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sysv_shmem.c File Reference
#include "postgres.h"
#include <signal.h>
#include <unistd.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include "miscadmin.h"
#include "portability/mem.h"
#include "storage/dsm.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "utils/guc.h"
Include dependency graph for sysv_shmem.c:

Go to the source code of this file.

Macros

#define USE_ANONYMOUS_SHMEM
 

Typedefs

typedef key_t IpcMemoryKey
 
typedef int IpcMemoryId
 

Functions

static void * InternalIpcMemoryCreate (IpcMemoryKey memKey, Size size)
 
static void IpcMemoryDetach (int status, Datum shmaddr)
 
static void IpcMemoryDelete (int status, Datum shmId)
 
static PGShmemHeaderPGSharedMemoryAttach (IpcMemoryKey key, IpcMemoryId *shmid)
 
bool PGSharedMemoryIsInUse (unsigned long id1, unsigned long id2)
 
static void * CreateAnonymousSegment (Size *size)
 
static void AnonymousShmemDetach (int status, Datum arg)
 
PGShmemHeaderPGSharedMemoryCreate (Size size, bool makePrivate, int port, PGShmemHeader **shim)
 
void PGSharedMemoryDetach (void)
 

Variables

unsigned long UsedShmemSegID = 0
 
void * UsedShmemSegAddr = NULL
 
static Size AnonymousShmemSize
 
static void * AnonymousShmem = NULL
 

Macro Definition Documentation

#define USE_ANONYMOUS_SHMEM

Definition at line 66 of file sysv_shmem.c.

Typedef Documentation

Definition at line 71 of file sysv_shmem.c.

Definition at line 70 of file sysv_shmem.c.

Function Documentation

static void AnonymousShmemDetach ( int  status,
Datum  arg 
)
static

Definition at line 503 of file sysv_shmem.c.

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

Referenced by PGSharedMemoryCreate().

504 {
505  /* Release anonymous shared memory block, if any. */
506  if (AnonymousShmem != NULL)
507  {
508  if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
509  elog(LOG, "munmap(%p, %zu) failed: %m",
512  }
513 }
static Size AnonymousShmemSize
Definition: sysv_shmem.c:78
#define LOG
Definition: elog.h:26
static void * AnonymousShmem
Definition: sysv_shmem.c:79
#define NULL
Definition: c.h:229
#define elog
Definition: elog.h:219
static void* CreateAnonymousSegment ( Size size)
static

Definition at line 435 of file sysv_shmem.c.

References Assert, DEBUG1, elog, ereport, errhint(), errmsg(), FATAL, huge_pages, HUGE_PAGES_ON, HUGE_PAGES_TRY, MAP_FAILED, NULL, and PG_MMAP_FLAGS.

Referenced by PGSharedMemoryCreate().

436 {
437  Size allocsize = *size;
438  void *ptr = MAP_FAILED;
439  int mmap_errno = 0;
440 
441 #ifndef MAP_HUGETLB
442  /* PGSharedMemoryCreate should have dealt with this case */
444 #else
446  {
447  /*
448  * Round up the request size to a suitable large value.
449  */
450  Size hugepagesize;
451  int mmap_flags;
452 
453  GetHugePageSize(&hugepagesize, &mmap_flags);
454 
455  if (allocsize % hugepagesize != 0)
456  allocsize += hugepagesize - (allocsize % hugepagesize);
457 
458  ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
459  PG_MMAP_FLAGS | mmap_flags, -1, 0);
460  mmap_errno = errno;
461  if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
462  elog(DEBUG1, "mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
463  allocsize);
464  }
465 #endif
466 
467  if (ptr == MAP_FAILED && huge_pages != HUGE_PAGES_ON)
468  {
469  /*
470  * Use the original size, not the rounded-up value, when falling back
471  * to non-huge pages.
472  */
473  allocsize = *size;
474  ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
475  PG_MMAP_FLAGS, -1, 0);
476  mmap_errno = errno;
477  }
478 
479  if (ptr == MAP_FAILED)
480  {
481  errno = mmap_errno;
482  ereport(FATAL,
483  (errmsg("could not map anonymous shared memory: %m"),
484  (mmap_errno == ENOMEM) ?
485  errhint("This error usually means that PostgreSQL's request "
486  "for a shared memory segment exceeded available memory, "
487  "swap space, or huge pages. To reduce the request size "
488  "(currently %zu bytes), reduce PostgreSQL's shared "
489  "memory usage, perhaps by reducing shared_buffers or "
490  "max_connections.",
491  *size) : 0));
492  }
493 
494  *size = allocsize;
495  return ptr;
496 }
#define MAP_FAILED
Definition: mem.h:45
#define DEBUG1
Definition: elog.h:25
int errhint(const char *fmt,...)
Definition: elog.c:987
#define FATAL
Definition: elog.h:52
#define PG_MMAP_FLAGS
Definition: mem.h:41
#define ereport(elevel, rest)
Definition: elog.h:122
#define NULL
Definition: c.h:229
#define Assert(condition)
Definition: c.h:675
size_t Size
Definition: c.h:356
int huge_pages
Definition: guc.c:490
int errmsg(const char *fmt,...)
Definition: elog.c:797
#define elog
Definition: elog.h:219
static void * InternalIpcMemoryCreate ( IpcMemoryKey  memKey,
Size  size 
)
static

Definition at line 102 of file sysv_shmem.c.

References AddToDataDirLockFile(), EIDRM, elog, ereport, errdetail(), errhint(), errmsg(), FATAL, Int32GetDatum, IPC_CREAT, IPC_EXCL, IPC_RMID, IpcMemoryDelete(), IpcMemoryDetach(), IPCProtection, LOCK_FILE_LINE_SHMEM_KEY, LOG, NULL, on_shmem_exit(), PG_SHMAT_FLAGS, and PointerGetDatum.

Referenced by PGSharedMemoryCreate().

103 {
104  IpcMemoryId shmid;
105  void *memAddress;
106 
107  shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
108 
109  if (shmid < 0)
110  {
111  int shmget_errno = errno;
112 
113  /*
114  * Fail quietly if error indicates a collision with existing segment.
115  * One would expect EEXIST, given that we said IPC_EXCL, but perhaps
116  * we could get a permission violation instead? Also, EIDRM might
117  * occur if an old seg is slated for destruction but not gone yet.
118  */
119  if (shmget_errno == EEXIST || shmget_errno == EACCES
120 #ifdef EIDRM
121  || shmget_errno == EIDRM
122 #endif
123  )
124  return NULL;
125 
126  /*
127  * Some BSD-derived kernels are known to return EINVAL, not EEXIST, if
128  * there is an existing segment but it's smaller than "size" (this is
129  * a result of poorly-thought-out ordering of error tests). To
130  * distinguish between collision and invalid size in such cases, we
131  * make a second try with size = 0. These kernels do not test size
132  * against SHMMIN in the preexisting-segment case, so we will not get
133  * EINVAL a second time if there is such a segment.
134  */
135  if (shmget_errno == EINVAL)
136  {
137  shmid = shmget(memKey, 0, IPC_CREAT | IPC_EXCL | IPCProtection);
138 
139  if (shmid < 0)
140  {
141  /* As above, fail quietly if we verify a collision */
142  if (errno == EEXIST || errno == EACCES
143 #ifdef EIDRM
144  || errno == EIDRM
145 #endif
146  )
147  return NULL;
148  /* Otherwise, fall through to report the original error */
149  }
150  else
151  {
152  /*
153  * On most platforms we cannot get here because SHMMIN is
154  * greater than zero. However, if we do succeed in creating a
155  * zero-size segment, free it and then fall through to report
156  * the original error.
157  */
158  if (shmctl(shmid, IPC_RMID, NULL) < 0)
159  elog(LOG, "shmctl(%d, %d, 0) failed: %m",
160  (int) shmid, IPC_RMID);
161  }
162  }
163 
164  /*
165  * Else complain and abort.
166  *
167  * Note: at this point EINVAL should mean that either SHMMIN or SHMMAX
168  * is violated. SHMALL violation might be reported as either ENOMEM
169  * (BSDen) or ENOSPC (Linux); the Single Unix Spec fails to say which
170  * it should be. SHMMNI violation is ENOSPC, per spec. Just plain
171  * not-enough-RAM is ENOMEM.
172  */
173  errno = shmget_errno;
174  ereport(FATAL,
175  (errmsg("could not create shared memory segment: %m"),
176  errdetail("Failed system call was shmget(key=%lu, size=%zu, 0%o).",
177  (unsigned long) memKey, size,
179  (shmget_errno == EINVAL) ?
180  errhint("This error usually means that PostgreSQL's request for a shared memory "
181  "segment exceeded your kernel's SHMMAX parameter, or possibly that "
182  "it is less than "
183  "your kernel's SHMMIN parameter.\n"
184  "The PostgreSQL documentation contains more information about shared "
185  "memory configuration.") : 0,
186  (shmget_errno == ENOMEM) ?
187  errhint("This error usually means that PostgreSQL's request for a shared "
188  "memory segment exceeded your kernel's SHMALL parameter. You might need "
189  "to reconfigure the kernel with larger SHMALL.\n"
190  "The PostgreSQL documentation contains more information about shared "
191  "memory configuration.") : 0,
192  (shmget_errno == ENOSPC) ?
193  errhint("This error does *not* mean that you have run out of disk space. "
194  "It occurs either if all available shared memory IDs have been taken, "
195  "in which case you need to raise the SHMMNI parameter in your kernel, "
196  "or because the system's overall limit for shared memory has been "
197  "reached.\n"
198  "The PostgreSQL documentation contains more information about shared "
199  "memory configuration.") : 0));
200  }
201 
202  /* Register on-exit routine to delete the new segment */
204 
205  /* OK, should be able to attach to the segment */
206  memAddress = shmat(shmid, NULL, PG_SHMAT_FLAGS);
207 
208  if (memAddress == (void *) -1)
209  elog(FATAL, "shmat(id=%d) failed: %m", shmid);
210 
211  /* Register on-exit routine to detach new segment before deleting */
213 
214  /*
215  * Store shmem key and ID in data directory lockfile. Format to try to
216  * keep it the same length always (trailing junk in the lockfile won't
217  * hurt, but might confuse humans).
218  */
219  {
220  char line[64];
221 
222  sprintf(line, "%9lu %9lu",
223  (unsigned long) memKey, (unsigned long) shmid);
225  }
226 
227  return memAddress;
228 }
#define IPC_CREAT
Definition: win32.h:115
#define IPC_EXCL
Definition: win32.h:116
int errhint(const char *fmt,...)
Definition: elog.c:987
static void IpcMemoryDetach(int status, Datum shmaddr)
Definition: sysv_shmem.c:236
void AddToDataDirLockFile(int target_line, const char *str)
Definition: miscinit.c:1156
#define PointerGetDatum(X)
Definition: postgres.h:562
#define IPCProtection
Definition: posix_sema.c:52
#define PG_SHMAT_FLAGS
Definition: mem.h:20
#define LOG
Definition: elog.h:26
#define FATAL
Definition: elog.h:52
void on_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:348
int errdetail(const char *fmt,...)
Definition: elog.c:873
#define ereport(elevel, rest)
Definition: elog.h:122
static void IpcMemoryDelete(int status, Datum shmId)
Definition: sysv_shmem.c:248
#define IPC_RMID
Definition: win32.h:114
#define LOCK_FILE_LINE_SHMEM_KEY
Definition: miscadmin.h:452
#define NULL
Definition: c.h:229
int IpcMemoryId
Definition: sysv_shmem.c:71
#define Int32GetDatum(X)
Definition: postgres.h:485
int errmsg(const char *fmt,...)
Definition: elog.c:797
#define EIDRM
Definition: win32.h:123
#define elog
Definition: elog.h:219
static void IpcMemoryDelete ( int  status,
Datum  shmId 
)
static

Definition at line 248 of file sysv_shmem.c.

References DatumGetInt32, elog, IPC_RMID, LOG, and NULL.

Referenced by InternalIpcMemoryCreate().

249 {
250  if (shmctl(DatumGetInt32(shmId), IPC_RMID, NULL) < 0)
251  elog(LOG, "shmctl(%d, %d, 0) failed: %m",
252  DatumGetInt32(shmId), IPC_RMID);
253 }
#define DatumGetInt32(X)
Definition: postgres.h:478
#define LOG
Definition: elog.h:26
#define IPC_RMID
Definition: win32.h:114
#define NULL
Definition: c.h:229
#define elog
Definition: elog.h:219
static void IpcMemoryDetach ( int  status,
Datum  shmaddr 
)
static

Definition at line 236 of file sysv_shmem.c.

References DatumGetPointer, elog, and LOG.

Referenced by InternalIpcMemoryCreate().

237 {
238  /* Detach System V shared memory block. */
239  if (shmdt(DatumGetPointer(shmaddr)) < 0)
240  elog(LOG, "shmdt(%p) failed: %m", DatumGetPointer(shmaddr));
241 }
#define LOG
Definition: elog.h:26
#define DatumGetPointer(X)
Definition: postgres.h:555
#define elog
Definition: elog.h:219
static PGShmemHeader * PGSharedMemoryAttach ( IpcMemoryKey  key,
IpcMemoryId shmid 
)
static

Definition at line 800 of file sysv_shmem.c.

References PGShmemHeader::magic, NULL, PG_SHMAT_FLAGS, PGShmemMagic, and UsedShmemSegAddr.

Referenced by PGSharedMemoryCreate().

801 {
802  PGShmemHeader *hdr;
803 
804  if ((*shmid = shmget(key, sizeof(PGShmemHeader), 0)) < 0)
805  return NULL;
806 
807  hdr = (PGShmemHeader *) shmat(*shmid, UsedShmemSegAddr, PG_SHMAT_FLAGS);
808 
809  if (hdr == (PGShmemHeader *) -1)
810  return NULL; /* failed: must be some other app's */
811 
812  if (hdr->magic != PGShmemMagic)
813  {
814  shmdt((void *) hdr);
815  return NULL; /* segment belongs to a non-Postgres app */
816  }
817 
818  return hdr;
819 }
#define PG_SHMAT_FLAGS
Definition: mem.h:20
void * UsedShmemSegAddr
Definition: sysv_shmem.c:75
int32 magic
Definition: pg_shmem.h:31
#define NULL
Definition: c.h:229
#define PGShmemMagic
Definition: pg_shmem.h:32
PGShmemHeader* PGSharedMemoryCreate ( Size  size,
bool  makePrivate,
int  port,
PGShmemHeader **  shim 
)

Definition at line 536 of file sysv_shmem.c.

Referenced by CreateSharedMemoryAndSemaphores().

538 {
539  IpcMemoryKey NextShmemSegID;
540  void *memAddress;
541  PGShmemHeader *hdr;
542  IpcMemoryId shmid;
543  struct stat statbuf;
544  Size sysvsize;
545 
546  /* Complain if hugepages demanded but we can't possibly support them */
547 #if !defined(USE_ANONYMOUS_SHMEM) || !defined(MAP_HUGETLB)
548  if (huge_pages == HUGE_PAGES_ON)
549  ereport(ERROR,
550  (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
551  errmsg("huge pages not supported on this platform")));
552 #endif
553 
554  /* Room for a header? */
555  Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
556 
557 #ifdef USE_ANONYMOUS_SHMEM
559  AnonymousShmemSize = size;
560 
561  /* Register on-exit routine to unmap the anonymous segment */
563 
564  /* Now we need only allocate a minimal-sized SysV shmem block. */
565  sysvsize = sizeof(PGShmemHeader);
566 #else
567  sysvsize = size;
568 #endif
569 
570  /* Make sure PGSharedMemoryAttach doesn't fail without need */
572 
573  /* Loop till we find a free IPC key */
574  NextShmemSegID = port * 1000;
575 
576  for (NextShmemSegID++;; NextShmemSegID++)
577  {
578  /* Try to create new segment */
579  memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
580  if (memAddress)
581  break; /* successful create and attach */
582 
583  /* Check shared memory and possibly remove and recreate */
584 
585  if (makePrivate) /* a standalone backend shouldn't do this */
586  continue;
587 
588  if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
589  continue; /* can't attach, not one of mine */
590 
591  /*
592  * If I am not the creator and it belongs to an extant process,
593  * continue.
594  */
595  hdr = (PGShmemHeader *) memAddress;
596  if (hdr->creatorPID != getpid())
597  {
598  if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
599  {
600  shmdt(memAddress);
601  continue; /* segment belongs to a live process */
602  }
603  }
604 
605  /*
606  * The segment appears to be from a dead Postgres process, or from a
607  * previous cycle of life in this same process. Zap it, if possible,
608  * and any associated dynamic shared memory segments, as well. This
609  * probably shouldn't fail, but if it does, assume the segment belongs
610  * to someone else after all, and continue quietly.
611  */
612  if (hdr->dsm_control != 0)
614  shmdt(memAddress);
615  if (shmctl(shmid, IPC_RMID, NULL) < 0)
616  continue;
617 
618  /*
619  * Now try again to create the segment.
620  */
621  memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
622  if (memAddress)
623  break; /* successful create and attach */
624 
625  /*
626  * Can only get here if some other process managed to create the same
627  * shmem key before we did. Let him have that one, loop around to try
628  * next key.
629  */
630  }
631 
632  /*
633  * OK, we created a new segment. Mark it as created by this process. The
634  * order of assignments here is critical so that another Postgres process
635  * can't see the header as valid but belonging to an invalid PID!
636  */
637  hdr = (PGShmemHeader *) memAddress;
638  hdr->creatorPID = getpid();
639  hdr->magic = PGShmemMagic;
640  hdr->dsm_control = 0;
641 
642  /* Fill in the data directory ID info, too */
643  if (stat(DataDir, &statbuf) < 0)
644  ereport(FATAL,
646  errmsg("could not stat data directory \"%s\": %m",
647  DataDir)));
648  hdr->device = statbuf.st_dev;
649  hdr->inode = statbuf.st_ino;
650 
651  /*
652  * Initialize space allocation status for segment.
653  */
654  hdr->totalsize = size;
655  hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
656  *shim = hdr;
657 
658  /* Save info for possible future use */
659  UsedShmemSegAddr = memAddress;
660  UsedShmemSegID = (unsigned long) NextShmemSegID;
661 
662  /*
663  * If AnonymousShmem is NULL here, then we're not using anonymous shared
664  * memory, and should return a pointer to the System V shared memory
665  * block. Otherwise, the System V shared memory block is only a shim, and
666  * we must return a pointer to the real block.
667  */
668 #ifdef USE_ANONYMOUS_SHMEM
669  if (AnonymousShmem == NULL)
670  return hdr;
671  memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
672  return (PGShmemHeader *) AnonymousShmem;
673 #else
674  return hdr;
675 #endif
676 }
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:800
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:503
#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:435
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:114
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:490
int errmsg(const char *fmt,...)
Definition: elog.c:797
char * DataDir
Definition: globals.c:59
void PGSharedMemoryDetach ( void  )

Definition at line 768 of file sysv_shmem.c.

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

769 {
770  if (UsedShmemSegAddr != NULL)
771  {
772  if ((shmdt(UsedShmemSegAddr) < 0)
773 #if defined(EXEC_BACKEND) && defined(__CYGWIN__)
774  /* Work-around for cygipc exec bug */
775  && shmdt(NULL) < 0
776 #endif
777  )
778  elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
780  }
781 
782 #ifdef USE_ANONYMOUS_SHMEM
783  if (AnonymousShmem != NULL)
784  {
785  if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
786  elog(LOG, "munmap(%p, %zu) failed: %m",
789  }
790 #endif
791 }
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 267 of file sysv_shmem.c.

Referenced by CreateLockFile().

268 {
269  IpcMemoryId shmId = (IpcMemoryId) id2;
270  struct shmid_ds shmStat;
271  struct stat statbuf;
272  PGShmemHeader *hdr;
273 
274  /*
275  * We detect whether a shared memory segment is in use by seeing whether
276  * it (a) exists and (b) has any processes attached to it.
277  */
278  if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
279  {
280  /*
281  * EINVAL actually has multiple possible causes documented in the
282  * shmctl man page, but we assume it must mean the segment no longer
283  * exists.
284  */
285  if (errno == EINVAL)
286  return false;
287 
288  /*
289  * EACCES implies that the segment belongs to some other userid, which
290  * means it is not a Postgres shmem segment (or at least, not one that
291  * is relevant to our data directory).
292  */
293  if (errno == EACCES)
294  return false;
295 
296  /*
297  * Some Linux kernel versions (in fact, all of them as of July 2007)
298  * sometimes return EIDRM when EINVAL is correct. The Linux kernel
299  * actually does not have any internal state that would justify
300  * returning EIDRM, so we can get away with assuming that EIDRM is
301  * equivalent to EINVAL on that platform.
302  */
303 #ifdef HAVE_LINUX_EIDRM_BUG
304  if (errno == EIDRM)
305  return false;
306 #endif
307 
308  /*
309  * Otherwise, we had better assume that the segment is in use. The
310  * only likely case is EIDRM, which implies that the segment has been
311  * IPC_RMID'd but there are still processes attached to it.
312  */
313  return true;
314  }
315 
316  /* If it has no attached processes, it's not in use */
317  if (shmStat.shm_nattch == 0)
318  return false;
319 
320  /*
321  * Try to attach to the segment and see if it matches our data directory.
322  * This avoids shmid-conflict problems on machines that are running
323  * several postmasters under the same userid.
324  */
325  if (stat(DataDir, &statbuf) < 0)
326  return true; /* if can't stat, be conservative */
327 
328  hdr = (PGShmemHeader *) shmat(shmId, NULL, PG_SHMAT_FLAGS);
329 
330  if (hdr == (PGShmemHeader *) -1)
331  return true; /* if can't attach, be conservative */
332 
333  if (hdr->magic != PGShmemMagic ||
334  hdr->device != statbuf.st_dev ||
335  hdr->inode != statbuf.st_ino)
336  {
337  /*
338  * It's either not a Postgres segment, or not one for my data
339  * directory. In either case it poses no threat.
340  */
341  shmdt((void *) hdr);
342  return false;
343  }
344 
345  /* Trouble --- looks a lot like there's still live backends */
346  shmdt((void *) hdr);
347 
348  return true;
349 }
#define PG_SHMAT_FLAGS
Definition: mem.h:20
#define IPC_STAT
Definition: win32.h:119
#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:59
#define EIDRM
Definition: win32.h:123

Variable Documentation

void* AnonymousShmem = NULL
static

Definition at line 79 of file sysv_shmem.c.

Referenced by AnonymousShmemDetach(), PGSharedMemoryCreate(), and PGSharedMemoryDetach().

Size AnonymousShmemSize
static

Definition at line 78 of file sysv_shmem.c.

Referenced by AnonymousShmemDetach(), PGSharedMemoryCreate(), and PGSharedMemoryDetach().

void* UsedShmemSegAddr = NULL

Definition at line 75 of file sysv_shmem.c.

Referenced by PGSharedMemoryAttach(), PGSharedMemoryCreate(), and PGSharedMemoryDetach().

unsigned long UsedShmemSegID = 0

Definition at line 74 of file sysv_shmem.c.

Referenced by PGSharedMemoryCreate().