#include "postgres.h"
#include "access/transam.h"
#include "fmgr.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/lwlock.h"
#include "storage/pg_shmem.h"
#include "storage/shmem.h"
#include "storage/spin.h"
#include "utils/builtins.h"

Include dependency graph for shmem.c:

Macros
#define	PG_GET_SHMEM_SIZES_COLS 4

Functions
static void *	ShmemAllocRaw (Size size, Size *allocated_size)

void	InitShmemAccess (void *seghdr)

void	InitShmemAllocation (void)

void *	ShmemAlloc (Size size)

void *	ShmemAllocNoError (Size size)

void *	ShmemAllocUnlocked (Size size)

bool	ShmemAddrIsValid (const void *addr)

void	InitShmemIndex (void)

HTAB *	ShmemInitHash (const char name, long init_size, long max_size, HASHCTL infoP, int hash_flags)

void *	ShmemInitStruct (const char name, Size size, bool foundPtr)

Size	add_size (Size s1, Size s2)

Size	mul_size (Size s1, Size s2)

Datum	pg_get_shmem_allocations (PG_FUNCTION_ARGS)

Variables
static PGShmemHeader *	ShmemSegHdr

static void *	ShmemBase

static void *	ShmemEnd

slock_t *	ShmemLock

static HTAB *	ShmemIndex = NULL

Macro Definition Documentation

◆ PG_GET_SHMEM_SIZES_COLS

#define PG_GET_SHMEM_SIZES_COLS 4

Function Documentation

◆ add_size()

Size add_size	(	Size	s1,
		Size	s2
	)

Definition at line 502 of file shmem.c.

 {
     Size        result;
  
     result = s1 + s2;
     /* We are assuming Size is an unsigned type here... */
     if (result < s1 || result < s2)
         ereport(ERROR,
                 (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                  errmsg("requested shared memory size overflows size_t")));
     return result;
 }

References ereport, errcode(), errmsg(), ERROR, s1, and s2.

Referenced by _bt_parallel_estimate_shared(), ApplyLauncherShmemSize(), AsyncShmemInit(), AsyncShmemSize(), AutoVacuumShmemSize(), BackendStatusShmemSize(), BackgroundWorkerShmemSize(), BTreeShmemSize(), BufferShmemSize(), CalculateShmemSize(), CheckpointerShmemSize(), CreateSharedProcArray(), estimate_variable_size(), EstimateComboCIDStateSpace(), EstimateGUCStateSpace(), EstimateLibraryStateSpace(), EstimateParamExecSpace(), EstimateParamListSpace(), EstimateSnapshotSpace(), EstimateTransactionStateSpace(), ExecAggEstimate(), ExecAppendEstimate(), ExecBitmapHeapEstimate(), ExecHashEstimate(), ExecIncrementalSortEstimate(), ExecMemoizeEstimate(), ExecSortEstimate(), expand_planner_arrays(), hash_estimate_size(), index_parallelscan_estimate(), index_parallelscan_initialize(), InitializeShmemGUCs(), LockShmemSize(), LWLockShmemSize(), MultiXactShmemSize(), PgArchShmemSize(), pgss_memsize(), PMSignalShmemSize(), PredicateLockShmemSize(), ProcArrayShmemSize(), ProcGlobalShmemSize(), ProcSignalShmemSize(), ReplicationOriginShmemSize(), ReplicationSlotsShmemSize(), RequestAddinShmemSpace(), SerializeTransactionState(), shm_toc_estimate(), SInvalShmemSize(), SnapMgrShmemSize(), StatsShmemSize(), StrategyShmemSize(), table_parallelscan_estimate(), tuplesort_estimate_shared(), TwoPhaseShmemSize(), WalRcvShmemSize(), WalSndShmemSize(), and XLOGShmemSize().

◆ InitShmemAccess()

void InitShmemAccess ( void * seghdr )

Definition at line 101 of file shmem.c.

 {
     PGShmemHeader *shmhdr = (PGShmemHeader *) seghdr;
  
     ShmemSegHdr = shmhdr;
     ShmemBase = (void *) shmhdr;
     ShmemEnd = (char *) ShmemBase + shmhdr->totalsize;
 }

References ShmemBase, ShmemEnd, ShmemSegHdr, and PGShmemHeader::totalsize.

Referenced by CreateSharedMemoryAndSemaphores().

◆ InitShmemAllocation()

void InitShmemAllocation ( void )

Definition at line 116 of file shmem.c.

 {
     PGShmemHeader *shmhdr = ShmemSegHdr;
     char       *aligned;
  
     Assert(shmhdr != NULL);
  
     /*
      * Initialize the spinlock used by ShmemAlloc.  We must use
      * ShmemAllocUnlocked, since obviously ShmemAlloc can't be called yet.
      */
     ShmemLock = (slock_t *) ShmemAllocUnlocked(sizeof(slock_t));
  
     SpinLockInit(ShmemLock);
  
     /*
      * Allocations after this point should go through ShmemAlloc, which
      * expects to allocate everything on cache line boundaries.  Make sure the
      * first allocation begins on a cache line boundary.
      */
     aligned = (char *)
         (CACHELINEALIGN((((char *) shmhdr) + shmhdr->freeoffset)));
     shmhdr->freeoffset = aligned - (char *) shmhdr;
  
     /* ShmemIndex can't be set up yet (need LWLocks first) */
     shmhdr->index = NULL;
     ShmemIndex = (HTAB *) NULL;
  
     /*
      * Initialize ShmemVariableCache for transaction manager. (This doesn't
      * really belong here, but not worth moving.)
      */
     ShmemVariableCache = (VariableCache)
         ShmemAlloc(sizeof(*ShmemVariableCache));
     memset(ShmemVariableCache, 0, sizeof(*ShmemVariableCache));
 }

References Assert(), CACHELINEALIGN, PGShmemHeader::freeoffset, PGShmemHeader::index, ShmemAlloc(), ShmemAllocUnlocked(), ShmemIndex, ShmemLock, ShmemSegHdr, ShmemVariableCache, and SpinLockInit.

Referenced by CreateSharedMemoryAndSemaphores().

◆ InitShmemIndex()

void InitShmemIndex ( void )

Definition at line 292 of file shmem.c.

 {
     HASHCTL     info;
  
     /*
      * Create the shared memory shmem index.
      *
      * Since ShmemInitHash calls ShmemInitStruct, which expects the ShmemIndex
      * hashtable to exist already, we have a bit of a circularity problem in
      * initializing the ShmemIndex itself.  The special "ShmemIndex" hash
      * table name will tell ShmemInitStruct to fake it.
      */
     info.keysize = SHMEM_INDEX_KEYSIZE;
     info.entrysize = sizeof(ShmemIndexEnt);
  
     ShmemIndex = ShmemInitHash("ShmemIndex",
                                SHMEM_INDEX_SIZE, SHMEM_INDEX_SIZE,
                                &info,
                                HASH_ELEM | HASH_STRINGS);
 }

References HASHCTL::entrysize, HASH_ELEM, HASH_STRINGS, HASHCTL::keysize, SHMEM_INDEX_KEYSIZE, SHMEM_INDEX_SIZE, ShmemIndex, and ShmemInitHash().

Referenced by CreateSharedMemoryAndSemaphores().

◆ mul_size()

Size mul_size	(	Size	s1,
		Size	s2
	)

Definition at line 519 of file shmem.c.

 {
     Size        result;
  
     if (s1 == 0 || s2 == 0)
         return 0;
     result = s1 * s2;
     /* We are assuming Size is an unsigned type here... */
     if (result / s2 != s1)
         ereport(ERROR,
                 (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                  errmsg("requested shared memory size overflows size_t")));
     return result;
 }

References ereport, errcode(), errmsg(), ERROR, s1, and s2.

Referenced by _bt_begin_parallel(), ApplyLauncherShmemSize(), AsyncShmemInit(), AsyncShmemSize(), AutoVacuumShmemSize(), BackendStatusShmemSize(), BackgroundWorkerShmemSize(), BTreeShmemSize(), BufferShmemSize(), CheckpointerShmemSize(), CreateSharedBackendStatus(), CreateSharedProcArray(), EstimateComboCIDStateSpace(), EstimatePendingSyncsSpace(), EstimateReindexStateSpace(), EstimateSnapshotSpace(), EstimateTransactionStateSpace(), ExecAggEstimate(), ExecHashEstimate(), ExecIncrementalSortEstimate(), ExecInitParallelPlan(), ExecMemoizeEstimate(), ExecParallelRetrieveInstrumentation(), ExecParallelRetrieveJitInstrumentation(), ExecParallelSetupTupleQueues(), ExecSortEstimate(), hash_estimate_size(), InitializeParallelDSM(), InitPredicateLocks(), LWLockShmemSize(), parallel_vacuum_init(), PGSemaphoreShmemSize(), PMSignalShmemSize(), PredicateLockShmemSize(), ProcArrayShmemSize(), ProcGlobalShmemSize(), ProcSignalShmemSize(), ReplicationOriginShmemSize(), ReplicationSlotsShmemSize(), shm_toc_estimate(), SInvalShmemSize(), SnapMgrShmemSize(), tuplesort_estimate_shared(), TwoPhaseShmemSize(), WalSndShmemSize(), and XLOGShmemSize().

◆ pg_get_shmem_allocations()

Datum pg_get_shmem_allocations ( PG_FUNCTION_ARGS )

Definition at line 536 of file shmem.c.

 {
 #define PG_GET_SHMEM_SIZES_COLS 4
     ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
     HASH_SEQ_STATUS hstat;
     ShmemIndexEnt *ent;
     Size        named_allocated = 0;
     Datum       values[PG_GET_SHMEM_SIZES_COLS];
     bool        nulls[PG_GET_SHMEM_SIZES_COLS];
  
     SetSingleFuncCall(fcinfo, 0);
  
     LWLockAcquire(ShmemIndexLock, LW_SHARED);
  
     hash_seq_init(&hstat, ShmemIndex);
  
     /* output all allocated entries */
     memset(nulls, 0, sizeof(nulls));
     while ((ent = (ShmemIndexEnt *) hash_seq_search(&hstat)) != NULL)
     {
         values[0] = CStringGetTextDatum(ent->key);
         values[1] = Int64GetDatum((char *) ent->location - (char *) ShmemSegHdr);
         values[2] = Int64GetDatum(ent->size);
         values[3] = Int64GetDatum(ent->allocated_size);
         named_allocated += ent->allocated_size;
  
         tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
                              values, nulls);
     }
  
     /* output shared memory allocated but not counted via the shmem index */
     values[0] = CStringGetTextDatum("<anonymous>");
     nulls[1] = true;
     values[2] = Int64GetDatum(ShmemSegHdr->freeoffset - named_allocated);
     values[3] = values[2];
     tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
  
     /* output as-of-yet unused shared memory */
     nulls[0] = true;
     values[1] = Int64GetDatum(ShmemSegHdr->freeoffset);
     nulls[1] = false;
     values[2] = Int64GetDatum(ShmemSegHdr->totalsize - ShmemSegHdr->freeoffset);
     values[3] = values[2];
     tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
  
     LWLockRelease(ShmemIndexLock);
  
     return (Datum) 0;
 }

References CStringGetTextDatum, PGShmemHeader::freeoffset, hash_seq_init(), hash_seq_search(), Int64GetDatum(), LW_SHARED, LWLockAcquire(), LWLockRelease(), PG_GET_SHMEM_SIZES_COLS, ReturnSetInfo::setDesc, ReturnSetInfo::setResult, SetSingleFuncCall(), ShmemIndex, ShmemSegHdr, PGShmemHeader::totalsize, tuplestore_putvalues(), and values.

◆ ShmemAddrIsValid()

bool ShmemAddrIsValid ( const void * addr )

Definition at line 283 of file shmem.c.

 {
     return (addr >= ShmemBase) && (addr < ShmemEnd);
 }

References ShmemBase, and ShmemEnd.

Referenced by NextPredXact(), ReleasePredXact(), ShmemInitStruct(), SHMQueueDelete(), SHMQueueElemInit(), SHMQueueEmpty(), SHMQueueInit(), SHMQueueInsertAfter(), SHMQueueInsertBefore(), SHMQueueIsDetached(), SHMQueueNext(), and SHMQueuePrev().

◆ ShmemAlloc()

void* ShmemAlloc ( Size size )

Definition at line 161 of file shmem.c.

 {
     void       *newSpace;
     Size        allocated_size;
  
     newSpace = ShmemAllocRaw(size, &allocated_size);
     if (!newSpace)
         ereport(ERROR,
                 (errcode(ERRCODE_OUT_OF_MEMORY),
                  errmsg("out of shared memory (%zu bytes requested)",
                         size)));
     return newSpace;
 }

References ereport, errcode(), errmsg(), ERROR, and ShmemAllocRaw().

Referenced by CreateLWLocks(), InitPredicateLocks(), InitProcGlobal(), InitShmemAllocation(), and ShmemInitStruct().

◆ ShmemAllocNoError()

void* ShmemAllocNoError ( Size size )

Definition at line 181 of file shmem.c.

 {
     Size        allocated_size;
  
     return ShmemAllocRaw(size, &allocated_size);
 }

References ShmemAllocRaw().

Referenced by ShmemInitHash().

◆ ShmemAllocRaw()

static void * ShmemAllocRaw	(	Size	size,
		Size *	allocated_size
	)

static

Definition at line 195 of file shmem.c.

 {
     Size        newStart;
     Size        newFree;
     void       *newSpace;
  
     /*
      * Ensure all space is adequately aligned.  We used to only MAXALIGN this
      * space but experience has proved that on modern systems that is not good
      * enough.  Many parts of the system are very sensitive to critical data
      * structures getting split across cache line boundaries.  To avoid that,
      * attempt to align the beginning of the allocation to a cache line
      * boundary.  The calling code will still need to be careful about how it
      * uses the allocated space - e.g. by padding each element in an array of
      * structures out to a power-of-two size - but without this, even that
      * won't be sufficient.
      */
     size = CACHELINEALIGN(size);
     *allocated_size = size;
  
     Assert(ShmemSegHdr != NULL);
  
     SpinLockAcquire(ShmemLock);
  
     newStart = ShmemSegHdr->freeoffset;
  
     newFree = newStart + size;
     if (newFree <= ShmemSegHdr->totalsize)
     {
         newSpace = (void *) ((char *) ShmemBase + newStart);
         ShmemSegHdr->freeoffset = newFree;
     }
     else
         newSpace = NULL;
  
     SpinLockRelease(ShmemLock);
  
     /* note this assert is okay with newSpace == NULL */
     Assert(newSpace == (void *) CACHELINEALIGN(newSpace));
  
     return newSpace;
 }

References Assert(), CACHELINEALIGN, PGShmemHeader::freeoffset, ShmemBase, ShmemLock, ShmemSegHdr, SpinLockAcquire, and SpinLockRelease.

Referenced by ShmemAlloc(), ShmemAllocNoError(), and ShmemInitStruct().

◆ ShmemAllocUnlocked()

void* ShmemAllocUnlocked ( Size size )

Definition at line 247 of file shmem.c.

 {
     Size        newStart;
     Size        newFree;
     void       *newSpace;
  
     /*
      * Ensure allocated space is adequately aligned.
      */
     size = MAXALIGN(size);
  
     Assert(ShmemSegHdr != NULL);
  
     newStart = ShmemSegHdr->freeoffset;
  
     newFree = newStart + size;
     if (newFree > ShmemSegHdr->totalsize)
         ereport(ERROR,
                 (errcode(ERRCODE_OUT_OF_MEMORY),
                  errmsg("out of shared memory (%zu bytes requested)",
                         size)));
     ShmemSegHdr->freeoffset = newFree;
  
     newSpace = (void *) ((char *) ShmemBase + newStart);
  
     Assert(newSpace == (void *) MAXALIGN(newSpace));
  
     return newSpace;
 }

References Assert(), ereport, errcode(), errmsg(), ERROR, PGShmemHeader::freeoffset, MAXALIGN, ShmemBase, ShmemSegHdr, and PGShmemHeader::totalsize.

Referenced by InitShmemAllocation(), PGReserveSemaphores(), and SpinlockSemaInit().

◆ ShmemInitHash()

HTAB* ShmemInitHash	(	const char *	name,
		long	init_size,
		long	max_size,
		HASHCTL *	infoP,
		int	hash_flags
	)

Definition at line 341 of file shmem.c.

 {
     bool        found;
     void       *location;
  
     /*
      * Hash tables allocated in shared memory have a fixed directory; it can't
      * grow or other backends wouldn't be able to find it. So, make sure we
      * make it big enough to start with.
      *
      * The shared memory allocator must be specified too.
      */
     infoP->dsize = infoP->max_dsize = hash_select_dirsize(max_size);
     infoP->alloc = ShmemAllocNoError;
     hash_flags |= HASH_SHARED_MEM | HASH_ALLOC | HASH_DIRSIZE;
  
     /* look it up in the shmem index */
     location = ShmemInitStruct(name,
                                hash_get_shared_size(infoP, hash_flags),
                                &found);
  
     /*
      * if it already exists, attach to it rather than allocate and initialize
      * new space
      */
     if (found)
         hash_flags |= HASH_ATTACH;
  
     /* Pass location of hashtable header to hash_create */
     infoP->hctl = (HASHHDR *) location;
  
     return hash_create(name, init_size, infoP, hash_flags);
 }

References HASHCTL::alloc, HASHCTL::dsize, HASH_ALLOC, HASH_ATTACH, hash_create(), HASH_DIRSIZE, hash_get_shared_size(), hash_select_dirsize(), HASH_SHARED_MEM, HASHCTL::hctl, HASHCTL::max_dsize, name, ShmemAllocNoError(), and ShmemInitStruct().

Referenced by InitBufTable(), InitLocks(), InitPredicateLocks(), InitShmemIndex(), and pgss_shmem_startup().

◆ ShmemInitStruct()

void* ShmemInitStruct	(	const char *	name,
		Size	size,
		bool *	foundPtr
	)

Definition at line 396 of file shmem.c.

 {
     ShmemIndexEnt *result;
     void       *structPtr;
  
     LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
  
     if (!ShmemIndex)
     {
         PGShmemHeader *shmemseghdr = ShmemSegHdr;
  
         /* Must be trying to create/attach to ShmemIndex itself */
         Assert(strcmp(name, "ShmemIndex") == 0);
  
         if (IsUnderPostmaster)
         {
             /* Must be initializing a (non-standalone) backend */
             Assert(shmemseghdr->index != NULL);
             structPtr = shmemseghdr->index;
             *foundPtr = true;
         }
         else
         {
             /*
              * If the shmem index doesn't exist, we are bootstrapping: we must
              * be trying to init the shmem index itself.
              *
              * Notice that the ShmemIndexLock is released before the shmem
              * index has been initialized.  This should be OK because no other
              * process can be accessing shared memory yet.
              */
             Assert(shmemseghdr->index == NULL);
             structPtr = ShmemAlloc(size);
             shmemseghdr->index = structPtr;
             *foundPtr = false;
         }
         LWLockRelease(ShmemIndexLock);
         return structPtr;
     }
  
     /* look it up in the shmem index */
     result = (ShmemIndexEnt *)
         hash_search(ShmemIndex, name, HASH_ENTER_NULL, foundPtr);
  
     if (!result)
     {
         LWLockRelease(ShmemIndexLock);
         ereport(ERROR,
                 (errcode(ERRCODE_OUT_OF_MEMORY),
                  errmsg("could not create ShmemIndex entry for data structure \"%s\"",
                         name)));
     }
  
     if (*foundPtr)
     {
         /*
          * Structure is in the shmem index so someone else has allocated it
          * already.  The size better be the same as the size we are trying to
          * initialize to, or there is a name conflict (or worse).
          */
         if (result->size != size)
         {
             LWLockRelease(ShmemIndexLock);
             ereport(ERROR,
                     (errmsg("ShmemIndex entry size is wrong for data structure"
                             " \"%s\": expected %zu, actual %zu",
                             name, size, result->size)));
         }
         structPtr = result->location;
     }
     else
     {
         Size        allocated_size;
  
         /* It isn't in the table yet. allocate and initialize it */
         structPtr = ShmemAllocRaw(size, &allocated_size);
         if (structPtr == NULL)
         {
             /* out of memory; remove the failed ShmemIndex entry */
             hash_search(ShmemIndex, name, HASH_REMOVE, NULL);
             LWLockRelease(ShmemIndexLock);
             ereport(ERROR,
                     (errcode(ERRCODE_OUT_OF_MEMORY),
                      errmsg("not enough shared memory for data structure"
                             " \"%s\" (%zu bytes requested)",
                             name, size)));
         }
         result->size = size;
         result->allocated_size = allocated_size;
         result->location = structPtr;
     }
  
     LWLockRelease(ShmemIndexLock);
  
     Assert(ShmemAddrIsValid(structPtr));
  
     Assert(structPtr == (void *) CACHELINEALIGN(structPtr));
  
     return structPtr;
 }