include/SDL_atomic.h
author Sam Lantinga <slouken@libsdl.org>
Mon, 17 Jan 2011 13:53:31 -0800
changeset 5012 2e282002bac3
parent 5006 8e8876e4aec6
child 5016 cc879bc6c4cf
permissions -rw-r--r--
Use compiler intrinsics, where available
     1 /*
     2     SDL - Simple DirectMedia Layer
     3     Copyright (C) 1997-2010 Sam Lantinga
     4 
     5     This library is free software; you can redistribute it and/or
     6     modify it under the terms of the GNU Lesser General Public
     7     License as published by the Free Software Foundation; either
     8     version 2.1 of the License, or (at your option) any later version.
     9 
    10     This library is distributed in the hope that it will be useful,
    11     but WITHOUT ANY WARRANTY; without even the implied warranty of
    12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    13     Lesser General Public License for more details.
    14 
    15     You should have received a copy of the GNU Lesser General Public
    16     License along with this library; if not, write to the Free Software
    17     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
    18 
    19     Sam Lantinga
    20     slouken@libsdl.org
    21  */
    22 
    23 /**
    24  * \file SDL_atomic.h
    25  * 
    26  * Atomic operations.
    27  * 
    28  * IMPORTANT:
    29  * If you are not an expert in concurrent lockless programming, you should
    30  * only be using the atomic lock and reference counting functions in this
    31  * file.  In all other cases you should be protecting your data structures
    32  * with full mutexes.
    33  * 
    34  * The list of "safe" functions to use are:
    35  *  SDL_AtomicLock()
    36  *  SDL_AtomicUnlock()
    37  *  SDL_AtomicIncRef()
    38  *  SDL_AtomicDecRef()
    39  * 
    40  * Seriously, here be dragons!
    41  *
    42  * These operations may, or may not, actually be implemented using
    43  * processor specific atomic operations. When possible they are
    44  * implemented as true processor specific atomic operations. When that
    45  * is not possible the are implemented using locks that *do* use the
    46  * available atomic operations.
    47  *
    48  * All of the atomic operations that modify memory are full memory barriers.
    49  */
    50 
    51 #ifndef _SDL_atomic_h_
    52 #define _SDL_atomic_h_
    53 
    54 #include "SDL_stdinc.h"
    55 #include "SDL_platform.h"
    56 
    57 #include "begin_code.h"
    58 
    59 /* Set up for C function definitions, even when using C++ */
    60 #ifdef __cplusplus
    61 /* *INDENT-OFF* */
    62 extern "C" {
    63 /* *INDENT-ON* */
    64 #endif
    65 
    66 /**
    67  * \name SDL AtomicLock
    68  * 
    69  * The atomic locks are efficient spinlocks using CPU instructions,
    70  * but are vulnerable to starvation and can spin forever if a thread
    71  * holding a lock has been terminated.  For this reason you should
    72  * minimize the code executed inside an atomic lock and never do
    73  * expensive things like API or system calls while holding them.
    74  *
    75  * The atomic locks are not safe to lock recursively.
    76  *
    77  * Porting Note:
    78  * The spin lock functions and type are required and can not be
    79  * emulated because they are used in the atomic emulation code.
    80  */
    81 /*@{*/
    82 
    83 typedef int SDL_SpinLock;
    84 
    85 /**
    86  * \brief Try to lock a spin lock by setting it to a non-zero value.
    87  * 
    88  * \param lock Points to the lock.
    89  *
    90  * \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.
    91  */
    92 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
    93 
    94 /**
    95  * \brief Lock a spin lock by setting it to a non-zero value.
    96  * 
    97  * \param lock Points to the lock.
    98  */
    99 extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
   100 
   101 /**
   102  * \brief Unlock a spin lock by setting it to 0. Always returns immediately
   103  *
   104  * \param lock Points to the lock.
   105  */
   106 extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
   107 
   108 /*@}*//*SDL AtomicLock*/
   109 
   110 /* Platform specific optimized versions of the atomic functions,
   111  * you can disable these by defining SDL_DISABLE_ATOMIC_INLINE
   112  */
   113 #ifndef SDL_DISABLE_ATOMIC_INLINE
   114 
   115 #if defined(__WIN32__)
   116 #include <intrin.h>
   117 
   118 #define SDL_AtomicSet(a, v)     _InterlockedExchange(&(a)->value, (v))
   119 #define SDL_AtomicGet(a)        ((a)->value)
   120 #define SDL_AtomicAdd(a, v)     _InterlockedExchangeAdd(&(a)->value, (v))
   121 #define SDL_AtomicCAS(a, oldval, newval) (_InterlockedCompareExchange(&(a)->value, (newval), (oldval)) == (oldval))
   122 #define SDL_AtomicSetPtr(a, v)  (void)_InterlockedExchangePointer((a), (v))
   123 #define SDL_AtomicGetPtr(a)     (*(a))
   124 #if _M_IX86
   125 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchange((long*)(a), (long)(newval), (long)(oldval)) == (long)(oldval))
   126 #else
   127 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchangePointer((a), (newval), (oldval)) == (oldval))
   128 #endif
   129 
   130 #elif defined(__MACOSX__)
   131 #include <libkern/OSAtomic.h>
   132 
   133 #define SDL_AtomicSet(a, v) \
   134 ({                          \
   135     int oldvalue;           \
   136                             \
   137     do {                    \
   138         oldvalue = (a)->value; \
   139     } while (!OSAtomicCompareAndSwap32Barrier(oldvalue, v, &(a)->value)); \
   140                             \
   141     oldvalue;               \
   142 })
   143 #define SDL_AtomicGet(a)        ((a)->value)
   144 #define SDL_AtomicAdd(a, v) \
   145 ({                          \
   146     int oldvalue;           \
   147                             \
   148     do {                    \
   149         oldvalue = (a)->value; \
   150     } while (!OSAtomicCompareAndSwap32Barrier(oldvalue, oldvalue+v, &(a)->value)); \
   151                             \
   152     oldvalue;               \
   153 })
   154 #define SDL_AtomicCAS(a, oldval, newval) OSAtomicCompareAndSwap32Barrier(oldval, newval, &(a)->value)
   155 #define SDL_AtomicSetPtr(a, v)  (*(a) = v, OSMemoryBarrier())
   156 #define SDL_AtomicGetPtr(a)     (*(a))
   157 #if SIZEOF_VOIDP == 4
   158 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((int32_t)(oldval), (int32_t)(newval), (int32_t*)(a))
   159 #elif SIZEOF_VOIDP == 8
   160 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap64Barrier((int64_t)(oldval), (int64_t)(newval), (int64_t*)(a))
   161 #endif
   162 
   163 #elif defined(HAVE_GCC_ATOMICS)
   164 
   165 #define SDL_AtomicSet(a, v)     __sync_lock_test_and_set(&(a)->value, v)
   166 #define SDL_AtomicGet(a)        ((a)->value)
   167 #define SDL_AtomicAdd(a, v)     __sync_fetch_and_add(&(a)->value, v)
   168 #define SDL_AtomicCAS(a, oldval, newval) __sync_bool_compare_and_swap(&(a)->value, oldval, newval)
   169 #define SDL_AtomicSetPtr(a, v)  (*(a) = v, __sync_synchronize())
   170 #define SDL_AtomicGetPtr(a)     (*(a))
   171 #define SDL_AtomicCASPtr(a, oldval, newval) __sync_bool_compare_and_swap(a, oldval, newval)
   172 
   173 #endif
   174 
   175 #endif /* !SDL_DISABLE_ATOMIC_INLINE */
   176 
   177 
   178 /**
   179  * \brief A type representing an atomic integer value.  It is a struct
   180  *        so people don't accidentally use numeric operations on it.
   181  */
   182 #ifndef SDL_atomic_t_defined
   183 typedef struct { int value; } SDL_atomic_t;
   184 #endif
   185 
   186 /**
   187  * \brief Set an atomic variable to a value.
   188  *
   189  * \return The previous value of the atomic variable.
   190  */
   191 #ifndef SDL_AtomicSet
   192 extern DECLSPEC int SDLCALL SDL_AtomicSet(SDL_atomic_t *a, int value);
   193 #endif
   194 
   195 /**
   196  * \brief Get the value of an atomic variable
   197  */
   198 #ifndef SDL_AtomicGet
   199 extern DECLSPEC int SDLCALL SDL_AtomicGet(SDL_atomic_t *a);
   200 #endif
   201 
   202 /**
   203  * \brief  Add to an atomic variable.
   204  *
   205  * \return The previous value of the atomic variable.
   206  */
   207 #ifndef SDL_AtomicAdd
   208 extern DECLSPEC int SDLCALL SDL_AtomicAdd(SDL_atomic_t *a, int value);
   209 #endif
   210 
   211 /**
   212  * \brief Increment an atomic variable used as a reference count.
   213  */
   214 #ifndef SDL_AtomicIncRef
   215 extern DECLSPEC void SDLCALL SDL_AtomicIncRef(SDL_atomic_t *a);
   216 #endif
   217 
   218 /**
   219  * \brief Decrement an atomic variable used as a reference count.
   220  *
   221  * \return SDL_TRUE if the variable has reached zero after decrementing,
   222  *         SDL_FALSE otherwise
   223  */
   224 #ifndef SDL_AtomicDecRef
   225 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicDecRef(SDL_atomic_t *a);
   226 #endif
   227 
   228 /**
   229  * \brief Set an atomic variable to a new value if it is currently an old value.
   230  *
   231  * \return SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
   232  *
   233  * \note If you don't know what this function is for, you shouldn't use it!
   234 */
   235 #ifndef SDL_AtomicCAS
   236 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
   237 #endif
   238 
   239 /**
   240  * \brief Set a pointer to a value atomically.
   241  */
   242 #ifndef SDL_AtomicSetPtr
   243 extern DECLSPEC void SDLCALL SDL_AtomicSetPtr(void** a, void* value);
   244 #endif
   245 
   246 /**
   247  * \brief Get the value of a pointer atomically.
   248  */
   249 #ifndef SDL_AtomicGetPtr
   250 extern DECLSPEC void* SDLCALL SDL_AtomicGetPtr(void** a);
   251 #endif
   252 
   253 /**
   254  * \brief Set a pointer to a new value if it is currently an old value.
   255  *
   256  * \return SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
   257  *
   258  * \note If you don't know what this function is for, you shouldn't use it!
   259 */
   260 #ifndef SDL_AtomicCASPtr
   261 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void **a, void *oldval, void *newval);
   262 #endif
   263 
   264 /* Ends C function definitions when using C++ */
   265 #ifdef __cplusplus
   266 /* *INDENT-OFF* */
   267 }
   268 /* *INDENT-ON* */
   269 #endif
   270 
   271 #include "close_code.h"
   272 
   273 #endif /* _SDL_atomic_h_ */
   274 
   275 /* vi: set ts=4 sw=4 expandtab: */