[RFC][Icedtea-Web]: Fix bug where you can clear cache while plugin is in use.
Dr Andrew John Hughes
ahughes at redhat.com
Wed Mar 16 11:18:20 PDT 2011
On 10:23 Wed 16 Mar , Andrew Su wrote:
>
>
> ----- Original Message -----
> > On 03/15/2011 04:29 PM, Andrew Su wrote:
> > > Hello Denis,
> > >
> > > ----- Original Message -----
> > >> Hi.
> > >>
> > >>>>> - Is it possible to get a race condition when calling
> > >>>>> markNetxRunning in JNLPRuntime. Since this now affects the
> > >>>>> plugin and not just javaws, this might be called multiple
> > >>>>> times by different threads? if so, I would synchronize it and
> > >>>>> since subsequent calls will instantly return if the first
> > >>>>> call succeeded in getting the lock, so there won't be much
> > >>>>> performance hit.
> > >>
> > >> I think that's a very good idea (making markNetxRunning
> > >> synchronized). I don't think we need to worry about performance at
> > >> all, seeing how rarely this function is called.
> > >
> > > It does get called every time it is about to launch an
> > > applet/application. but as a counter measure it will return right
> > > away if we obtained the lock already.
> > >
> >
> > Without appropriate synchronization, another thread may not see that
> > it's null already. Being a shared variable that's being read and set
> > by
> > multiple threads, it needs appropriate synchronization.
> >
> > Take a look at
> > http://download.oracle.com/javase/tutorial/essential/concurrency/memconsist.html
> >
>
> Yes, that is what I meant when I said that I will synchronize it. The check for null is so we don't execute the rest of the body not for synchronization purposes.
>
> Well, here's the updated patch.
>
> Cheers,
> Andrew
>
> > Cheers,
> > Omair
Should markNetxRunning be able to run at the same time as markNetxStopped?
You only have the former synchronized, and not the latter. I think they
both should be.
> diff -r 2d359e723fef netx/net/sourceforge/jnlp/Launcher.java
> --- a/netx/net/sourceforge/jnlp/Launcher.java Wed Mar 16 12:01:58 2011 +0100
> +++ b/netx/net/sourceforge/jnlp/Launcher.java Wed Mar 16 10:21:21 2011 -0400
> @@ -28,7 +28,6 @@
> import java.net.InetAddress;
> import java.net.URL;
> import java.net.UnknownHostException;
> -import java.nio.channels.FileChannel;
> import java.nio.channels.FileLock;
> import java.util.LinkedList;
> import java.util.List;
> @@ -37,7 +36,6 @@
> import net.sourceforge.jnlp.cache.CacheUtil;
> import net.sourceforge.jnlp.cache.ResourceTracker;
> import net.sourceforge.jnlp.cache.UpdatePolicy;
> -import net.sourceforge.jnlp.config.DeploymentConfiguration;
> import net.sourceforge.jnlp.runtime.AppThreadGroup;
> import net.sourceforge.jnlp.runtime.AppletInstance;
> import net.sourceforge.jnlp.runtime.ApplicationInstance;
> @@ -45,7 +43,6 @@
> import net.sourceforge.jnlp.runtime.JNLPRuntime;
> import net.sourceforge.jnlp.services.InstanceExistsException;
> import net.sourceforge.jnlp.services.ServiceUtil;
> -import net.sourceforge.jnlp.util.FileUtils;
>
> import javax.swing.SwingUtilities;
> import javax.swing.text.html.parser.ParserDelegator;
> @@ -214,6 +211,8 @@
> }
> }
>
> + JNLPRuntime.markNetxRunning();
> +
> if (file instanceof PluginBridge && cont != null)
> tg = new TgThread(file, cont, true);
> else if (cont == null)
> @@ -387,13 +386,6 @@
> if (!file.isApplication())
> throw launchError(new LaunchException(file, null, R("LSFatal"), R("LCClient"), R("LNotApplication"), R("LNotApplicationInfo")));
>
> - markNetxRunning();
> - Runtime.getRuntime().addShutdownHook(new Thread() {
> - public void run() {
> - markNetxStopped();
> - }
> - });
> -
> try {
>
> try {
> @@ -699,66 +691,6 @@
> }
>
> /**
> - * Indicate that netx is running by creating the {@link JNLPRuntime#INSTANCE_FILE} and
> - * acquiring a shared lock on it
> - */
> - private void markNetxRunning() {
> - try {
> - String message = "This file is used to check if netx is running";
> -
> - File netxRunningFile = new File(JNLPRuntime.getConfiguration()
> - .getProperty(DeploymentConfiguration.KEY_USER_NETX_RUNNING_FILE));
> - if (!netxRunningFile.exists()) {
> - FileUtils.createParentDir(netxRunningFile);
> - FileUtils.createRestrictedFile(netxRunningFile, true);
> - FileOutputStream fos = new FileOutputStream(netxRunningFile);
> - try {
> - fos.write(message.getBytes());
> - } finally {
> - fos.close();
> - }
> - }
> -
> - FileInputStream is = new FileInputStream(netxRunningFile);
> - FileChannel channel = is.getChannel();
> - fileLock = channel.tryLock(0, Long.MAX_VALUE, true);
> - if (fileLock != null && fileLock.isShared()) {
> - if (JNLPRuntime.isDebug()) {
> - System.out.println("Acquired shared lock on " +
> - netxRunningFile.toString() + " to indicate javaws is running");
> - }
> - } else {
> - fileLock = null;
> - }
> - } catch (IOException e) {
> - e.printStackTrace();
> - }
> -
> - }
> -
> - /**
> - * Indicate that netx is stopped by releasing the shared lock on
> - * {@link JNLPRuntime#INSTANCE_FILE}.
> - */
> - private void markNetxStopped() {
> - if (fileLock == null) {
> - return;
> - }
> - try {
> - fileLock.release();
> - fileLock.channel().close();
> - fileLock = null;
> - if (JNLPRuntime.isDebug()) {
> - String file = JNLPRuntime.getConfiguration()
> - .getProperty(DeploymentConfiguration.KEY_USER_NETX_RUNNING_FILE);
> - System.out.println("Release shared lock on " + file);
> - }
> - } catch (IOException e) {
> - e.printStackTrace();
> - }
> - }
> -
> - /**
> * Do hacks on per-application level to allow different AppContexts to work
> *
> * @see JNLPRuntime#doMainAppContextHacks
> diff -r 2d359e723fef netx/net/sourceforge/jnlp/runtime/JNLPRuntime.java
> --- a/netx/net/sourceforge/jnlp/runtime/JNLPRuntime.java Wed Mar 16 12:01:58 2011 +0100
> +++ b/netx/net/sourceforge/jnlp/runtime/JNLPRuntime.java Wed Mar 16 10:21:21 2011 -0400
> @@ -19,6 +19,8 @@
> import java.io.*;
> import java.net.Authenticator;
> import java.net.ProxySelector;
> +import java.nio.channels.FileChannel;
> +import java.nio.channels.FileLock;
> import java.awt.*;
> import java.text.*;
> import java.util.*;
> @@ -122,6 +124,9 @@
> /** contains the arguments passed to the jnlp runtime */
> private static List<String> initialArguments;
>
> + /** lock to file that indicates NetX is running */
> + private static FileLock fileLock = null;
> +
> public static final String STDERR_FILE = "java.stderr";
> public static final String STDOUT_FILE = "java.stdout";
>
> @@ -627,4 +632,69 @@
> return initialArguments;
> }
>
> + /**
> + * Indicate that netx is running by creating the {@link JNLPRuntime#INSTANCE_FILE} and
> + * acquiring a shared lock on it
> + */
> + public synchronized static void markNetxRunning() {
> + if (fileLock != null) return;
> + try {
> + String message = "This file is used to check if netx is running";
> +
> + File netxRunningFile = new File(JNLPRuntime.getConfiguration()
> + .getProperty(DeploymentConfiguration.KEY_USER_NETX_RUNNING_FILE));
> + if (!netxRunningFile.exists()) {
> + FileUtils.createParentDir(netxRunningFile);
> + FileUtils.createRestrictedFile(netxRunningFile, true);
> + FileOutputStream fos = new FileOutputStream(netxRunningFile);
> + try {
> + fos.write(message.getBytes());
> + } finally {
> + fos.close();
> + }
> + }
> +
> + FileInputStream is = new FileInputStream(netxRunningFile);
> + FileChannel channel = is.getChannel();
> + fileLock = channel.tryLock(0, Long.MAX_VALUE, true);
> + if (fileLock != null && fileLock.isShared()) {
> + if (JNLPRuntime.isDebug()) {
> + System.out.println("Acquired shared lock on " +
> + netxRunningFile.toString() + " to indicate javaws is running");
> + }
> + } else {
> + fileLock = null;
> + }
> + } catch (IOException e) {
> + e.printStackTrace();
> + }
> +
> + Runtime.getRuntime().addShutdownHook(new Thread() {
> + public void run() {
> + markNetxStopped();
> + }
> + });
> + }
> +
> + /**
> + * Indicate that netx is stopped by releasing the shared lock on
> + * {@link JNLPRuntime#INSTANCE_FILE}.
> + */
> + private static void markNetxStopped() {
> + if (fileLock == null) {
> + return;
> + }
> + try {
> + fileLock.release();
> + fileLock.channel().close();
> + fileLock = null;
> + if (JNLPRuntime.isDebug()) {
> + String file = JNLPRuntime.getConfiguration()
> + .getProperty(DeploymentConfiguration.KEY_USER_NETX_RUNNING_FILE);
> + System.out.println("Release shared lock on " + file);
> + }
> + } catch (IOException e) {
> + e.printStackTrace();
> + }
> + }
> }
--
Andrew :)
Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)
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