ipc.c

/*-------------------------------------------------------------------------
 *
 * ipc.c--
 *    POSTGRES inter-process communication definitions.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipc.c,v 1.10 1997/01/08 08:32:01 bryanh Exp $
 *
 * NOTES
 *
 *    Currently, semaphores are used (my understanding anyway) in two
 *    different ways:
 *      1. as mutexes on machines that don't have test-and-set (eg.
 *         mips R3000).
 *      2. for putting processes to sleep when waiting on a lock 
 *         and waking them up when the lock is free.
 *    The number of semaphores in (1) is fixed and those are shared
 *    among all backends. In (2), there is 1 semaphore per process and those
 *    are not shared with anyone else.
 *                                                        -ay 4/95
 *
 *-------------------------------------------------------------------------
 */
#include <sys/types.h>
#include <sys/file.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>


#include "postgres.h"
#include "storage/ipc.h"
/* In Ultrix, sem.h and shm.h must be included AFTER ipc.h */
#include <sys/sem.h>
#include <sys/shm.h>
#include "utils/memutils.h"

#if defined(sparc_solaris)
#include <string.h>
#include <sys/ipc.h>
#endif

#if defined(bsd44)
int UsePrivateMemory = 1;
#else
int UsePrivateMemory = 0;
#endif

/* ----------------------------------------------------------------
 *			exit() handling stuff
 * ----------------------------------------------------------------
 */

#define MAX_ON_EXITS 20

static struct ONEXIT {
    void (*function)();
    caddr_t arg;
} onexit_list[ MAX_ON_EXITS ];

static int onexit_index;
static void IpcConfigTip(void);

typedef struct _PrivateMemStruct {
    int id;
    char *memptr;
} PrivateMem;

PrivateMem IpcPrivateMem[16];

static int
PrivateMemoryCreate(IpcMemoryKey memKey,
		    uint32 size)
{
    static int memid = 0;
    
    UsePrivateMemory = 1;
    
    IpcPrivateMem[memid].id = memid;
    IpcPrivateMem[memid].memptr = malloc(size);
    if (IpcPrivateMem[memid].memptr == NULL)
	elog(WARN, "PrivateMemoryCreate: not enough memory to malloc");
    memset(IpcPrivateMem[memid].memptr, 0, size);	/* XXX PURIFY */
    
    return (memid++);
}

static char *
PrivateMemoryAttach(IpcMemoryId memid)
{
    return ( IpcPrivateMem[memid].memptr );
}


/* ----------------------------------------------------------------
 *	exitpg
 *
 *	this function calls all the callbacks registered
 *	for it (to free resources) and then calls exit.
 *	This should be the only function to call exit().
 *	-cim 2/6/90
 * ----------------------------------------------------------------
 */
static int exitpg_inprogress = 0;

void
exitpg(int code)
{
    int i;
    
    /* ----------------
     *	if exitpg_inprocess is true, then it means that we
     *  are being invoked from within an on_exit() handler
     *  and so we return immediately to avoid recursion.
     * ----------------
     */
    if (exitpg_inprogress)
	return;
    
    exitpg_inprogress = 1;
    
    /* ----------------
     *	call all the callbacks registered before calling exit().
     * ----------------
     */
    for (i = onexit_index - 1; i >= 0; --i)
	(*onexit_list[i].function)(code, onexit_list[i].arg);
    
    exit(code);
}

/* ------------------
 * Run all of the on_exitpg routines but don't exit in the end.
 * This is used by the postmaster to re-initialize shared memory and
 * semaphores after a backend dies horribly
 * ------------------
 */
void
quasi_exitpg()
{
    int i;
    
    /* ----------------
     *	if exitpg_inprocess is true, then it means that we
     *  are being invoked from within an on_exit() handler
     *  and so we return immediately to avoid recursion.
     * ----------------
     */
    if (exitpg_inprogress)
	return;
    
    exitpg_inprogress = 1;
    
    /* ----------------
     *	call all the callbacks registered before calling exit().
     * ----------------
     */
    for (i = onexit_index - 1; i >= 0; --i)
	(*onexit_list[i].function)(0, onexit_list[i].arg);
    
    onexit_index = 0;
    exitpg_inprogress = 0;
}

/* ----------------------------------------------------------------
 *	on_exitpg
 *
 *	this function adds a callback function to the list of
 *	functions invoked by exitpg().	-cim 2/6/90
 * ----------------------------------------------------------------
 */
int
on_exitpg(void (*function)(), caddr_t arg)
{
    if (onexit_index >= MAX_ON_EXITS)
	return(-1);
    
    onexit_list[ onexit_index ].function = function;
    onexit_list[ onexit_index ].arg = arg;
    
    ++onexit_index;
    
    return(0);
}

/****************************************************************************/
/*   IPCPrivateSemaphoreKill(status, semId)				    */
/*									    */
/****************************************************************************/
static void
IPCPrivateSemaphoreKill(int status,
			int semId) /* caddr_t */
{
    union semun	semun;
    semctl(semId, 0, IPC_RMID, semun);
}


/****************************************************************************/
/*   IPCPrivateMemoryKill(status, shmId)				    */
/*									    */
/****************************************************************************/
static void
IPCPrivateMemoryKill(int status,
		     int shmId)	/* caddr_t */
{
    if ( UsePrivateMemory ) {
	/* free ( IpcPrivateMem[shmId].memptr ); */
    } else {
	if (shmctl(shmId, IPC_RMID, (struct shmid_ds *) NULL) < 0) {
	    elog(NOTICE, "IPCPrivateMemoryKill: shmctl(%d, %d, 0) failed: %m",
		 shmId, IPC_RMID);
	}
    } 
}


/****************************************************************************/
/*   IpcSemaphoreCreate(semKey, semNum, permission, semStartValue)          */
/*    									    */
/*    - returns a semaphore identifier:					    */
/*    									    */
/* if key doesn't exist: return a new id,      status:= IpcSemIdNotExist    */
/* if key exists:        return the old id,    status:= IpcSemIdExist	    */
/* if semNum > MAX :     return # of argument, status:=IpcInvalidArgument   */
/*									    */
/****************************************************************************/

/*
 * Note:
 * XXX	This should be split into two different calls.  One should
 * XXX	be used to create a semaphore set.  The other to "attach" a
 * XXX	existing set.  It should be an error for the semaphore set
 * XXX	to to already exist or for it not to, respectively.
 *
 *	Currently, the semaphore sets are "attached" and an error
 *	is detected only when a later shared memory attach fails.
 */

IpcSemaphoreId
IpcSemaphoreCreate(IpcSemaphoreKey semKey,
		   int semNum,
		   int permission,
		   int semStartValue,
		   int removeOnExit,
		   int *status)
{
    int		i;
    int		errStatus;
    int		semId;
    u_short	array[IPC_NMAXSEM];
    union semun	semun;

    /* get a semaphore if non-existent */
    /* check arguments	*/
    if (semNum > IPC_NMAXSEM || semNum <= 0)  {
	*status = IpcInvalidArgument;
	return(2);	/* returns the number of the invalid argument	*/
    }
    
    semId = semget(semKey, 0, 0);

    if (semId == -1) {
	*status = IpcSemIdNotExist;	/* there doesn't exist a semaphore */
#ifdef DEBUG_IPC
	fprintf(stderr,"calling semget with %d, %d , %d\n",
		semKey,
		semNum,
		IPC_CREAT|permission );
#endif
	semId = semget(semKey, semNum, IPC_CREAT|permission);

	if (semId < 0) {
	    perror("semget");
	    IpcConfigTip();
	    exitpg(3);
	}
	for (i = 0; i < semNum; i++) {
	    array[i] = semStartValue;
	}
	semun.array = array;
	errStatus = semctl(semId, 0, SETALL, semun);
	if (errStatus == -1) {
	    perror("semctl");
	    IpcConfigTip();
	}
	
	if (removeOnExit)
	    on_exitpg(IPCPrivateSemaphoreKill, (caddr_t)semId);
	
    } else {
	/* there is a semaphore id for this key */
	*status = IpcSemIdExist;
    }
    
#ifdef DEBUG_IPC
    fprintf(stderr,"\nIpcSemaphoreCreate, status %d, returns %d\n",
	    *status,
	    semId );
    fflush(stdout);
    fflush(stderr);
#endif
    return(semId);
}


/****************************************************************************/
/*   IpcSemaphoreSet()		- sets the initial value of the semaphore   */
/*									    */
/*	note: the xxx_return variables are only used for debugging.	    */
/****************************************************************************/
static int IpcSemaphoreSet_return;

void
IpcSemaphoreSet(int semId, int semno, int value)
{
    int		errStatus;
    union semun	semun;
    
    semun.val = value;
    errStatus = semctl(semId, semno, SETVAL, semun);
    IpcSemaphoreSet_return = errStatus;
    
    if (errStatus == -1)
    {
	perror("semctl");
	IpcConfigTip();
    }
}

/****************************************************************************/
/*   IpcSemaphoreKill(key)	- removes a semaphore			    */
/*									    */
/****************************************************************************/
void
IpcSemaphoreKill(IpcSemaphoreKey key)
{
    int 	semId;
    union semun	semun;
    
    /* kill semaphore if existent */
    
    semId = semget(key, 0, 0);
    if (semId != -1)
	semctl(semId, 0, IPC_RMID, semun);
}

/****************************************************************************/
/*   IpcSemaphoreLock(semId, sem, lock)	- locks a semaphore		    */
/*									    */
/*	note: the xxx_return variables are only used for debugging.	    */
/****************************************************************************/
static int IpcSemaphoreLock_return;

void
IpcSemaphoreLock(IpcSemaphoreId semId, int sem, int lock)
{
    extern int		errno;
    int			errStatus;
    struct sembuf	sops;
    
    sops.sem_op = lock;
    sops.sem_flg = 0;
    sops.sem_num = sem;
    
    /* ----------------
     *	Note: if errStatus is -1 and errno == EINTR then it means we
     *        returned from the operation prematurely because we were
     *	      sent a signal.  So we try and lock the semaphore again.
     *	      I am not certain this is correct, but the semantics aren't
     *	      clear it fixes problems with parallel abort synchronization,
     *	      namely that after processing an abort signal, the semaphore
     *	      call returns with -1 (and errno == EINTR) before it should.
     *	      -cim 3/28/90
     * ----------------
     */
    do {
	errStatus = semop(semId, &sops, 1);
    } while (errStatus == -1 && errno == EINTR);
    
    IpcSemaphoreLock_return = errStatus;
    
    if (errStatus == -1) {
	perror("semop");
	IpcConfigTip();
	exitpg(255);
    }
}

/****************************************************************************/
/*   IpcSemaphoreUnlock(semId, sem, lock)	- unlocks a semaphore	    */
/*									    */
/*	note: the xxx_return variables are only used for debugging.	    */
/****************************************************************************/
static int IpcSemaphoreUnlock_return;

void
IpcSemaphoreUnlock(IpcSemaphoreId semId, int sem, int lock)
{
    extern int		errno;
    int			errStatus;
    struct sembuf	sops;
    
    sops.sem_op = -lock;
    sops.sem_flg = 0;
    sops.sem_num = sem;
    
    
    /* ----------------
     *	Note: if errStatus is -1 and errno == EINTR then it means we
     *        returned from the operation prematurely because we were
     *	      sent a signal.  So we try and lock the semaphore again.
     *	      I am not certain this is correct, but the semantics aren't
     *	      clear it fixes problems with parallel abort synchronization,
     *	      namely that after processing an abort signal, the semaphore
     *	      call returns with -1 (and errno == EINTR) before it should.
     *	      -cim 3/28/90
     * ----------------
     */
    do {
	errStatus = semop(semId, &sops, 1);
    } while (errStatus == -1 && errno == EINTR);
    
    IpcSemaphoreUnlock_return = errStatus;
    
    if (errStatus == -1) {
	perror("semop");
	IpcConfigTip();
	exitpg(255);
    }
}

int
IpcSemaphoreGetCount(IpcSemaphoreId	semId, int sem)
{
    int semncnt;
    union semun dummy; /* for Solaris */
    
    semncnt = semctl(semId, sem, GETNCNT, dummy);
    return semncnt;
}

int
IpcSemaphoreGetValue(IpcSemaphoreId	semId, int sem)
{
    int semval;
    union semun dummy; /* for Solaris */
    
    semval = semctl(semId, sem, GETVAL, dummy);
    return semval;
}

/****************************************************************************/
/*   IpcMemoryCreate(memKey)						    */
/*									    */
/*    - returns the memory identifier, if creation succeeds		    */
/*	returns IpcMemCreationFailed, if failure			    */
/****************************************************************************/

IpcMemoryId
IpcMemoryCreate(IpcMemoryKey memKey, uint32 size, int permission)
{
    IpcMemoryId	 shmid;
    
    if (memKey == PrivateIPCKey) {
	/* private */
	shmid = PrivateMemoryCreate(memKey, size);
    }else {
    	shmid = shmget(memKey, size, IPC_CREAT|permission); 
    }

    if (shmid < 0) {
	fprintf(stderr,"IpcMemoryCreate: memKey=%d , size=%d , permission=%d", 
		memKey, size , permission );
	perror("IpcMemoryCreate: shmget(..., create, ...) failed");
	IpcConfigTip();
	return(IpcMemCreationFailed);
    }
    
    /* if (memKey == PrivateIPCKey) */
    on_exitpg(IPCPrivateMemoryKill, (caddr_t)shmid);
    
    return(shmid);
}

/****************************************************************************/
/*  IpcMemoryIdGet(memKey, size)    returns the shared memory Id 	    */
/*				    or IpcMemIdGetFailed	            */
/****************************************************************************/
IpcMemoryId
IpcMemoryIdGet(IpcMemoryKey memKey, uint32 size)
{
    IpcMemoryId	shmid;
    
    shmid = shmget(memKey, size, 0);
    
    if (shmid < 0) {
	fprintf(stderr,"IpcMemoryIdGet: memKey=%d , size=%d , permission=%d", 
		memKey, size , 0 );
	perror("IpcMemoryIdGet:  shmget() failed");
	IpcConfigTip();
	return(IpcMemIdGetFailed);
    }
    
    return(shmid);
}

/****************************************************************************/
/*  IpcMemoryDetach(status, shmaddr)	removes a shared memory segment	    */
/*					from a backend address space	    */
/*  (only called by backends running under the postmaster)		    */
/****************************************************************************/
void
IpcMemoryDetach(int status, char *shmaddr)
{
    if (shmdt(shmaddr) < 0) {
	elog(NOTICE, "IpcMemoryDetach: shmdt(0x%x): %m", shmaddr);
    }
}

/****************************************************************************/
/*  IpcMemoryAttach(memId)    returns the adress of shared memory	    */
/*			      or IpcMemAttachFailed			    */
/*							                    */
/* CALL IT:  addr = (struct <MemoryStructure> *) IpcMemoryAttach(memId);    */
/*									    */
/****************************************************************************/
char *
IpcMemoryAttach(IpcMemoryId memId)
{
    char	*memAddress;
    
    if (UsePrivateMemory) {
	memAddress = (char *) PrivateMemoryAttach(memId);
    } else {
	memAddress = (char *) shmat(memId, 0, 0);
    }
    
    /*	if ( *memAddress == -1) { XXX ??? */
    if ( memAddress == (char *)-1) {
	perror("IpcMemoryAttach: shmat() failed");
	IpcConfigTip();
	return(IpcMemAttachFailed);
    }
    
    if (!UsePrivateMemory)
	on_exitpg(IpcMemoryDetach, (caddr_t) memAddress);
    
    return((char *) memAddress);
}


/****************************************************************************/
/*  IpcMemoryKill(memKey)    		removes a shared memory segment     */
/*  (only called by the postmaster and standalone backends)		    */
/****************************************************************************/
void
IpcMemoryKill(IpcMemoryKey memKey)
{	
    IpcMemoryId		shmid;
    
    if (!UsePrivateMemory && (shmid = shmget(memKey, 0, 0)) >= 0) {
	if (shmctl(shmid, IPC_RMID, (struct shmid_ds *) NULL) < 0) {
	    elog(NOTICE, "IpcMemoryKill: shmctl(%d, %d, 0) failed: %m",
		 shmid, IPC_RMID);
	}
    }
} 

#ifdef HAS_TEST_AND_SET
/* ------------------
 *  use hardware locks to replace semaphores for sequent machines
 *  to avoid costs of swapping processes and to provide unlimited
 *  supply of locks.
 * ------------------
 */
static SLock *SLockArray = NULL;
static SLock **FreeSLockPP;
static int *UnusedSLockIP;
static slock_t *SLockMemoryLock;
static IpcMemoryId SLockMemoryId = -1;

struct ipcdummy {		/* to get alignment/size right */
    SLock	*free;
    int		unused;
    slock_t	memlock;
    SLock	slocks[NSLOCKS];
};
static int SLockMemorySize = sizeof(struct ipcdummy);

void
CreateAndInitSLockMemory(IPCKey key)
{
    int id;
    SLock *slckP;
    
    SLockMemoryId = IpcMemoryCreate(key,
				    SLockMemorySize,
				    0700);
    AttachSLockMemory(key);
    *FreeSLockPP = NULL;
    *UnusedSLockIP = (int)FIRSTFREELOCKID;
    for (id=0; id<(int)FIRSTFREELOCKID; id++) {
	slckP = &(SLockArray[id]);
	S_INIT_LOCK(&(slckP->locklock));
	slckP->flag = NOLOCK;
	slckP->nshlocks = 0;
	S_INIT_LOCK(&(slckP->shlock));
	S_INIT_LOCK(&(slckP->exlock));
	S_INIT_LOCK(&(slckP->comlock));
	slckP->next = NULL;
    }
    return;
}

void
AttachSLockMemory(IPCKey key)
{
    struct ipcdummy *slockM;
    
    if (SLockMemoryId == -1)
	SLockMemoryId = IpcMemoryIdGet(key,SLockMemorySize);
    if (SLockMemoryId == -1)
	elog(FATAL, "SLockMemory not in shared memory");
    slockM = (struct ipcdummy *) IpcMemoryAttach(SLockMemoryId);
    if (slockM == IpcMemAttachFailed)
	elog(FATAL, "AttachSLockMemory: could not attach segment");
    FreeSLockPP = (SLock **) &(slockM->free);
    UnusedSLockIP = (int *) &(slockM->unused);
    SLockMemoryLock = (slock_t *) &(slockM->memlock);
    S_INIT_LOCK(SLockMemoryLock);
    SLockArray = (SLock *) &(slockM->slocks[0]);
    return;
}


#ifdef LOCKDEBUG
#define PRINT_LOCK(LOCK) printf("(locklock = %d, flag = %d, nshlocks = %d, \
shlock = %d, exlock =%d)\n", LOCK->locklock, \
				LOCK->flag, LOCK->nshlocks, LOCK->shlock, \
				LOCK->exlock)
#endif

void
ExclusiveLock(int lockid)
{
    SLock *slckP;
    slckP = &(SLockArray[lockid]);
#ifdef LOCKDEBUG
    printf("ExclusiveLock(%d)\n", lockid);
    printf("IN: ");
    PRINT_LOCK(slckP);
#endif
 ex_try_again:
    S_LOCK(&(slckP->locklock));
    switch (slckP->flag) {
    case NOLOCK:
	slckP->flag = EXCLUSIVELOCK;
	S_LOCK(&(slckP->exlock));
	S_LOCK(&(slckP->shlock));
	S_UNLOCK(&(slckP->locklock));
#ifdef LOCKDEBUG
	printf("OUT: ");
	PRINT_LOCK(slckP);
#endif
	return;
    case SHAREDLOCK:
    case EXCLUSIVELOCK:
	S_UNLOCK(&(slckP->locklock));
	S_LOCK(&(slckP->exlock));
	S_UNLOCK(&(slckP->exlock));
	goto ex_try_again;
    }
}

void
ExclusiveUnlock(int lockid)
{
    SLock *slckP;
    
    slckP = &(SLockArray[lockid]);
#ifdef LOCKDEBUG
    printf("ExclusiveUnlock(%d)\n", lockid);
    printf("IN: ");
    PRINT_LOCK(slckP);
#endif
    S_LOCK(&(slckP->locklock));
    /* -------------
     *  give favor to read processes
     * -------------
     */
    slckP->flag = NOLOCK;
    if (slckP->nshlocks > 0) {
	while (slckP->nshlocks > 0) {
	    S_UNLOCK(&(slckP->shlock));
	    S_LOCK(&(slckP->comlock));
	}
	S_UNLOCK(&(slckP->shlock));
    }
    else {
	S_UNLOCK(&(slckP->shlock));
    }
    S_UNLOCK(&(slckP->exlock));
    S_UNLOCK(&(slckP->locklock));
#ifdef LOCKDEBUG
    printf("OUT: ");
    PRINT_LOCK(slckP);
#endif
    return;
}

bool
LockIsFree(int lockid)
{
    return(SLockArray[lockid].flag == NOLOCK);
}

#endif /* HAS_TEST_AND_SET */

static void
IpcConfigTip(void)
{
	fprintf(stderr,"This type of error is usually caused by improper\n");
	fprintf(stderr,"shared memory or System V IPC semaphore configuration.\n");
	fprintf(stderr,"See the FAQ for more detailed information\n");
}