#include "postgres.h"
#include <time.h>
#include <unistd.h>
#include "common/pg_prng.h"
#include "port/atomics.h"
#include "storage/s_lock.h"
#include "utils/wait_event.h"

Include dependency graph for s_lock.c:

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	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
slock_t	dummy_spinlock

static int	spins_per_delay = DEFAULT_SPINS_PER_DELAY

Macro Definition Documentation

◆ MAX_DELAY_USEC

#define MAX_DELAY_USEC 1000000L

Definition at line 62 of file s_lock.c.

◆ MAX_SPINS_PER_DELAY

#define MAX_SPINS_PER_DELAY 1000

Definition at line 59 of file s_lock.c.

◆ MIN_DELAY_USEC

#define MIN_DELAY_USEC 1000L

Definition at line 61 of file s_lock.c.

◆ MIN_SPINS_PER_DELAY

#define MIN_SPINS_PER_DELAY 10

Definition at line 58 of file s_lock.c.

◆ NUM_DELAYS

#define NUM_DELAYS 1000

Definition at line 60 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.

 {
     if (status->cur_delay == 0)
     {
         /* we never had to delay */
         if (spins_per_delay < MAX_SPINS_PER_DELAY)
             spins_per_delay = Min(spins_per_delay + 100, MAX_SPINS_PER_DELAY);
     }
     else
     {
         if (spins_per_delay > MIN_SPINS_PER_DELAY)
             spins_per_delay = Max(spins_per_delay - 1, MIN_SPINS_PER_DELAY);
     }
 }

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.

 {
     /* CPU-specific delay each time through the loop */
     SPIN_DELAY();
  
     /* Block the process every spins_per_delay tries */
     if (++(status->spins) >= spins_per_delay)
     {
         if (++(status->delays) > NUM_DELAYS)
             s_lock_stuck(status->file, status->line, status->func);
  
         if (status->cur_delay == 0) /* first time to delay? */
             status->cur_delay = MIN_DELAY_USEC;
  
         /*
          * Once we start sleeping, the overhead of reporting a wait event is
          * justified. Actively spinning easily stands out in profilers, but
          * sleeping with an exponential backoff is harder to spot...
          *
          * We might want to report something more granular at some point, but
          * this is better than nothing.
          */
         pgstat_report_wait_start(WAIT_EVENT_SPIN_DELAY);
         pg_usleep(status->cur_delay);
         pgstat_report_wait_end();
  
 #if defined(S_LOCK_TEST)
         fprintf(stdout, "*");
         fflush(stdout);
 #endif
  
         /* increase delay by a random fraction between 1X and 2X */
         status->cur_delay += (int) (status->cur_delay *
                                     pg_prng_double(&pg_global_prng_state) + 0.5);
         /* wrap back to minimum delay when max is exceeded */
         if (status->cur_delay > MAX_DELAY_USEC)
             status->cur_delay = MIN_DELAY_USEC;
  
         status->spins = 0;
     }
 }

References SpinDelayStatus::cur_delay, SpinDelayStatus::delays, fflush(), 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 93 of file s_lock.c.

 {
     SpinDelayStatus delayStatus;
  
     init_spin_delay(&delayStatus, file, line, func);
  
     while (TAS_SPIN(lock))
     {
         perform_spin_delay(&delayStatus);
     }
  
     finish_spin_delay(&delayStatus);
  
     return delayStatus.delays;
 }

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 74 of file s_lock.c.

 {
     if (!func)
         func = "(unknown)";
 #if defined(S_LOCK_TEST)
     fprintf(stderr,
             "\nStuck spinlock detected at %s, %s:%d.\n",
             func, file, line);
     exit(1);
 #else
     elog(PANIC, "stuck spinlock detected at %s, %s:%d",
          func, file, line);
 #endif
 }

References elog(), exit(), fprintf, and PANIC.

Referenced by perform_spin_delay().

◆ set_spins_per_delay()

void set_spins_per_delay ( int shared_spins_per_delay )

Definition at line 207 of file s_lock.c.

 {
     spins_per_delay = shared_spins_per_delay;
 }

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.

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