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atomic: Spin locks now try to use the x86 PAUSE instruction for short waits.

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Fixes Bugzilla #4151.
This commit is contained in:
Ryan C. Gordon 2018-06-25 15:58:35 -04:00
parent 5a8ecf4e79
commit 5f123e31a3
1 changed files with 24 additions and 1 deletions
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25
src/atomic/SDL_spinlock.c
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@ -32,6 +32,10 @@
#include <atomic.h> #include <atomic.h>
#endif #endif
#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
#include <xmmintrin.h>
#endif
#if defined(__WATCOMC__) && defined(__386__) #if defined(__WATCOMC__) && defined(__386__)
SDL_COMPILE_TIME_ASSERT(locksize, 4==sizeof(SDL_SpinLock)); SDL_COMPILE_TIME_ASSERT(locksize, 4==sizeof(SDL_SpinLock));
extern _inline int _SDL_xchg_watcom(volatile int *a, int v); extern _inline int _SDL_xchg_watcom(volatile int *a, int v);
@ -116,12 +120,31 @@ SDL_AtomicTryLock(SDL_SpinLock *lock)
#endif #endif
} }
/* "REP NOP" is PAUSE, coded for tools that don't know it by that name. */
#if (defined(__GNUC__) || defined(__clang__)) && (defined(__i386__) || defined(__x86_64__))
#define PAUSE_INSTRUCTION() __asm__ __volatile__("rep nop\n")
#elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
#define PAUSE_INSRUCTION() _mm_pause() /* this is actually "rep nop" and not a SIMD instruction. */
#elif defined(__WATCOMC__) && defined(__386__)
extern _inline void PAUSE_INSTRUCTION(void);
#pragma aux PAUSE_INSTRUCTION = "rep nop"
#else
#define PAUSE_INSTRUCTION()
#endif
void void
SDL_AtomicLock(SDL_SpinLock *lock) SDL_AtomicLock(SDL_SpinLock *lock)
{ {
int iterations = 0;
/* FIXME: Should we have an eventual timeout? */ /* FIXME: Should we have an eventual timeout? */
while (!SDL_AtomicTryLock(lock)) { while (!SDL_AtomicTryLock(lock)) {
SDL_Delay(0); if (iterations < 32) {
iterations++;
PAUSE_INSTRUCTION();
} else {
/* !!! FIXME: this doesn't definitely give up the current timeslice, it does different things on various platforms. */
SDL_Delay(0);
}
} }
} }