alert.c

#include "postgres.h"
#include "executor/spi.h"

#if PG_VERSION_NUM >= 90300
#include "access/htup_details.h"
#endif
#include "catalog/pg_type.h"
#include "commands/trigger.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "string.h"
#include "storage/lwlock.h"
#include "utils/timestamp.h"

#include "orafce.h"
#include "builtins.h"
#include "pipe.h"
#include "shmmc.h"
#include "utils/rel.h"

PG_FUNCTION_INFO_V1(dbms_alert_register);
PG_FUNCTION_INFO_V1(dbms_alert_remove);
PG_FUNCTION_INFO_V1(dbms_alert_removeall);
PG_FUNCTION_INFO_V1(dbms_alert_set_defaults);
PG_FUNCTION_INFO_V1(dbms_alert_signal);
PG_FUNCTION_INFO_V1(dbms_alert_waitany);
PG_FUNCTION_INFO_V1(dbms_alert_waitone);
PG_FUNCTION_INFO_V1(dbms_alert_defered_signal);

extern unsigned int sid;
float8 sensitivity = 250.0;
extern LWLockId shmem_lock;

#ifndef _GetCurrentTimestamp
#define _GetCurrentTimestamp()		GetCurrentTimestamp()
#endif

#ifndef GetNowFloat
#ifdef HAVE_INT64_TIMESTAMP
#define GetNowFloat()   ((float8) _GetCurrentTimestamp() / 1000000.0)
#else
#define GetNowFloat()   _GetCurrentTimestamp()
#endif
#endif

#define TDAYS (1000*24*3600)


/*
 * There are maximum 30 events and 255 collaborating sessions
 *
 */

alert_event *events;
alert_lock  *locks;

alert_lock *session_lock = NULL;

#define NOT_FOUND  -1
#define NOT_USED -1

/*
 * Compare text and cstr
 */

static int
textcmpm(text *txt, char *str)
{
	int retval;
	char *p;
	int len;

	len = VARSIZE(txt) - VARHDRSZ;
	p = VARDATA(txt);

	while (len-- && *p != '\0')
	{

		if (0 != (retval = *p++ - *str++))
			return retval;
	}

	if (len > 0)
		return 1;

	if (*str != '\0')
		return -1;

	return 0;
}


/*
 * find or create event rec
 *
 */

static alert_lock*
find_lock(int sid, bool create)
{
	int i;
	int first_free = NOT_FOUND;

	if (session_lock != NULL)
		return session_lock;

	for (i = 0; i < MAX_LOCKS; i++)
	{
		if (locks[i].sid == sid)
			return &locks[i];
		else if (locks[i].sid == NOT_USED && first_free == NOT_FOUND)
			first_free = i;
	}

	if (create)
	{
		if (first_free != NOT_FOUND)
		{
			locks[first_free].sid = sid;
			locks[first_free].echo = NULL;
			session_lock = &locks[first_free];
			return &locks[first_free];
		}
		else
			ereport(ERROR,
    				(errcode(ERRCODE_ORA_PACKAGES_LOCK_REQUEST_ERROR),
        			 errmsg("lock request error"),
					 errdetail("Failed to create session lock."),
        			 errhint("There are too many collaborating sessions. Increase MAX_LOCKS in 'pipe.h'.")));
	}

	return NULL;
}


static alert_event*
find_event(text *event_name, bool create, int *event_id)
{
	int i;

	for (i = 0; i < MAX_EVENTS;i++)
	{
		if (events[i].event_name != NULL && textcmpm(event_name,events[i].event_name) == 0)
		{
			if (event_id != NULL)
				*event_id = i;
			return &events[i];
		}
	}

	if (create)
	{
		for (i=0; i < MAX_EVENTS; i++)
		{
			if (events[i].event_name == NULL)
			{
				events[i].event_name = ora_scstring(event_name);

				events[i].max_receivers = 0;
				events[i].receivers = NULL;
				events[i].messages = NULL;
				events[i].receivers_number = 0;

				if (event_id != NULL)
					*event_id = i;
				return &events[i];
			}
		}

		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("event registeration error"),
				 errdetail("Too many registered events."),
				 errhint("There are too many collaborating sessions. Increase MAX_EVENTS in 'pipe.h'.")));
	}

	return NULL;
}


static void
register_event(text *event_name)
{
	alert_event *ev;
	int *new_receivers;
	int first_free;
	int i;

	find_lock(sid, true);
	ev = find_event(event_name, true, NULL);

	first_free = NOT_FOUND;
	for (i = 0; i < ev->max_receivers; i++)
	{
		if (ev->receivers[i] == sid)
			return;   /* event is registered */
		if (ev->receivers[i] == NOT_USED && first_free == NOT_FOUND)
			first_free = i;
	}

	/*
	 * I can have a maximum of MAX_LOCKS receivers for one event.
	 * Array receivers is increased for 16 fields
	 */
	if (first_free == NOT_FOUND)
	{
		if (ev->max_receivers + 16 > MAX_LOCKS)
			ereport(ERROR,
    				(errcode(ERRCODE_ORA_PACKAGES_LOCK_REQUEST_ERROR),
        			 errmsg("lock request error"),
					 errdetail("Failed to create session lock."),
        			 errhint("There are too many collaborating sessions. Increase MAX_LOCKS in 'pipe.h'.")));

		/* increase receiver's array */

		new_receivers = (int*)salloc((ev->max_receivers + 16)*sizeof(int));

		for (i = 0; i < ev->max_receivers + 16; i++)
		{
			if (i < ev->max_receivers)
				new_receivers[i] = ev->receivers[i];
			else
				new_receivers[i] = NOT_USED;
		}

		ev->max_receivers += 16;
		if (ev->receivers)
			ora_sfree(ev->receivers);

		ev->receivers = new_receivers;

		first_free = ev->max_receivers - 16;
	}

	ev->receivers_number += 1;
	ev->receivers[first_free] = sid;
}

/*
 * Remove receiver from default receivers of message,
 * I expect clean all message_items
 */

static void
unregister_event(int event_id, int sid)
{
	alert_event *ev;
	int i;

	ev = &events[event_id];
	if (ev->receivers_number > 0)
	{
		for (i = 0; i < ev->max_receivers; i++)
		{
			if (ev->receivers[i] == sid)
			{
				ev->receivers[i] = NOT_USED;
				ev->receivers_number -= 1;
				break;
			}
		}
		if (ev->receivers_number == 0)
		{
			ora_sfree(ev->receivers);
			ora_sfree(ev->event_name);
			ev->receivers = NULL;
			ev->event_name = NULL;
		}
	}
}


/*
 * remove receiver from list of receivers.
 * Message has always minimal one receiver
 * Return true, if exist other receiver
 */

static bool
remove_receiver(message_item *msg, int sid)
{
	int i;
	bool find_other = false;
	bool found = false;

	for (i = 0; i < msg->receivers_number; i++)
	{
		if (msg->receivers[i] == sid)
		{
			msg->receivers[i] = NOT_USED;
			found = true;
		}
		else if (msg->receivers[i] != NOT_USED)
		{
			find_other = true;
		}
		if (found && find_other)
			break;
	}

	return find_other;
}

/*
 *
 * Reads message message_id for user sid. If arg:all is true,
 * then get any message. If arg:remove_all then remove all
 * signaled messages for sid. If arg:filter_message then
 * skip other messages than message_id, else read and remove
 * all others messages than message_id.
 *
 */


static char*
find_and_remove_message_item(int message_id, int sid,
							 bool all, bool remove_all,
							 bool filter_message,
							 int *sleep, char **event_name)
{
	alert_lock *alck;
	int _message_id;

	char *result = NULL;
	if (sleep != NULL)
		*sleep = 0;

	alck = find_lock(sid, false);

	if (event_name)
		*event_name = NULL;

	if (alck != NULL && alck->echo != NULL)
	{
		/* if I have registered and created item */
		struct _message_echo *echo, *last_echo;

		echo = alck->echo;
		last_echo = NULL;

		while (echo != NULL)
		{
			char *message_text;
			bool destroy_msg_item = false;

			if (filter_message && echo->message_id != message_id)
			{
				last_echo = echo;
				echo = echo->next_echo;
				continue;
			}

			message_text = echo->message->message;
			_message_id = echo->message_id;

			if (!remove_receiver(echo->message, sid))
			{
				destroy_msg_item = true;
				if (echo->message->prev_message != NULL)
					echo->message->prev_message->next_message =
						echo->message->next_message;
				else
					events[echo->message_id].messages =
						echo->message->next_message;
				if (echo->message->next_message != NULL)
					echo->message->next_message->prev_message =
						echo->message->prev_message;
				ora_sfree(echo->message->receivers);
				ora_sfree(echo->message);
			}
			if (last_echo == NULL)
			{
				alck->echo = echo->next_echo;
				ora_sfree(echo);
				echo = alck->echo;
			}
			else
			{
				last_echo->next_echo = echo->next_echo;
				ora_sfree(echo);
				echo = last_echo;
			}
			if (remove_all)
			{
				if (message_text != NULL && destroy_msg_item)
					ora_sfree(message_text);

				continue;
			}
			else if (_message_id == message_id || all)
			{
				/* I have to do local copy */
				if (message_text)
				{
					result = pstrdup(message_text);
					if (destroy_msg_item)
						ora_sfree(message_text);
				}

				if (event_name != NULL)
					*event_name = pstrdup(events[_message_id].event_name);

				break;
			}
		}
	}

	return result;
}

/*
 * Queue mustn't to contain duplicate messages
 */

static void
create_message(text *event_name, text *message)
{
	int event_id;
	alert_event *ev;
	message_item *msg_item = NULL;
	int i,j,k;

	find_event(event_name, false, &event_id);

	/* process event only when any recipient exitsts */
	if (NULL != (ev = find_event(event_name, false, &event_id)))
	{
		if (ev->receivers_number > 0)
		{
			msg_item = ev->messages;
			while (msg_item != NULL)
			{
				if (msg_item->message == NULL && message == NULL)
				    return;
				if (msg_item->message != NULL && message != NULL)
					if (0 == textcmpm(message,msg_item->message))
						return;

				msg_item = msg_item->next_message;
			}

			msg_item = salloc(sizeof(message_item));

			msg_item->receivers = salloc( ev->receivers_number*sizeof(int));
			msg_item->receivers_number = ev->receivers_number;


			if (message != NULL)
				msg_item->message = ora_scstring(message);
			else
				msg_item->message = NULL;

			msg_item->message_id = event_id;
			for (i = j = 0; j < ev->max_receivers; j++)
			{
				if (ev->receivers[j] != NOT_USED)
				{
					msg_item->receivers[i++] = ev->receivers[j];
					for (k = 0; k < MAX_LOCKS; k++)
						if (locks[k].sid == ev->receivers[j])
						{
							/* create echo */

							message_echo *echo = salloc(sizeof(message_echo));
							echo->message = msg_item;
							echo->message_id = event_id;
							echo->next_echo = NULL;

							if (locks[k].echo == NULL)
								locks[k].echo = echo;
							else
							{
								message_echo *p;
								p = locks[k].echo;

								while (p->next_echo != NULL)
									p = p->next_echo;

								p->next_echo = echo;
							}
						}

				}
			}

			msg_item->next_message = NULL;
			if (ev->messages == NULL)
			{
				msg_item->prev_message = NULL;
				ev->messages = msg_item;
			}
			else
			{
				message_item *p;
				p = ev->messages;
				while (p->next_message != NULL)
					p = p->next_message;

				p->next_message = msg_item;
				msg_item->prev_message = p;
			}

		}
	}
}


#define WATCH_PRE(t, et, c) \
et = GetNowFloat() + (float8)t; c = 0; \
do \
{ \

#define WATCH_POST(t,et,c) \
if (GetNowFloat() >= et) \
break; \
if (cycle++ % 100 == 0) \
CHECK_FOR_INTERRUPTS(); \
pg_usleep(10000L); \
} while(t != 0);


/*
 *
 *  PROCEDURE DBMS_ALERT.REGISTER (name IN VARCHAR2);
 *
 *  Registers the calling session to receive notification of alert name.
 *
 */

Datum
dbms_alert_register(PG_FUNCTION_ARGS)
{
	text *name = PG_GETARG_TEXT_P(0);
	int cycle = 0;
	float8 endtime;
	float8 timeout = 2;

	WATCH_PRE(timeout, endtime, cycle);
	if (ora_lock_shmem(SHMEMMSGSZ, MAX_PIPES, MAX_EVENTS, MAX_LOCKS, false))
	{
		register_event(name);
		LWLockRelease(shmem_lock);
		PG_RETURN_VOID();
	}
	WATCH_POST(timeout, endtime, cycle);
	LOCK_ERROR();
	PG_RETURN_VOID();
}


/*
 *
 *  PROCEDURE DBMS_ALERT.REMOVE(name IN VARCHAR2);
 *
 *  Unregisters the calling session from receiving notification of alert name.
 *  Don't raise any exceptions.
 *
 */

Datum
dbms_alert_remove(PG_FUNCTION_ARGS)
{
	text *name = PG_GETARG_TEXT_P(0);

	alert_event *ev;
	int ev_id;
	int cycle = 0;
	float8 endtime;
	float8 timeout = 2;

	WATCH_PRE(timeout, endtime, cycle);
	if (ora_lock_shmem(SHMEMMSGSZ, MAX_PIPES,MAX_EVENTS,MAX_LOCKS,false))
	{
		ev = find_event(name, false, &ev_id);
		if (NULL != ev)
		{
			find_and_remove_message_item(ev_id, sid,
							 false, true, true, NULL, NULL);
			unregister_event(ev_id, sid);
		}
		LWLockRelease(shmem_lock);
		PG_RETURN_VOID();
	}
	WATCH_POST(timeout, endtime, cycle);
	LOCK_ERROR();
	PG_RETURN_VOID();
}


/*
 *
 *  PROCEDURE DBMS_ALERT.REMOVEALL;
 *
 *  Unregisters the calling session from notification of all alerts.
 *
 */

Datum
dbms_alert_removeall(PG_FUNCTION_ARGS)
{
	int i;
	int cycle = 0;
	float8 endtime;
	float8 timeout = 2;

	WATCH_PRE(timeout, endtime, cycle);
	if (ora_lock_shmem(SHMEMMSGSZ, MAX_PIPES,MAX_EVENTS,MAX_LOCKS,false))
	{
		for (i = 0; i < MAX_EVENTS; i++)
			if (events[i].event_name != NULL)
			{
				find_and_remove_message_item(i, sid,
								 false, true, true, NULL, NULL);
				unregister_event(i, sid);

			}
		LWLockRelease(shmem_lock);
		PG_RETURN_VOID();
	}
	WATCH_POST(timeout, endtime, cycle);
	LOCK_ERROR();
	PG_RETURN_VOID();
}



/*
 *
 *  PROCEDURE DBMS_ALERT.WAITANY(name OUT VARCHAR2 ,message OUT VARCHAR2
 *                              ,status OUT INTEGER
 *                              ,timeout IN NUMBER DEFAULT MAXWAIT);
 *
 *  Waits for up to timeout seconds to be notified of any alerts for which
 *  the session is registered. If status = 0 then name and message contain
 *  alert information. If status = 1 then timeout seconds elapsed without
 *  notification of any alert.
 *
 */

Datum
dbms_alert_waitany(PG_FUNCTION_ARGS)
{
	float8 timeout;
	TupleDesc   tupdesc;
	AttInMetadata       *attinmeta;
	HeapTuple   tuple;
	Datum       result;
	char *str[3] = {NULL, NULL, "1"};
	int cycle = 0;
	float8 endtime;
	TupleDesc	btupdesc;

	if (PG_ARGISNULL(0))
		timeout = TDAYS;
	else
		timeout = PG_GETARG_FLOAT8(0);

	WATCH_PRE(timeout, endtime, cycle);
	if (ora_lock_shmem(SHMEMMSGSZ, MAX_PIPES, MAX_EVENTS, MAX_LOCKS, false))
	{
		str[1]  = find_and_remove_message_item(-1, sid,
							   true, false, false, NULL, &str[0]);
		if (str[0])
		{
			str[2] = "0";
			LWLockRelease(shmem_lock);
			break;
		}
		LWLockRelease(shmem_lock);
	}
	WATCH_POST(timeout, endtime, cycle);

	get_call_result_type(fcinfo, NULL, &tupdesc);
	btupdesc = BlessTupleDesc(tupdesc);
	attinmeta = TupleDescGetAttInMetadata(btupdesc);
	tuple = BuildTupleFromCStrings(attinmeta, str);
	result = HeapTupleGetDatum(tuple);

	if (str[0])
		pfree(str[0]);

	if (str[1])
		pfree(str[1]);

	return result;
}


/*
 *
 *  PROCEDURE DBMS_ALERT.WAITONE(name IN VARCHAR2, message OUT VARCHAR2
 *                              ,status OUT INTEGER
 *                              ,timeout IN NUMBER DEFAULT MAXWAIT);
 *
 *  Waits for up to timeout seconds for notification of alert name. If status = 0
 *  then message contains alert information. If status = 1 then timeout
 *  seconds elapsed without notification.
 *
 */

Datum
dbms_alert_waitone(PG_FUNCTION_ARGS)
{
	text *name;
	float8 timeout;
	TupleDesc   tupdesc;
	AttInMetadata       *attinmeta;
	HeapTuple   tuple;
	Datum       result;
	int message_id;
	char *str[2] = {NULL,"1"};
	char *event_name;
	int cycle = 0;
	float8 endtime;
	TupleDesc	btupdesc;

	if (PG_ARGISNULL(0))
		ereport(ERROR,
				(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
				 errmsg("event name is NULL"),
				 errdetail("Eventname may not be NULL.")));

	if (PG_ARGISNULL(1))
		timeout = TDAYS;
	else
		timeout = PG_GETARG_FLOAT8(1);

	name = PG_GETARG_TEXT_P(0);

	WATCH_PRE(timeout, endtime, cycle);
	if (ora_lock_shmem(SHMEMMSGSZ, MAX_PIPES, MAX_EVENTS, MAX_LOCKS, false))
	{
		if (NULL != find_event(name, false, &message_id))
		{
			str[0] = find_and_remove_message_item(message_id, sid,
								  false, false, false, NULL, &event_name);
			if (event_name != NULL)
			{
				str[1] = "0";
				pfree(event_name);
				LWLockRelease(shmem_lock);
				break;
			}
		}
		LWLockRelease(shmem_lock);
	}
	WATCH_POST(timeout, endtime, cycle);

	get_call_result_type(fcinfo, NULL, &tupdesc);
	btupdesc = BlessTupleDesc(tupdesc);
	attinmeta = TupleDescGetAttInMetadata(btupdesc);
	tuple = BuildTupleFromCStrings(attinmeta, str);
	result = HeapTupleGetDatum(tuple);

	if (str[0])
		pfree(str[0]);

	return result;
}


/*
 *
 *  PROCEDURE DBMS_ALERT.SET_DEFAULTS(sensitivity IN NUMBER);
 *
 *  The SET_DEFAULTS procedure is used to set session configurable settings
 *  used by the DBMS_ALERT package. Currently, the polling loop interval sleep time
 *  is the only session setting that can be modified using this procedure. The
 *  header for this procedure is,
 *
 */

Datum
dbms_alert_set_defaults(PG_FUNCTION_ARGS)
{
	ereport(ERROR,
		(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
		 errmsg("feature not supported"),
		 errdetail("Sensitivity isn't supported.")));

	PG_RETURN_VOID();
}



/*
 * This code was originally in plpgsql
 *
 */

/*
CREATE OR REPLACE FUNCTION dbms_alert._defered_signal() RETURNS trigger AS $$
BEGIN
  PERFORM dbms_alert._signal(NEW.event, NEW.message);
  DELETE FROM ora_alerts WHERE oid=NEW.oid;
  RETURN NEW;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER VOLATILE;
*/

#define DatumGetItemPointer(X)   ((ItemPointer) DatumGetPointer(X))
#define ItemPointerGetDatum(X)   PointerGetDatum(X)

Datum
dbms_alert_defered_signal(PG_FUNCTION_ARGS)
{
	TriggerData *trigdata = (TriggerData *) fcinfo->context;
	TupleDesc tupdesc;
	HeapTuple rettuple;
	char *relname;
	text *name;
	text *message;
	int event_col;
	int message_col;

	Datum datum;
	bool isnull;
	int cycle = 0;
	float8 endtime;
	float8 timeout = 2;

	if (!CALLED_AS_TRIGGER(fcinfo))
		ereport(ERROR,
			(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
			 errmsg("not called by trigger manager")));

	if (!TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
		ereport(ERROR,
			(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
			 errmsg("not called on valid event")));

	if (SPI_connect() < 0)
		ereport(ERROR,
			(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
			 errmsg("SPI_connect failed")));

	if (strcmp((relname = SPI_getrelname(trigdata->tg_relation)), "ora_alerts") != 0)
		ereport(ERROR,
			(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
			 errmsg("not called with valid relation")));

	rettuple = trigdata->tg_trigtuple;
	tupdesc = trigdata->tg_relation->rd_att;

	if (SPI_ERROR_NOATTRIBUTE == (event_col = SPI_fnumber(tupdesc, "event")))
		ereport(ERROR,
			(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
			 errmsg("attribute event not found")));


	if (SPI_ERROR_NOATTRIBUTE == (message_col = SPI_fnumber(tupdesc, "message")))
		ereport(ERROR,
			(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
			 errmsg("attribute message not found")));

	datum = SPI_getbinval(rettuple, tupdesc, event_col, &isnull);
	if (isnull)
		ereport(ERROR,
    			(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
        		 errmsg("event name is NULL"),
			 errdetail("Eventname may not be NULL.")));
	name = DatumGetTextP(datum);

	datum = SPI_getbinval(rettuple, tupdesc, message_col, &isnull);
	if (isnull)
		message = NULL;
	else
		message = DatumGetTextP(datum);

	WATCH_PRE(timeout, endtime, cycle);
	if (ora_lock_shmem(SHMEMMSGSZ, MAX_PIPES, MAX_EVENTS, MAX_LOCKS, false))
	{
		ItemPointer tid;
		Oid argtypes[1] = {TIDOID};
		char nulls[1] = {' '};
		Datum values[1];
		void *plan;

		create_message(name, message);
		LWLockRelease(shmem_lock);

		tid = &rettuple->t_data->t_ctid;

		if (!(plan = SPI_prepare("DELETE FROM ora_alerts WHERE ctid = $1", 1, argtypes)))
			ereport(ERROR,
				(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
				 errmsg("SPI_prepare failed")));

		values[0] = ItemPointerGetDatum(tid);

		if (SPI_OK_DELETE != SPI_execute_plan(plan, values, nulls, false, 1))
			ereport(ERROR,
				(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
				errmsg("can't execute sql")));

		SPI_finish();
		return PointerGetDatum(rettuple);
	}
	WATCH_POST(timeout, endtime, cycle);
	LOCK_ERROR();

	PG_RETURN_NULL();
}


/*
 *
 *  PROCEDURE DBMS_ALERT.SIGNAL(name IN VARCHAR2,message IN VARCHAR2);
 *
 *  Signals the occurrence of alert name and attaches message. (Sessions
 *  registered for alert name are notified only when the signaling transaction
 *  commits.)
 *
 */

/*

CREATE OR REPLACE FUNCTION dbms_alert.signal(_event text, _message text) RETURNS void AS $$
BEGIN
  PERFORM 1 FROM pg_catalog.pg_class c
            WHERE pg_catalog.pg_table_is_visible(c.oid)
            AND c.relkind='r' AND c.relname = 'ora_alerts';
  IF NOT FOUND THEN
    CREATE TEMP TABLE ora_alerts(event text, message text) WITH OIDS;
    REVOKE ALL ON TABLE ora_alerts FROM PUBLIC;
    CREATE CONSTRAINT TRIGGER ora_alert_signal AFTER INSERT ON ora_alerts
      INITIALLY DEFERRED FOR EACH ROW EXECUTE PROCEDURE dbms_alert._defered_signal();
  END IF;
  INSERT INTO ora_alerts(event, message) VALUES(_event, _message);
END;
$$ LANGUAGE plpgsql VOLATILE SECURITY DEFINER;
*/

#define SPI_EXEC(cmd,_type_) \
if (SPI_OK_##_type_ != SPI_exec(cmd, 1)) \
		ereport(ERROR, \
    			(errcode(ERRCODE_INTERNAL_ERROR), \
        		 errmsg("SPI execute error"), \
			 errdetail("Can't execute %s.", cmd)));

Datum
dbms_alert_signal(PG_FUNCTION_ARGS)
{
	void *plan;
	Oid argtypes[] = {TEXTOID, TEXTOID};
	Datum values[2];
	char nulls[2] = {' ',' '};

	if (PG_ARGISNULL(0))
		ereport(ERROR,
    			(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
        		 errmsg("event name is NULL"),
			 errdetail("Eventname may not be NULL.")));

	if (PG_ARGISNULL(1))
		nulls[1] = 'n';

	values[0] = PG_GETARG_DATUM(0);
	values[1] = PG_GETARG_DATUM(1);


	if (SPI_connect() < 0)
		ereport(ERROR,
			(errcode(ERRCODE_INTERNAL_ERROR),
			 errmsg("SPI_connect failed")));

	SPI_EXEC("SELECT 1 FROM pg_catalog.pg_class c "
                    "WHERE pg_catalog.pg_table_is_visible(c.oid) "
                            "AND c.relkind='r' AND c.relname = 'ora_alerts'", SELECT);
	if (0 == SPI_processed)
	{
		SPI_EXEC("CREATE TEMP TABLE ora_alerts(event text, message text)", UTILITY);
		SPI_EXEC("REVOKE ALL ON TABLE ora_alerts FROM PUBLIC", UTILITY);
		SPI_EXEC("CREATE CONSTRAINT TRIGGER ora_alert_signal AFTER INSERT ON ora_alerts "
    		    "INITIALLY DEFERRED FOR EACH ROW EXECUTE PROCEDURE dbms_alert.defered_signal()", UTILITY);
	}


	if (!(plan = SPI_prepare(
			"INSERT INTO ora_alerts(event,message) VALUES($1, $2)",
			2,
			argtypes)))
			ereport(ERROR,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("SPI_prepare failed")));

	if (SPI_OK_INSERT != SPI_execute_plan(plan, values, nulls, false, 1))
			ereport(ERROR,
				(errcode(ERRCODE_INTERNAL_ERROR),
				errmsg("can't execute sql")));


	SPI_finish();
	PG_RETURN_VOID();
}