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s_lock.h File Reference
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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 714 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 745 of file s_lock.h.

◆ S_INIT_LOCK

#define S_INIT_LOCK (   lock)    S_UNLOCK(lock)

Definition at line 689 of file s_lock.h.

◆ S_LOCK

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

Definition at line 658 of file s_lock.h.

◆ S_LOCK_FREE

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

Definition at line 663 of file s_lock.h.

◆ S_UNLOCK

#define S_UNLOCK (   lock)    s_unlock(lock)

Definition at line 685 of file s_lock.h.

◆ SPIN_DELAY

#define SPIN_DELAY ( )    ((void) 0)

Definition at line 693 of file s_lock.h.

◆ TAS

#define TAS (   lock)    tas(lock)

Definition at line 700 of file s_lock.h.

◆ TAS_SPIN

#define TAS_SPIN (   lock)    TAS(lock)

Definition at line 704 of file s_lock.h.

◆ USE_DEFAULT_S_UNLOCK

#define USE_DEFAULT_S_UNLOCK

Definition at line 683 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.

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:1007
#define Max(x, y)
Definition: c.h:1001
#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

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 734 of file s_lock.h.

736 {
737  status->spins = 0;
738  status->delays = 0;
739  status->cur_delay = 0;
740  status->file = file;
741  status->line = line;
742  status->func = func;
743 }
const char * file
Definition: s_lock.h:728
const char * func
Definition: s_lock.h:730

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.

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 }
static void const char fflush(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 fprintf
Definition: port.h:242
#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:693
void pg_usleep(long microsec)
Definition: signal.c:53
static void pgstat_report_wait_start(uint32 wait_event_info)
Definition: wait_event.h:85
static void pgstat_report_wait_end(void)
Definition: wait_event.h:101

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 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:704
static void init_spin_delay(SpinDelayStatus *status, const char *file, int line, const char *func)
Definition: s_lock.h:734

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.

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().

◆ 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.

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().