1 /*-------------------------------------------------------------------------
4 * This file contains the implementation (if any) for spinlocks.
6 * Copyright (c) 1994, Regents of the University of California
10 * $Header: /cvsroot/pgsql/src/include/storage/s_lock.h,v 1.36 1998/06/16 07:18:16 momjian Exp $
12 *-------------------------------------------------------------------------
17 * The public macros that must be provided are:
19 * void S_INIT_LOCK(slock_t *lock)
21 * void S_LOCK(slock_t *lock)
23 * void S_UNLOCK(slock_t *lock)
25 * void S_LOCK_FREE(slock_t *lock)
26 * Tests if the lock is free. Returns non-zero if free, 0 if locked.
28 * The S_LOCK() macro implements a primitive but still useful random
29 * backoff to avoid hordes of busywaiting lockers chewing CPU.
33 * S_LOCK(slock_t *lock)
37 * // back off the cpu for a semi-random short time
41 * This implementation takes advantage of a tas function written
42 * (in assembly language) on machines that have a native test-and-set
43 * instruction. Alternative mutex implementations may also be used.
44 * This function is hidden under the TAS macro to allow substitutions.
46 * #define TAS(lock) tas(lock)
47 * int tas(slock_t *lock) // True if lock already set
49 * There are default implementations for all these macros at the bottom
50 * of this file. Check if your platform can use these or needs to
54 * If none of this can be done, POSTGRES will default to using
55 * System V semaphores (and take a large performance hit -- around 40%
56 * of its time on a DS5000/240 is spent in semop(3)...).
58 * AIX has a test-and-set but the recommended interface is the cs(3)
59 * system call. This provides an 8-instruction (plus system call
60 * overhead) uninterruptible compare-and-set operation. True
61 * spinlocks might be faster but using cs(3) still speeds up the
62 * regression test suite by about 25%. I don't have an assembler
63 * manual for POWER in any case.
66 #if !defined(S_LOCK_H)
69 #include "storage/ipc.h"
71 #if defined(HAS_TEST_AND_SET)
75 /*************************************************************************
80 #define TAS(lock) tas(lock)
81 #define S_UNLOCK(lock) { __asm__("mb"); *(lock) = 0; }
84 tas(volatile slock_t *lock)
86 register slock_t _res;
88 __asm__(" ldq $0, %0 \n\
89 bne $0, already_set \n\
91 bne $0, already_set \n\
95 success: bis $31, $31, %1 \n\
98 stqc_fail: or $31, 1, $0 \n\
99 already_set: bis $0, $0, %1 \n\
100 end: nop " : "=m"(*lock), "=r"(_res) : : "0");
109 #define TAS(lock) tas(lock)
111 static __inline__ int
112 tas(volatile slock_t *lock)
114 register slock_t _res = 1;
116 __asm__("lock; xchgb %0,%1" : "=q"(_res), "=m"(*lock) : "0"(_res) );
124 #define TAS(lock) tas(lock)
126 static __inline__ int
127 tas(volatile slock_t *lock)
129 register slock_t _res = 1;
131 __asm__("ldstub [%1], %0" \
132 : "=r"(_res), "=m"(*lock) \
140 #if defined(NEED_VAX_TAS_ASM)
142 * VAXen -- even multiprocessor ones
143 * (thanks to Tom Ivar Helbekkmo)
145 #define TAS(lock) tas(lock)
147 typedef unsigned char slock_t;
149 static __inline__ int
150 tas(volatile slock_t *lock)
154 __asm__(" movl $1, r0
158 : "=r"(_res) /* return value, in register */
159 : "r"(lock) /* argument, 'lock pointer', in register */
160 : "r0"); /* inline code uses this register */
163 #endif /* NEED_VAX_TAS_ASM */
169 /***************************************************************************
173 #if defined (nextstep)
176 * slock_t is defined as a struct mutex.
179 #define S_LOCK(lock) mutex_lock(lock)
180 #define S_UNLOCK(lock) mutex_unlock(lock)
181 #define S_INIT_LOCK(lock) mutex_init(lock)
182 /* For Mach, we have to delve inside the entrails of `struct mutex'. Ick! */
183 #define S_LOCK_FREE(alock) ((alock)->lock == 0)
184 #endif /* nextstep */
191 * slock_t is defined as a struct abilock_t, which has a single unsigned long
194 * This stuff may be supplemented in the future with Masato Kataoka's MIPS-II
195 * assembly from his NECEWS SVR4 port, but we probably ought to retain this
196 * for the R3000 chips out there.
198 #define TAS(lock) (!acquire_lock(lock))
199 #define S_UNLOCK(lock) release_lock(lock)
200 #define S_INIT_LOCK(lock) init_lock(lock)
201 #define S_LOCK_FREE(lock) (stat_lock(lock) == UNLOCKED)
210 * Note that slock_t on the Alpha AXP is msemaphore instead of char
211 * (see storage/ipc.h).
213 #define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0)
214 #define S_UNLOCK(lock) msem_unlock((lock), 0)
215 #define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED)
216 #define S_LOCK_FREE(lock) (!(lock)->msem_state)
225 * Note that slock_t on POWER/POWER2/PowerPC is int instead of char
226 * (see storage/ipc.h).
228 #define TAS(lock) cs((int *) (lock), 0, 1)
237 * Note that slock_t on PA-RISC is a structure instead of char
238 * (see storage/ipc.h).
240 * a "set" slock_t has a single word cleared. a "clear" slock_t has
241 * all words set to non-zero. tas() in tas.s
243 static slock_t clear_lock =
246 #define S_UNLOCK(lock) (*(lock) = clear_lock) /* struct assignment */
247 #define S_LOCK_FREE(lock) ( *(int *) (((long) (lock) + 15) & ~15) != 0)
252 #if defined(NEED_I386_TAS_ASM)
253 /* non gcc i386 based things */
256 #if defined(USE_UNIVEL_CC)
257 #define TAS(lock) tas(lock)
263 /* Upon entry, %eax will contain the pointer to the lock byte */
272 #endif /* USE_UNIVEL_CC */
275 #endif /* NEED_I386_TAS_ASM */
278 #endif /* else defined(__GNUC__) */
283 /****************************************************************************
284 * Default Definitions - override these above as needed.
288 extern void s_lock(volatile slock_t *lock, const char *file, const int line);
289 #define S_LOCK(lock) \
290 if (TAS((volatile slock_t *) lock)) {\
291 s_lock((volatile slock_t *) lock, __FILE__, __LINE__); \
295 #if !defined(S_LOCK_FREE)
296 #define S_LOCK_FREE(lock) (*(lock) == 0)
297 #endif /* S_LOCK_FREE */
299 #if !defined(S_UNLOCK)
300 #define S_UNLOCK(lock) (*(lock) = 0)
301 #endif /* S_UNLOCK */
303 #if !defined(S_INIT_LOCK)
304 #define S_INIT_LOCK(lock) S_UNLOCK(lock)
305 #endif /* S_INIT_LOCK */
308 int tas(volatile slock_t *lock); /* port/.../tas.s, or s_lock.c */
309 #define TAS(lock) tas((volatile slock_t *) lock)
313 #endif /* HAS_TEST_AND_SET */
314 #endif /* S_LOCK_H */