|
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 <lockname> into catalog dbms_lock_allocated.
|
|
ORU-10003
|
Unable to find or insert lock <lockname> into catalog dbms_lock_allocated.
|
|
|
Object Privileges
|
GRANT execute ON dbms_lock TO <schema_name>
|
|
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;
|