Source Code Cross Referenced for LinkPortal.java in  » 6.0-JDK-Modules » j2me » com » sun » midp » links » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » 6.0 JDK Modules » j2me » com.sun.midp.links 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         *
003:         *
004:         * Copyright  1990-2007 Sun Microsystems, Inc. All Rights Reserved.
005:         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
006:         * 
007:         * This program is free software; you can redistribute it and/or
008:         * modify it under the terms of the GNU General Public License version
009:         * 2 only, as published by the Free Software Foundation.
010:         * 
011:         * This program is distributed in the hope that it will be useful, but
012:         * WITHOUT ANY WARRANTY; without even the implied warranty of
013:         * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014:         * General Public License version 2 for more details (a copy is
015:         * included at /legal/license.txt).
016:         * 
017:         * You should have received a copy of the GNU General Public License
018:         * version 2 along with this work; if not, write to the Free Software
019:         * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
020:         * 02110-1301 USA
021:         * 
022:         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
023:         * Clara, CA 95054 or visit www.sun.com if you need additional
024:         * information or have any questions.
025:         */
026:
027:        package com.sun.midp.links;
028:
029:        import com.sun.cldc.isolate.Isolate;
030:
031:        /**
032:         * This class provides foreign methods of the Isolate class. (For discussion 
033:         * of foreign methods, see Fowler, _Refactoring_, "Introduce Foreign Method", 
034:         * p. 162.)
035:         *
036:         * The technique for passing links between isolates is implemented as a
037:         * separate class in order to avoid short term dependencies on the
038:         * implementation of the Isolate class in CLDC. These functions will 
039:         * eventually be moved to the Isolate class of CLDC.
040:         *
041:         * IMPL_NOTE
042:         * 
043:         * The current arrangement is highly problematic and therefore should be 
044:         * considered only as a temporary solution. The portal keeps track of links by 
045:         * isolate ID. However, an isolate ID is only assigned after the isolate has 
046:         * been started. Therefore, getLinks() must block until the parent isolate has 
047:         * had a chance to call setLinks(). The sender and receiver must agree to pass 
048:         * this initial set of links. This is pretty fragile, but it's only necessary 
049:         * for passing the initial set of links. Any additional links can be passed 
050:         * via the initial set of links.
051:         *
052:         * If an isolate dies before it gets its links, they'll be stranded in the 
053:         * portal. The parent isolate can overwrite them, though, and they should be 
054:         * collected. Worse, if an isolate dies and another isolate is created and 
055:         * gets the same IDs, it can get the links that were destined for the first. 
056:         * This requires the parent isolate to be responsible for cleaning up any 
057:         * unused links passed to its children, which could be difficult in general.
058:         */
059:        public class LinkPortal {
060:
061:            /**
062:             * Gets the links for this isolate that had been set by its creator.  If
063:             * links are available, this returns immediately. If no links are
064:             * available, this method will block until the creator sets them. This
065:             * requires close cooperation between the creator isolate and the newly
066:             * created isolate. The typical usage is that the creator creates the new
067:             * isolate and passes one set of links to it, and the first thing the new
068:             * new isolate does is to get this initial set of links. Any subsequent 
069:             * links should be passed through the initial set of links.
070:             */
071:            public synchronized static Link[] getLinks() {
072:                int count = getLinkCount0();
073:
074:                Link[] la = new Link[count];
075:
076:                for (int i = 0; i < count; i++) {
077:                    la[i] = new Link();
078:                }
079:
080:                /*
081:                 * IMPL_NOTE - race condition
082:                 * The creator could change the number of links between the call to 
083:                 * getCount0() and the call to getLinks0().
084:                 */
085:
086:                getLinks0(la);
087:                return la;
088:            }
089:
090:            /**
091:             * Sets the array of links for the given isolate. Once set, the array of 
092:             * links can be retrieved by the designated isolate using the getLinks() 
093:             * method.
094:             *
095:             * Setting of links should be done after the isolate is started and before 
096:             * it terminates, so that a valid id is available. However, this 
097:             * introduces a race condition between the starting of the isolate, the 
098:             * call to setLinks(), and the new isolate calling getLinks(). This means 
099:             * that the new isolate code will need to call getLinks() until it gets 
100:             * the array of links it expects.
101:             *
102:             * The linkarray parameter may be null, in which case it removes any links
103:             * that had been previously set for isolate.  If getLinks() is called at
104:             * this point, it will block until a non-null array is set.  Passing a
105:             * null linkarray to setLinks() differs from passing a zero-length array,
106:             * which will satisfy a call to getLinks() and cause it to return a
107:             * zero-length array.
108:             *
109:             * If linkarray is an array whose length is greater than zero, every entry 
110:             * must be a valid (non-null) Link object.
111:             *
112:             * @throws NullPointerException if isolate is null
113:             * @throws NullPointerException if any entry in linkarray is null
114:             * @throws IllegalArgumentException if any link in linkarray is closed
115:             * @throws IllegalStateException if isolate hasn't been started or has 
116:             *         been terminated
117:             */
118:            public static void setLinks(Isolate isolate, Link[] linkarray) {
119:                if (isolate == null) {
120:                    throw new NullPointerException();
121:                }
122:
123:                if (linkarray != null) {
124:                    for (int i = 0; i < linkarray.length; i++) {
125:                        if (linkarray[i] == null) {
126:                            throw new NullPointerException();
127:                        }
128:                    }
129:                }
130:
131:                int id = isolate.id();
132:                if (id == -1 || isolate.isTerminated()) {
133:                    throw new IllegalStateException();
134:                }
135:
136:                /*
137:                 * IMPL_NOTE - race conditions
138:                 * The array could change between these checks and the call to
139:                 * setLinks0(). The state of the isolate could also change.
140:                 */
141:
142:                setLinks0(id, linkarray);
143:            }
144:
145:            /**
146:             * Prevents construction of any instances.
147:             */
148:            private LinkPortal() {
149:            }
150:
151:            private static native int getLinkCount0();
152:
153:            private static native void getLinks0(Link[] linkarray);
154:
155:            private static native void setLinks0(int isolateid, Link[] linkarray);
156:        }
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