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 1.47 1998/09/12 16:07:53 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");
110 #define TAS(lock) tas(lock)
112 static __inline__ int
113 tas(volatile slock_t *lock)
115 register slock_t _res = 1;
117 __asm__("lock; xchgb %0,%1": "=q"(_res), "=m"(*lock):"0"(_res));
126 #define TAS(lock) tas(lock)
128 static __inline__ int
129 tas(volatile slock_t *lock)
131 register slock_t _res = 1;
133 __asm__("ldstub [%2], %0" \
134 : "=r"(_res), "=m"(*lock) \
143 #if defined(NEED_VAX_TAS_ASM)
145 * VAXen -- even multiprocessor ones
146 * (thanks to Tom Ivar Helbekkmo)
148 #define TAS(lock) tas(lock)
150 typedef unsigned char slock_t;
152 static __inline__ int
153 tas(volatile slock_t *lock)
157 __asm__(" movl $1, r0 \
158 bbssi $0, (%1), 1 f \
161 : "=r"(_res) /* return value, in register */
162 : "r"(lock) /* argument, 'lock pointer', in register */
163 : "r0"); /* inline code uses this register */
167 #endif /* NEED_VAX_TAS_ASM */
173 /***************************************************************************
181 * Note that slock_t on the Alpha AXP is msemaphore instead of char
182 * (see storage/ipc.h).
184 #define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0)
185 #define S_UNLOCK(lock) msem_unlock((lock), 0)
186 #define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED)
187 #define S_LOCK_FREE(lock) (!(lock)->msem_state)
192 #if defined(NEED_I386_TAS_ASM)
193 /* non gcc i386 based things */
195 #if defined(USE_UNIVEL_CC)
196 #define TAS(lock) tas(lock)
201 /* UNIVEL wants %mem in column 1, so we don't pg_indent this file */
211 #endif /* USE_UNIVEL_CC */
213 #endif /* NEED_I386_TAS_ASM */
217 #if defined(NEED_NS32K_TAS_ASM)
219 #define S_LOCK(lock) \
223 __asm__("movqd 0, r0"); \
224 __asm__("sbitd r0, %0" : "=m"(*lock)); \
225 __asm__("sprb us, %0" : "=r" (res)); \
226 res = ((res >> 5) & 1); \
230 #endif /* NEED_NS32K_TAS_ASM */
233 #endif /* defined(__GNUC__) */
237 /*************************************************************************
238 * These are the platforms that have common code for gcc and non-gcc
245 * Note that slock_t on PA-RISC is a structure instead of char
246 * (see storage/ipc.h).
248 * a "set" slock_t has a single word cleared. a "clear" slock_t has
249 * all words set to non-zero. tas() in tas.s
251 static const slock_t clear_lock =
254 #define S_UNLOCK(lock) (*(lock) = clear_lock) /* struct assignment */
255 #define S_LOCK_FREE(lock) ( *(int *) (((long) (lock) + 15) & ~15) != 0)
262 * slock_t is defined as a struct abilock_t, which has a single unsigned long
265 * This stuff may be supplemented in the future with Masato Kataoka's MIPS-II
266 * assembly from his NECEWS SVR4 port, but we probably ought to retain this
267 * for the R3000 chips out there.
270 #define TAS(lock) (test_and_set(lock,1))
271 #define S_UNLOCK(lock) (test_then_and(lock,0))
272 #define S_INIT_LOCK(lock) (test_then_and(lock,0))
273 #define S_LOCK_FREE(lock) (test_then_add(lock,0) == 0)
281 * Note that slock_t on POWER/POWER2/PowerPC is int instead of char
282 * (see storage/ipc.h).
284 #define TAS(lock) cs((int *) (lock), 0, 1)
288 #if defined (nextstep)
291 * slock_t is defined as a struct mutex.
294 #define S_LOCK(lock) mutex_lock(lock)
295 #define S_UNLOCK(lock) mutex_unlock(lock)
296 #define S_INIT_LOCK(lock) mutex_init(lock)
297 /* For Mach, we have to delve inside the entrails of `struct mutex'. Ick! */
298 #define S_LOCK_FREE(alock) ((alock)->lock == 0)
299 #endif /* nextstep */
304 /****************************************************************************
305 * Default Definitions - override these above as needed.
309 extern void s_lock(volatile slock_t *lock, const char *file, const int line);
311 #define S_LOCK(lock) \
312 if (TAS((volatile slock_t *) lock)) {\
313 s_lock((volatile slock_t *) lock, __FILE__, __LINE__); \
317 #if !defined(S_LOCK_FREE)
318 #define S_LOCK_FREE(lock) (*(lock) == 0)
319 #endif /* S_LOCK_FREE */
321 #if !defined(S_UNLOCK)
322 #define S_UNLOCK(lock) (*(lock) = 0)
323 #endif /* S_UNLOCK */
325 #if !defined(S_INIT_LOCK)
326 #define S_INIT_LOCK(lock) S_UNLOCK(lock)
327 #endif /* S_INIT_LOCK */
330 int tas(volatile slock_t *lock); /* port/.../tas.s, or
333 #define TAS(lock) tas((volatile slock_t *) lock)
336 #endif /* HAS_TEST_AND_SET */
337 #endif /* S_LOCK_H */