1
/*-------------------------------------------------------------------------
4
* Hardware-dependent implementation of spinlocks.
7
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
8
* Portions Copyright (c) 1994, Regents of the University of California
12
* $PostgreSQL: pgsql/src/backend/storage/lmgr/s_lock.c,v 1.35 2004-12-31 22:01:05 pgsql Exp $
14
*-------------------------------------------------------------------------
21
#include "storage/s_lock.h"
22
#include "miscadmin.h"
25
* s_lock_stuck() - complain about a stuck spinlock
28
s_lock_stuck(volatile slock_t *lock, const char *file, int line)
30
#if defined(S_LOCK_TEST)
32
"\nStuck spinlock (%p) detected at %s:%d.\n",
36
elog(PANIC, "stuck spinlock (%p) detected at %s:%d",
43
* s_lock(lock) - platform-independent portion of waiting for a spinlock.
46
s_lock(volatile slock_t *lock, const char *file, int line)
49
* We loop tightly for awhile, then delay using pg_usleep() and try
50
* again. Preferably, "awhile" should be a small multiple of the
51
* maximum time we expect a spinlock to be held. 100 iterations seems
52
* about right. In most multi-CPU scenarios, the spinlock is probably
53
* held by a process on another CPU and will be released before we
54
* finish 100 iterations. However, on a uniprocessor, the tight loop
55
* is just a waste of cycles, so don't iterate thousands of times.
57
* Once we do decide to block, we use randomly increasing pg_usleep()
58
* delays. The first delay is 10 msec, then the delay randomly
59
* increases to about one second, after which we reset to 10 msec and
60
* start again. The idea here is that in the presence of heavy
61
* contention we need to increase the delay, else the spinlock holder
62
* may never get to run and release the lock. (Consider situation
63
* where spinlock holder has been nice'd down in priority by the
64
* scheduler --- it will not get scheduled until all would-be
65
* acquirers are sleeping, so if we always use a 10-msec sleep, there
66
* is a real possibility of starvation.) But we can't just clamp the
67
* delay to an upper bound, else it would take a long time to make a
68
* reasonable number of tries.
70
* We time out and declare error after NUM_DELAYS delays (thus, exactly
71
* that many tries). With the given settings, this will usually take
72
* 3 or so minutes. It seems better to fix the total number of tries
73
* (and thus the probability of unintended failure) than to fix the
76
* The pg_usleep() delays are measured in centiseconds (0.01 sec) because
77
* 10 msec is a common resolution limit at the OS level.
79
#define SPINS_PER_DELAY 100
80
#define NUM_DELAYS 1000
81
#define MIN_DELAY_CSEC 1
82
#define MAX_DELAY_CSEC 100
86
int cur_delay = MIN_DELAY_CSEC;
90
/* CPU-specific delay each time through the loop */
93
/* Block the process every SPINS_PER_DELAY tries */
94
if (++spins > SPINS_PER_DELAY)
96
if (++delays > NUM_DELAYS)
97
s_lock_stuck(lock, file, line);
99
pg_usleep(cur_delay * 10000L);
101
#if defined(S_LOCK_TEST)
102
fprintf(stdout, "*");
106
/* increase delay by a random fraction between 1X and 2X */
107
cur_delay += (int) (cur_delay *
108
(((double) random()) / ((double) MAX_RANDOM_VALUE)) + 0.5);
109
/* wrap back to minimum delay when max is exceeded */
110
if (cur_delay > MAX_DELAY_CSEC)
111
cur_delay = MIN_DELAY_CSEC;
119
* Various TAS implementations that cannot live in s_lock.h as no inline
120
* definition exists (yet).
121
* In the future, get rid of tas.[cso] and fold it into this file.
123
* If you change something here, you will likely need to modify s_lock.h too,
124
* because the definitions for these are split between this file and s_lock.h.
128
#ifdef HAVE_SPINLOCKS /* skip spinlocks if requested */
131
#if defined(__GNUC__)
134
* All the gcc flavors that are not inlined
138
#if defined(__m68k__)
139
/* really means: extern int tas(slock_t* **lock); */
143
__asm__ __volatile__(
144
#if defined(__NetBSD__) && defined(__ELF__)
145
/* no underscore for label and % for registers */
149
movel %sp@(0x4),%a0 \n\
161
movel sp@(0x4),a0 \n\
169
#endif /* __NetBSD__ && __ELF__ */
172
#endif /* __m68k__ */
175
#if defined(__mips__) && !defined(__sgi)
179
__asm__ __volatile__(
183
.frame $sp, 0, $31 \n\
193
.livereg 0x2000FF0E,0x00000FFF \n\
200
#endif /* __mips__ && !__sgi */
203
#else /* not __GNUC__ */
212
tas_dummy() /* really means: extern int tas(slock_t
221
asm("|#PROLOGUE# 1");
222
asm(" movel sp@(0x4),a0");
225
asm(" moveq #-128,d0");
235
#if defined(__sparc__) || defined(__sparc)
237
* sparc machines not using gcc
240
tas_dummy() /* really means: extern int tas(slock_t
245
asm(".seg \"data\"");
246
asm(".seg \"text\"");
248
asm(".section \"data\"");
249
asm(".section \"text\"");
255
* Sparc atomic test and set (sparc calls it "atomic load-store")
257
asm("ldstub [%r8], %r8");
261
#endif /* __sparc || __sparc__ */
262
#endif /* not __GNUC__ */
263
#endif /* HAVE_SPINLOCKS */
267
/*****************************************************************************/
268
#if defined(S_LOCK_TEST)
271
* test program for verifying a port's spinlock support.
274
struct test_lock_struct
281
volatile struct test_lock_struct test_lock;
286
srandom((unsigned int) time(NULL));
288
test_lock.pad1 = test_lock.pad2 = 0x44;
290
S_INIT_LOCK(&test_lock.lock);
292
if (test_lock.pad1 != 0x44 || test_lock.pad2 != 0x44)
294
printf("S_LOCK_TEST: failed, declared datatype is wrong size\n");
298
if (!S_LOCK_FREE(&test_lock.lock))
300
printf("S_LOCK_TEST: failed, lock not initialized\n");
304
S_LOCK(&test_lock.lock);
306
if (test_lock.pad1 != 0x44 || test_lock.pad2 != 0x44)
308
printf("S_LOCK_TEST: failed, declared datatype is wrong size\n");
312
if (S_LOCK_FREE(&test_lock.lock))
314
printf("S_LOCK_TEST: failed, lock not locked\n");
318
S_UNLOCK(&test_lock.lock);
320
if (test_lock.pad1 != 0x44 || test_lock.pad2 != 0x44)
322
printf("S_LOCK_TEST: failed, declared datatype is wrong size\n");
326
if (!S_LOCK_FREE(&test_lock.lock))
328
printf("S_LOCK_TEST: failed, lock not unlocked\n");
332
S_LOCK(&test_lock.lock);
334
if (test_lock.pad1 != 0x44 || test_lock.pad2 != 0x44)
336
printf("S_LOCK_TEST: failed, declared datatype is wrong size\n");
340
if (S_LOCK_FREE(&test_lock.lock))
342
printf("S_LOCK_TEST: failed, lock not re-locked\n");
346
printf("S_LOCK_TEST: this will print %d stars and then\n", NUM_DELAYS);
347
printf(" exit with a 'stuck spinlock' message\n");
348
printf(" if S_LOCK() and TAS() are working.\n");
351
s_lock(&test_lock.lock, __FILE__, __LINE__);
353
printf("S_LOCK_TEST: failed, lock not locked\n");
357
#endif /* S_LOCK_TEST */