| [incquery-dev] debugger tooling |
Hi allI have started to deal with the IncQuery Debugger Support: https://bugs.eclipse.org/bugs/show_bug.cgi?id=405556 Initially I just wanted to try out the Debugger API but I ended up implementing an "EMF-IncQuery Variables View" which is similar to the Variables View in Eclipse. The attached screenshot was taken during the debugging of an OSGi test application with pattern matching. Here you can see on the top level of the tree hierarchy the IncQueryEngine instances in the target JVM. Note that this View is usually one level below the target Eclipse instance, this case is special in the sense, that the debugger and the target app run "in the same Eclipse instance" (of course in different JVMs). This view would briefly correspond to point 2 in the issue description. Nevertheless, I do not really understand what does it mean to "point my debugger" (@Gaben).
These things are accessible through the Debugger API, basically I can retrieve the ClassLoader object (a special one, these things are under the com.sun.jdi package) from the stack frame when the view is notified that the application has stopped at a breakpoint. Then I can get all the instances of the given class (engines) and access attributes of these instances similarly to Java Reflection. I can even call methods in the target VM with the Debugger API, but at the moment it is a bit problematic. Consider the following snippet:
Method method = null;
try {
List<Method> methods =
ref.referenceType().methodsByName(methodName);
for (Method m : methods) {
if (m.arguments().isEmpty()) {
method = m;
break;
}
}
}
catch (AbsentInformationException e) {
//ignore
}
if (method != null) {
while (result == null && t < 10) {
try {
result = ref.invokeMethod(threadReference, method,
new ArrayList<Value>(), 0);
} catch (Exception e) {
result = null;
}
t++;
}
}
The classes here are from the com.sun.jdi package.
This method body tries to call the given method (parameterless!) on the
given ObjectReference instance. However, sometimes I get an
InvalidThreadStateException during the invocation.
The JavaDoc says that this Exception is thrown when the thread has not
been suspended by an event
(http://download.java.net/jdk8/docs/jdk/api/jpda/jdi/com/sun/jdi/ObjectReference.html#invokeMethod%28com.sun.jdi.ThreadReference,%20com.sun.jdi.Method,%20java.util.List,%20int%29).
What I have found out (and is surprising) is that consecutive
invocations (2-3 tries) usually (99% of the time) succeed. This method
implementation with the while loop may seem strange but it works most of
the time, I just wanted to restrict the possibility of an infinite loop.
This whole method invocation is necessary because I cannot get the
matches of a matcher from an instance field.
It would be great if someone knowledgeable could help me out with this issue. I tried to search for similar problems but haven't really found anything. I also searched for the implementation of the debugger itself (which executes such method invocations in the target VM) to be able to see what is happening when the Exception is thrown. Again, no luck :( I could only figure out that such calls are passed as messages and the protocol itself is described here http://docs.oracle.com/javase/1.5.0/docs/guide/jpda/jdwp/jdwp-protocol.html.
Cheers, Tomi -- Tamas Szabo Software engineer Tel.: +49 711 342 191 0 Fax.: +49 711 342 191 29 Mobil: +49 171 565 416 9 Web: www.itemis.de Mail: tamas.szabo@xxxxxxxxx Skype: szabta89 itemis AG Niederlassung Süd Meitnerstr. 10 70563 Stuttgart Rechtlicher Hinweis: Registergericht: Amtsgericht Dortmund HRB 20621 | Sitz der Gesellschaft: Lünen Vorstand: Jens Wagener (Vorsitzender) | Wolfgang Neuhaus | Dr. Georg Pietrek | Jens Trompeter | Sebastian Neus Aufsichtsrat: Prof. Dr. Burkhard Igel (Vorsitzender) | Stephan Grollmann | Michael Neuhaus
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