 * If the result of the operation is zero, the return zero. 131 * If the result of the operation is not zero, the sign of returned value 132 * is the same as the sign of the result, but the returned value itself may 133 * be different from the result of the operation. 134 */ 135 U_CAPI int32_t U_EXPORT2 umtx_atomic_inc(int32_t *); 136 U_CAPI int32_t U_EXPORT2 umtx_atomic_dec(int32_t *); 137 138 139 #endif /*_CMUTEX*/ 140 /*eof*/ 141 142 143 144