@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $ PostgreSQL : pgsql / src / backend / storage / ipc / shmem . c , v 1.97 2006 / 10 / 04 00 : 29 : 57 momjian Exp $
* $ PostgreSQL : pgsql / src / backend / storage / ipc / shmem . c , v 1.98 2006 / 10 / 15 22 : 04 : 07 tgl Exp $
*
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
@ -53,7 +53,7 @@
* postmaster . However , this does not work in the EXEC_BACKEND case .
* In ports using EXEC_BACKEND , new backends have to set up their local
* pointers using the method described in ( b ) above .
*
* ( d ) memory allocation model : shared memory can never be
* freed , once allocated . Each hash table has its own free list ,
* so hash buckets can be reused when an item is deleted . However ,
@ -61,15 +61,6 @@
* cannot be redistributed to other tables . We could build a simple
* hash bucket garbage collector if need be . Right now , it seems
* unnecessary .
*
* ( e ) Add - ins can request their own logical shared memory segments
* by calling RegisterAddinContext ( ) from the preload - libraries hook .
* Each call establishes a uniquely named add - in shared memopry
* context which will be set up as part of postgres intialisation .
* Memory can be allocated from these contexts using
* ShmemAllocFromContext ( ) , and can be reset to its initial condition
* using ShmemResetContext ( ) . Also , RegisterAddinLWLock ( LWLockid * lock_ptr )
* can be used to request that a LWLock be allocated , placed into * lock_ptr .
*/
# include "postgres.h"
@ -95,19 +86,6 @@ slock_t *ShmemLock; /* spinlock for shared memory and LWLock
static HTAB * ShmemIndex = NULL ; /* primary index hashtable for shmem */
/* Structures and globals for managing add-in shared memory contexts */
typedef struct context
{
char * name ;
Size size ;
PGShmemHeader * seg_hdr ;
struct context * next ;
} ContextNode ;
static ContextNode * addin_contexts = NULL ;
static Size addin_contexts_size = 0 ;
/*
* InitShmemAccess ( ) - - - set up basic pointers to shared memory .
@ -162,99 +140,7 @@ InitShmemAllocation(void)
}
/*
* RegisterAddinContext - - Register the requirement for a named shared
* memory context .
*/
void
RegisterAddinContext ( const char * name , Size size )
{
char * newstr = malloc ( strlen ( name ) + 1 ) ;
ContextNode * node = malloc ( sizeof ( ContextNode ) ) ;
strcpy ( newstr , name ) ;
node - > name = newstr ;
/* Round up to typical page size */
node - > size = add_size ( size , 8192 - ( size % 8192 ) ) ;
node - > next = addin_contexts ;
addin_contexts = node ;
addin_contexts_size = add_size ( addin_contexts_size , node - > size ) ;
}
/*
* ContextFromName - - Return the ContextNode for the given named
* context , or NULL if not found .
*/
static ContextNode *
ContextFromName ( const char * name )
{
ContextNode * context = addin_contexts ;
while ( context )
{
if ( strcmp ( name , context - > name ) = = 0 )
return context ;
context = context - > next ;
}
return NULL ;
}
/*
* InitAddinContexts - - Initialise the registered addin shared memory
* contexts .
*/
void
InitAddinContexts ( void * start )
{
PGShmemHeader * next_segment = ( PGShmemHeader * ) start ;
ContextNode * context = addin_contexts ;
while ( context )
{
context - > seg_hdr = next_segment ;
next_segment - > totalsize = context - > size ;
next_segment - > freeoffset = MAXALIGN ( sizeof ( PGShmemHeader ) ) ;
next_segment = ( PGShmemHeader * )
( ( char * ) next_segment + context - > size ) ;
context = context - > next ;
}
}
/*
* ShmemResetContext - - Re - initialise the named addin shared memory context .
*/
void
ShmemResetContext ( const char * name )
{
PGShmemHeader * segment ;
ContextNode * context = ContextFromName ( name ) ;
if ( ! context )
ereport ( ERROR ,
( errcode ( ERRCODE_INTERNAL_ERROR ) ,
errmsg ( " cannot reset unknown shared memory context %s " ,
name ) ) ) ;
segment = context - > seg_hdr ;
segment - > freeoffset = MAXALIGN ( sizeof ( PGShmemHeader ) ) ;
}
/*
* AddinShmemSize - - Report how much shared memory has been registered
* for add - ins .
*/
Size
AddinShmemSize ( void )
{
return addin_contexts_size ;
}
/*
* ShmemAllocFromContext - - allocate max - aligned chunk from shared memory
* ShmemAlloc - - allocate max - aligned chunk from shared memory
*
* Assumes ShmemLock and ShmemSegHdr are initialized .
*
@ -263,30 +149,15 @@ AddinShmemSize(void)
* to be compatible with malloc ( ) .
*/
void *
ShmemAllocFromContext ( Size size , const char * context_nam e )
ShmemAlloc ( Size size )
{
Size newStart ;
Size newFree ;
void * newSpace ;
ContextNode * context ;
/* use volatile pointer to prevent code rearrangement */
volatile PGShmemHeader * shmemseghdr = ShmemSegHdr ;
/*
* if context_name is provided , allocate from the named context
*/
if ( context_name )
{
context = ContextFromName ( context_name ) ;
if ( ! context )
ereport ( ERROR ,
( errcode ( ERRCODE_INTERNAL_ERROR ) ,
errmsg ( " cannot reset unknown shared memory context %s " ,
context_name ) ) ) ;
shmemseghdr = context - > seg_hdr ;
}
/*
* ensure all space is adequately aligned .
*/
@ -305,7 +176,7 @@ ShmemAllocFromContext(Size size, const char *context_name)
newFree = newStart + size ;
if ( newFree < = shmemseghdr - > totalsize )
{
newSpace = ( void * ) MAKE_PTRFROM ( ( SHMEM_OFFSET ) shmemseghdr , newStart ) ;
newSpace = ( void * ) MAKE_PTR ( newStart ) ;
shmemseghdr - > freeoffset = newFree ;
}
else
@ -321,22 +192,6 @@ ShmemAllocFromContext(Size size, const char *context_name)
return newSpace ;
}
/*
* ShmemAlloc - - allocate max - aligned chunk from shared memory
*
* Assumes ShmemLock and ShmemSegHdr are initialized .
*
* Returns : real pointer to memory or NULL if we are out
* of space . Has to return a real pointer in order
* to be compatible with malloc ( ) .
*/
void *
ShmemAlloc ( Size size )
{
return ShmemAllocFromContext ( size , NULL ) ;
}
/*
* ShmemIsValid - - test if an offset refers to valid shared memory
*
Tom Lane
19 years ago