include/SDL_atomic.h
author Sam Lantinga <slouken@libsdl.org>
Wed, 10 Jul 2013 18:31:17 -0700
changeset 7393 358696c354a8
parent 7191 75360622e65f
child 7394 38dc4961ab15
permissions -rw-r--r--
Added release/acquire memory barriers to the atomic API
* Added a destructor to clean up TLS memory at thread shutdown
* Refactored the TLS code to have platform independent code and a small platform dependent core with a fallback to generic code if platform dependent functions fail.
* Fixed recursion issues with SDL_GetErrBuf()
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 */
    21 
    22 /**
    23  * \file SDL_atomic.h
    24  *
    25  * Atomic operations.
    26  *
    27  * IMPORTANT:
    28  * If you are not an expert in concurrent lockless programming, you should
    29  * only be using the atomic lock and reference counting functions in this
    30  * file.  In all other cases you should be protecting your data structures
    31  * with full mutexes.
    32  *
    33  * The list of "safe" functions to use are:
    34  *  SDL_AtomicLock()
    35  *  SDL_AtomicUnlock()
    36  *  SDL_AtomicIncRef()
    37  *  SDL_AtomicDecRef()
    38  *
    39  * Seriously, here be dragons!
    40  * ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    41  *
    42  * You can find out a little more about lockless programming and the
    43  * subtle issues that can arise here:
    44  * http://msdn.microsoft.com/en-us/library/ee418650%28v=vs.85%29.aspx
    45  *
    46  * There's also lots of good information here:
    47  * http://www.1024cores.net/home/lock-free-algorithms
    48  * http://preshing.com/
    49  *
    50  * These operations may or may not actually be implemented using
    51  * processor specific atomic operations. When possible they are
    52  * implemented as true processor specific atomic operations. When that
    53  * is not possible the are implemented using locks that *do* use the
    54  * available atomic operations.
    55  *
    56  * All of the atomic operations that modify memory are full memory barriers.
    57  */
    58 
    59 #ifndef _SDL_atomic_h_
    60 #define _SDL_atomic_h_
    61 
    62 #include "SDL_stdinc.h"
    63 #include "SDL_platform.h"
    64 
    65 #include "begin_code.h"
    66 
    67 /* Need to do this here because intrin.h has C++ code in it */
    68 /* Visual Studio 2005 has a bug where intrin.h conflicts with winnt.h */
    69 #if defined(_MSC_VER) && (_MSC_VER >= 1500)
    70 #include <intrin.h>
    71 #define HAVE_MSC_ATOMICS 1
    72 #endif
    73 
    74 /* Set up for C function definitions, even when using C++ */
    75 #ifdef __cplusplus
    76 extern "C" {
    77 #endif
    78 
    79 /**
    80  * \name SDL AtomicLock
    81  *
    82  * The atomic locks are efficient spinlocks using CPU instructions,
    83  * but are vulnerable to starvation and can spin forever if a thread
    84  * holding a lock has been terminated.  For this reason you should
    85  * minimize the code executed inside an atomic lock and never do
    86  * expensive things like API or system calls while holding them.
    87  *
    88  * The atomic locks are not safe to lock recursively.
    89  *
    90  * Porting Note:
    91  * The spin lock functions and type are required and can not be
    92  * emulated because they are used in the atomic emulation code.
    93  */
    94 /*@{*/
    95 
    96 typedef int SDL_SpinLock;
    97 
    98 /**
    99  * \brief Try to lock a spin lock by setting it to a non-zero value.
   100  *
   101  * \param lock Points to the lock.
   102  *
   103  * \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.
   104  */
   105 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
   106 
   107 /**
   108  * \brief Lock a spin lock by setting it to a non-zero value.
   109  *
   110  * \param lock Points to the lock.
   111  */
   112 extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
   113 
   114 /**
   115  * \brief Unlock a spin lock by setting it to 0. Always returns immediately
   116  *
   117  * \param lock Points to the lock.
   118  */
   119 extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
   120 
   121 /*@}*//*SDL AtomicLock*/
   122 
   123 
   124 /**
   125  * The compiler barrier prevents the compiler from reordering
   126  * reads and writes to globally visible variables across the call.
   127  */
   128 #if defined(_MSC_VER) && (_MSC_VER > 1200)
   129 void _ReadWriteBarrier(void);
   130 #pragma intrinsic(_ReadWriteBarrier)
   131 #define SDL_CompilerBarrier()   _ReadWriteBarrier()
   132 #elif defined(__GNUC__)
   133 #define SDL_CompilerBarrier()   __asm__ __volatile__ ("" : : : "memory")
   134 #else
   135 #define SDL_CompilerBarrier()   \
   136 { SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); }
   137 #endif
   138 
   139 /**
   140  * Memory barriers are designed to prevent reads and writes from being
   141  * reordered by the compiler and being seen out of order on multi-core CPUs.
   142  *
   143  * A typical pattern would be for thread A to write some data and a flag,
   144  * and for thread B to read the flag and get the data. In this case you
   145  * would insert a release barrier between writing the data and the flag,
   146  * guaranteeing that the data write completes no later than the flag is
   147  * written, and you would insert an acquire barrier between reading the
   148  * flag and reading the data, to ensure that all the reads associated
   149  * with the flag have completed.
   150  *
   151  * In this pattern you should always see a release barrier paired with
   152  * an acquire barrier and you should gate the data reads/writes with a
   153  * single flag variable.
   154  *
   155  * For more information on these semantics, take a look at the blog post:
   156  * http://preshing.com/20120913/acquire-and-release-semantics
   157  */
   158 /* FIXME: This is correct for x86 and x64 but not other CPUs
   159    For PPC we need the lwsync instruction, and on ARM some variant of dmb
   160  */
   161 #define SDL_MemoryBarrierRelease()  SDL_CompilerBarrier()
   162 #define SDL_MemoryBarrierAcquire()  SDL_CompilerBarrier()
   163 
   164 
   165 /* Platform specific optimized versions of the atomic functions,
   166  * you can disable these by defining SDL_DISABLE_ATOMIC_INLINE
   167  */
   168 #if defined(SDL_ATOMIC_DISABLED) && SDL_ATOMIC_DISABLED
   169 #define SDL_DISABLE_ATOMIC_INLINE
   170 #endif
   171 #ifndef SDL_DISABLE_ATOMIC_INLINE
   172 
   173 #ifdef HAVE_MSC_ATOMICS
   174 
   175 #define SDL_AtomicSet(a, v)     _InterlockedExchange((long*)&(a)->value, (v))
   176 #define SDL_AtomicAdd(a, v)     _InterlockedExchangeAdd((long*)&(a)->value, (v))
   177 #define SDL_AtomicCAS(a, oldval, newval) (_InterlockedCompareExchange((long*)&(a)->value, (newval), (oldval)) == (oldval))
   178 #define SDL_AtomicSetPtr(a, v)  _InterlockedExchangePointer((a), (v))
   179 #if _M_IX86
   180 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchange((long*)(a), (long)(newval), (long)(oldval)) == (long)(oldval))
   181 #else
   182 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchangePointer((a), (newval), (oldval)) == (oldval))
   183 #endif
   184 
   185 #elif defined(__MACOSX__)
   186 #include <libkern/OSAtomic.h>
   187 
   188 #define SDL_AtomicCAS(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((oldval), (newval), &(a)->value)
   189 #ifdef __LP64__
   190 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap64Barrier((int64_t)(oldval), (int64_t)(newval), (int64_t*)(a))
   191 #else
   192 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((int32_t)(oldval), (int32_t)(newval), (int32_t*)(a))
   193 #endif
   194 
   195 #elif defined(HAVE_GCC_ATOMICS)
   196 
   197 #define SDL_AtomicSet(a, v)     __sync_lock_test_and_set(&(a)->value, v)
   198 #define SDL_AtomicAdd(a, v)     __sync_fetch_and_add(&(a)->value, v)
   199 #define SDL_AtomicSetPtr(a, v)  __sync_lock_test_and_set(a, v)
   200 #define SDL_AtomicCAS(a, oldval, newval) __sync_bool_compare_and_swap(&(a)->value, oldval, newval)
   201 #define SDL_AtomicCASPtr(a, oldval, newval) __sync_bool_compare_and_swap(a, oldval, newval)
   202 
   203 #endif
   204 
   205 #endif /* !SDL_DISABLE_ATOMIC_INLINE */
   206 
   207 
   208 /**
   209  * \brief A type representing an atomic integer value.  It is a struct
   210  *        so people don't accidentally use numeric operations on it.
   211  */
   212 #ifndef SDL_atomic_t_defined
   213 typedef struct { int value; } SDL_atomic_t;
   214 #endif
   215 
   216 /**
   217  * \brief Set an atomic variable to a new value if it is currently an old value.
   218  *
   219  * \return SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
   220  *
   221  * \note If you don't know what this function is for, you shouldn't use it!
   222 */
   223 #ifndef SDL_AtomicCAS
   224 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
   225 #endif
   226 
   227 /**
   228  * \brief Set an atomic variable to a value.
   229  *
   230  * \return The previous value of the atomic variable.
   231  */
   232 #ifndef SDL_AtomicSet
   233 SDL_FORCE_INLINE int SDL_AtomicSet(SDL_atomic_t *a, int v)
   234 {
   235     int value;
   236     do {
   237         value = a->value;
   238     } while (!SDL_AtomicCAS(a, value, v));
   239     return value;
   240 }
   241 #endif
   242 
   243 /**
   244  * \brief Get the value of an atomic variable
   245  */
   246 #ifndef SDL_AtomicGet
   247 SDL_FORCE_INLINE int SDL_AtomicGet(SDL_atomic_t *a)
   248 {
   249     int value = a->value;
   250     SDL_CompilerBarrier();
   251     return value;
   252 }
   253 #endif
   254 
   255 /**
   256  * \brief Add to an atomic variable.
   257  *
   258  * \return The previous value of the atomic variable.
   259  *
   260  * \note This same style can be used for any number operation
   261  */
   262 #ifndef SDL_AtomicAdd
   263 SDL_FORCE_INLINE int SDL_AtomicAdd(SDL_atomic_t *a, int v)
   264 {
   265     int value;
   266     do {
   267         value = a->value;
   268     } while (!SDL_AtomicCAS(a, value, (value + v)));
   269     return value;
   270 }
   271 #endif
   272 
   273 /**
   274  * \brief Increment an atomic variable used as a reference count.
   275  */
   276 #ifndef SDL_AtomicIncRef
   277 #define SDL_AtomicIncRef(a)    SDL_AtomicAdd(a, 1)
   278 #endif
   279 
   280 /**
   281  * \brief Decrement an atomic variable used as a reference count.
   282  *
   283  * \return SDL_TRUE if the variable reached zero after decrementing,
   284  *         SDL_FALSE otherwise
   285  */
   286 #ifndef SDL_AtomicDecRef
   287 #define SDL_AtomicDecRef(a)    (SDL_AtomicAdd(a, -1) == 1)
   288 #endif
   289 
   290 /**
   291  * \brief Set a pointer to a new value if it is currently an old value.
   292  *
   293  * \return SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
   294  *
   295  * \note If you don't know what this function is for, you shouldn't use it!
   296 */
   297 #ifndef SDL_AtomicCASPtr
   298 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void* *a, void *oldval, void *newval);
   299 #endif
   300 
   301 /**
   302  * \brief Set a pointer to a value atomically.
   303  *
   304  * \return The previous value of the pointer.
   305  */
   306 #ifndef SDL_AtomicSetPtr
   307 SDL_FORCE_INLINE void* SDL_AtomicSetPtr(void* *a, void* v)
   308 {
   309     void* value;
   310     do {
   311         value = *a;
   312     } while (!SDL_AtomicCASPtr(a, value, v));
   313     return value;
   314 }
   315 #endif
   316 
   317 /**
   318  * \brief Get the value of a pointer atomically.
   319  */
   320 #ifndef SDL_AtomicGetPtr
   321 SDL_FORCE_INLINE void* SDL_AtomicGetPtr(void* *a)
   322 {
   323     void* value = *a;
   324     SDL_CompilerBarrier();
   325     return value;
   326 }
   327 #endif
   328 
   329 
   330 /* Ends C function definitions when using C++ */
   331 #ifdef __cplusplus
   332 }
   333 #endif
   334 
   335 #include "close_code.h"
   336 
   337 #endif /* _SDL_atomic_h_ */
   338 
   339 /* vi: set ts=4 sw=4 expandtab: */