Oracle DBMS_LOCK Locks Locking

General Information
Source	{ORACLE_HOME}/rdbms/admin/dbmslock.sql
First Available	7.3.4
Constants	Name Description Data Type Value nl_mode NuLl INTEGER 1 ss_mode Sub Shared: used on an aggregate object to indicate that share locks are being acquired on subparts of the object INTEGER 2 sx_mode Sub eXclusive: used on an aggregate object to indicate that exclusive locks are being acquired on sub-parts of the object INTEGER 3 s_mode Shared: indicates that the entire aggregate object has a share lock, but some of the sub-parts may additionally have exclusive locks INTEGER 4 ssx_mod Shared SubeXclusive INTEGER 5 x_mode eXclusive INTEGER 6
Dependencies	SELECT referenced_name FROM dba_dependencies WHERE name = 'DBMS_LOCK' UNION SELECT name FROM dba_dependencies WHERE referenced_name = 'DBMS_LOCK';
Exceptions	Error Number Description ORA-20000 Unable to find or insert lock into catalog dbms_lock_allocated. ORU-10003 Unable to find or insert lock into catalog dbms_lock_allocated.
Object Privileges	GRANT execute ON dbms_lock TO
	GRANT execute ON dbms_lock TO uwclass;
ALLOCATE_UNIQUE
Allocates a unique lock identifier (in the range of 1073741824 to 1999999999) given a lock name. Lock identifiers are used to enable applications to coordinate their use of locks	dbms_lock.allocate_unique( lockname IN VARCHAR2, lockhandle OUT VARCHAR2, expiration_secs IN INTEGER DEFAULT 864000);
	See dbms_lock demo
CONVERT
Converts a lock from one mode to another Overload 1	dbms_lock.convert( id IN INTEGER, lockmode IN INTEGER, timeout IN NUMBER DEFAULT maxwait) RETURN INTEGER; Return Values 0 Success 1 Timeout 2 Deadlock 3 Parameter error 4 Don't own lock specified by id or lockhandle 5 Illegal lock handle
	See dbms_lock demo
Overload 2	dbms_lock.convert( lockhandle IN VARCHAR2, lockmode IN INTEGER, timeout IN NUMBER DEFAULT maxwait) RETURN INTEGER;
	See dbms_lock demo
RELEASE
Explicitly releases a lock previously acquired using the REQUEST function Overload 1	dbms_lock.release(id IN INTEGER) RETURN INTEGER; Return Values 0 Success 3 Parameter error 4 Don't own lock specified by id or lockhandle 5 Illegal lock handle
	See dbms_lock demo
Overload 2	dbms_lock.release(lockhandle IN VARCHAR2) RETURN INTEGER;
	See dbms_lock demo
REQUEST
Requests a lock with a given mode Overload 1	dbms_lock.request( id IN INTEGER, lockmode IN INTEGER DEFAULT x_mode, timeout IN INTEGER DEFAULT maxwait, release_on_commit IN BOOLEAN DEFAULT FALSE) RETURN INTEGER; Return Values 0 Success 1 Timeout 2 Deadlock 3 Parameter error 4 Don't own lock specified by id or lockhandle 5 Illegal lock handle
	See dbms_lock demo
Overload 2	dbms_lock.request( lockhandle IN VARCHAR2, lockmode IN INTEGER DEFAULT x_mode, timeout IN INTEGER DEFAULT maxwait, release_on_commit IN BOOLEAN DEFAULT FALSE) RETURN INTEGER;
	See dbms_lock demo
SLEEP
Suspends the session for a given period of time	dbms_lock.sleep(seconds IN NUMBER);
	exec dbms_lock.sleep(1.00);
Demo
-- create demo table CREATE TABLE lock_test ( action VARCHAR2(10), when TIMESTAMP(9)); GRANT insert ON lock_test TO public; CREATE OR REPLACE PACKAGE lock_demo IS v_lockname VARCHAR2(12) := 'control_lock'; v_lockhandle VARCHAR2(200); v_result PLS_INTEGER; -- obtain a lock PROCEDURE request_lock(p_ltype INTEGER, p_retval OUT INTEGER); -- release an existing lock PROCEDURE release_lock(p_retval OUT INTEGER); -- view the stored handle FUNCTION see_handle RETURN VARCHAR2; -- decode lock request FUNCTION decode_req(p_result PLS_INTEGER) RETURN VARCHAR2; -- decode lock release FUNCTION decode_rel(p_result PLS_INTEGER) RETURN VARCHAR2; END lock_demo; / CREATE OR REPLACE PACKAGE BODY lock_demo IS PROCEDURE request_lock(p_ltype IN INTEGER, p_retval OUT INTEGER) IS BEGIN IF v_lockhandle IS NULL THEN dbms_lock.allocate_unique(v_lockname, v_lockhandle); p_retval := dbms_lock.request(v_lockhandle, p_ltype); END IF; END request_lock; ------------------------------------------------------------ PROCEDURE release_lock(p_retval OUT INTEGER) IS BEGIN IF v_lockhandle IS NOT NULL THEN p_retval := dbms_lock.release(v_lockhandle); END IF; END release_lock; ------------------------------------------------------------ FUNCTION see_handle RETURN VARCHAR2 IS BEGIN IF v_lockhandle IS NOT NULL THEN RETURN v_lockhandle; ELSE RETURN 'Not Allocated'; END IF; END see_handle; ------------------------------------------------------------ FUNCTION decode_req(p_result PLS_INTEGER) RETURN VARCHAR2 IS retval VARCHAR2(20); BEGIN SELECT DECODE(p_result,0,'Success',1,'Timeout',2,'Deadlock', 3,'Parameter Error',4,'Already owned',5,'Illegal Lock Handle') INTO retval FROM dual; RETURN retval; END decode_req; ------------------------------------------------------------ FUNCTION decode_rel(p_result PLS_INTEGER) RETURN VARCHAR2 IS retval VARCHAR2(20); BEGIN SELECT DECODE(p_result,0,3, 'Parameter Error',4, 'Already owned', 5, 'Illegal Lock Handle') INTO retval FROM dual; RETURN retval; END decode_rel; ------------------------------------------------------------ END lock_demo; / GRANT execute ON lock_demo TO public; set serveroutput on -- get an exclusive lock in the current session (Session 1) DECLARE s VARCHAR2(200); BEGIN lock_demo.request_lock(6, s); dbms_output.put_line(s); END; / /* Two session request a shared lock (ss_mode). The shared lock cannot be acquired because session 1 holds an exclusive lock. Execution will stop on the request until the the exclusive lock is released. */ Session 2 Session 3 set serveroutput on DECLARE s VARCHAR2(200); BEGIN uwclass.lock_demo.request_lock( dbms_lock.ss_mode, s); dbms_output.put_line(s); INSERT INTO uwclass.lock_test (action, when) VALUES ('started', SYSTIMESTAMP); dbms_lock.sleep(5); INSERT INTO uwclass.lock_test (action, when) VALUES ('ended', SYSTIMESTAMP); COMMIT; END; / set serveroutput on DECLARE s VARCHAR2(200); BEGIN uwclass.lock_demo.request_lock( dbms_lock.ss_mode, s); dbms_output.put_line(s); INSERT INTO uwclass.lock_test (action, when) VALUES ('started', SYSTIMESTAMP); dbms_lock.sleep(5); INSERT INTO uwclass.lock_test (action, when) VALUES ('ended' , SYSTIMESTAMP); COMMIT; END; / -- Session 1 releases its lock DECLARE s VARCHAR2(200); BEGIN lock_demo.release_lock(s); dbms_output.put_line(s); END; / -- Execution resumes when the exclusive lock is released SELECT TO_CHAR(when,'dd.mm.yyyy hh24:mi:ss'), action FROM lock_test ORDER BY when;