icuSources/common/umutex.h

   1 /*
   2 **********************************************************************
   3 *   Copyright (C) 1997-2004, 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  * \def UMTX_CHECK
  43  * Encapsulates a safe check for an expression (usually a condition)
  44  * for lazy variable inititialization.
  45  * On CPUs with weak memory models, this must use memory fence instructions
  46  * or mutexes.
  47  * @internal
  48  */
  49 #if UMTX_STRONG_MEMORY_MODEL
  50
  51 #define UMTX_CHECK(pMutex, expression, result) \
  52     (result)=(expression);
  53
  54 #else
  55
  56 #define UMTX_CHECK(pMutex, expression, result) \
  57     umtx_lock(pMutex); \
  58     (result)=(expression); \
  59     umtx_unlock(pMutex);
  60
  61 #endif
  62
  63 /*
  64  * Code within ICU that accesses shared static or global data should
  65  * instantiate a Mutex object while doing so.  The unnamed global mutex
  66  * is used throughout ICU, so keep locking short and sweet.
  67  *
  68  * For example:
  69  *
  70  * void Function(int arg1, int arg2)
  71  * {
  72  *   static Object* foo;     // Shared read-write object
  73  *   umtx_lock(NULL);        // Lock the ICU global mutex
  74  *   foo->Method();
  75  *   umtx_unlock(NULL);
  76  * }
  77  *
  78  * an alternative C++ mutex API is defined in the file common/mutex.h
  79  */
  80
  81 /* Lock a mutex.
  82  * @param mutex The given mutex to be locked.  Pass NULL to specify
  83  *              the global ICU mutex.  Recursive locks are an error
  84  *              and may cause a deadlock on some platforms.
  85  */
  86 U_CAPI void U_EXPORT2 umtx_lock   ( UMTX* mutex );
  87
  88 /* Unlock a mutex. Pass in NULL if you want the single global
  89    mutex.
  90  * @param mutex The given mutex to be unlocked.  Pass NULL to specify
  91  *              the global ICU mutex.
  92  */
  93 U_CAPI void U_EXPORT2 umtx_unlock ( UMTX* mutex );
  94
  95 /* Initialize a mutex. Use it this way:
  96    umtx_init( &aMutex );
  97  * ICU Mutexes do not need explicit initialization before use.  Use of this
  98  *   function is not necessary.
  99  * Initialization of an already initialized mutex has no effect, and is safe to do.
 100  * Initialization of mutexes is thread safe.  Two threads can concurrently
 101  *   initialize the same mutex without causing problems.
 102  * @param mutex The given mutex to be initialized
 103  */
 104 U_CAPI void U_EXPORT2 umtx_init   ( UMTX* mutex );
 105
 106 /* Destroy a mutex. This will free the resources of a mutex.
 107  * Use it this way:
 108  *   umtx_destroy( &aMutex );
 109  * Destroying an already destroyed mutex has no effect, and causes no problems.
 110  * This function is not thread safe.  Two threads must not attempt to concurrently
 111  *   destroy the same mutex.
 112  * @param mutex The given mutex to be destroyed.
 113  */
 114 U_CAPI void U_EXPORT2 umtx_destroy( UMTX *mutex );
 115
 116
 117
 118 /*
 119  * Atomic Increment and Decrement of an int32_t value.
 120  *
 121  * Return Values:
 122  *   If the result of the operation is zero, the return zero.
 123  *   If the result of the operation is not zero, the sign of returned value
 124  *      is the same as the sign of the result, but the returned value itself may
 125  *      be different from the result of the operation.
 126  */
 127 U_CAPI int32_t U_EXPORT2 umtx_atomic_inc(int32_t *);
 128 U_CAPI int32_t U_EXPORT2 umtx_atomic_dec(int32_t *);
 129
 130
 131 #endif /*_CMUTEX*/
 132 /*eof*/
 133
 134
 135