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pg_shmem.h File Reference
#include "storage/dsm_impl.h"
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Data Structures

struct  PGShmemHeader
 

Macros

#define PGShmemMagic   679834894
 

Typedefs

typedef struct PGShmemHeader PGShmemHeader
 

Enumerations

enum  HugePagesType { HUGE_PAGES_OFF, HUGE_PAGES_ON, HUGE_PAGES_TRY }
 

Functions

PGShmemHeaderPGSharedMemoryCreate (Size size, bool makePrivate, int port, PGShmemHeader **shim)
 
bool PGSharedMemoryIsInUse (unsigned long id1, unsigned long id2)
 
void PGSharedMemoryDetach (void)
 

Variables

int huge_pages
 
unsigned long UsedShmemSegID
 
void * UsedShmemSegAddr
 

Macro Definition Documentation

#define PGShmemMagic   679834894

Typedef Documentation

Enumeration Type Documentation

Enumerator
HUGE_PAGES_OFF 
HUGE_PAGES_ON 
HUGE_PAGES_TRY 

Definition at line 48 of file pg_shmem.h.

Function Documentation

PGShmemHeader* PGSharedMemoryCreate ( Size  size,
bool  makePrivate,
int  port,
PGShmemHeader **  shim 
)

Definition at line 557 of file sysv_shmem.c.

References AnonymousShmem, AnonymousShmemDetach(), AnonymousShmemSize, Assert, CreateAnonymousSegment(), PGShmemHeader::creatorPID, DataDir, PGShmemHeader::device, dsm_cleanup_using_control_segment(), PGShmemHeader::dsm_control, elog, ereport, errcode(), errcode_for_file_access(), errdetail(), errhint(), errmsg(), ERROR, FATAL, free, PGShmemHeader::freeoffset, GetSharedMemName(), huge_pages, HUGE_PAGES_ON, i, PGShmemHeader::inode, InternalIpcMemoryCreate(), IPC_RMID, LOG, PGShmemHeader::magic, MAXALIGN, NULL, on_shmem_exit(), PGSharedMemoryAttach(), PGShmemMagic, pgwin32_SharedMemoryDelete(), PointerGetDatum, PGShmemHeader::totalsize, TRUE, UsedShmemSegAddr, UsedShmemSegID, and UsedShmemSegSize.

Referenced by CreateSharedMemoryAndSemaphores().

559 {
560  IpcMemoryKey NextShmemSegID;
561  void *memAddress;
562  PGShmemHeader *hdr;
563  IpcMemoryId shmid;
564  struct stat statbuf;
565  Size sysvsize;
566 
567  /* Complain if hugepages demanded but we can't possibly support them */
568 #if !defined(USE_ANONYMOUS_SHMEM) || !defined(MAP_HUGETLB)
569  if (huge_pages == HUGE_PAGES_ON)
570  ereport(ERROR,
571  (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
572  errmsg("huge pages not supported on this platform")));
573 #endif
574 
575  /* Room for a header? */
576  Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
577 
578 #ifdef USE_ANONYMOUS_SHMEM
580  AnonymousShmemSize = size;
581 
582  /* Register on-exit routine to unmap the anonymous segment */
584 
585  /* Now we need only allocate a minimal-sized SysV shmem block. */
586  sysvsize = sizeof(PGShmemHeader);
587 #else
588  sysvsize = size;
589 #endif
590 
591  /* Make sure PGSharedMemoryAttach doesn't fail without need */
593 
594  /* Loop till we find a free IPC key */
595  NextShmemSegID = port * 1000;
596 
597  for (NextShmemSegID++;; NextShmemSegID++)
598  {
599  /* Try to create new segment */
600  memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
601  if (memAddress)
602  break; /* successful create and attach */
603 
604  /* Check shared memory and possibly remove and recreate */
605 
606  if (makePrivate) /* a standalone backend shouldn't do this */
607  continue;
608 
609  if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
610  continue; /* can't attach, not one of mine */
611 
612  /*
613  * If I am not the creator and it belongs to an extant process,
614  * continue.
615  */
616  hdr = (PGShmemHeader *) memAddress;
617  if (hdr->creatorPID != getpid())
618  {
619  if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
620  {
621  shmdt(memAddress);
622  continue; /* segment belongs to a live process */
623  }
624  }
625 
626  /*
627  * The segment appears to be from a dead Postgres process, or from a
628  * previous cycle of life in this same process. Zap it, if possible,
629  * and any associated dynamic shared memory segments, as well. This
630  * probably shouldn't fail, but if it does, assume the segment belongs
631  * to someone else after all, and continue quietly.
632  */
633  if (hdr->dsm_control != 0)
635  shmdt(memAddress);
636  if (shmctl(shmid, IPC_RMID, NULL) < 0)
637  continue;
638 
639  /*
640  * Now try again to create the segment.
641  */
642  memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
643  if (memAddress)
644  break; /* successful create and attach */
645 
646  /*
647  * Can only get here if some other process managed to create the same
648  * shmem key before we did. Let him have that one, loop around to try
649  * next key.
650  */
651  }
652 
653  /*
654  * OK, we created a new segment. Mark it as created by this process. The
655  * order of assignments here is critical so that another Postgres process
656  * can't see the header as valid but belonging to an invalid PID!
657  */
658  hdr = (PGShmemHeader *) memAddress;
659  hdr->creatorPID = getpid();
660  hdr->magic = PGShmemMagic;
661  hdr->dsm_control = 0;
662 
663  /* Fill in the data directory ID info, too */
664  if (stat(DataDir, &statbuf) < 0)
665  ereport(FATAL,
667  errmsg("could not stat data directory \"%s\": %m",
668  DataDir)));
669  hdr->device = statbuf.st_dev;
670  hdr->inode = statbuf.st_ino;
671 
672  /*
673  * Initialize space allocation status for segment.
674  */
675  hdr->totalsize = size;
676  hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
677  *shim = hdr;
678 
679  /* Save info for possible future use */
680  UsedShmemSegAddr = memAddress;
681  UsedShmemSegID = (unsigned long) NextShmemSegID;
682 
683  /*
684  * If AnonymousShmem is NULL here, then we're not using anonymous shared
685  * memory, and should return a pointer to the System V shared memory
686  * block. Otherwise, the System V shared memory block is only a shim, and
687  * we must return a pointer to the real block.
688  */
689 #ifdef USE_ANONYMOUS_SHMEM
690  if (AnonymousShmem == NULL)
691  return hdr;
692  memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
693  return (PGShmemHeader *) AnonymousShmem;
694 #else
695  return hdr;
696 #endif
697 }
pid_t creatorPID
Definition: pg_shmem.h:33
void dsm_cleanup_using_control_segment(dsm_handle old_control_handle)
Definition: dsm.c:210
static PGShmemHeader * PGSharedMemoryAttach(IpcMemoryKey key, IpcMemoryId *shmid)
Definition: sysv_shmem.c:821
dsm_handle dsm_control
Definition: pg_shmem.h:36
struct PGShmemHeader PGShmemHeader
static Size AnonymousShmemSize
Definition: sysv_shmem.c:78
int errcode(int sqlerrcode)
Definition: elog.c:575
static void * InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
Definition: sysv_shmem.c:102
#define ERROR
Definition: elog.h:43
#define FATAL
Definition: elog.h:52
void on_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:348
key_t IpcMemoryKey
Definition: sysv_shmem.c:70
int errcode_for_file_access(void)
Definition: elog.c:598
void * UsedShmemSegAddr
Definition: sysv_shmem.c:75
static void AnonymousShmemDetach(int status, Datum arg)
Definition: sysv_shmem.c:524
#define ereport(elevel, rest)
Definition: elog.h:122
static int port
Definition: pg_regress.c:89
int32 magic
Definition: pg_shmem.h:31
static void * CreateAnonymousSegment(Size *size)
Definition: sysv_shmem.c:456
Size totalsize
Definition: pg_shmem.h:34
uintptr_t Datum
Definition: postgres.h:372
unsigned long UsedShmemSegID
Definition: sysv_shmem.c:74
#define IPC_RMID
Definition: win32.h:106
static void * AnonymousShmem
Definition: sysv_shmem.c:79
ino_t inode
Definition: pg_shmem.h:40
dev_t device
Definition: pg_shmem.h:39
#define NULL
Definition: c.h:229
#define Assert(condition)
Definition: c.h:675
#define PGShmemMagic
Definition: pg_shmem.h:32
Size freeoffset
Definition: pg_shmem.h:35
size_t Size
Definition: c.h:356
#define MAXALIGN(LEN)
Definition: c.h:588
int IpcMemoryId
Definition: sysv_shmem.c:71
int huge_pages
Definition: guc.c:487
int errmsg(const char *fmt,...)
Definition: elog.c:797
char * DataDir
Definition: globals.c:60
void PGSharedMemoryDetach ( void  )

Definition at line 789 of file sysv_shmem.c.

References AnonymousShmem, AnonymousShmemSize, elog, LOG, NULL, UsedShmemSegAddr, and UsedShmemSegID.

Referenced by pgarch_start(), PGSharedMemoryNoReAttach(), pgstat_start(), pgwin32_SharedMemoryDelete(), StartBackgroundWorker(), and SysLogger_Start().

790 {
791  if (UsedShmemSegAddr != NULL)
792  {
793  if ((shmdt(UsedShmemSegAddr) < 0)
794 #if defined(EXEC_BACKEND) && defined(__CYGWIN__)
795  /* Work-around for cygipc exec bug */
796  && shmdt(NULL) < 0
797 #endif
798  )
799  elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
801  }
802 
803 #ifdef USE_ANONYMOUS_SHMEM
804  if (AnonymousShmem != NULL)
805  {
806  if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
807  elog(LOG, "munmap(%p, %zu) failed: %m",
810  }
811 #endif
812 }
static Size AnonymousShmemSize
Definition: sysv_shmem.c:78
#define LOG
Definition: elog.h:26
void * UsedShmemSegAddr
Definition: sysv_shmem.c:75
static void * AnonymousShmem
Definition: sysv_shmem.c:79
#define NULL
Definition: c.h:229
#define elog
Definition: elog.h:219
bool PGSharedMemoryIsInUse ( unsigned long  id1,
unsigned long  id2 
)

Definition at line 288 of file sysv_shmem.c.

References DataDir, EIDRM, FALSE, free, GetSharedMemName(), IPC_STAT, NULL, PG_SHMAT_FLAGS, and PGShmemMagic.

Referenced by CreateLockFile().

289 {
290  IpcMemoryId shmId = (IpcMemoryId) id2;
291  struct shmid_ds shmStat;
292  struct stat statbuf;
293  PGShmemHeader *hdr;
294 
295  /*
296  * We detect whether a shared memory segment is in use by seeing whether
297  * it (a) exists and (b) has any processes attached to it.
298  */
299  if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
300  {
301  /*
302  * EINVAL actually has multiple possible causes documented in the
303  * shmctl man page, but we assume it must mean the segment no longer
304  * exists.
305  */
306  if (errno == EINVAL)
307  return false;
308 
309  /*
310  * EACCES implies that the segment belongs to some other userid, which
311  * means it is not a Postgres shmem segment (or at least, not one that
312  * is relevant to our data directory).
313  */
314  if (errno == EACCES)
315  return false;
316 
317  /*
318  * Some Linux kernel versions (in fact, all of them as of July 2007)
319  * sometimes return EIDRM when EINVAL is correct. The Linux kernel
320  * actually does not have any internal state that would justify
321  * returning EIDRM, so we can get away with assuming that EIDRM is
322  * equivalent to EINVAL on that platform.
323  */
324 #ifdef HAVE_LINUX_EIDRM_BUG
325  if (errno == EIDRM)
326  return false;
327 #endif
328 
329  /*
330  * Otherwise, we had better assume that the segment is in use. The
331  * only likely case is EIDRM, which implies that the segment has been
332  * IPC_RMID'd but there are still processes attached to it.
333  */
334  return true;
335  }
336 
337  /* If it has no attached processes, it's not in use */
338  if (shmStat.shm_nattch == 0)
339  return false;
340 
341  /*
342  * Try to attach to the segment and see if it matches our data directory.
343  * This avoids shmid-conflict problems on machines that are running
344  * several postmasters under the same userid.
345  */
346  if (stat(DataDir, &statbuf) < 0)
347  return true; /* if can't stat, be conservative */
348 
349  hdr = (PGShmemHeader *) shmat(shmId, NULL, PG_SHMAT_FLAGS);
350 
351  if (hdr == (PGShmemHeader *) -1)
352  return true; /* if can't attach, be conservative */
353 
354  if (hdr->magic != PGShmemMagic ||
355  hdr->device != statbuf.st_dev ||
356  hdr->inode != statbuf.st_ino)
357  {
358  /*
359  * It's either not a Postgres segment, or not one for my data
360  * directory. In either case it poses no threat.
361  */
362  shmdt((void *) hdr);
363  return false;
364  }
365 
366  /* Trouble --- looks a lot like there's still live backends */
367  shmdt((void *) hdr);
368 
369  return true;
370 }
#define PG_SHMAT_FLAGS
Definition: mem.h:20
#define IPC_STAT
Definition: win32.h:111
#define NULL
Definition: c.h:229
#define PGShmemMagic
Definition: pg_shmem.h:32
int IpcMemoryId
Definition: sysv_shmem.c:71
char * DataDir
Definition: globals.c:60
#define EIDRM
Definition: win32.h:115

Variable Documentation

int huge_pages

Definition at line 487 of file guc.c.

Referenced by CreateAnonymousSegment(), and PGSharedMemoryCreate().

unsigned long UsedShmemSegID