Oracle dequeue function is not working through different user.

Question

I created an Oracle queue, an anonymous block to enqueue messages in it and a dequeue function. when i use the dequeue function with the same user i've created queue its working fine, but when i am executing same function with different user it is returning null.
Please see the code i've used ----
-- Create q_table
begin
DBMS_AQADM.create_queue_table (
queue_table => 'QUEUE_QTAB' , queue_payload_type => 'SYS.XMLTYPE'
,multiple_consumers => TRUE, message_grouping => DBMS_AQADM.none);
end;
--Create queue:-
begin
DBMS_AQADM.create_queue (
queue_name => 'QUEUE_Q', queue_table => 'QUEUE_QTAB');
end;
-- Start queue:-
begin
dbms_aqadm.start_queue (
queue_name => 'QUEUE_Q');
end;
--Add subscriber:-
begin
DBMS_AQADM.add_subscriber (
queue_name  => 'QUEUE_Q',
subscriber  => sys.aq$_agent ('B_USER', NULL, NULL));
end;
GRANT SELECT ON A_USER.QUEUE_QTAB  TO DBMONITOR;
GRANT SELECT ON A_USER.QUEUE_QTAB TO IDSCORE;
GRANT SELECT ON A_USER.QUEUE_QTAB TO IDSREAD;
GRANT SELECT ON A_USER.QUEUE_QTAB TO IDS_READ;
-- View Creation:-
CREATE VIEW QUEUE_QTAB _VW
AS
  SELECT * FROM QUEUE_QTAB
  WHERE Q_NAME = QUEUE_Q';
Grants:-
GRANT SELECT ON A_USER.QUEUE_QTAB _VW TO B_USER;
    --Enqueue
    DECLARE
   enqueue_options     dbms_aq.enqueue_options_t;
   message_properties  dbms_aq.message_properties_t;
   message_handle      RAW(16);
   message           XMLTYPE;
BEGIN
   message := XMLType('<?xml version="1.0"?><tns:ISO8583-87 xmlns:tns="http://www.tsys.com/prime/online/iso8583"><I000>0120</I000><I002>491693******9989</I002><I003>280000</I003><I004>000000003000</I004><I006>0000091050.23</I006><I007>0406131721</I007><I011>039622</I011><I012>094121</I012><I013>0224</I013><I018>5999</I018><I022>0000</I022><I032>06123496</I032><I033>06198745</I033><I037>123456787012</I037><I038>026446</I038><I039>00</I039><I041>A1234567</I041><I042>CARD ACCEPTER  </I042><I043>ACQUIRER NAME            CITY NAME    UK</I043><I048>1001O</I048><I049>978</I049><I051>826</I051><I056>37120300692340000012300004800456005600</I056><I102>0890220150</I102></tns:ISO8583-87>');
   dbms_aq.enqueue(queue_name => 'QUEUE_Q',          
         enqueue_options      => enqueue_options,      
         message_properties   => message_properties,    
         payload              => message,              
         msgid                => message_handle);
   COMMIT;
end;
Dequeuing is actually done through two function   fn_dequeue function calls fn_dequeue_payment_msg, both are under different packages
fn_dequeue---
FUNCTION fn_dequeue (p_consumer_i IN VARCHAR2 DEFAULT USER)
      RETURN CLOB
   AS
      v_msg          xmltype;
      v_msg_found    BOOLEAN := FALSE;
      v_return       clob;
      c_procedure_name constant varchar2 (100) := 'FN_DEQUEUE';
      v_locn         idsc_globals_pck.styp_locn;
      v_q_name_i varchar2(35) := 'QUEUE_Q';
   begin
        v_locn := '80';
      idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => 'Function called by ' || USER
       v_msg_found :=
         idsph_queues_pck.fn_dequeue_payment_msg (
                                                  p_q_name_i => v_q_name_i , p_message_o => v_msg, p_consumer_i => p_consumer_i
         v_locn := '90';
      if v_msg_found then
         v_locn := '100';
         idsc_lib_pck.pr_debug (
                                p_program_name => c_procedure_name, p_ids_req_id => NULL
                               ,p_locn => v_locn, p_debug_message => 'Message found'
         v_return := v_msg.getstringval ();
      end if;
         v_locn := '110';
      idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => 'Returning'
      RETURN v_return;
   EXCEPTION
      WHEN OTHERS THEN
         idsc_errors_pck.pr_raise_app_error (
                                             p_proc_name_i => c_procedure_name, p_locn_i => v_locn, p_err_msg_i => SQLERRM
   END fn_dequeue_iso8583;
fn_dequeue_payment_msg-----
FUNCTION fn_dequeue_payment_msg (
                                    p_q_name_i IN VARCHAR2
                                   ,p_consumer_i IN VARCHAR2 DEFAULT USER
                                   ,p_message_o   OUT XMLTYPE
      RETURN BOOLEAN
   IS
      v_dequeue_options DBMS_AQ.dequeue_options_t;
      v_message_properties DBMS_AQ.message_properties_t;
      v_message_handle RAW (16);
      v_message      XMLTYPE;
      e_no_messages exception;
      PRAGMA EXCEPTION_INIT (e_no_messages, -25228);
      c_procedure_name CONSTANT VARCHAR2 (100) := 'IDSPH_QUEUES_PCK.FN_DEQUEUE_PAYMENT_MESSAGE';
      v_locn         idsc_globals_pck.styp_locn;
   BEGIN
      v_locn := '10';
      idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => 'Setting dequeue options'
      v_dequeue_options.wait := dbms_aq.no_wait;      
      v_locn := '20';
      v_dequeue_options.navigation := DBMS_AQ.first_message;
      v_locn := '30';
      v_dequeue_options.consumer_name := p_consumer_i;
      v_locn := '40';
      idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => 'Dequeuing next message'
                            idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => 'p_consumer_i' || p_consumer_i                         
      DBMS_AQ.dequeue (
                       queue_name => p_q_name_i, dequeue_options => v_dequeue_options, message_properties => v_message_properties
                      ,payload => v_message, msgid => v_message_handle
      v_locn := '50';
      idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => 'Dequeue successful'
      p_message_o := v_message;
      RETURN TRUE;
   EXCEPTION
      WHEN e_no_messages THEN
         -- Not an error just no messages currently in queue so return success
         v_locn := '160';
         idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => SQLERRM
         RETURN FALSE;
      WHEN OTHERS THEN
         idsc_errors_pck.pr_raise_app_error (
                                             p_proc_name_i => c_procedure_name, p_locn_i => v_locn, p_err_msg_i => SQLERRM
   END fn_dequeue_payment_msg;
fn_dequeue function returns null while executing from B_USER , while same functions works fine for A_USER, please suggest

Answer 1

I got the error , we need append schema name where queue is created before assigning it to a variable, this problem is now resolved.
fn_dequeue---
FUNCTION fn_dequeue (p_consumer_i IN VARCHAR2 DEFAULT USER)
      RETURN CLOB
   AS
      v_msg          xmltype;
      v_msg_found    BOOLEAN := FALSE;
      v_return       clob;
      c_procedure_name constant varchar2 (100) := 'FN_DEQUEUE';
      v_locn         idsc_globals_pck.styp_locn;
      v_q_name_i varchar2(35) := 'A_USER.QUEUE_Q';
   begin
        v_locn := '80';
      idsc_lib_pck.pr_debug (
                             p_program_name => c_procedure_name, p_ids_req_id => NULL
                            ,p_locn => v_locn, p_debug_message => 'Function called by ' || USER