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pg_sema.h File Reference
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Typedefs

typedef struct PGSemaphoreData *  PGSemaphore
 

Functions

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)
 

Typedef Documentation

◆ PGSemaphore

typedef struct PGSemaphoreData* PGSemaphore

Definition at line 34 of file pg_sema.h.

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)
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.
221 */
224#endif
225
226 numSems = 0;
227 maxSems = maxSemas;
228 nextSemKey = statbuf.st_ino;
229
231}
int errcode_for_file_access(void)
Definition: elog.c:877
int errmsg(const char *fmt,...)
Definition: elog.c:1071
#define FATAL
Definition: elog.h:41
#define PANIC
Definition: elog.h:42
#define elog(elevel,...)
Definition: elog.h:226
#define ereport(elevel,...)
Definition: elog.h:150
char * DataDir
Definition: globals.c:71
#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:239
void * ShmemAllocUnlocked(Size size)
Definition: shmem.c:238
Definition: win32_port.h:255
#define stat
Definition: win32_port.h:274

References DataDir, elog, ereport, errcode_for_file_access(), errmsg(), FATAL, malloc, maxSemaSets, maxSems, maxSharedSemas, mySemaSets, mySemSet, nextSemaKey, nextSemaNumber, nextSemKey, numSemaSets, numSems, numSharedSemas, on_shmem_exit(), PANIC, PGSemaphoreShmemSize(), ReleaseSemaphores(), SEMAS_PER_SET, sharedSemas, ShmemAllocUnlocked(), stat::st_ino, and stat.

Referenced by CreateSharedMemoryAndSemaphores().

◆ PGSemaphoreCreate()

PGSemaphore PGSemaphoreCreate ( void  )

Definition at line 261 of file posix_sema.c.

262{
263 PGSemaphore sema;
264 sem_t *newsem;
265
266 /* Can't do this in a backend, because static state is postmaster's */
268
269 if (numSems >= maxSems)
270 elog(PANIC, "too many semaphores created");
271
272#ifdef USE_NAMED_POSIX_SEMAPHORES
273 newsem = PosixSemaphoreCreate();
274 /* Remember new sema for ReleaseSemaphores */
275 mySemPointers[numSems] = newsem;
276 sema = (PGSemaphore) newsem;
277#else
278 sema = &sharedSemas[numSems];
279 newsem = PG_SEM_REF(sema);
280 PosixSemaphoreCreate(newsem);
281#endif
282
283 numSems++;
284
285 return sema;
286}
bool IsUnderPostmaster
Definition: globals.c:120
Assert(PointerIsAligned(start, uint64))
static void PosixSemaphoreCreate(sem_t *sem)
Definition: posix_sema.c:135
#define PG_SEM_REF(x)
Definition: posix_sema.c:57

References Assert(), elog, ereport, errmsg(), IpcSemaphoreCreate(), IpcSemaphoreInitialize(), IsUnderPostmaster, maxSemaSets, maxSems, maxSharedSemas, mySemaSets, mySemSet, nextSemaNumber, numSemaSets, numSems, numSharedSemas, PANIC, PG_SEM_REF, PosixSemaphoreCreate(), SEMAS_PER_SET, PGSemaphoreData::semId, PGSemaphoreData::semNum, and sharedSemas.

Referenced by InitProcGlobal().

◆ PGSemaphoreLock()

void PGSemaphoreLock ( PGSemaphore  sema )

Definition at line 319 of file posix_sema.c.

320{
321 int errStatus;
322
323 /* See notes in sysv_sema.c's implementation of PGSemaphoreLock. */
324 do
325 {
326 errStatus = sem_wait(PG_SEM_REF(sema));
327 } while (errStatus < 0 && errno == EINTR);
328
329 if (errStatus < 0)
330 elog(FATAL, "sem_wait failed: %m");
331}
#define EINTR
Definition: win32_port.h:364

References CHECK_FOR_INTERRUPTS, EINTR, elog, ereport, errmsg(), FATAL, PG_SEM_REF, pgwin32_dispatch_queued_signals(), pgwin32_signal_event, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

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

◆ PGSemaphoreReset()

void PGSemaphoreReset ( PGSemaphore  sema )

Definition at line 294 of file posix_sema.c.

295{
296 /*
297 * There's no direct API for this in POSIX, so we have to ratchet the
298 * semaphore down to 0 with repeated trywait's.
299 */
300 for (;;)
301 {
302 if (sem_trywait(PG_SEM_REF(sema)) < 0)
303 {
304 if (errno == EAGAIN || errno == EDEADLK)
305 break; /* got it down to 0 */
306 if (errno == EINTR)
307 continue; /* can this happen? */
308 elog(FATAL, "sem_trywait failed: %m");
309 }
310 }
311}
#define EAGAIN
Definition: win32_port.h:362

References EAGAIN, EINTR, elog, FATAL, IpcSemaphoreInitialize(), PG_SEM_REF, PGSemaphoreTryLock(), PGSemaphoreData::semId, and PGSemaphoreData::semNum.

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 364 of file posix_sema.c.

365{
366 int errStatus;
367
368 /*
369 * Note: if errStatus is -1 and errno == EINTR then it means we returned
370 * from the operation prematurely because we were sent a signal. So we
371 * try and lock the semaphore again.
372 */
373 do
374 {
375 errStatus = sem_trywait(PG_SEM_REF(sema));
376 } while (errStatus < 0 && errno == EINTR);
377
378 if (errStatus < 0)
379 {
380 if (errno == EAGAIN || errno == EDEADLK)
381 return false; /* failed to lock it */
382 /* Otherwise we got trouble */
383 elog(FATAL, "sem_trywait failed: %m");
384 }
385
386 return true;
387}

References EAGAIN, EINTR, elog, ereport, errmsg(), EWOULDBLOCK, FATAL, IPC_NOWAIT, PG_SEM_REF, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by PGSemaphoreReset().

◆ PGSemaphoreUnlock()

void PGSemaphoreUnlock ( PGSemaphore  sema )

Definition at line 339 of file posix_sema.c.

340{
341 int errStatus;
342
343 /*
344 * Note: if errStatus is -1 and errno == EINTR then it means we returned
345 * from the operation prematurely because we were sent a signal. So we
346 * try and unlock the semaphore again. Not clear this can really happen,
347 * but might as well cope.
348 */
349 do
350 {
351 errStatus = sem_post(PG_SEM_REF(sema));
352 } while (errStatus < 0 && errno == EINTR);
353
354 if (errStatus < 0)
355 elog(FATAL, "sem_post failed: %m");
356}

References EINTR, elog, ereport, errmsg(), FATAL, PG_SEM_REF, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

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

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