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Data Structures
struct	SpinDelayStatus

Macros
#define	S_LOCK(lock) (TAS(lock) ? s_lock((lock), __FILE__, __LINE__, __func__) : 0)

#define	S_LOCK_FREE(lock) (*(lock) == 0)

#define	USE_DEFAULT_S_UNLOCK

#define	S_UNLOCK(lock) s_unlock(lock)

#define	S_INIT_LOCK(lock) S_UNLOCK(lock)

#define	SPIN_DELAY() ((void) 0)

#define	TAS(lock) tas(lock)

#define	TAS_SPIN(lock) TAS(lock)

#define	DEFAULT_SPINS_PER_DELAY 100

#define	init_local_spin_delay(status) init_spin_delay(status, __FILE__, __LINE__, __func__)

Functions
void	s_unlock (volatile slock_t *lock)

int	tas (volatile slock_t *lock)

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

void	set_spins_per_delay (int shared_spins_per_delay)

int	update_spins_per_delay (int shared_spins_per_delay)

static void	init_spin_delay (SpinDelayStatus status, const char file, int line, const char *func)

void	perform_spin_delay (SpinDelayStatus *status)

void	finish_spin_delay (SpinDelayStatus *status)

Macro Definition Documentation

◆ DEFAULT_SPINS_PER_DELAY

#define DEFAULT_SPINS_PER_DELAY 100

Definition at line 720 of file s_lock.h.

◆ init_local_spin_delay

#define init_local_spin_delay ( status ) init_spin_delay(status, __FILE__, __LINE__, __func__)

Definition at line 751 of file s_lock.h.

◆ S_INIT_LOCK

#define S_INIT_LOCK ( lock ) S_UNLOCK(lock)

Definition at line 695 of file s_lock.h.

◆ S_LOCK

#define S_LOCK ( lock ) (TAS(lock) ? s_lock((lock), __FILE__, __LINE__, __func__) : 0)

Definition at line 664 of file s_lock.h.

◆ S_LOCK_FREE

#define S_LOCK_FREE ( lock ) (*(lock) == 0)

Definition at line 669 of file s_lock.h.

◆ S_UNLOCK

#define S_UNLOCK ( lock ) s_unlock(lock)

Definition at line 691 of file s_lock.h.

◆ SPIN_DELAY

#define SPIN_DELAY ( ) ((void) 0)

Definition at line 699 of file s_lock.h.

◆ TAS

#define TAS ( lock ) tas(lock)

Definition at line 706 of file s_lock.h.

◆ TAS_SPIN

#define TAS_SPIN ( lock ) TAS(lock)

Definition at line 710 of file s_lock.h.

◆ USE_DEFAULT_S_UNLOCK

#define USE_DEFAULT_S_UNLOCK

Definition at line 689 of file s_lock.h.

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().

◆ init_spin_delay()

static void init_spin_delay	(	SpinDelayStatus *	status,
		const char *	file,
		int	line,
		const char *	func
	)

inlinestatic

Definition at line 740 of file s_lock.h.

{
    status->spins = 0;
    status->delays = 0;
    status->cur_delay = 0;
    status->file = file;
    status->line = line;
    status->func = func;
}

References SpinDelayStatus::cur_delay, SpinDelayStatus::delays, SpinDelayStatus::file, SpinDelayStatus::func, SpinDelayStatus::line, and SpinDelayStatus::spins.

Referenced by s_lock().

◆ 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, 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.

{
    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_unlock()

void s_unlock ( volatile slock_t * lock )

Definition at line 116 of file s_lock.c.

{
    *lock = 0;
}

◆ 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().

◆ tas()

int tas ( volatile slock_t * lock )

◆ 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;
}