| /* |
| Simple DirectMedia Layer |
| Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org> |
| |
| This software is provided 'as-is', without any express or implied |
| warranty. In no event will the authors be held liable for any damages |
| arising from the use of this software. |
| |
| Permission is granted to anyone to use this software for any purpose, |
| including commercial applications, and to alter it and redistribute it |
| freely, subject to the following restrictions: |
| |
| 1. The origin of this software must not be misrepresented; you must not |
| claim that you wrote the original software. If you use this software |
| in a product, an acknowledgment in the product documentation would be |
| appreciated but is not required. |
| 2. Altered source versions must be plainly marked as such, and must not be |
| misrepresented as being the original software. |
| 3. This notice may not be removed or altered from any source distribution. |
| */ |
| #include "SDL_config.h" |
| |
| #include "SDL_atomic.h" |
| |
| /* Note that we undefine the atomic operations here, in case they are |
| defined as compiler intrinsics while building SDL but the library user |
| doesn't have that compiler. That way we always have a working set of |
| atomic operations built into the library. |
| */ |
| #undef SDL_AtomicCAS |
| #undef SDL_AtomicCASPtr |
| |
| /* |
| If any of the operations are not provided then we must emulate some |
| of them. That means we need a nice implementation of spin locks |
| that avoids the "one big lock" problem. We use a vector of spin |
| locks and pick which one to use based on the address of the operand |
| of the function. |
| |
| To generate the index of the lock we first shift by 3 bits to get |
| rid on the zero bits that result from 32 and 64 bit allignment of |
| data. We then mask off all but 5 bits and use those 5 bits as an |
| index into the table. |
| |
| Picking the lock this way insures that accesses to the same data at |
| the same time will go to the same lock. OTOH, accesses to different |
| data have only a 1/32 chance of hitting the same lock. That should |
| pretty much eliminate the chances of several atomic operations on |
| different data from waiting on the same "big lock". If it isn't |
| then the table of locks can be expanded to a new size so long as |
| the new size is a power of two. |
| |
| Contributed by Bob Pendleton, bob@pendleton.com |
| */ |
| |
| static SDL_SpinLock locks[32]; |
| |
| static __inline__ void |
| enterLock(void *a) |
| { |
| uintptr_t index = ((((uintptr_t)a) >> 3) & 0x1f); |
| |
| SDL_AtomicLock(&locks[index]); |
| } |
| |
| static __inline__ void |
| leaveLock(void *a) |
| { |
| uintptr_t index = ((((uintptr_t)a) >> 3) & 0x1f); |
| |
| SDL_AtomicUnlock(&locks[index]); |
| } |
| |
| DECLSPEC SDL_bool SDLCALL |
| SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval) |
| { |
| SDL_bool retval = SDL_FALSE; |
| |
| enterLock(a); |
| if (a->value == oldval) { |
| a->value = newval; |
| retval = SDL_TRUE; |
| } |
| leaveLock(a); |
| |
| return retval; |
| } |
| |
| DECLSPEC SDL_bool SDLCALL |
| SDL_AtomicCASPtr(void **a, void *oldval, void *newval) |
| { |
| SDL_bool retval = SDL_FALSE; |
| |
| enterLock(a); |
| if (*a == oldval) { |
| *a = newval; |
| retval = SDL_TRUE; |
| } |
| leaveLock(a); |
| |
| return retval; |
| } |
| |
| #if defined(__GNUC__) && defined(__arm__) && \ |
| (defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6T2__) || defined(__ARM_ARCH_6Z__) || defined(__ARM_ARCH_6ZK__)) |
| __asm__( |
| " .align 2\n" |
| " .globl _SDL_MemoryBarrierRelease\n" |
| " .globl _SDL_MemoryBarrierAcquire\n" |
| "_SDL_MemoryBarrierRelease:\n" |
| "_SDL_MemoryBarrierAcquire:\n" |
| " mov r0, #0\n" |
| " mcr p15, 0, r0, c7, c10, 5\n" |
| " bx lr\n" |
| ); |
| #endif /* __GNUC__ && __arm__ && ARMV6 */ |
| |
| /* vi: set ts=4 sw=4 expandtab: */ |