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Java > Open Source Codes > org > apache > derby > iapi > services > daemon > DaemonFactory


1 /*
2
3    Derby - Class org.apache.derby.iapi.services.daemon.DaemonFactory
4
5    Licensed to the Apache Software Foundation (ASF) under one or more
6    contributor license agreements. See the NOTICE file distributed with
7    this work for additional information regarding copyright ownership.
8    The ASF licenses this file to you under the Apache License, Version 2.0
9    (the "License"); you may not use this file except in compliance with
10    the License. You may obtain a copy of the License at
11
12       http://www.apache.org/licenses/LICENSE-2.0
13
14    Unless required by applicable law or agreed to in writing, software
15    distributed under the License is distributed on an "AS IS" BASIS,
16    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17    See the License for the specific language governing permissions and
18    limitations under the License.
19
20  */
21
22 package org.apache.derby.iapi.services.daemon;
23
24 import org.apache.derby.iapi.error.StandardException;
25
26 /**
27     Daemon Factory can create new DaemonService, which runs on seperate
28     background threads. One can use these DaemonService to handle background
29     clean up task by implementing Serviceable and subscribing to a DaemonService.
30
31     A DaemonService is a background worker thread which does asynchronous I/O and
32     general clean up. It should not be used as a general worker thread for
33     parallel execution. A DaemonService can be subscribe to by many Serviceable
34     objects and a daemon will call that object's performWork from time to
35     time. These performWork method should be well behaved - in other words,
36     it should not take too long or hog too many resources or deadlock with
37     anyone else. And it cannot (should not) error out.
38
39     The best way to use a daemon is to have an existing DaemonService and subscribe to it.
40     If you can't find an existing one, then make one thusly:
41
42     DaemonService daemon = DaemonFactory.createNewDaemon();
43
44     After you have a daemon, you can subscribe to it by
45     int myClientNumber = daemon.subscribe(serviceableObject);
46
47     and ask it to run performWork for you ASAP by
48     daemon.serviceNow(myClientNumber);
49
50     Or, for one time service, you can enqueue a Serviceable Object by
51     daemon.enqueue(serviceableObject, true); - urgent service
52     daemon.enqueue(serviceableObject, false); - non-urgent service
53
54     @see DaemonService
55     @see Serviceable
56 */
57 public interface DaemonFactory
58 {
59     /**
60         Create a new DaemonService with the default daemon timer delay.
61
62         @exception StandardException Standard cloudscape error policy
63      */
64     public DaemonService createNewDaemon(String JavaDoc name) throws StandardException;
65 }
66
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