#include "storage/spin.h"
#include "utils/builtins.h"
+/*
+ * This is the first data structure stored in the shared memory segment, at
+ * the offset that PGShmemHeader->content_offset points to. Allocations by
+ * ShmemAlloc() are carved out of the space after this.
+ *
+ * For the base pointer and the total size of the shmem segment, we rely on
+ * the PGShmemHeader.
+ */
+typedef struct ShmemAllocatorData
+{
+ Size free_offset; /* offset to first free space from ShmemBase */
+ HTAB *index; /* copy of ShmemIndex */
+
+ /* protects shared memory and LWLock allocation */
+ slock_t shmem_lock;
+} ShmemAllocatorData;
+
static void *ShmemAllocRaw(Size size, Size *allocated_size);
-static void *ShmemAllocUnlocked(Size size);
/* shared memory global variables */
static PGShmemHeader *ShmemSegHdr; /* shared mem segment header */
-
static void *ShmemBase; /* start address of shared memory */
-
static void *ShmemEnd; /* end+1 address of shared memory */
-slock_t *ShmemLock; /* spinlock for shared memory and LWLock
- * allocation */
-
+static ShmemAllocatorData *ShmemAllocator;
+slock_t *ShmemLock; /* points to ShmemAllocator->shmem_lock */
static HTAB *ShmemIndex = NULL; /* primary index hashtable for shmem */
/* To get reliable results for NUMA inquiry we need to "touch pages" once */
Datum pg_numa_available(PG_FUNCTION_ARGS);
/*
- * InitShmemAccess() --- set up basic pointers to shared memory.
+ * InitShmemAllocator() --- set up basic pointers to shared memory.
+ *
+ * Called at postmaster or stand-alone backend startup, to initialize the
+ * allocator's data structure in the shared memory segment. In EXEC_BACKEND,
+ * this is also called at backend startup, to set up pointers to the shared
+ * memory areas.
*/
void
-InitShmemAccess(PGShmemHeader *seghdr)
+InitShmemAllocator(PGShmemHeader *seghdr)
{
+ Assert(seghdr != NULL);
+
+ /*
+ * We assume the pointer and offset are MAXALIGN. Not a hard requirement,
+ * but it's true today and keeps the math below simpler.
+ */
+ Assert(seghdr == (void *) MAXALIGN(seghdr));
+ Assert(seghdr->content_offset == MAXALIGN(seghdr->content_offset));
+
ShmemSegHdr = seghdr;
ShmemBase = seghdr;
ShmemEnd = (char *) ShmemBase + seghdr->totalsize;
-}
-/*
- * InitShmemAllocation() --- set up shared-memory space allocation.
- *
- * This should be called only in the postmaster or a standalone backend.
- */
-void
-InitShmemAllocation(void)
-{
- PGShmemHeader *shmhdr = ShmemSegHdr;
- char *aligned;
+#ifndef EXEC_BACKEND
+ Assert(!IsUnderPostmaster);
+#endif
+ if (IsUnderPostmaster)
+ {
+ PGShmemHeader *shmhdr = ShmemSegHdr;
- Assert(shmhdr != NULL);
+ ShmemAllocator = (ShmemAllocatorData *) ((char *) shmhdr + shmhdr->content_offset);
+ ShmemLock = &ShmemAllocator->shmem_lock;
+ }
+ else
+ {
+ Size offset;
- /*
- * 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));
+ /*
+ * 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.
+ */
+ offset = CACHELINEALIGN(seghdr->content_offset + sizeof(ShmemAllocatorData));
+ if (offset > seghdr->totalsize)
+ ereport(ERROR,
+ (errcode(ERRCODE_OUT_OF_MEMORY),
+ errmsg("out of shared memory (%zu bytes requested)",
+ offset)));
- SpinLockInit(ShmemLock);
+ ShmemAllocator = (ShmemAllocatorData *) ((char *) seghdr + seghdr->content_offset);
- /*
- * 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;
+ SpinLockInit(&ShmemAllocator->shmem_lock);
+ ShmemLock = &ShmemAllocator->shmem_lock;
+ ShmemAllocator->free_offset = offset;
+ /* ShmemIndex can't be set up yet (need LWLocks first) */
+ ShmemAllocator->index = NULL;
+ ShmemIndex = (HTAB *) NULL;
+ }
}
/*
SpinLockAcquire(ShmemLock);
- newStart = ShmemSegHdr->freeoffset;
+ newStart = ShmemAllocator->free_offset;
newFree = newStart + size;
if (newFree <= ShmemSegHdr->totalsize)
{
newSpace = (char *) ShmemBase + newStart;
- ShmemSegHdr->freeoffset = newFree;
+ ShmemAllocator->free_offset = newFree;
}
else
newSpace = NULL;
return newSpace;
}
-/*
- * ShmemAllocUnlocked -- allocate max-aligned chunk from shared memory
- *
- * Allocate space without locking ShmemLock. This should be used for,
- * and only for, allocations that must happen before ShmemLock is ready.
- *
- * We consider maxalign, rather than cachealign, sufficient here.
- */
-static void *
-ShmemAllocUnlocked(Size size)
-{
- 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 = (char *) ShmemBase + newStart;
-
- Assert(newSpace == (void *) MAXALIGN(newSpace));
-
- return newSpace;
-}
-
/*
* ShmemAddrIsValid -- test if an address refers to shared memory
*
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;
+ Assert(ShmemAllocator->index != NULL);
+ structPtr = ShmemAllocator->index;
*foundPtr = true;
}
else
* index has been initialized. This should be OK because no other
* process can be accessing shared memory yet.
*/
- Assert(shmemseghdr->index == NULL);
+ Assert(ShmemAllocator->index == NULL);
structPtr = ShmemAlloc(size);
- shmemseghdr->index = structPtr;
+ ShmemAllocator->index = structPtr;
*foundPtr = false;
}
LWLockRelease(ShmemIndexLock);
/* 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[2] = Int64GetDatum(ShmemAllocator->free_offset - 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);
+ values[1] = Int64GetDatum(ShmemAllocator->free_offset);
nulls[1] = false;
- values[2] = Int64GetDatum(ShmemSegHdr->totalsize - ShmemSegHdr->freeoffset);
+ values[2] = Int64GetDatum(ShmemSegHdr->totalsize - ShmemAllocator->free_offset);
values[3] = values[2];
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
projects / thirdparty / postgresql.git / commitdiff
