/*------------------------------------------------------------------------- * * s_lock.h-- * This file contains the implementation (if any) for spinlocks. * * Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $Header: /cvsroot/pgsql/src/include/storage/s_lock.h,v 1.33 1998/05/04 23:49:17 scrappy Exp $ * *------------------------------------------------------------------------- */ /* * DESCRIPTION * The public functions that must be provided are: * * void S_INIT_LOCK(slock_t *lock) * * void S_LOCK(slock_t *lock) * * void S_UNLOCK(slock_t *lock) * * void S_LOCK_FREE(slock_t *lock) * Tests if the lock is free. Returns non-zero if free, 0 if locked. * * The S_LOCK() macro implements a primitive but still useful random * backoff to avoid hordes of busywaiting lockers chewing CPU. * * Effectively: * void * S_LOCK(slock_t *lock) * { * while (TAS(lock)) * { * // back off the cpu for a semi-random short time * } * } * * This implementation takes advantage of a tas function written * (in assembly language) on machines that have a native test-and-set * instruction. Alternative mutex implementations may also be used. * This function is hidden under the TAS macro to allow substitutions. * * #define TAS(lock) tas(lock) * int tas(slock_t *lock) // True if lock already set * * If none of this can be done, POSTGRES will default to using * System V semaphores (and take a large performance hit -- around 40% * of its time on a DS5000/240 is spent in semop(3)...). * * NOTES * AIX has a test-and-set but the recommended interface is the cs(3) * system call. This provides an 8-instruction (plus system call * overhead) uninterruptible compare-and-set operation. True * spinlocks might be faster but using cs(3) still speeds up the * regression test suite by about 25%. I don't have an assembler * manual for POWER in any case. * * There are default implementations for all these macros at the bottom * of this file. Check if your platform can use these or needs to * override them. * */ #if !defined(S_LOCK_H) #define S_LOCK_H #include "storage/ipc.h" #if defined(HAS_TEST_AND_SET) #if defined(linux) /*************************************************************************** * All Linux */ #if defined(__alpha) #define S_UNLOCK(lock) { __asm__("mb"); *(lock) = 0; } #endif /* __alpha */ #else /* linux */ /*************************************************************************** * All non Linux */ #if defined (nextstep) /* * NEXTSTEP (mach) * slock_t is defined as a struct mutex. */ #define S_LOCK(lock) mutex_lock(lock) #define S_UNLOCK(lock) mutex_unlock(lock) #define S_INIT_LOCK(lock) mutex_init(lock) /* For Mach, we have to delve inside the entrails of `struct mutex'. Ick! */ #define S_LOCK_FREE(alock) ((alock)->lock == 0) #endif /* nextstep */ #if defined(__sgi) /* * SGI IRIX 5 * slock_t is defined as a struct abilock_t, which has a single unsigned long * member. * * This stuff may be supplemented in the future with Masato Kataoka's MIPS-II * assembly from his NECEWS SVR4 port, but we probably ought to retain this * for the R3000 chips out there. */ #define TAS(lock) (!acquire_lock(lock)) #define S_UNLOCK(lock) release_lock(lock) #define S_INIT_LOCK(lock) init_lock(lock) #define S_LOCK_FREE(lock) (stat_lock(lock) == UNLOCKED) #endif /* __sgi */ #if (defined(__alpha) /* * OSF/1 (Alpha AXP) * * Note that slock_t on the Alpha AXP is msemaphore instead of char * (see storage/ipc.h). */ #define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0) #define S_UNLOCK(lock) msem_unlock((lock), 0) #define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED) #define S_LOCK_FREE(lock) (!(lock)->msem_state) #endif /* __alpha */ #if defined(_AIX) /* * AIX (POWER) * * Note that slock_t on POWER/POWER2/PowerPC is int instead of char * (see storage/ipc.h). */ #define TAS(lock) cs((int *) (lock), 0, 1) #endif /* _AIX */ #if defined(__hpux) /* * HP-UX (PA-RISC) * * Note that slock_t on PA-RISC is a structure instead of char * (see storage/ipc.h). * * a "set" slock_t has a single word cleared. a "clear" slock_t has * all words set to non-zero. tas() in tas.s */ static slock_t clear_lock = {-1, -1, -1, -1}; #define S_UNLOCK(lock) (*(lock) = clear_lock) /* struct assignment */ #define S_LOCK_FREE(lock) ( *(int *) (((long) (lock) + 15) & ~15) != 0) #endif /* __hpux */ #endif /* else defined(linux) */ /**************************************************************************** * Default Definitions - override these above as needed. */ #if !defined(S_LOCK) #include #define S_NSPINCYCLE 16 #define S_MAX_BUSY 1000 * S_NSPINCYCLE extern int s_spincycle[]; extern void s_lock_stuck(slock_t *lock, char *file, int line); #if defined(S_LOCK_DEBUG) extern void s_lock(slock_t *lock); #define S_LOCK(lock) s_lock(lock, __FILE__, __LINE__) #else /* S_LOCK_DEBUG */ #define S_LOCK(lock) if (1) { \ int spins = 0; \ while (TAS(lock)) { \ struct timeval delay; \ delay.tv_sec = 0; \ delay.tv_usec = s_spincycle[spins++ % S_NSPINCYCLE]; \ (void) select(0, NULL, NULL, NULL, &delay); \ if (spins > S_MAX_BUSY) { \ /* It's been well over a minute... */ \ s_lock_stuck(lock, __FILE__, __LINE__); \ } \ } \ } else #endif /* S_LOCK_DEBUG */ #endif /* S_LOCK */ #if !defined(S_LOCK_FREE) #define S_LOCK_FREE(lock) ((*lock) == 0) #endif /* S_LOCK_FREE */ #if !defined(S_UNLOCK) #define S_UNLOCK(lock) (*(lock) = 0) #endif /* S_UNLOCK */ #if !defined(S_INIT_LOCK) #define S_INIT_LOCK(lock) S_UNLOCK(lock) #endif /* S_INIT_LOCK */ #if !defined(TAS) int tas(slock_t *lock); /* port/.../tas.s, or s_lock.c */ #define TAS(lock) tas(lock) #endif /* TAS */ #endif /* HAS_TEST_AND_SET */ #endif /* S_LOCK_H */