src/atomic/SDL_atomic.c
author Sam Lantinga <slouken@libsdl.org>
Wed, 10 Jul 2013 20:17:20 -0700
changeset 7394 38dc4961ab15
parent 7191 75360622e65f
child 7860 2b0bcdea3a79
permissions -rw-r--r--
Added PowerPC and ARM versions of the memory barrier functions.
     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 #include "SDL_config.h"
    22 
    23 #include "SDL_atomic.h"
    24 
    25 /* Note that we undefine the atomic operations here, in case they are
    26    defined as compiler intrinsics while building SDL but the library user
    27    doesn't have that compiler.  That way we always have a working set of
    28    atomic operations built into the library.
    29 */
    30 #undef SDL_AtomicCAS
    31 #undef SDL_AtomicCASPtr
    32 
    33 /*
    34   If any of the operations are not provided then we must emulate some
    35   of them. That means we need a nice implementation of spin locks
    36   that avoids the "one big lock" problem. We use a vector of spin
    37   locks and pick which one to use based on the address of the operand
    38   of the function.
    39 
    40   To generate the index of the lock we first shift by 3 bits to get
    41   rid on the zero bits that result from 32 and 64 bit allignment of
    42   data. We then mask off all but 5 bits and use those 5 bits as an
    43   index into the table.
    44 
    45   Picking the lock this way insures that accesses to the same data at
    46   the same time will go to the same lock. OTOH, accesses to different
    47   data have only a 1/32 chance of hitting the same lock. That should
    48   pretty much eliminate the chances of several atomic operations on
    49   different data from waiting on the same "big lock". If it isn't
    50   then the table of locks can be expanded to a new size so long as
    51   the new size is a power of two.
    52 
    53   Contributed by Bob Pendleton, bob@pendleton.com
    54 */
    55 
    56 static SDL_SpinLock locks[32];
    57 
    58 static __inline__ void
    59 enterLock(void *a)
    60 {
    61     uintptr_t index = ((((uintptr_t)a) >> 3) & 0x1f);
    62 
    63     SDL_AtomicLock(&locks[index]);
    64 }
    65 
    66 static __inline__ void
    67 leaveLock(void *a)
    68 {
    69     uintptr_t index = ((((uintptr_t)a) >> 3) & 0x1f);
    70 
    71     SDL_AtomicUnlock(&locks[index]);
    72 }
    73 
    74 DECLSPEC SDL_bool SDLCALL
    75 SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval)
    76 {
    77     SDL_bool retval = SDL_FALSE;
    78 
    79     enterLock(a);
    80     if (a->value == oldval) {
    81         a->value = newval;
    82         retval = SDL_TRUE;
    83     }
    84     leaveLock(a);
    85 
    86     return retval;
    87 }
    88 
    89 DECLSPEC SDL_bool SDLCALL
    90 SDL_AtomicCASPtr(void **a, void *oldval, void *newval)
    91 {
    92     SDL_bool retval = SDL_FALSE;
    93 
    94     enterLock(a);
    95     if (*a == oldval) {
    96         *a = newval;
    97         retval = SDL_TRUE;
    98     }
    99     leaveLock(a);
   100 
   101     return retval;
   102 }
   103 
   104 #if defined(__GNUC__) && defined(__arm__) && \
   105    (defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6T2__) || defined(__ARM_ARCH_6Z__) || defined(__ARM_ARCH_6ZK__))
   106 __asm__(
   107 "   .align 2\n"
   108 "   .globl _SDL_MemoryBarrierRelease\n"
   109 "   .globl _SDL_MemoryBarrierAcquire\n"
   110 "_SDL_MemoryBarrierRelease:\n"
   111 "_SDL_MemoryBarrierAcquire:\n"
   112 "   mov r0, #0\n"
   113 "   mcr p15, 0, r0, c7, c10, 5\n"
   114 "   bx lr\n"
   115 );
   116 #endif /* __GNUC__ && __arm__ && ARMV6 */
   117 
   118 /* vi: set ts=4 sw=4 expandtab: */