RFC: Netx - implement -Xclearcache command line option
Dr Andrew John Hughes
ahughes at redhat.com
Tue Oct 5 16:19:41 PDT 2010
On 14:45 Tue 05 Oct , Omair Majid wrote:
> On 10/04/2010 03:17 PM, Omair Majid wrote:
> > On 09/30/2010 05:27 PM, Deepak Bhole wrote:
> >> * Omair Majid<omajid at redhat.com> [2010-09-30 16:50]:
> >>> On 09/30/2010 04:32 PM, Deepak Bhole wrote:
> >>>> * Omair Majid<omajid at redhat.com> [2010-09-30 16:10]:
> >>>>> Hi,
> >>>>>
> >>>>> I posted this patch way back in 2009, but it looks like it got
> >>>>> lost/ignored.
> >>>>>
> >>>
> >>> Ok, turns out it was my fault: just noticed
> >>> http://mail.openjdk.java.net/pipermail/distro-pkg-dev/2009-August/006666.html.
> >>>
> >>> Somehow it slipped off my radar.
> >>>
> >>
> >> Doh. Glad it was re-visited. I doubt the issue will be encountered, but
> >> we might as well fix it instead of waiting for a bug report.
> >>
> >>>>> On 07/30/2009 05:18 PM, Omair Majid wrote:
> >>>>>> The attached patch adds the option -Xclearcache to Netx.
> >>>>>>
> >>>>>
> >>>>> Which (and I neglected to explain this last time) makes javaws clean
> >>>>> out its cache by deleting the contents of ~/.netx/cache/
> >>>>>
> >>>>
> >>>> Hmm, what happens if I have another netx app running and javaws is
> >>>> called
> >>>> with -Xclearcache? AFAIK the code has no provisioning to detect if a
> >>>> cache file has been deleted, and to re-download it... does it?
> >>>>
> >>>
> >>> As far as I can tell, very bad things (not eating babies kind of
> >>> bad, but still...). Depending on the exact timing either the VM will
> >>> crash or a java Exception might be thrown. If the JVM has opened the
> >>> (missing) jar earlier and and wants to open it again to load
> >>> additional classes the VM will most probably crash. Otherwise javaws
> >>> simply wont be able to find the needed jar and will fail to start.
> >>>
> >>> I suppose I could make some sort of global application lock to stop
> >>> any other javaws instances from starting while -Xclearcache is
> >>> running and to make sure -Xclearcache does not start if any other
> >>> javaws applications are running.
> >>>
> >>
> >> It would be hard to set up a locking system that can handle odd cases
> >> like crashed application, multiple instances of same app., etc.
> >>
> >
> > Yeah, you are right. I thought about it for a bit, and I dont see a
> > simple way to make it work using locks.
> >
> >> Easiest way I think is to execute jps -l and see if there is more than
> >> one instance of net.sourceforge.jnlp.runtime.Boot. If there is, refuse
> >> to run with -Xclearcache. I am not as worried about the 'don't start
> >> while -Xclearcache is running' case, as there is a far smaller window
> >> where things can go wrong. Plus if they do, it will be right away (as
> >> opposed to an already started app that has modified data, crashing).
> >>
> >
> > That's a great idea! Unfortunately I dont think we can rely on jps. jps
> > is part of the JDK as opposed to the JRE - we can not be sure that users
> > have it on their machine. I tried looking into the sources for jps to
> > find out how it works. The JVM creates /tmp/hsperfdata_$USER/$PID files
> > which contain the information that jps can parse and display. The files
> > are in a binary format so parsing it is not trivial (and the file format
> > is not guaranteed to be final). I am going to dig around a bit to see if
> > there is any other simple solution to this
> >
>
> I am attaching the updated patch. This one uses an alternate
> implementation based on file locks (exclusive and shared). A normal
> javaws process acquires a shared lock on /tmp/$USER/netx/instance during
> startup (when an instance of Launcher is created), and releases the lock
> when the JVM shutsdown. Multiple javaws processes can share the lock and
> run simultaneously.
>
> The javaws process that is trying to clear the cache checks for the file
> and tries to acquire an exclusive lock. If it succeeds, it goes ahead
> and clears the cache; otherwise it prints out an error to the user and
> exits.
>
> Thoughts?
>
Sounds good to me. I was actually going to suggest this before Deepak weighed
in with the jps option. Not knowing what jps was, I didn't no any pros or cons
as to using it.
Could you not just reuse LOCKS_DIR for this rather than introducing something
new? Also your mail says 'instance' but the code says 'instances' :-)
> + FileChannel channel = fileLock.channel();
> + fileLock.release();
> + channel.close();
could be just:
fileLock.release();
fileLock.channel().close();
Why do we have a method called just 'R' in CacheUtil?
Should we really be catching IOExceptions rather than allowing them to propogate?
> Cheers,
> Omair
> diff -r f41b0a7fbd70 netx/net/sourceforge/jnlp/Launcher.java
> --- a/netx/net/sourceforge/jnlp/Launcher.java Mon Oct 04 18:13:02 2010 -0400
> +++ b/netx/net/sourceforge/jnlp/Launcher.java Tue Oct 05 14:30:05 2010 -0400
> @@ -20,12 +20,17 @@
> import java.applet.Applet;
> import java.awt.Container;
> import java.io.File;
> +import java.io.FileInputStream;
> +import java.io.FileOutputStream;
> +import java.io.IOException;
> import java.lang.management.ManagementFactory;
> import java.lang.management.ThreadMXBean;
> import java.lang.reflect.Method;
> 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;
> import java.util.jar.JarFile;
> @@ -78,6 +83,8 @@
> /** If the application should call System.exit on fatal errors */
> private boolean exitOnFailure = true;
>
> + private FileLock fileLock;
> +
> /**
> * Create a launcher with the runtime's default update policy
> * and launch handler.
> @@ -127,6 +134,11 @@
>
> this.handler = handler;
> this.updatePolicy = policy;
> +
> + markJavawsRunning();
> + Runtime.getRuntime().addShutdownHook(new Thread() {
> + public void run() { markJavawsStopped(); }
> + });
> }
>
> /**
> @@ -686,6 +698,70 @@
> return null; // chose to continue, or no handler
> }
>
> + /**
> + * Indicate that netx is running by creating the {@link JNLPRuntime#INSTANCE_FILE} and
> + * acquiring a shared lock on it
> + */
> + private void markJavawsRunning() {
> + try {
> + String message = "This file is used to check if netx is running";
> +
> + File javawsRunningFile = new File(JNLPRuntime.INSTANCE_FILE);
> + javawsRunningFile.getParentFile().mkdirs();
> + if (javawsRunningFile.createNewFile()) {
> + FileOutputStream fos = new FileOutputStream(javawsRunningFile);
> + try {
> + fos.write(message.getBytes());
> + } finally {
> + fos.close();
> + }
> + }
> +
> + if (!javawsRunningFile.isFile()) {
> + if (JNLPRuntime.isDebug()) {
> + System.err.println("Unable to create instance file");
> + }
> + fileLock = null;
> + return;
> + }
> +
> + FileInputStream is = new FileInputStream(javawsRunningFile);
> + 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 " +
> + JNLPRuntime.INSTANCE_FILE + " to indicate javaws is running");
> + }
> + } else {
> + fileLock = null;
> + }
> + } catch (IOException e) {
> + e.printStackTrace();
> + }
> +
> + }
> +
> + /**
> + * Indicate that javaws is stopped by releasing the shared lock on
> + * {@link JNLPRuntime#INSTANCE_FILE}.
> + */
> + private void markJavawsStopped() {
> + if (fileLock == null) {
> + return;
> + }
> + try {
> + FileChannel channel = fileLock.channel();
> + fileLock.release();
> + channel.close();
> + fileLock = null;
> + if (JNLPRuntime.isDebug()) {
> + System.out.println("Release shared lock on " + JNLPRuntime.INSTANCE_FILE);
> + }
> + } catch (IOException e) {
> + e.printStackTrace();
> + }
> + }
>
>
> /**
> diff -r f41b0a7fbd70 netx/net/sourceforge/jnlp/cache/CacheUtil.java
> --- a/netx/net/sourceforge/jnlp/cache/CacheUtil.java Mon Oct 04 18:13:02 2010 -0400
> +++ b/netx/net/sourceforge/jnlp/cache/CacheUtil.java Tue Oct 05 14:30:05 2010 -0400
> @@ -19,6 +19,7 @@
>
> import java.io.*;
> import java.net.*;
> +import java.nio.channels.FileChannel;
> import java.util.*;
> import java.lang.reflect.*;
> import java.security.*;
> @@ -37,6 +38,10 @@
> */
> public class CacheUtil {
>
> + private static String R(String key) {
> + return JNLPRuntime.getMessage(key);
> + }
> +
> private static String R(String key, Object param) {
> return JNLPRuntime.getMessage(key, new Object[] {param});
> }
> @@ -129,6 +134,72 @@
> }
>
> /**
> + * Clears the cache by deleting all the Netx cache files
> + *
> + * Note: Because of how our caching system works, deleting jars of another javaws
> + * process is using them can be quite disasterous. Hence why Launcher creates lock files
> + * and we check for those by calling {@link #okToClearCache()}
> + */
> + public static void clearCache() {
> +
> + if (!okToClearCache()) {
> + System.err.println(R("CCannotClearCache"));
> + return;
> + }
> +
> + File cacheDir = new File(JNLPRuntime.getBaseDir() + File.separator + "cache");
> + if (!(cacheDir.isDirectory())) {
> + return;
> + }
> +
> + if (JNLPRuntime.isDebug()) {
> + System.err.println("Clearing cache directory: " + cacheDir);
> + }
> + try {
> + FileUtils.recursiveDelete(cacheDir, JNLPRuntime.getBaseDir());
> + } catch (IOException e) {
> + throw new RuntimeException(e);
> + }
> + }
> +
> + /**
> + * Returns a boolean indicating if it ok to clear the netx application cache at this point
> + * @return true if the cache can be cleared at this time without problems
> + */
> + private static boolean okToClearCache() {
> + File otherJavawsRunning = new File(JNLPRuntime.INSTANCE_FILE);
> + try {
> + if (otherJavawsRunning.isFile()) {
> + FileOutputStream fis = new FileOutputStream(otherJavawsRunning);
> + try {
> + FileChannel channel = fis.getChannel();
> + if (channel.tryLock() == null) {
> + if (JNLPRuntime.isDebug()) {
> + System.out.println("Other instances; can not clear cache");
> + }
> + return false;
> + }
> +
> + if (JNLPRuntime.isDebug()) {
> + System.out.println("No other instances; proceeding to clear cache");
> + }
> + return true;
> +
> + } finally {
> + fis.close();
> + }
> + } else {
> + if (JNLPRuntime.isDebug()) {
> + System.out.println("No instance file; proceeding to clear cache");
> + }
> + return true;
> + }
> + } catch (IOException e) {
> + return false;
> + }
> + }
> +
> + /**
> * Returns whether there is a version of the URL contents in the
> * cache and it is up to date. This method may not return
> * immediately.
> diff -r f41b0a7fbd70 netx/net/sourceforge/jnlp/resources/Messages.properties
> --- a/netx/net/sourceforge/jnlp/resources/Messages.properties Mon Oct 04 18:13:02 2010 -0400
> +++ b/netx/net/sourceforge/jnlp/resources/Messages.properties Tue Oct 05 14:30:05 2010 -0400
> @@ -139,6 +139,7 @@
> BOViewer = Shows the trusted certificate viewer.
> BOUmask = Sets the umask for files created by an application.
> BXnofork = Do not create another JVM.
> +BXclearcache= Clean the JNLP application cache.
> BOHelp = Print this message and exit.
>
> # Cache
> @@ -149,6 +150,8 @@
> CChooseCache=Choose a cache directory...
> CChooseCacheInfo=Netx needs a location for storing cache files.
> CChooseCacheDir=Cache directory
> +CConfirmClearCache=Are you sure you want to clear the cache? This may running javaws applications to misbehave.
> +CCannotClearCache=Can not clear cache at this time
>
> # Security
> SFileReadAccess=The application has requested read access to {0}. Do you want to allow this action?
> diff -r f41b0a7fbd70 netx/net/sourceforge/jnlp/runtime/Boot.java
> --- a/netx/net/sourceforge/jnlp/runtime/Boot.java Mon Oct 04 18:13:02 2010 -0400
> +++ b/netx/net/sourceforge/jnlp/runtime/Boot.java Tue Oct 05 14:30:05 2010 -0400
> @@ -40,6 +40,7 @@
> import net.sourceforge.jnlp.ParseException;
> import net.sourceforge.jnlp.PropertyDesc;
> import net.sourceforge.jnlp.ResourcesDesc;
> +import net.sourceforge.jnlp.cache.CacheUtil;
> import net.sourceforge.jnlp.cache.UpdatePolicy;
> import net.sourceforge.jnlp.security.VariableX509TrustManager;
> import net.sourceforge.jnlp.security.viewer.CertificateViewer;
> @@ -114,6 +115,7 @@
> + " -strict "+R("BOStrict")+"\n"
> + " -umask=value "+R("BOUmask")+"\n"
> + " -Xnofork "+R("BXnofork")+"\n"
> + + " -Xclearcache "+R("BXclearcache")+"\n"
> + " -help "+R("BOHelp")+"\n";
>
> private static final String doubleArgs = "-basedir -jnlp -arg -param -property -update";
> @@ -202,6 +204,17 @@
> JNLPRuntime.setSecurityEnabled(null == getOption("-nosecurity"));
> JNLPRuntime.initialize(true);
>
> + /*
> + * FIXME
> + * This should have been done with the rest of the argument parsing
> + * code. But we need to know what the cache and base directories are,
> + * and baseDir is initialized here
> + */
> + if (null != getOption("-Xclearcache")) {
> + CacheUtil.clearCache();
> + return null;
> + }
> +
> try {
> new Launcher().launch(getFile());
> }
> diff -r f41b0a7fbd70 netx/net/sourceforge/jnlp/runtime/JNLPRuntime.java
> --- a/netx/net/sourceforge/jnlp/runtime/JNLPRuntime.java Mon Oct 04 18:13:02 2010 -0400
> +++ b/netx/net/sourceforge/jnlp/runtime/JNLPRuntime.java Tue Oct 05 14:30:05 2010 -0400
> @@ -18,6 +18,7 @@
> package net.sourceforge.jnlp.runtime;
>
> import java.io.*;
> +import java.nio.channels.FileLock;
> import java.awt.*;
> import java.text.*;
> import java.util.*;
> @@ -132,6 +133,12 @@
> public static final String LOCKS_DIR = TMP_DIR + File.separator + USER + File.separator
> + "netx" + File.separator + "locks";
>
> + /** this file is used to indicate if any other instances of netx are running
> + * if this file can be locked (using a {@link FileLock} in exclusive mode, then other
> + * netx instances are not running */
> + public static final String INSTANCE_FILE = TMP_DIR + File.separator + USER + File.separator
> + + "netx" + File.separator + "instances";
> +
> /** the java.home directory */
> public static final String JAVA_HOME_DIR = System.getProperty("java.home");
>
> diff -r f41b0a7fbd70 netx/net/sourceforge/jnlp/util/FileUtils.java
> --- a/netx/net/sourceforge/jnlp/util/FileUtils.java Mon Oct 04 18:13:02 2010 -0400
> +++ b/netx/net/sourceforge/jnlp/util/FileUtils.java Tue Oct 05 14:30:05 2010 -0400
> @@ -17,6 +17,9 @@
> package net.sourceforge.jnlp.util;
>
> import java.io.File;
> +import java.io.IOException;
> +
> +import net.sourceforge.jnlp.runtime.JNLPRuntime;
>
> /**
> * This class contains a few file-related utility functions.
> @@ -121,4 +124,36 @@
> return prefix + OMITTED + suffix;
> }
>
> + /**
> + * Recursively delete everything under a directory. Works on either files or
> + * directories
> + *
> + * @param file the file object representing what to delete. Can be either a
> + * file or a directory.
> + * @param base the directory under which the file and its subdirectories must be located
> + * @throws IOException on an io exception or if trying to delete something
> + * outside the base
> + */
> + public static void recursiveDelete(File file, File base) throws IOException {
> + if (JNLPRuntime.isDebug()) {
> + System.err.println("Deleting: " + file);
> + }
> +
> + if (!(file.getCanonicalPath().startsWith(base.getCanonicalPath()))) {
> + throw new IOException("Trying to delete a file outside Netx's basedir: "
> + + file.getCanonicalPath());
> + }
> +
> + if (file.isDirectory()) {
> + File[] children = file.listFiles();
> + for (int i = 0; i < children.length; i++) {
> + recursiveDelete(children[i], base);
> + }
> + }
> + if (!file.delete()) {
> + throw new IOException("Unable to delete file: " + file);
> + }
> +
> + }
> +
> }
--
Andrew :)
Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)
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