Java example source code file (ImageFetcher.java)
The ImageFetcher.java Java example source code
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package sun.awt.image;
import java.util.Vector;
import sun.awt.AppContext;
/**
* An ImageFetcher is a thread used to fetch ImageFetchable objects.
* Once an ImageFetchable object has been fetched, the ImageFetcher
* thread may also be used to animate it if necessary, via the
* startingAnimation() / stoppingAnimation() methods.
*
* There can be up to FetcherInfo.MAX_NUM_FETCHERS_PER_APPCONTEXT
* ImageFetcher threads for each AppContext. A per-AppContext queue
* of ImageFetchables is used to track objects to fetch.
*
* @author Jim Graham
* @author Fred Ecks
*/
class ImageFetcher extends Thread {
static final int HIGH_PRIORITY = 8;
static final int LOW_PRIORITY = 3;
static final int ANIM_PRIORITY = 2;
static final int TIMEOUT = 5000; // Time in milliseconds to wait for an
// ImageFetchable to be added to the
// queue before an ImageFetcher dies
/**
* Constructor for ImageFetcher -- only called by add() below.
*/
private ImageFetcher(ThreadGroup threadGroup, int index) {
super(threadGroup, "Image Fetcher " + index);
setDaemon(true);
}
/**
* Adds an ImageFetchable to the queue of items to fetch. Instantiates
* a new ImageFetcher if it's reasonable to do so.
* If there is no available fetcher to process an ImageFetchable, then
* reports failure to caller.
*/
public static boolean add(ImageFetchable src) {
final FetcherInfo info = FetcherInfo.getFetcherInfo();
synchronized(info.waitList) {
if (!info.waitList.contains(src)) {
info.waitList.addElement(src);
if (info.numWaiting == 0 &&
info.numFetchers < info.fetchers.length) {
createFetchers(info);
}
/* Creation of new fetcher may fail due to high vm load
* or some other reason.
* If there is already exist, but busy, fetcher, we leave
* the src in queue (it will be handled by existing
* fetcher later).
* Otherwise, we report failure: there is no fetcher
* to handle the src.
*/
if (info.numFetchers > 0) {
info.waitList.notify();
} else {
info.waitList.removeElement(src);
return false;
}
}
}
return true;
}
/**
* Removes an ImageFetchable from the queue of items to fetch.
*/
public static void remove(ImageFetchable src) {
final FetcherInfo info = FetcherInfo.getFetcherInfo();
synchronized(info.waitList) {
if (info.waitList.contains(src)) {
info.waitList.removeElement(src);
}
}
}
/**
* Checks to see if the given thread is one of the ImageFetchers.
*/
public static boolean isFetcher(Thread t) {
final FetcherInfo info = FetcherInfo.getFetcherInfo();
synchronized(info.waitList) {
for (int i = 0; i < info.fetchers.length; i++) {
if (info.fetchers[i] == t) {
return true;
}
}
}
return false;
}
/**
* Checks to see if the current thread is one of the ImageFetchers.
*/
public static boolean amFetcher() {
return isFetcher(Thread.currentThread());
}
/**
* Returns the next ImageFetchable to be processed. If TIMEOUT
* elapses in the mean time, or if the ImageFetcher is interrupted,
* null is returned.
*/
private static ImageFetchable nextImage() {
final FetcherInfo info = FetcherInfo.getFetcherInfo();
synchronized(info.waitList) {
ImageFetchable src = null;
long end = System.currentTimeMillis() + TIMEOUT;
while (src == null) {
while (info.waitList.size() == 0) {
long now = System.currentTimeMillis();
if (now >= end) {
return null;
}
try {
info.numWaiting++;
info.waitList.wait(end - now);
} catch (InterruptedException e) {
// A normal occurrence as an AppContext is disposed
return null;
} finally {
info.numWaiting--;
}
}
src = (ImageFetchable) info.waitList.elementAt(0);
info.waitList.removeElement(src);
}
return src;
}
}
/**
* The main run() method of an ImageFetcher Thread. Calls fetchloop()
* to do the work, then removes itself from the array of ImageFetchers.
*/
public void run() {
final FetcherInfo info = FetcherInfo.getFetcherInfo();
try {
fetchloop();
} catch (Exception e) {
e.printStackTrace();
} finally {
synchronized(info.waitList) {
Thread me = Thread.currentThread();
for (int i = 0; i < info.fetchers.length; i++) {
if (info.fetchers[i] == me) {
info.fetchers[i] = null;
info.numFetchers--;
}
}
}
}
}
/**
* The main ImageFetcher loop. Repeatedly calls nextImage(), and
* fetches the returned ImageFetchable objects until nextImage()
* returns null.
*/
private void fetchloop() {
Thread me = Thread.currentThread();
while (isFetcher(me)) {
// we're ignoring the return value and just clearing
// the interrupted flag, instead of bailing out if
// the fetcher was interrupted, as we used to,
// because there may be other images waiting
// to be fetched (see 4789067)
me.interrupted();
me.setPriority(HIGH_PRIORITY);
ImageFetchable src = nextImage();
if (src == null) {
return;
}
try {
src.doFetch();
} catch (Exception e) {
System.err.println("Uncaught error fetching image:");
e.printStackTrace();
}
stoppingAnimation(me);
}
}
/**
* Recycles this ImageFetcher thread as an image animator thread.
* Removes this ImageFetcher from the array of ImageFetchers, and
* resets the thread name to "ImageAnimator".
*/
static void startingAnimation() {
final FetcherInfo info = FetcherInfo.getFetcherInfo();
Thread me = Thread.currentThread();
synchronized(info.waitList) {
for (int i = 0; i < info.fetchers.length; i++) {
if (info.fetchers[i] == me) {
info.fetchers[i] = null;
info.numFetchers--;
me.setName("Image Animator " + i);
if(info.waitList.size() > info.numWaiting) {
createFetchers(info);
}
return;
}
}
}
me.setPriority(ANIM_PRIORITY);
me.setName("Image Animator");
}
/**
* Returns this image animator thread back to service as an ImageFetcher
* if possible. Puts it back into the array of ImageFetchers and sets
* the thread name back to "Image Fetcher". If there are already the
* maximum number of ImageFetchers, this method simply returns, and
* fetchloop() will drop out when it sees that this thread isn't one of
* the ImageFetchers, and this thread will die.
*/
private static void stoppingAnimation(Thread me) {
final FetcherInfo info = FetcherInfo.getFetcherInfo();
synchronized(info.waitList) {
int index = -1;
for (int i = 0; i < info.fetchers.length; i++) {
if (info.fetchers[i] == me) {
return;
}
if (info.fetchers[i] == null) {
index = i;
}
}
if (index >= 0) {
info.fetchers[index] = me;
info.numFetchers++;
me.setName("Image Fetcher " + index);
return;
}
}
}
/**
* Create and start ImageFetcher threads in the appropriate ThreadGroup.
*/
private static void createFetchers(final FetcherInfo info) {
// We need to instantiate a new ImageFetcher thread.
// First, figure out which ThreadGroup we'll put the
// new ImageFetcher into
final AppContext appContext = AppContext.getAppContext();
ThreadGroup threadGroup = appContext.getThreadGroup();
ThreadGroup fetcherThreadGroup;
try {
if (threadGroup.getParent() != null) {
// threadGroup is not the root, so we proceed
fetcherThreadGroup = threadGroup;
} else {
// threadGroup is the root ("system") ThreadGroup.
// We instead want to use its child: the "main"
// ThreadGroup. Thus, we start with the current
// ThreadGroup, and go up the tree until
// threadGroup.getParent().getParent() == null.
threadGroup = Thread.currentThread().getThreadGroup();
ThreadGroup parent = threadGroup.getParent();
while ((parent != null)
&& (parent.getParent() != null)) {
threadGroup = parent;
parent = threadGroup.getParent();
}
fetcherThreadGroup = threadGroup;
}
} catch (SecurityException e) {
// Not allowed access to parent ThreadGroup -- just use
// the AppContext's ThreadGroup
fetcherThreadGroup = appContext.getThreadGroup();
}
final ThreadGroup fetcherGroup = fetcherThreadGroup;
java.security.AccessController.doPrivileged(
new java.security.PrivilegedAction() {
public Object run() {
for (int i = 0; i < info.fetchers.length; i++) {
if (info.fetchers[i] == null) {
ImageFetcher f = new ImageFetcher(
fetcherGroup, i);
try {
f.start();
info.fetchers[i] = f;
info.numFetchers++;
break;
} catch (Error e) {
}
}
}
return null;
}
});
return;
}
}
/**
* The FetcherInfo class encapsulates the per-AppContext ImageFetcher
* information. This includes the array of ImageFetchers, as well as
* the queue of ImageFetchable objects.
*/
class FetcherInfo {
static final int MAX_NUM_FETCHERS_PER_APPCONTEXT = 4;
Thread[] fetchers;
int numFetchers;
int numWaiting;
Vector waitList;
private FetcherInfo() {
fetchers = new Thread[MAX_NUM_FETCHERS_PER_APPCONTEXT];
numFetchers = 0;
numWaiting = 0;
waitList = new Vector();
}
/* The key to put()/get() the FetcherInfo into/from the AppContext. */
private static final Object FETCHER_INFO_KEY =
new StringBuffer("FetcherInfo");
static FetcherInfo getFetcherInfo() {
AppContext appContext = AppContext.getAppContext();
synchronized(appContext) {
FetcherInfo info = (FetcherInfo)appContext.get(FETCHER_INFO_KEY);
if (info == null) {
info = new FetcherInfo();
appContext.put(FETCHER_INFO_KEY, info);
}
return info;
}
}
}
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