PostgreSQL Source Code git master
Macros | Functions | Variables
s_lock.c File Reference
#include "postgres.h"
#include <time.h>
#include <unistd.h>
#include "common/pg_prng.h"
#include "storage/s_lock.h"
#include "utils/wait_event.h"
Include dependency graph for s_lock.c:

Go to the source code of this file.

Macros

#define  MIN_SPINS_PER_DELAY   10
 
#define  MAX_SPINS_PER_DELAY   1000
 
#define  NUM_DELAYS   1000
 
#define  MIN_DELAY_USEC   1000L
 
#define  MAX_DELAY_USEC   1000000L
 

Functions

static void  s_lock_stuck (const char *file, int line, const char *func)
 
int  s_lock (volatile slock_t *lock, const char *file, int line, const char *func)
 
void  s_unlock (volatile slock_t *lock)
 
void  perform_spin_delay (SpinDelayStatus *status)
 
void  finish_spin_delay (SpinDelayStatus *status)
 
void  set_spins_per_delay (int shared_spins_per_delay)
 
int  update_spins_per_delay (int shared_spins_per_delay)
 

Variables

static int  spins_per_delay = DEFAULT_SPINS_PER_DELAY
 

Macro Definition Documentation

◆ MAX_DELAY_USEC

#define MAX_DELAY_USEC   1000000L

Definition at line 61 of file s_lock.c.

◆ MAX_SPINS_PER_DELAY

#define MAX_SPINS_PER_DELAY   1000

Definition at line 58 of file s_lock.c.

◆ MIN_DELAY_USEC

#define MIN_DELAY_USEC   1000L

Definition at line 60 of file s_lock.c.

◆ MIN_SPINS_PER_DELAY

#define MIN_SPINS_PER_DELAY   10

Definition at line 57 of file s_lock.c.

◆ NUM_DELAYS

#define NUM_DELAYS   1000

Definition at line 59 of file s_lock.c.

Function Documentation

◆ finish_spin_delay()

void finish_spin_delay ( SpinDelayStatus *  status )

Definition at line 186 of file s_lock.c.

187{
188 if (status->cur_delay == 0)
189 {
190 /* we never had to delay */
193 }
194 else
195 {
198 }
199}
#define Min(x, y)
Definition: c.h:1003
#define Max(x, y)
Definition: c.h:997
#define MAX_SPINS_PER_DELAY
Definition: s_lock.c:58
#define MIN_SPINS_PER_DELAY
Definition: s_lock.c:57
static int spins_per_delay
Definition: s_lock.c:72
int cur_delay
Definition: s_lock.h:715

References SpinDelayStatus::cur_delay, Max, MAX_SPINS_PER_DELAY, Min, MIN_SPINS_PER_DELAY, and spins_per_delay.

Referenced by LockBufHdr(), LWLockWaitListLock(), s_lock(), and WaitBufHdrUnlocked().

◆ perform_spin_delay()

void perform_spin_delay ( SpinDelayStatus *  status )

Definition at line 126 of file s_lock.c.

127{
128 /* CPU-specific delay each time through the loop */
129 SPIN_DELAY();
130
131 /* Block the process every spins_per_delay tries */
132 if (++(status->spins) >= spins_per_delay)
133 {
134 if (++(status->delays) > NUM_DELAYS)
135 s_lock_stuck(status->file, status->line, status->func);
136
137 if (status->cur_delay == 0) /* first time to delay? */
138 status->cur_delay = MIN_DELAY_USEC;
139
140 /*
141 * Once we start sleeping, the overhead of reporting a wait event is
142 * justified. Actively spinning easily stands out in profilers, but
143 * sleeping with an exponential backoff is harder to spot...
144 *
145 * We might want to report something more granular at some point, but
146 * this is better than nothing.
147 */
148 pgstat_report_wait_start(WAIT_EVENT_SPIN_DELAY);
149 pg_usleep(status->cur_delay);
151
152#if defined(S_LOCK_TEST)
153 fprintf(stdout, "*");
154 fflush(stdout);
155#endif
156
157 /* increase delay by a random fraction between 1X and 2X */
158 status->cur_delay += (int) (status->cur_delay *
160 /* wrap back to minimum delay when max is exceeded */
161 if (status->cur_delay > MAX_DELAY_USEC)
162 status->cur_delay = MIN_DELAY_USEC;
163
164 status->spins = 0;
165 }
166}
#define fprintf(file, fmt, msg)
Definition: cubescan.l:21
stdout
double pg_prng_double(pg_prng_state *state)
Definition: pg_prng.c:268
pg_prng_state pg_global_prng_state
Definition: pg_prng.c:34
#define MIN_DELAY_USEC
Definition: s_lock.c:60
#define NUM_DELAYS
Definition: s_lock.c:59
#define MAX_DELAY_USEC
Definition: s_lock.c:61
static void s_lock_stuck(const char *file, int line, const char *func)
Definition: s_lock.c:79
#define SPIN_DELAY()
Definition: s_lock.h:681
void pg_usleep(long microsec)
Definition: signal.c:53
int delays
Definition: s_lock.h:714
const char * file
Definition: s_lock.h:716
const char * func
Definition: s_lock.h:718
int spins
Definition: s_lock.h:713
int line
Definition: s_lock.h:717
static void pgstat_report_wait_start(uint32 wait_event_info)
Definition: wait_event.h:69
static void pgstat_report_wait_end(void)
Definition: wait_event.h:85

References SpinDelayStatus::cur_delay, SpinDelayStatus::delays, SpinDelayStatus::file, fprintf, SpinDelayStatus::func, SpinDelayStatus::line, MAX_DELAY_USEC, MIN_DELAY_USEC, NUM_DELAYS, pg_global_prng_state, pg_prng_double(), pg_usleep(), pgstat_report_wait_end(), pgstat_report_wait_start(), s_lock_stuck(), SPIN_DELAY, SpinDelayStatus::spins, spins_per_delay, and generate_unaccent_rules::stdout.

Referenced by LockBufHdr(), LWLockWaitListLock(), s_lock(), and WaitBufHdrUnlocked().

◆ s_lock()

int s_lock ( volatile slock_t *  lock,
const char *  file,
int  line,
const char *  func 
)

Definition at line 98 of file s_lock.c.

99{
100 SpinDelayStatus delayStatus;
101
102 init_spin_delay(&delayStatus, file, line, func);
103
104 while (TAS_SPIN(lock))
105 {
106 perform_spin_delay(&delayStatus);
107 }
108
109 finish_spin_delay(&delayStatus);
110
111 return delayStatus.delays;
112}
void perform_spin_delay(SpinDelayStatus *status)
Definition: s_lock.c:126
void finish_spin_delay(SpinDelayStatus *status)
Definition: s_lock.c:186
#define TAS_SPIN(lock)
Definition: s_lock.h:692
static void init_spin_delay(SpinDelayStatus *status, const char *file, int line, const char *func)
Definition: s_lock.h:722

References SpinDelayStatus::delays, finish_spin_delay(), init_spin_delay(), perform_spin_delay(), and TAS_SPIN.

Referenced by test_spinlock().

◆ s_lock_stuck()

static void s_lock_stuck ( const char *  file,
int  line,
const char *  func 
)
static

Definition at line 79 of file s_lock.c.

80{
81 if (!func)
82 func = "(unknown)";
83#if defined(S_LOCK_TEST)
84 fprintf(stderr,
85 "\nStuck spinlock detected at %s, %s:%d.\n",
86 func, file, line);
87 exit(1);
88#else
89 elog(PANIC, "stuck spinlock detected at %s, %s:%d",
90 func, file, line);
91#endif
92}
#define PANIC
Definition: elog.h:42
#define elog(elevel,...)
Definition: elog.h:226

References elog, fprintf, and PANIC.

Referenced by perform_spin_delay().

◆ s_unlock()

void s_unlock ( volatile slock_t *  lock )

Definition at line 116 of file s_lock.c.

117{
118 *lock = 0;
119}

◆ set_spins_per_delay()

void set_spins_per_delay ( int  shared_spins_per_delay )

Definition at line 207 of file s_lock.c.

208{
209 spins_per_delay = shared_spins_per_delay;
210}

References spins_per_delay.

Referenced by InitAuxiliaryProcess(), and InitProcess().

◆ update_spins_per_delay()

int update_spins_per_delay ( int  shared_spins_per_delay )

Definition at line 218 of file s_lock.c.

219{
220 /*
221 * We use an exponential moving average with a relatively slow adaption
222 * rate, so that noise in any one backend's result won't affect the shared
223 * value too much. As long as both inputs are within the allowed range,
224 * the result must be too, so we need not worry about clamping the result.
225 *
226 * We deliberately truncate rather than rounding; this is so that single
227 * adjustments inside a backend can affect the shared estimate (see the
228 * asymmetric adjustment rules above).
229 */
230 return (shared_spins_per_delay * 15 + spins_per_delay) / 16;
231}

References spins_per_delay.

Referenced by AuxiliaryProcKill(), and ProcKill().

Variable Documentation

◆ spins_per_delay

int spins_per_delay = DEFAULT_SPINS_PER_DELAY
static

Definition at line 72 of file s_lock.c.

Referenced by finish_spin_delay(), perform_spin_delay(), set_spins_per_delay(), and update_spins_per_delay().

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