/*-------------------------------------------------------------------------
 *
 * async.c--
 *    Asynchronous notification
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/commands/async.c,v 1.12 1997/01/24 23:48:25 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
/* New Async Notification Model:
 * 1. Multiple backends on same machine.  Multiple backends listening on
 *    one relation.
 *
 * 2. One of the backend does a 'notify <relname>'.  For all backends that
 *    are listening to this relation (all notifications take place at the
 *    end of commit),
 *    2.a  If the process is the same as the backend process that issued
 *         notification (we are notifying something that we are listening),
 *         signal the corresponding frontend over the comm channel using the
 *         out-of-band channel.
 *    2.b  For all other listening processes, we send kill(2) to wake up
 *         the listening backend.
 * 3. Upon receiving a kill(2) signal from another backend process notifying
 *    that one of the relation that we are listening is being notified,
 *    we can be in either of two following states:
 *    3.a  We are sleeping, wake up and signal our frontend.
 *    3.b  We are in middle of another transaction, wait until the end of
 *         of the current transaction and signal our frontend.
 * 4. Each frontend receives this notification and prcesses accordingly.
 *
 * -- jw, 12/28/93
 *
 */
/*
 * The following is the old model which does not work.
 */
/*
 * Model is:
 * 1. Multiple backends on same machine.
 *
 * 2. Query on one backend sends stuff over an asynchronous portal by 
 *    appending to a relation, and then doing an async. notification
 *    (which takes place after commit) to all listeners on this relation.
 *
 * 3. Async. notification results in all backends listening on relation 
 *    to be woken up, by a process signal kill(2), with name of relation
 *    passed in shared memory.
 *
 * 4. Each backend notifies its respective frontend over the comm
 *    channel using the out-of-band channel.
 *
 * 5. Each frontend receives this notification and processes accordingly.
 *
 * #4,#5 are changing soon with pending rewrite of portal/protocol.
 *
 */
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>    /* Needed by in.h on Ultrix */
#include <netinet/in.h>

#include <postgres.h>

#include <utils/syscache.h>
#include <access/relscan.h>
#include <access/xact.h>
#include <lib/dllist.h>
#include <tcop/dest.h>
#include <catalog/pg_proc.h>
#include <catalog/catname.h>
#include <catalog/pg_listener.h>
#include <access/heapam.h> 
#include <storage/bufmgr.h>
#include <nodes/memnodes.h>
#include <utils/mcxt.h>
#include <commands/async.h>
#include <libpq/libpq.h>

#include <port-protos.h>  /* for strdup() */

static int notifyFrontEndPending = 0;
static int notifyIssued = 0;
static Dllist *pendingNotifies = NULL;


static int AsyncExistsPendingNotify(char *);
static void ClearPendingNotify(void);
     
/*
 *--------------------------------------------------------------
 * Async_NotifyHandler --
 *
 *      This is the signal handler for SIGUSR2.  When the backend
 *      is signaled, the backend can be in two states.
 *      1. If the backend is in the middle of another transaction,
 *         we set the flag, notifyFrontEndPending, and wait until
 *         the end of the transaction to notify the front end.
 *      2. If the backend is not in the middle of another transaction,
 *         we notify the front end immediately.
 *
 *      -- jw, 12/28/93
 * Results:
 *      none
 *
 * Side effects:
 *      none
 */
void
Async_NotifyHandler(SIGNAL_ARGS)
{
    extern TransactionState CurrentTransactionState;
    
    if ((CurrentTransactionState->state == TRANS_DEFAULT) &&
	(CurrentTransactionState->blockState == TRANS_DEFAULT)) {

#ifdef ASYNC_DEBUG
	elog(DEBUG, "Waking up sleeping backend process");
#endif
	Async_NotifyFrontEnd();

    }else {
#ifdef ASYNC_DEBUG
	elog(DEBUG, "Process is in the middle of another transaction, state = %d, block state = %d",
	     CurrentTransactionState->state,
	     CurrentTransactionState->blockState);
#endif
	notifyFrontEndPending = 1;
    }
}

/*
 *--------------------------------------------------------------
 * Async_Notify --
 *
 *      Adds the relation to the list of pending notifies.
 *      All notification happens at end of commit.
 *      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 *
 *      All notification of backend processes happens here,
 *      then each backend notifies its corresponding front end at
 *      the end of commit.
 *
 *      This correspond to 'notify <relname>' command
 *      -- jw, 12/28/93
 *
 * Results:
 *      XXX
 *
 * Side effects:
 *      All tuples for relname in pg_listener are updated.
 *
 *--------------------------------------------------------------
 */
void
Async_Notify(char *relname)
{
    
    HeapTuple lTuple, rTuple;
    Relation lRel;
    HeapScanDesc sRel;
    TupleDesc tdesc;
    ScanKeyData key;
    Buffer b;
    Datum d, value[3];
    bool isnull;
    char repl[3], nulls[3];
    
    char *notifyName;
    
#ifdef ASYNC_DEBUG
    elog(DEBUG,"Async_Notify: %s",relname);
#endif
    
    if (!pendingNotifies) 
      pendingNotifies = DLNewList();

    /* 
     * Allocate memory from the global malloc pool because it needs to be
     * referenced also when the transaction is finished.  DZ - 26-08-1996
     */
    notifyName = strdup(relname);
    DLAddHead(pendingNotifies, DLNewElem(notifyName));
    
    ScanKeyEntryInitialize(&key, 0,
			   Anum_pg_listener_relname,
			   NameEqualRegProcedure,
			   PointerGetDatum(notifyName));
    
    lRel = heap_openr(ListenerRelationName);
    tdesc = RelationGetTupleDescriptor(lRel);
    sRel = heap_beginscan(lRel, 0, NowTimeQual, 1, &key);
    
    nulls[0] = nulls[1] = nulls[2] = ' ';
    repl[0] = repl[1] = repl[2] = ' ';
    repl[Anum_pg_listener_notify - 1] = 'r';
    value[0] = value[1] = value[2] = (Datum) 0;
    value[Anum_pg_listener_notify - 1] = Int32GetDatum(1);
    
    while (HeapTupleIsValid(lTuple = heap_getnext(sRel, 0, &b))) {
	d = (Datum) heap_getattr(lTuple, b, Anum_pg_listener_notify,
				 tdesc, &isnull);
	if (!DatumGetInt32(d)) {
	    rTuple = heap_modifytuple(lTuple, b, lRel, value, nulls, repl);
	    (void) heap_replace(lRel, &lTuple->t_ctid, rTuple);
	}
	ReleaseBuffer(b);
    }
    heap_endscan(sRel);
    heap_close(lRel);
    notifyIssued = 1;
}

/*
 *--------------------------------------------------------------
 * Async_NotifyAtCommit --
 *
 *      Signal our corresponding frontend process on relations that
 *      were notified.  Signal all other backend process that
 *      are listening also.
 *
 *      -- jw, 12/28/93
 *
 * Results:
 *      XXX
 *
 * Side effects:
 *      Tuples in pg_listener that has our listenerpid are updated so
 *      that the notification is 0.  We do not want to notify frontend
 *      more than once.
 *
 *      -- jw, 12/28/93
 *
 *--------------------------------------------------------------
 */
void
Async_NotifyAtCommit()
{
    HeapTuple lTuple;
    Relation lRel;
    HeapScanDesc sRel;
    TupleDesc tdesc;
    ScanKeyData key;
    Datum d;
    int ourpid;
    bool isnull;
    Buffer b;
    extern TransactionState CurrentTransactionState;
    
    if (!pendingNotifies)
      pendingNotifies = DLNewList();
    
    if ((CurrentTransactionState->state == TRANS_DEFAULT) &&
	(CurrentTransactionState->blockState == TRANS_DEFAULT)) {
	
	if (notifyIssued) {		/* 'notify <relname>' issued by us */
	    notifyIssued = 0;
	    StartTransactionCommand();
#ifdef ASYNC_DEBUG
	    elog(DEBUG, "Async_NotifyAtCommit.");
#endif
	    ScanKeyEntryInitialize(&key, 0,
				   Anum_pg_listener_notify,
				   Integer32EqualRegProcedure,
				   Int32GetDatum(1));
	    lRel = heap_openr(ListenerRelationName);
	    sRel = heap_beginscan(lRel, 0, NowTimeQual, 1, &key);
	    tdesc = RelationGetTupleDescriptor(lRel);
	    ourpid = getpid();
	    
	    while (HeapTupleIsValid(lTuple = heap_getnext(sRel,0, &b))) {
		d = (Datum) heap_getattr(lTuple, b, Anum_pg_listener_relname,
					 tdesc, &isnull);
		
		if (AsyncExistsPendingNotify((char *) DatumGetPointer(d))) {
		    d = (Datum) heap_getattr(lTuple, b, Anum_pg_listener_pid,
					     tdesc, &isnull);
		    
		    if (ourpid == DatumGetInt32(d)) {
#ifdef ASYNC_DEBUG
			elog(DEBUG, "Notifying self, setting notifyFronEndPending to 1");
#endif
			notifyFrontEndPending = 1;
		    } else {
#ifdef ASYNC_DEBUG
			elog(DEBUG, "Notifying others");
#endif
#ifdef HAVE_KILL
			if (kill(DatumGetInt32(d), SIGUSR2) < 0) {
			    if (errno == ESRCH) {
				heap_delete(lRel, &lTuple->t_ctid);
			    }
			}
#endif 
		    }
		}
		ReleaseBuffer(b);
	    }
	    heap_endscan(sRel);
	    heap_close(lRel);

	    CommitTransactionCommand();
	    ClearPendingNotify();
	}
	
	if (notifyFrontEndPending) {	/* we need to notify the frontend of
					   all pending notifies. */
	    notifyFrontEndPending = 1;
	    Async_NotifyFrontEnd();
	}
    }
}

/*
 *--------------------------------------------------------------
 * Async_NotifyAtAbort --
 *
 *      Gets rid of pending notifies.  List elements are automatically
 *      freed through memory context.
 *      
 *
 * Results:
 *      XXX
 *
 * Side effects:
 *      XXX
 *
 *--------------------------------------------------------------
 */
void
Async_NotifyAtAbort()
{
    extern TransactionState CurrentTransactionState;
    
    if (notifyIssued) {
	ClearPendingNotify();
    }
    notifyIssued = 0;
    if (pendingNotifies)
	DLFreeList(pendingNotifies);
    pendingNotifies = DLNewList();

    if ((CurrentTransactionState->state == TRANS_DEFAULT) &&
	(CurrentTransactionState->blockState == TRANS_DEFAULT)) {
	if (notifyFrontEndPending) { /* don't forget to notify front end */
	    Async_NotifyFrontEnd();
	}
    }
}

/*
 *--------------------------------------------------------------
 * Async_Listen --
 *
 *      Register a backend (identified by its Unix PID) as listening
 *      on the specified relation.  
 *
 *      This corresponds to the 'listen <relation>' command in SQL
 *
 *      One listener per relation, pg_listener relation is keyed
 *      on (relname,pid) to provide multiple listeners in future.
 *
 * Results:
 *      pg_listeners is updated.
 *
 * Side effects:
 *      XXX
 *
 *--------------------------------------------------------------
 */
void
Async_Listen(char *relname, int pid)
{
    Datum values[Natts_pg_listener];
    char nulls[Natts_pg_listener];
    TupleDesc tdesc;
    HeapScanDesc s;
    HeapTuple htup,tup;
    Relation lDesc;
    Buffer b;
    Datum d;
    int i;
    bool isnull;
    int alreadyListener = 0;
    int ourPid = getpid();
    char *relnamei;
    TupleDesc tupDesc;
    
#ifdef ASYNC_DEBUG
    elog(DEBUG,"Async_Listen: %s",relname);
#endif
    for (i = 0 ; i < Natts_pg_listener; i++) {
        nulls[i] = ' ';
        values[i] = PointerGetDatum(NULL);
    }
    
    i = 0;
    values[i++] = (Datum) relname;
    values[i++] = (Datum) pid;
    values[i++] = (Datum) 0;	/* no notifies pending */
    
    lDesc = heap_openr(ListenerRelationName);
    
    /* is someone already listening.  One listener per relation */
    tdesc = RelationGetTupleDescriptor(lDesc);
    s = heap_beginscan(lDesc,0,NowTimeQual,0,(ScanKey)NULL);
    while (HeapTupleIsValid(htup = heap_getnext(s,0,&b))) {
	d = (Datum) heap_getattr(htup,b,Anum_pg_listener_relname,tdesc,
				 &isnull);
	relnamei = DatumGetPointer(d);
	if (!strncmp(relnamei,relname, NAMEDATALEN)) {
	    d = (Datum) heap_getattr(htup,b,Anum_pg_listener_pid,tdesc,&isnull);
	    pid = DatumGetInt32(d);
	    if (pid == ourPid) {
		alreadyListener = 1;
	    }
	}
	ReleaseBuffer(b);
    }
    heap_endscan(s);
    
    if (alreadyListener) {
	elog(NOTICE, "Async_Listen: We are already listening on %s",
	     relname);
	return;
    }
    
    tupDesc = lDesc->rd_att;
    tup = heap_formtuple(tupDesc,
			 values,
			 nulls);
    heap_insert(lDesc, tup);
    
    pfree(tup);
    /*    if (alreadyListener) {
	  elog(NOTICE,"Async_Listen: already one listener on %s (possibly dead)",relname);
	  }*/
    heap_close(lDesc);
    
    /*
     * now that we are listening, we should make a note to ourselves 
     * to unlisten prior to dying.
     */
    relnamei = malloc(NAMEDATALEN); /* persists to process exit */
    memset (relnamei, 0, NAMEDATALEN);
    strncpy(relnamei, relname, NAMEDATALEN);
    on_exitpg(Async_UnlistenOnExit, (caddr_t) relnamei);
}

/*
 *--------------------------------------------------------------
 * Async_Unlisten --
 *
 *      Remove the backend from the list of listening backends
 *      for the specified relation.
 *    
 *      This would correspond to the 'unlisten <relation>' 
 *      command, but there isn't one yet.
 *
 * Results:
 *      pg_listeners is updated.
 *
 * Side effects:
 *      XXX
 *
 *--------------------------------------------------------------
 */
void
Async_Unlisten(char *relname, int pid)
{
    Relation lDesc;
    HeapTuple lTuple;
    
    lTuple = SearchSysCacheTuple(LISTENREL, PointerGetDatum(relname),
				 Int32GetDatum(pid),
				 0,0);
    lDesc = heap_openr(ListenerRelationName);
    if (lTuple != NULL) {
	heap_delete(lDesc,&lTuple->t_ctid);
    }
    heap_close(lDesc);
}

void
Async_UnlistenOnExit(int code,	/* from exitpg */
		     char *relname)
{
    Async_Unlisten((char *) relname, getpid());
}

/*
 * --------------------------------------------------------------
 * Async_NotifyFrontEnd --
 *
 *      Perform an asynchronous notification to front end over
 *      portal comm channel.  The name of the relation which contains the
 *      data is sent to the front end.
 *
 *      We remove the notification flag from the pg_listener tuple
 *      associated with our process.
 *
 * Results:
 *      XXX
 *
 * Side effects:
 *
 *      We make use of the out-of-band channel to transmit the
 *      notification to the front end.  The actual data transfer takes
 *      place at the front end's request.
 *
 * --------------------------------------------------------------
 */
GlobalMemory notifyContext = NULL;

void
Async_NotifyFrontEnd()
{
    extern CommandDest whereToSendOutput;
    HeapTuple lTuple, rTuple;
    Relation lRel;
    HeapScanDesc sRel;
    TupleDesc tdesc;
    ScanKeyData key[2];
    Datum d, value[3];
    char repl[3], nulls[3];
    Buffer b;
    int ourpid;
    bool isnull;
    
    notifyFrontEndPending = 0;
    
#ifdef ASYNC_DEBUG
    elog(DEBUG, "Async_NotifyFrontEnd: notifying front end.");
#endif
    
    StartTransactionCommand();
    ourpid = getpid();
    ScanKeyEntryInitialize(&key[0], 0,
			   Anum_pg_listener_notify,
			   Integer32EqualRegProcedure,
			   Int32GetDatum(1));
    ScanKeyEntryInitialize(&key[1], 0,
			   Anum_pg_listener_pid,
			   Integer32EqualRegProcedure,
			   Int32GetDatum(ourpid));
    lRel = heap_openr(ListenerRelationName);
    tdesc = RelationGetTupleDescriptor(lRel);
    sRel = heap_beginscan(lRel, 0, NowTimeQual, 2, key);
    
    nulls[0] = nulls[1] = nulls[2] = ' ';
    repl[0] = repl[1] = repl[2] = ' ';
    repl[Anum_pg_listener_notify - 1] = 'r';
    value[0] = value[1] = value[2] = (Datum) 0;
    value[Anum_pg_listener_notify - 1] = Int32GetDatum(0);
    
    while (HeapTupleIsValid(lTuple = heap_getnext(sRel, 0,&b))) {
	d = (Datum) heap_getattr(lTuple, b, Anum_pg_listener_relname,
				 tdesc, &isnull);
	rTuple = heap_modifytuple(lTuple, b, lRel, value, nulls, repl);
	(void) heap_replace(lRel, &lTuple->t_ctid, rTuple);
	
	/* notifying the front end */
	
	if (whereToSendOutput == Remote) {
	    pq_putnchar("A", 1);
	    pq_putint(ourpid, 4);
	    pq_putstr(DatumGetName(d)->data);
	    pq_flush();
	} else {
	    elog(NOTICE, "Async_NotifyFrontEnd: no asynchronous notification to frontend on interactive sessions");
	}
	ReleaseBuffer(b);
    }
    CommitTransactionCommand();
}

static int
AsyncExistsPendingNotify(char *relname)
{
    Dlelem* p;
    for (p = DLGetHead(pendingNotifies); 
	 p != NULL;
	 p = DLGetSucc(p)) {
      /* Use NAMEDATALEN for relname comparison.    DZ - 26-08-1996 */
      if (!strncmp(DLE_VAL(p), relname, NAMEDATALEN))
	return 1;
    }

    return 0;
}

static void
ClearPendingNotify()
{
    Dlelem* p;
    while ( (p = DLRemHead(pendingNotifies)) != NULL)
	free(DLE_VAL(p));
}

