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Re: [equinox-dev] buddy classloading & deadlock
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Tom,
Yes, what a silly restriction!
Anyway, if you download the "IBM Development Package for Eclipse", that contains a copy of the J9 VM that runs on any PC, not just genuine IBM (ahem, Lenovo) kit.
- Neil
On 8/3/06, Tom Huybrechts <tom.huybrechts@xxxxxxxxx> wrote:
Unfortunately, 'this is not an IBM pc. Installation cannot continue'. Anyway, I managed to avoid the deadlock issue by initializing the classes that caused the problem as early as possible.
Tom
On 8/3/06, John Arthorne <John_Arthorne@xxxxxxxxxx
> wrote:
I'm using Sun JDK 1.5.0_06. You're probably talking about this bug (
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4670071 ) which is still number 1 in Sun's bug top 25.
Is the IBM VM publicly available ?
Tom
On 8/3/06, Thomas Watson <tjwatson@xxxxxxxxxx
> wrote:
What vendor/version of the VM are you using?
There has been a long standing bug open against Sun on a similar issue. It all boils down to the native VM locking the classloader before loading a class from it using the
ClassLoader.loadClassInternal method. In your stacktrace below this happens when the VM calls ClassLoader.loadClassInternal (DefaultClassLoader(ClassLoader).loadClassInternal(String) line: 319). The VM locks the classloader in native code before it ever calls into the ClassLoader. This leaves us with no options, even if we override the loadClassInternal method to make it non-synchronized it will make no difference because the native code locks the ClassLoader no matter what the method signature is for loadClassInternal. I have been told that Sun plans to fix this in a future release of the VM, it may be fixed in the latest
1.5 Sun VM. The IBM VMs have fixed this issue, they will NOT lock the classloader before invoking it from the native VM code.
Tom
Hi all,
I noticed that multithreading combined with buddy classloading can
produce some scary deadlocks. I had one in a project last week and
managed to recreate it in a toy example. Now I'm wondering if this is
just one of the dangers of breaking the classloading hierarchy or if
the framework could do something to avoid this ?
My toy example (also in attachment):
The main project has just one Application class:
public class Application implements IPlatformRunnable{
public Object run(Object args) throws Exception {
new Activator();
return true;
}
}
and the dependent project has an Activator
public class Activator implements BundleActivator {
public void start(BundleContext context) throws Exception {
new Thread(new Runnable() {
public void run() {
try {
Class.forName("main.Application");
} catch (ClassNotFoundException e) { }
}).start();
// let other thread run to induce deadlock
try { Thread.sleep(100); } catch (InterruptedException e) {}
}
public void stop(BundleContext context) throws Exception {}
}
The main project depends on dependent, and the dependent project has a
global buddy policy.
This causes the following deadlock:
Thread [main] (Suspended)
owns: DefaultClassLoader (id=16)
waiting for: DefaultClassLoader (id=15)
ClasspathManager.findLocalClassImpl(String, ClassLoadingStatsHook[]) line: 422
ClasspathManager.findLocalClass
(String) line: 410
DefaultClassLoader.findLocalClass(String) line: 188
BundleLoader.findLocalClass(String) line: 339
SingleSourcePackage.loadClass(String) line: 37
BundleLoader.findClass(String, boolean) line: 388
BundleLoader.findClass(String) line: 352
DefaultClassLoader.loadClass(String, boolean) line: 83
DefaultClassLoader(ClassLoader).loadClass(String) line: 251
DefaultClassLoader(ClassLoader).loadClassInternal(String) line: 319
Application.run(Object) line: 11
PlatformActivator$1.run(Object) line: 78
EclipseAppLauncher.runApplication(Object) line: 92
EclipseAppLauncher.start(Object) line: 68
EclipseStarter.run(Object) line: 400
EclipseStarter.run(String[], Runnable) line: 177
NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not
available [native method]
NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39
DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25
Method.invoke(Object, Object...) line: 585
Main.invokeFramework(String[], URL[]) line: 336
Main.basicRun(String[]) line: 280
Main.run(String[]) line: 977
Main.main(String[]) line: 952
Thread [Thread-1] (Suspended)
owns: DefaultClassLoader (id=15)
waiting for: DefaultClassLoader (id=16)
ClasspathManager.findLocalClassImpl(String, ClassLoadingStatsHook[]) line: 422
ClasspathManager.findLocalClass(String) line: 410
DefaultClassLoader.findLocalClass(String) line: 188
BundleLoader.findLocalClass(String) line: 339
BundleLoader.findClass(String, boolean) line: 391
BundleLoader.findClass(String) line: 352
DefaultClassLoader.loadClass(String, boolean) line: 83
DefaultClassLoader(ClassLoader).loadClass(String) line: 251
BundleLoader.loadClass(String) line: 276
BundleHost.loadClass(String, boolean) line: 227
BundleHost(AbstractBundle).loadClass(String) line: 1245
GlobalPolicy.loadClass(String) line: 39
PolicyHandler.doBuddyClassLoading(String) line: 138
BundleLoader.findClass(String, boolean) line: 402
BundleLoader.findClass(String) line: 352
DefaultClassLoader.loadClass(String, boolean) line: 83
DefaultClassLoader(ClassLoader).loadClass(String) line: 251
DefaultClassLoader(ClassLoader).loadClassInternal(String) line: 319
Class<T>.forName0(String, boolean, ClassLoader) line: not available
[native method]
Class<T>.forName(String) line: 164
Activator$1.run() line: 12
Thread.run() line: 595
[attachment "buddy-classloading-deadlock.zip" deleted by Thomas Watson/Austin/IBM] _______________________________________________
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--
Neil Bartlett
Senior Technical Consultant, Integility Ltd
Tel: +44 (0) 20 7043 8328
Fax: +44 (0) 20 7043 8329
LinkedIn Profile:
https://www.linkedin.com/in/neilbartlett
