DBMS_LOCK包的学习

DBMS_LOCK包的学习

    学习一下DBMS_LOCK包的用法。这份材料的说明和举例都很详细了，好不容易才找到的，哈哈。

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;

http://www.blogjava.net/decode360/archive/2009/08/19/291823.html