@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $ Header : / cvsroot / pgsql / src / backend / storage / lmgr / proc . c , v 1.48 1999 / 02 / 13 23 : 18 : 28 momjian Exp $
* $ Header : / cvsroot / pgsql / src / backend / storage / lmgr / proc . c , v 1.49 1999 / 02 / 19 06 : 06 : 08 tgl Exp $
*
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
@ -46,7 +46,7 @@
* This is so that we can support more backends . ( system - wide semaphore
* sets run out pretty fast . ) - ay 4 / 95
*
* $ Header : / cvsroot / pgsql / src / backend / storage / lmgr / proc . c , v 1.48 1999 / 02 / 13 23 : 18 : 28 momjian Exp $
* $ Header : / cvsroot / pgsql / src / backend / storage / lmgr / proc . c , v 1.49 1999 / 02 / 19 06 : 06 : 08 tgl Exp $
*/
# include <sys/time.h>
# include <unistd.h>
@ -108,13 +108,24 @@ static void ProcFreeSem(IpcSemaphoreKey semKey, int semNum);
/*
* InitProcGlobal -
* initializes the global process table . We put it here so that
* the postmaster can do this initialization . ( ProcFreeAllSem needs
* the postmaster can do this initialization . ( ProcFreeAllSemaphores needs
* to read this table on exiting the postmaster . If we have the first
* backend do this , starting up and killing the postmaster without
* starting any backends will be a problem . )
*
* We also allocate all the per - process semaphores we will need to support
* the requested number of backends . We used to allocate semaphores
* only when backends were actually started up , but that is bad because
* it lets Postgres fail under load - - - a lot of Unix systems are
* ( mis ) configured with small limits on the number of semaphores , and
* running out when trying to start another backend is a common failure .
* So , now we grab enough semaphores to support the desired max number
* of backends immediately at initialization - - - if the sysadmin has set
* MaxBackends higher than his kernel will support , he ' ll find out sooner
* rather than later .
*/
void
InitProcGlobal ( IPCKey key )
InitProcGlobal ( IPCKey key , int maxBackends )
{
bool found = false ;
@ -134,6 +145,24 @@ InitProcGlobal(IPCKey key)
ProcGlobal - > currKey = IPCGetProcessSemaphoreInitKey ( key ) ;
for ( i = 0 ; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET ; i + + )
ProcGlobal - > freeSemMap [ i ] = 0 ;
/* Pre-create the semaphores for the first maxBackends processes */
for ( i = 0 ;
i < ( maxBackends + PROC_NSEMS_PER_SET - 1 ) / PROC_NSEMS_PER_SET ;
i + + )
{
IPCKey semKey = ProcGlobal - > currKey + i ;
int semId ;
int semstat ;
semId = IpcSemaphoreCreate ( semKey ,
PROC_NSEMS_PER_SET ,
IPCProtection ,
IpcSemaphoreDefaultStartValue ,
0 ,
& semstat ) ;
/* mark this sema set allocated */
ProcGlobal - > freeSemMap [ i ] = ( 1 < < PROC_NSEMS_PER_SET ) ;
}
}
}
@ -222,6 +251,11 @@ InitProcess(IPCKey key)
ProcGetNewSemKeyAndNum ( & semKey , & semNum ) ;
/* Note: because of the pre-allocation done in InitProcGlobal,
* this call should always attach to an existing semaphore .
* It will ( try to ) create a new group of semaphores only if
* the postmaster tries to start more backends than it said it would .
*/
semId = IpcSemaphoreCreate ( semKey ,
PROC_NSEMS_PER_SET ,
IPCProtection ,
@ -823,20 +857,20 @@ ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
{
int i ;
int32 * freeSemMap = ProcGlobal - > freeSemMap ;
unsigned int fullmask ;
int32 fullmask = ( 1 < < ( PROC_NSEMS_PER_SET + 1 ) ) - 1 ;
/*
* we hold ProcStructLock when entering this routine . We scan through
* the bitmap to look for a free semaphore .
*/
fullmask = ~ 0 > > ( 32 - PROC_NSEMS_PER_SET ) ;
for ( i = 0 ; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET ; i + + )
{
int mask = 1 ;
int j ;
if ( freeSemMap [ i ] = = fullmask )
continue ; /* none free for this set */
continue ; /* this set is fully allocated */
for ( j = 0 ; j < PROC_NSEMS_PER_SET ; j + + )
{
@ -845,8 +879,9 @@ ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
/*
* a free semaphore found . Mark it as allocated .
* Also set the bit indicating whole set is allocated .
*/
freeSemMap [ i ] | = mask ;
freeSemMap [ i ] | = mask + ( 1 < < PROC_NSEMS_PER_SET ) ;
* key = ProcGlobal - > currKey + i ;
* semNum = j ;
@ -862,8 +897,7 @@ ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
/*
* ProcFreeSem -
* free up our semaphore in the semaphore set . If we ' re the last one
* in the set , also remove the semaphore set .
* free up our semaphore in the semaphore set .
*/
static void
ProcFreeSem ( IpcSemaphoreKey semKey , int semNum )
@ -876,14 +910,19 @@ ProcFreeSem(IpcSemaphoreKey semKey, int semNum)
mask = ~ ( 1 < < semNum ) ;
freeSemMap [ i ] & = mask ;
if ( freeSemMap [ i ] = = 0 )
IpcSemaphoreKill ( semKey ) ;
/* Formerly we'd release a semaphore set if it was now completely unused,
* but now we keep the semaphores to ensure we won ' t run out when
* starting new backends - - - cf . InitProcGlobal . Note that the
* PROC_NSEMS_PER_SET + 1 ' st bit of the freeSemMap entry remains set to
* indicate it is still allocated ; ProcFreeAllSemaphores ( ) needs that .
*/
}
/*
* ProcFreeAllSemaphores -
* on exiting the postmaster , we free up all the semaphores allocated
* to the lmgrs of the backends .
* called at shmem_exit time , ie when exiting the postmaster or
* destroying shared state for a failed set of backends .
* Free up all the semaphores allocated to the lmgrs of the backends .
*/
void
ProcFreeAllSemaphores ( )
Tom Lane
27 years ago