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Vadim B. Mikheev authoredVadim B. Mikheev authored
async.c 25.46 KiB
/*-------------------------------------------------------------------------
*
* async.c--
* Asynchronous notification: NOTIFY, LISTEN, UNLISTEN
*
* Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/commands/async.c,v 1.42 1998/11/27 19:51:53 vadim Exp $
*
*-------------------------------------------------------------------------
*/
/*-------------------------------------------------------------------------
* New Async Notification Model:
* 1. Multiple backends on same machine. Multiple backends listening on
* one relation. (Note: "listening on a relation" is not really the
* right way to think about it, since the notify names need not have
* anything to do with the names of relations actually in the database.
* But this terminology is all over the code and docs, and I don't feel
* like trying to replace it.)
*
* 2. There is a tuple in relation "pg_listener" for each active LISTEN,
* ie, each relname/listenerPID pair. The "notification" field of the
* tuple is zero when no NOTIFY is pending for that listener, or the PID
* of the originating backend when a cross-backend NOTIFY is pending.
* (We skip writing to pg_listener when doing a self-NOTIFY, so the
* notification field should never be equal to the listenerPID field.)
*
* 3. The NOTIFY statement itself (routine Async_Notify) just adds the target
* relname to a list of outstanding NOTIFY requests. Actual processing
* happens if and only if we reach transaction commit. At that time (in
* routine AtCommit_Notify) we scan pg_listener for matching relnames.
* If the listenerPID in a matching tuple is ours, we just send a notify
* message to our own front end. If it is not ours, and "notification"
* is not already nonzero, we set notification to our own PID and send a
* SIGUSR2 signal to the receiving process (indicated by listenerPID).
* BTW: if the signal operation fails, we presume that the listener backend
* crashed without removing this tuple, and remove the tuple for it.
*
* 4. Upon receipt of a SIGUSR2 signal, the signal handler can call inbound-
* notify processing immediately if this backend is idle (ie, it is
* waiting for a frontend command and is not within a transaction block).
* Otherwise the handler may only set a flag, which will cause the
* processing to occur just before we next go idle.
*
* 5. Inbound-notify processing consists of scanning pg_listener for tuples
* matching our own listenerPID and having nonzero notification fields.
* For each such tuple, we send a message to our frontend and clear the
* notification field. BTW: this routine has to start/commit its own
* transaction, since by assumption it is only called from outside any
* transaction.
*
* Note that the system's use of pg_listener is confined to very short
* intervals at the end of a transaction that contains NOTIFY statements,
* or during the transaction caused by an inbound SIGUSR2. So the fact that
* pg_listener is a global resource shouldn't cause too much performance
* problem. But application authors ought to be discouraged from doing
* LISTEN or UNLISTEN near the start of a long transaction --- that would
* result in holding the pg_listener write lock for a long time, possibly
* blocking unrelated activity. It could even lead to deadlock against another
* transaction that touches the same user tables and then tries to NOTIFY.
* Probably best to do LISTEN or UNLISTEN outside of transaction blocks.
*
* An application that listens on the same relname it notifies will get
* NOTIFY messages for its own NOTIFYs. These can be ignored, if not useful,
* by comparing be_pid in the NOTIFY message to the application's own backend's
* PID. (As of FE/BE protocol 2.0, the backend's PID is provided to the
* frontend during startup.) The above design guarantees that notifies from
* other backends will never be missed by ignoring self-notifies. Note, * however, that we do *not* guarantee that a separate frontend message will
* be sent for every outside NOTIFY. Since there is only room for one
* originating PID in pg_listener, outside notifies occurring at about the
* same time may be collapsed into a single message bearing the PID of the
* first outside backend to perform the NOTIFY.
*-------------------------------------------------------------------------
*/
#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 "commands/async.h"
#include "access/heapam.h"
#include "access/relscan.h"
#include "access/xact.h"
#include "catalog/catname.h"
#include "catalog/pg_listener.h"
#include "fmgr.h"
#include "lib/dllist.h"
#include "libpq/libpq.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "tcop/dest.h"
#include "utils/syscache.h"
#include <utils/trace.h>
#include <utils/ps_status.h>
/* stuff that we really ought not be touching directly :-( */
extern TransactionState CurrentTransactionState;
extern CommandDest whereToSendOutput;
/*
* State for outbound notifies consists of a list of all relnames NOTIFYed
* in the current transaction. We do not actually perform a NOTIFY until
* and unless the transaction commits. pendingNotifies is NULL if no
* NOTIFYs have been done in the current transaction.
*/
static Dllist *pendingNotifies = NULL;
/*
* State for inbound notifies consists of two flags: one saying whether
* the signal handler is currently allowed to call ProcessIncomingNotify
* directly, and one saying whether the signal has occurred but the handler
* was not allowed to call ProcessIncomingNotify at the time.
*
* NB: the "volatile" on these declarations is critical! If your compiler
* does not grok "volatile", you'd be best advised to compile this file
* with all optimization turned off.
*/
static volatile int notifyInterruptEnabled = 0;
static volatile int notifyInterruptOccurred = 0;
/* True if we've registered an on_shmem_exit cleanup (or at least tried to). */
static int unlistenExitRegistered = 0;
static void Async_UnlistenAll(void);
static void Async_UnlistenOnExit(void);
static void ProcessIncomingNotify(void);
static void NotifyMyFrontEnd(char *relname, int32 listenerPID);
static int AsyncExistsPendingNotify(char *relname);
static void ClearPendingNotifies(void);
/*
*--------------------------------------------------------------
* Async_Notify --
*
* This is executed by the SQL notify command.
*
* Adds the relation to the list of pending notifies.
* Actual notification happens during transaction commit.
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
*
* Results:
* XXX
*
*--------------------------------------------------------------
*/
void
Async_Notify(char *relname)
{
char *notifyName;
TPRINTF(TRACE_NOTIFY, "Async_Notify: %s", relname);
/*
* We allocate list memory from the global malloc pool to ensure that
* it will live until we want to use it. This is probably not necessary
* any longer, since we will use it before the end of the transaction.
* DLList only knows how to use malloc() anyway, but we could probably
* palloc() the strings...
*/
if (!pendingNotifies)
pendingNotifies = DLNewList();
notifyName = strdup(relname);
DLAddHead(pendingNotifies, DLNewElem(notifyName));
/*
* NOTE: we could check to see if pendingNotifies already has an entry
* for relname, and thus avoid making duplicate entries. However, most
* apps probably don't notify the same name multiple times per transaction,
* so we'd likely just be wasting cycles to make such a check.
* AsyncExistsPendingNotify() doesn't really care whether the list
* contains duplicates...
*/
}
/*
*--------------------------------------------------------------
* Async_Listen --
*
* This is executed by the SQL listen command.
*
* Register a backend (identified by its Unix PID) as listening
* on the specified relation.
*
* Results:
* XXX
*
* Side effects:
* pg_listener is updated.
*
*--------------------------------------------------------------
*/
void
Async_Listen(char *relname, int pid)
{
Relation lRel;
TupleDesc tdesc;
HeapScanDesc scan;
HeapTuple tuple,
newtup;
Datum values[Natts_pg_listener]; char nulls[Natts_pg_listener];
Datum d;
int i;
bool isnull;
int alreadyListener = 0;
TupleDesc tupDesc;
TPRINTF(TRACE_NOTIFY, "Async_Listen: %s", relname);
lRel = heap_openr(ListenerRelationName);
RelationSetLockForWrite(lRel);
tdesc = RelationGetDescr(lRel);
/* Detect whether we are already listening on this relname */
scan = heap_beginscan(lRel, 0, SnapshotNow, 0, (ScanKey) NULL);
while (HeapTupleIsValid(tuple = heap_getnext(scan, 0)))
{
d = heap_getattr(tuple, Anum_pg_listener_relname, tdesc, &isnull);
if (!strncmp((char *) DatumGetPointer(d), relname, NAMEDATALEN))
{
d = heap_getattr(tuple, Anum_pg_listener_pid, tdesc, &isnull);
if (DatumGetInt32(d) == pid)
{
alreadyListener = 1;
/* No need to scan the rest of the table */
break;
}
}
}
heap_endscan(scan);
if (alreadyListener)
{
elog(NOTICE, "Async_Listen: We are already listening on %s", relname);
RelationUnsetLockForWrite(lRel);
heap_close(lRel);
return;
}
/*
* OK to insert a new tuple
*/
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 */
tupDesc = lRel->rd_att;
newtup = heap_formtuple(tupDesc, values, nulls);
heap_insert(lRel, newtup);
pfree(newtup);
RelationUnsetLockForWrite(lRel);
heap_close(lRel);
/*
* now that we are listening, make sure we will unlisten before dying.
*/
if (! unlistenExitRegistered)
{
if (on_shmem_exit(Async_UnlistenOnExit, (caddr_t) NULL) < 0)
elog(NOTICE, "Async_Listen: out of shmem_exit slots");
unlistenExitRegistered = 1; }
}
/*
*--------------------------------------------------------------
* Async_Unlisten --
*
* This is executed by the SQL unlisten command.
*
* Remove the backend from the list of listening backends
* for the specified relation.
*
* Results:
* XXX
*
* Side effects:
* pg_listener is updated.
*
*--------------------------------------------------------------
*/
void
Async_Unlisten(char *relname, int pid)
{
Relation lRel;
HeapTuple lTuple;
/* Handle specially the `unlisten "*"' command */
if ((!relname) || (*relname == '\0') || (strcmp(relname, "*") == 0))
{
Async_UnlistenAll();
return;
}
TPRINTF(TRACE_NOTIFY, "Async_Unlisten %s", relname);
/* Note we assume there can be only one matching tuple. */
lTuple = SearchSysCacheTuple(LISTENREL, PointerGetDatum(relname),
Int32GetDatum(pid),
0, 0);
if (lTuple != NULL)
{
lRel = heap_openr(ListenerRelationName);
RelationSetLockForWrite(lRel);
heap_delete(lRel, &lTuple->t_self);
RelationUnsetLockForWrite(lRel);
heap_close(lRel);
}
/* We do not complain about unlistening something not being listened;
* should we?
*/
}
/*
*--------------------------------------------------------------
* Async_UnlistenAll --
*
* Unlisten all relations for this backend.
*
* This is invoked by UNLISTEN "*" command, and also at backend exit.
*
* Results:
* XXX
*
* Side effects:
* pg_listener is updated.
*
*--------------------------------------------------------------
*/
static void
Async_UnlistenAll(){
Relation lRel;
TupleDesc tdesc;
HeapScanDesc sRel;
HeapTuple lTuple;
ScanKeyData key[1];
TPRINTF(TRACE_NOTIFY, "Async_UnlistenAll");
lRel = heap_openr(ListenerRelationName);
RelationSetLockForWrite(lRel);
tdesc = RelationGetDescr(lRel);
/* Find and delete all entries with my listenerPID */
ScanKeyEntryInitialize(&key[0], 0,
Anum_pg_listener_pid,
F_INT4EQ,
Int32GetDatum(MyProcPid));
sRel = heap_beginscan(lRel, 0, SnapshotNow, 1, key);
while (HeapTupleIsValid(lTuple = heap_getnext(sRel, 0)))
heap_delete(lRel, &lTuple->t_self);
heap_endscan(sRel);
RelationUnsetLockForWrite(lRel);
heap_close(lRel);
}
/*
*--------------------------------------------------------------
* Async_UnlistenOnExit --
*
* Clean up the pg_listener table at backend exit.
*
* This is executed if we have done any LISTENs in this backend.
* It might not be necessary anymore, if the user UNLISTENed everything,
* but we don't try to detect that case.
*
* Results:
* XXX
*
* Side effects:
* pg_listener is updated if necessary.
*
*--------------------------------------------------------------
*/
static void
Async_UnlistenOnExit()
{
/*
* We need to start/commit a transaction for the unlisten,
* but if there is already an active transaction we had better
* abort that one first. Otherwise we'd end up committing changes
* that probably ought to be discarded.
*/
AbortOutOfAnyTransaction();
/* Now we can do the unlisten */
StartTransactionCommand();
Async_UnlistenAll();
CommitTransactionCommand();
}
/*
*--------------------------------------------------------------
* AtCommit_Notify --
*
* This is called at transaction commit.
*
* If there are outbound notify requests in the pendingNotifies list,
* scan pg_listener for matching tuples, and either signal the other * backend or send a message to our own frontend.
*
* NOTE: we are still inside the current transaction, therefore can
* piggyback on its committing of changes.
*
* Results:
* XXX
*
* Side effects:
* Tuples in pg_listener that have matching relnames and other peoples'
* listenerPIDs are updated with a nonzero notification field.
*
*--------------------------------------------------------------
*/
void
AtCommit_Notify()
{
Relation lRel;
TupleDesc tdesc;
HeapScanDesc sRel;
HeapTuple lTuple,
rTuple;
Datum d,
value[Natts_pg_listener];
char repl[Natts_pg_listener],
nulls[Natts_pg_listener];
bool isnull;
char *relname;
int32 listenerPID;
if (!pendingNotifies)
return; /* no NOTIFY statements in this transaction */
/* NOTIFY is disabled if not normal processing mode.
* This test used to be in xact.c, but it seems cleaner to do it here.
*/
if (! IsNormalProcessingMode())
{
ClearPendingNotifies();
return;
}
TPRINTF(TRACE_NOTIFY, "AtCommit_Notify");
lRel = heap_openr(ListenerRelationName);
RelationSetLockForWrite(lRel);
tdesc = RelationGetDescr(lRel);
sRel = heap_beginscan(lRel, 0, SnapshotNow, 0, (ScanKey) NULL);
/* preset data to update notify column to MyProcPid */
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(MyProcPid);
while (HeapTupleIsValid(lTuple = heap_getnext(sRel, 0)))
{
d = heap_getattr(lTuple, Anum_pg_listener_relname, tdesc, &isnull);
relname = (char *) DatumGetPointer(d);
if (AsyncExistsPendingNotify(relname))
{
d = heap_getattr(lTuple, Anum_pg_listener_pid, tdesc, &isnull);
listenerPID = DatumGetInt32(d);
if (listenerPID == MyProcPid)
{
/* Self-notify: no need to bother with table update.
* Indeed, we *must not* clear the notification field in * this path, or we could lose an outside notify, which'd be
* bad for applications that ignore self-notify messages.
*/
TPRINTF(TRACE_NOTIFY, "AtCommit_Notify: notifying self");
NotifyMyFrontEnd(relname, listenerPID);
}
else
{
TPRINTF(TRACE_NOTIFY, "AtCommit_Notify: notifying pid %d",
listenerPID);
/*
* If someone has already notified this listener,
* we don't bother modifying the table, but we do still send
* a SIGUSR2 signal, just in case that backend missed the
* earlier signal for some reason. It's OK to send the signal
* first, because the other guy can't read pg_listener until
* we unlock it.
*/
#ifdef HAVE_KILL
if (kill(listenerPID, SIGUSR2) < 0)
{
/* Get rid of pg_listener entry if it refers to a PID
* that no longer exists. Presumably, that backend
* crashed without deleting its pg_listener entries.
* This code used to only delete the entry if errno==ESRCH,
* but as far as I can see we should just do it for any
* failure (certainly at least for EPERM too...)
*/
heap_delete(lRel, &lTuple->t_self);
}
else
#endif
{
d = heap_getattr(lTuple, Anum_pg_listener_notify,
tdesc, &isnull);
if (DatumGetInt32(d) == 0)
{
rTuple = heap_modifytuple(lTuple, lRel,
value, nulls, repl);
heap_replace(lRel, &lTuple->t_self, rTuple);
}
}
}
}
}
heap_endscan(sRel);
/*
* We do not do RelationUnsetLockForWrite(lRel) here, because the
* transaction is about to be committed anyway.
*/
heap_close(lRel);
ClearPendingNotifies();
TPRINTF(TRACE_NOTIFY, "AtCommit_Notify: done");
}
/*
*--------------------------------------------------------------
* AtAbort_Notify --
*
* This is called at transaction abort.
*
* Gets rid of pending outbound notifies that we would have executed
* if the transaction got committed.
*
* Results:
* XXX
* *--------------------------------------------------------------
*/
void
AtAbort_Notify()
{
ClearPendingNotifies();
}
/*
*--------------------------------------------------------------
* Async_NotifyHandler --
*
* This is the signal handler for SIGUSR2.
*
* If we are idle (notifyInterruptEnabled is set), we can safely invoke
* ProcessIncomingNotify directly. Otherwise, just set a flag
* to do it later.
*
* Results:
* none
*
* Side effects:
* per above
*--------------------------------------------------------------
*/
void
Async_NotifyHandler(SIGNAL_ARGS)
{
/*
* Note: this is a SIGNAL HANDLER. You must be very wary what you do here.
* Some helpful soul had this routine sprinkled with TPRINTFs, which would
* likely lead to corruption of stdio buffers if they were ever turned on.
*/
if (notifyInterruptEnabled)
{
/* I'm not sure whether some flavors of Unix might allow another
* SIGUSR2 occurrence to recursively interrupt this routine.
* To cope with the possibility, we do the same sort of dance that
* EnableNotifyInterrupt must do --- see that routine for comments.
*/
notifyInterruptEnabled = 0; /* disable any recursive signal */
notifyInterruptOccurred = 1; /* do at least one iteration */
for (;;)
{
notifyInterruptEnabled = 1;
if (! notifyInterruptOccurred)
break;
notifyInterruptEnabled = 0;
if (notifyInterruptOccurred)
{
/* Here, it is finally safe to do stuff. */
TPRINTF(TRACE_NOTIFY,
"Async_NotifyHandler: perform async notify");
ProcessIncomingNotify();
TPRINTF(TRACE_NOTIFY, "Async_NotifyHandler: done");
}
}
}
else
{
/* In this path it is NOT SAFE to do much of anything, except this: */
notifyInterruptOccurred = 1;
}
}
/*
* --------------------------------------------------------------
* EnableNotifyInterrupt -- *
* This is called by the PostgresMain main loop just before waiting
* for a frontend command. If we are truly idle (ie, *not* inside
* a transaction block), then process any pending inbound notifies,
* and enable the signal handler to process future notifies directly.
*
* NOTE: the signal handler starts out disabled, and stays so until
* PostgresMain calls this the first time.
* --------------------------------------------------------------
*/
void
EnableNotifyInterrupt(void)
{
if (CurrentTransactionState->blockState != TRANS_DEFAULT)
return; /* not really idle */
/*
* This code is tricky because we are communicating with a signal
* handler that could interrupt us at any point. If we just checked
* notifyInterruptOccurred and then set notifyInterruptEnabled, we
* could fail to respond promptly to a signal that happens in between
* those two steps. (A very small time window, perhaps, but Murphy's
* Law says you can hit it...) Instead, we first set the enable flag,
* then test the occurred flag. If we see an unserviced interrupt
* has occurred, we re-clear the enable flag before going off to do
* the service work. (That prevents re-entrant invocation of
* ProcessIncomingNotify() if another interrupt occurs.)
* If an interrupt comes in between the setting and clearing of
* notifyInterruptEnabled, then it will have done the service
* work and left notifyInterruptOccurred zero, so we have to check
* again after clearing enable. The whole thing has to be in a loop
* in case another interrupt occurs while we're servicing the first.
* Once we get out of the loop, enable is set and we know there is no
* unserviced interrupt.
*
* NB: an overenthusiastic optimizing compiler could easily break this
* code. Hopefully, they all understand what "volatile" means these days.
*/
for (;;)
{
notifyInterruptEnabled = 1;
if (! notifyInterruptOccurred)
break;
notifyInterruptEnabled = 0;
if (notifyInterruptOccurred)
{
TPRINTF(TRACE_NOTIFY,
"EnableNotifyInterrupt: perform async notify");
ProcessIncomingNotify();
TPRINTF(TRACE_NOTIFY, "EnableNotifyInterrupt: done");
}
}
}
/*
* --------------------------------------------------------------
* DisableNotifyInterrupt --
*
* This is called by the PostgresMain main loop just after receiving
* a frontend command. Signal handler execution of inbound notifies
* is disabled until the next EnableNotifyInterrupt call.
* --------------------------------------------------------------
*/
void
DisableNotifyInterrupt(void)
{
notifyInterruptEnabled = 0;
}
/*
* --------------------------------------------------------------
* ProcessIncomingNotify --
*
* Deal with arriving NOTIFYs from other backends.
* This is called either directly from the SIGUSR2 signal handler,
* or the next time control reaches the outer idle loop.
* Scan pg_listener for arriving notifies, report them to my front end,
* and clear the notification field in pg_listener until next time.
*
* NOTE: since we are outside any transaction, we must create our own.
*
* Results:
* XXX
*
* --------------------------------------------------------------
*/
static void
ProcessIncomingNotify(void)
{
Relation lRel;
TupleDesc tdesc;
ScanKeyData key[1];
HeapScanDesc sRel;
HeapTuple lTuple,
rTuple;
Datum d,
value[Natts_pg_listener];
char repl[Natts_pg_listener],
nulls[Natts_pg_listener];
bool isnull;
char *relname;
int32 sourcePID;
TPRINTF(TRACE_NOTIFY, "ProcessIncomingNotify");
PS_SET_STATUS("async_notify");
notifyInterruptOccurred = 0;
StartTransactionCommand();
lRel = heap_openr(ListenerRelationName);
RelationSetLockForWrite(lRel);
tdesc = RelationGetDescr(lRel);
/* Scan only entries with my listenerPID */
ScanKeyEntryInitialize(&key[0], 0,
Anum_pg_listener_pid,
F_INT4EQ,
Int32GetDatum(MyProcPid));
sRel = heap_beginscan(lRel, 0, SnapshotNow, 1, key);
/* Prepare data for rewriting 0 into notification field */
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)))
{
d = heap_getattr(lTuple, Anum_pg_listener_notify, tdesc, &isnull);
sourcePID = DatumGetInt32(d);
if (sourcePID != 0)
{
d = heap_getattr(lTuple, Anum_pg_listener_relname, tdesc, &isnull);
relname = (char *) DatumGetPointer(d);
/* Notify the frontend */
TPRINTF(TRACE_NOTIFY, "ProcessIncomingNotify: received %s from %d", relname, (int) sourcePID);
NotifyMyFrontEnd(relname, sourcePID);
/* Rewrite the tuple with 0 in notification column */
rTuple = heap_modifytuple(lTuple, lRel, value, nulls, repl);
heap_replace(lRel, &lTuple->t_self, rTuple);
}
}
heap_endscan(sRel);
/*
* We do not do RelationUnsetLockForWrite(lRel) here, because the
* transaction is about to be committed anyway.
*/
heap_close(lRel);
CommitTransactionCommand();
/* Must flush the notify messages to ensure frontend gets them promptly. */
pq_flush();
PS_SET_STATUS("idle");
TPRINTF(TRACE_NOTIFY, "ProcessIncomingNotify: done");
}
/* Send NOTIFY message to my front end. */
static void
NotifyMyFrontEnd(char *relname, int32 listenerPID)
{
if (whereToSendOutput == Remote)
{
pq_putnchar("A", 1);
pq_putint(listenerPID, sizeof(int32));
pq_putstr(relname);
/* NOTE: we do not do pq_flush() here. For a self-notify, it will
* happen at the end of the transaction, and for incoming notifies
* ProcessIncomingNotify will do it after finding all the notifies.
*/
}
else
{
elog(NOTICE, "NOTIFY for %s", relname);
}
}
/* Does pendingNotifies include the given relname?
*
* NB: not called unless pendingNotifies != NULL.
*/
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((const char *) DLE_VAL(p), relname, NAMEDATALEN))
return 1;
}
return 0;
}
/* Clear the pendingNotifies list. */
static void
ClearPendingNotifies(){
Dlelem *p;
if (pendingNotifies)
{
/* Since the referenced strings are malloc'd, we have to scan the
* list and delete them individually. If we used palloc for the
* strings then we could just do DLFreeList to get rid of both
* the list nodes and the list base...
*/
while ((p = DLRemHead(pendingNotifies)) != NULL)
{
free(DLE_VAL(p));
DLFreeElem(p);
}
DLFreeList(pendingNotifies);
pendingNotifies = NULL;
}
}