Calls to custom context returning incorrect value.

From: Ralph.in.NZ_at_googlemail.com <ralph.in.nz_at_googlemail.com>
Date: Wed, 15 Sep 2010 07:59:29 -0700 (PDT)
Message-ID: <6ac44420-8184-4f73-9773-b3bac1c25cdb_at_q26g2000vbn.googlegroups.com>

Hi Guys,

This is already posted on OTN forums, but thought I'd post here as well, though am a bit dismayed by the amount of spam that this group seems to be on the receiving end of, hopefully some old hands are still around to lend a hand...

Ta

Ralph

Hi,

I am writing a web application. One of the features is that the transactions of one user can cause an alert to be raised to another user.
This other user's session is polling the database every n seconds to see whether or not there is an alert for them. The application makes use of custom application contexts to store information relevent to a users session. Included in this context is a flag which denotes whether or not there is an alert for that user (which makes the polling calls extremely light weight).
In order to set that flag the user causing the alert spoofs into the other users context and sets the flag. This works a treat. The problem I have comes with the polling routine clearing the alert flag once it has been set and read as such.

The check alert function looks like this...

	FUNCTION check_alert return varchar2
	IS
	   	i_am constant varchar2(128) := 'fe.check_alert';
	    ret_val varchar2(1);
	BEGIN
		ret_val := nvl(sysadmin_ctx.ctx_pkg.get_ctx(p_attr =>

'alert_flag'),'N');

		if ret_val = 'Y' then
			-- clear alert flag
			sys_utl.log(p_level => 'DEBUG', p_module => i_am, p_message =>
'Alert flag was Y. Clearing flag.');
			sysadmin_ctx.ctx_pkg.set_ctx(p_attr => 'alert_flag',  p_value =>
'N');
			sys_utl.log(p_level => 'DEBUG', p_module => i_am, p_message =>

'Cleared flag. value now :'||nvl(sysadmin_ctx.ctx_pkg.get_ctx(p_attr
=> 'alert_flag'),'N'));

                end if;

		return ret_val;
	EXCEPTION
			when OTHERS then
				sys_utl.err_and_stop (p_module => i_am ,p_sqlcode => sqlcode,

p_errstack => dbms_utility.format_error_stack, p_backtrace => dbms_utility.format_error_backtrace);

        END check_alert;

The relevent parts of the ctx_pkg are standard and look like this.

		PROCEDURE set_ctx(p_attr IN VARCHAR2, p_value IN VARCHAR2)
		  AS
		  BEGIN
		   DBMS_SESSION.SET_CONTEXT(
		    namespace  => 'custom_ctx',
		    attribute  => p_attr,
		    value      => p_value,
		    username   => USER, -- Retrieves the session user, will always
be same for web users
		    client_id  => session_id_global);
		  END set_ctx;

		  FUNCTION get_ctx (p_attr varchar2) return varchar2
		  is
		  begin
		  	return(sys_context('custom_ctx',p_attr));
		  end get_ctx;

Now what is interesting is the resulting debug messages. They look like this...most of the time...

15-SEP-2010 14:02:21 22      fe.check_alert                  DEBUG
Alert flag was Y. Clearing flag.
15-SEP-2010 14:02:21 22      fe.check_alert                  DEBUG

Cleared flag. value now :Y

Occasionally it works and they look like this...which is what i'd expect.

15-SEP-2010 13:37:11 22      fe.check_alert                  DEBUG
Alert flag was Y. Clearing flag.
15-SEP-2010 13:37:11 22      fe.check_alert                  DEBUG

Cleared flag. value now :N

Now I am stumped as to what is going on. Any ideas welcome.

Cheers

Ralph Received on Wed Sep 15 2010 - 09:59:29 CDT