PostgreSQL Source Code  git master
posix_sema.c File Reference
#include "postgres.h"
#include <fcntl.h>
#include <semaphore.h>
#include <signal.h>
#include <unistd.h>
#include <sys/stat.h>
#include "miscadmin.h"
#include "storage/ipc.h"
#include "storage/pg_sema.h"
#include "storage/shmem.h"
Include dependency graph for posix_sema.c:

Go to the source code of this file.

Data Structures

union  SemTPadded
 
struct  PGSemaphoreData
 

Macros

#define PG_SEM_REF(x)   (&(x)->sem_padded.pgsem)
 
#define IPCProtection   (0600) /* access/modify by user only */
 

Typedefs

typedef union SemTPadded SemTPadded
 
typedef struct PGSemaphoreData PGSemaphoreData
 

Functions

static void ReleaseSemaphores (int status, Datum arg)
 
static void PosixSemaphoreCreate (sem_t *sem)
 
static void PosixSemaphoreKill (sem_t *sem)
 
Size PGSemaphoreShmemSize (int maxSemas)
 
void PGReserveSemaphores (int maxSemas)
 
PGSemaphore PGSemaphoreCreate (void)
 
void PGSemaphoreReset (PGSemaphore sema)
 
void PGSemaphoreLock (PGSemaphore sema)
 
void PGSemaphoreUnlock (PGSemaphore sema)
 
bool PGSemaphoreTryLock (PGSemaphore sema)
 

Variables

static PGSemaphore sharedSemas
 
static int numSems
 
static int maxSems
 
static int nextSemKey
 

Macro Definition Documentation

◆ IPCProtection

#define IPCProtection   (0600) /* access/modify by user only */

Definition at line 59 of file posix_sema.c.

◆ PG_SEM_REF

#define PG_SEM_REF (   x)    (&(x)->sem_padded.pgsem)

Definition at line 57 of file posix_sema.c.

Typedef Documentation

◆ PGSemaphoreData

◆ SemTPadded

typedef union SemTPadded SemTPadded

Function Documentation

◆ PGReserveSemaphores()

void PGReserveSemaphores ( int  maxSemas)

Definition at line 196 of file posix_sema.c.

197 {
198  struct stat statbuf;
199 
200  /*
201  * We use the data directory's inode number to seed the search for free
202  * semaphore keys. This minimizes the odds of collision with other
203  * postmasters, while maximizing the odds that we will detect and clean up
204  * semaphores left over from a crashed postmaster in our own directory.
205  */
206  if (stat(DataDir, &statbuf) < 0)
207  ereport(FATAL,
209  errmsg("could not stat data directory \"%s\": %m",
210  DataDir)));
211 
212 #ifdef USE_NAMED_POSIX_SEMAPHORES
213  mySemPointers = (sem_t **) malloc(maxSemas * sizeof(sem_t *));
214  if (mySemPointers == NULL)
215  elog(PANIC, "out of memory");
216 #else
217 
218  /*
219  * We must use ShmemAllocUnlocked(), since the spinlock protecting
220  * ShmemAlloc() won't be ready yet. (This ordering is necessary when we
221  * are emulating spinlocks with semaphores.)
222  */
225 #endif
226 
227  numSems = 0;
228  maxSems = maxSemas;
229  nextSemKey = statbuf.st_ino;
230 
232 }
int errcode_for_file_access(void)
Definition: elog.c:882
int errmsg(const char *fmt,...)
Definition: elog.c:1072
#define FATAL
Definition: elog.h:41
#define PANIC
Definition: elog.h:42
#define elog(elevel,...)
Definition: elog.h:224
#define ereport(elevel,...)
Definition: elog.h:149
char * DataDir
Definition: globals.c:68
#define malloc(a)
Definition: header.h:50
void on_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:365
struct PGSemaphoreData * PGSemaphore
Definition: pg_sema.h:34
Size PGSemaphoreShmemSize(int maxSemas)
Definition: posix_sema.c:165
static int maxSems
Definition: posix_sema.c:67
static int nextSemKey
Definition: posix_sema.c:68
static int numSems
Definition: posix_sema.c:66
static PGSemaphore sharedSemas
Definition: posix_sema.c:64
static void ReleaseSemaphores(int status, Datum arg)
Definition: posix_sema.c:240
void * ShmemAllocUnlocked(Size size)
Definition: shmem.c:238
#define stat
Definition: win32_port.h:284

References DataDir, elog, ereport, errcode_for_file_access(), errmsg(), FATAL, malloc, maxSems, nextSemKey, numSems, on_shmem_exit(), PANIC, PGSemaphoreShmemSize(), ReleaseSemaphores(), sharedSemas, ShmemAllocUnlocked(), stat::st_ino, and stat.

Referenced by CreateSharedMemoryAndSemaphores().

◆ PGSemaphoreCreate()

PGSemaphore PGSemaphoreCreate ( void  )

Definition at line 262 of file posix_sema.c.

263 {
264  PGSemaphore sema;
265  sem_t *newsem;
266 
267  /* Can't do this in a backend, because static state is postmaster's */
269 
270  if (numSems >= maxSems)
271  elog(PANIC, "too many semaphores created");
272 
273 #ifdef USE_NAMED_POSIX_SEMAPHORES
274  newsem = PosixSemaphoreCreate();
275  /* Remember new sema for ReleaseSemaphores */
276  mySemPointers[numSems] = newsem;
277  sema = (PGSemaphore) newsem;
278 #else
279  sema = &sharedSemas[numSems];
280  newsem = PG_SEM_REF(sema);
281  PosixSemaphoreCreate(newsem);
282 #endif
283 
284  numSems++;
285 
286  return sema;
287 }
bool IsUnderPostmaster
Definition: globals.c:117
Assert(fmt[strlen(fmt) - 1] !='\n')
static void PosixSemaphoreCreate(sem_t *sem)
Definition: posix_sema.c:135
#define PG_SEM_REF(x)
Definition: posix_sema.c:57

References Assert(), elog, IsUnderPostmaster, maxSems, numSems, PANIC, PG_SEM_REF, PosixSemaphoreCreate(), and sharedSemas.

Referenced by InitProcGlobal(), and SpinlockSemaInit().

◆ PGSemaphoreLock()

void PGSemaphoreLock ( PGSemaphore  sema)

Definition at line 320 of file posix_sema.c.

321 {
322  int errStatus;
323 
324  /* See notes in sysv_sema.c's implementation of PGSemaphoreLock. */
325  do
326  {
327  errStatus = sem_wait(PG_SEM_REF(sema));
328  } while (errStatus < 0 && errno == EINTR);
329 
330  if (errStatus < 0)
331  elog(FATAL, "sem_wait failed: %m");
332 }
#define EINTR
Definition: win32_port.h:374

References EINTR, elog, FATAL, and PG_SEM_REF.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), LWLockDequeueSelf(), LWLockWaitForVar(), ProcArrayGroupClearXid(), and TransactionGroupUpdateXidStatus().

◆ PGSemaphoreReset()

void PGSemaphoreReset ( PGSemaphore  sema)

Definition at line 295 of file posix_sema.c.

296 {
297  /*
298  * There's no direct API for this in POSIX, so we have to ratchet the
299  * semaphore down to 0 with repeated trywait's.
300  */
301  for (;;)
302  {
303  if (sem_trywait(PG_SEM_REF(sema)) < 0)
304  {
305  if (errno == EAGAIN || errno == EDEADLK)
306  break; /* got it down to 0 */
307  if (errno == EINTR)
308  continue; /* can this happen? */
309  elog(FATAL, "sem_trywait failed: %m");
310  }
311  }
312 }
#define EAGAIN
Definition: win32_port.h:372

References EAGAIN, EINTR, elog, FATAL, and PG_SEM_REF.

Referenced by InitAuxiliaryProcess(), and InitProcess().

◆ PGSemaphoreShmemSize()

Size PGSemaphoreShmemSize ( int  maxSemas)

Definition at line 165 of file posix_sema.c.

166 {
167 #ifdef USE_NAMED_POSIX_SEMAPHORES
168  /* No shared memory needed in this case */
169  return 0;
170 #else
171  /* Need a PGSemaphoreData per semaphore */
172  return mul_size(maxSemas, sizeof(PGSemaphoreData));
173 #endif
174 }
Size mul_size(Size s1, Size s2)
Definition: shmem.c:510

References mul_size().

Referenced by CalculateShmemSize(), and PGReserveSemaphores().

◆ PGSemaphoreTryLock()

bool PGSemaphoreTryLock ( PGSemaphore  sema)

Definition at line 365 of file posix_sema.c.

366 {
367  int errStatus;
368 
369  /*
370  * Note: if errStatus is -1 and errno == EINTR then it means we returned
371  * from the operation prematurely because we were sent a signal. So we
372  * try and lock the semaphore again.
373  */
374  do
375  {
376  errStatus = sem_trywait(PG_SEM_REF(sema));
377  } while (errStatus < 0 && errno == EINTR);
378 
379  if (errStatus < 0)
380  {
381  if (errno == EAGAIN || errno == EDEADLK)
382  return false; /* failed to lock it */
383  /* Otherwise we got trouble */
384  elog(FATAL, "sem_trywait failed: %m");
385  }
386 
387  return true;
388 }

References EAGAIN, EINTR, elog, FATAL, and PG_SEM_REF.

Referenced by tas_sema().

◆ PGSemaphoreUnlock()

void PGSemaphoreUnlock ( PGSemaphore  sema)

Definition at line 340 of file posix_sema.c.

341 {
342  int errStatus;
343 
344  /*
345  * Note: if errStatus is -1 and errno == EINTR then it means we returned
346  * from the operation prematurely because we were sent a signal. So we
347  * try and unlock the semaphore again. Not clear this can really happen,
348  * but might as well cope.
349  */
350  do
351  {
352  errStatus = sem_post(PG_SEM_REF(sema));
353  } while (errStatus < 0 && errno == EINTR);
354 
355  if (errStatus < 0)
356  elog(FATAL, "sem_post failed: %m");
357 }

References EINTR, elog, FATAL, and PG_SEM_REF.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), LWLockDequeueSelf(), LWLockUpdateVar(), LWLockWaitForVar(), LWLockWakeup(), ProcArrayGroupClearXid(), s_unlock_sema(), and TransactionGroupUpdateXidStatus().

◆ PosixSemaphoreCreate()

static void PosixSemaphoreCreate ( sem_t *  sem)
static

Definition at line 135 of file posix_sema.c.

136 {
137  if (sem_init(sem, 1, 1) < 0)
138  elog(FATAL, "sem_init failed: %m");
139 }

References elog, and FATAL.

Referenced by PGSemaphoreCreate().

◆ PosixSemaphoreKill()

static void PosixSemaphoreKill ( sem_t *  sem)
static

Definition at line 147 of file posix_sema.c.

148 {
149 #ifdef USE_NAMED_POSIX_SEMAPHORES
150  /* Got to use sem_close for named semaphores */
151  if (sem_close(sem) < 0)
152  elog(LOG, "sem_close failed: %m");
153 #else
154  /* Got to use sem_destroy for unnamed semaphores */
155  if (sem_destroy(sem) < 0)
156  elog(LOG, "sem_destroy failed: %m");
157 #endif
158 }
#define LOG
Definition: elog.h:31

References elog, and LOG.

Referenced by ReleaseSemaphores().

◆ ReleaseSemaphores()

static void ReleaseSemaphores ( int  status,
Datum  arg 
)
static

Definition at line 240 of file posix_sema.c.

241 {
242  int i;
243 
244 #ifdef USE_NAMED_POSIX_SEMAPHORES
245  for (i = 0; i < numSems; i++)
246  PosixSemaphoreKill(mySemPointers[i]);
247  free(mySemPointers);
248 #endif
249 
250 #ifdef USE_UNNAMED_POSIX_SEMAPHORES
251  for (i = 0; i < numSems; i++)
253 #endif
254 }
#define free(a)
Definition: header.h:65
int i
Definition: isn.c:73
static void PosixSemaphoreKill(sem_t *sem)
Definition: posix_sema.c:147

References free, i, numSems, PG_SEM_REF, PosixSemaphoreKill(), and sharedSemas.

Referenced by PGReserveSemaphores().

Variable Documentation

◆ maxSems

int maxSems
static

Definition at line 67 of file posix_sema.c.

Referenced by PGReserveSemaphores(), and PGSemaphoreCreate().

◆ nextSemKey

int nextSemKey
static

Definition at line 68 of file posix_sema.c.

Referenced by PGReserveSemaphores().

◆ numSems

◆ sharedSemas

PGSemaphore sharedSemas
static

Definition at line 64 of file posix_sema.c.

Referenced by PGReserveSemaphores(), PGSemaphoreCreate(), and ReleaseSemaphores().