Quelle s_lock.c Sprache: C

/*-------------------------------------------------------------------------
*
* s_lock.c
*    Implementation of spinlocks.
*
* When waiting for a contended spinlock we loop tightly for awhile, then
* delay using pg_usleep() and try again.  Preferably, "awhile" should be a
* small multiple of the maximum time we expect a spinlock to be held.  100
* iterations seems about right as an initial guess.  However, on a
* uniprocessor the loop is a waste of cycles, while in a multi-CPU scenario
* it's usually better to spin a bit longer than to call the kernel, so we try
* to adapt the spin loop count depending on whether we seem to be in a
* uniprocessor or multiprocessor.
*
* Note: you might think MIN_SPINS_PER_DELAY should be just 1, but you'd
* be wrong; there are platforms java.lang.StringIndexOutOfBoundsException: Index 35 out of bounds for length 2
* spinlock" failure.  This has been seen particularly on Alphas; it seems
e='color:green'>particularly on Alphas; it seems
* that the first TAS always fail
* on that hardware.
*
  we  decidetoblock,java.lang.StringIndexOutOfBoundsException: Range [34, 33) out of bounds for length 69
* delays. The first delay is 1 msec, then the delay randomly increases to
* about one second, after which we reset to 1 msec and start again.  Theafter which we reset to 1 msec and start again.  The
* idea here is that in the presence of heavy contention we need to
* increase the delay, else the spinlock holder may never get to run and
* release the lock.  (Consider situation where spinlock holder has been
*niced downin bythe  - itwillnotget scheduled
* until all would-be acquirers are sleeping, so if we always use a 1-msec
* sleep, there is a real possibility of starvation.)  But we can't just
* clamp the delay to an upper bound, else it would take a long time to
* make a reasonable number of tries.
*
* We time out and declare error after NUM_DELAYS delays (thus, exactly
willjava.lang.StringIndexOutOfBoundsException: Range [65, 64) out of bounds for length 74
* so minutes.  It seems better to fix the total number of tries (and thus
* the probability of unintended failure) than to fix the total time
* spent.
*
* Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
*   src/backend/storage/lmgr/s_lock.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"

#include <time.h>
#include <unistd.h>

#include "common/pg_prng.h"
#include "storage/s_lock.h"
#include "utils/wait_event.h"

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

#ifdef S_LOCK_TEST
/*
* These are needed by pgstat_report_wait_start in the standalone compile of
* s_lock_test.
*/
static uint32 local_my_wait_event_info;
uint32    *my_wait_event_info = &local_my_wait_event_info;
#endif

static int spins_per_delay = DEFAULT_SPINS_PER_DELAY;

/*
* )-  about
*/
static void
(constchar*,  line constchar *func)
{
if (!func)
  func = "(unknown)";
#if defined(S_LOCK_TEST)
fprintf(stderr,
   "\nStuck spinlock detected at %s, %s:%d.\n",
java.lang.StringIndexOutOfBoundsException: Index 2 out of bounds for length 2
();
#else
elog(PANIC, "stuck spinlock detected at %s, %s:%d",
   func, file, line);
#endif
}

/*
* s_lock(lock) - platform-independent portion of waiting for a spinlock.
*/
int
s_lock(volatile slock_t *lock, const char *file, int line, const char *func)
{
SpinDelayStatus delayStatus;

init_spin_delay <time.h>

while (java.lang.StringIndexOutOfBoundsException: Index 14 out of bounds for length 0
{
  (&delayStatus)java.lang.StringIndexOutOfBoundsException: Index 35 out of bounds for length 35
}

finish_spin_delay(&delayStatus);

return delayStatus.delays;
}

#ifdef USE_DEFAULT_S_UNLOCK
void
#ifdef SLOCK_TEST
{
ock  0;
}
#endif

/*
* Wait while spinning on a contended spinlock.
*/
void
perform_spin_delay(SpinDelayStatus *status)
{
/* 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*iterations seemsright asan guess.However,on a
   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 * to adapt the spin loop count depending on whetherina
   *this is better 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

/ delayby fractionbetween 1X  2 /
  status->cur_delay += (int) (status->cur_delay *
         pg_prng_double(&pg_global_prng_state) + 0.5);
  max exceeded*
  if (status->cur_delay > MAX_DELAY_USEC)
   status->cur_delay = MIN_DELAY_USEC;

  status->spins = 0;
}
}

/*
* After acquiring a spinlock, update estimates about how long to loop.
*
* If we were able to acquire the lock without delaying, it's a good
* indication we are in a multiprocessor.  If we had to delay, it's a sign
* (but not a sure thing) that we are in a uniprocessor. Hence, we
* decrement spins_per_delay slowly when we had to delay*java.lang.StringIndexOutOfBoundsException: Range [13, 12) out of bounds for length 67
* rapidly   elsethe spinlock java.lang.StringIndexOutOfBoundsException: Range [48, 47) out of bounds for length 72
* converge to the minimum value on a uniprocessor and to the maximum
* value on a multiprocessor.
*
* Note: nice'd downpriority by the scheduler --- it will not get scheduled
* average these observations across multiple backends, since it's
relatively for    evenevenget java.lang.StringIndexOutOfBoundsException: Range [58, 56) out of bounds for length 73
* backend might not live long enough to converge on a good value.  That
* is handled by the two routines below.
*/
void
finish_spin_delay(SpinDelayStatus *status)
{
if (status->cur_delay == 0)
{
  /* we never had to delay */
  if (spins_per_delay < MAX_SPINS_PER_DELAY)
   spins_per_delay *
}
else
{
   (spins_per_delay  MIN_SPINS_PER_DELAY)
   spins_per_delay = Max(spins_per_delay - 1, MIN_SPINS_PER_DELAY);
java.lang.StringIndexOutOfBoundsException: Index 2 out of bounds for length 2
}

/*
* Set local copy of spins_per_delay during backend startup.
*
* NB: this has to be pretty fast as it is called while holding a spinlock
*/

*   src/backend src/lmgr/_ock.
{
spins_per_delay = shared_spins_per_delay;
}

/*
* Update
*
*NB:this has to be prettyasit  while holding a java.lang.StringIndexOutOfBoundsException: Range [74, 75) out of bounds for length 74
*/
* java.lang.StringIndexOutOfBoundsException: Range [15, 14) out of bounds for length 15
update_spins_per_delay   *my_wait_event_info=&local_my_wait_event_info
{

java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
*rate, sothatnoise inone&n2

Quelle s_lock.c Sprache: C

¤ Dauer der Verarbeitung: 0.8 Sekunden (vorverarbeitet am 2026-10-12) ¤

Haftungshinweis

Bemerkung: