How to trace methods:
How to access information about the current method?
- How to associate a called method with its caller?
Other tracing approaches: TODO: Move to child page
Method Invocations in JVM
In Java the current executed methods are represented as frames, that are stored on a stack. Each frame contains all information that an invocation tracer might need.
When a method is started, it's frame is put on the stack and when it is done the associated frame is removed from the stack. In this way, the current executed method is always on top of the stack.
Each thread has a private stack containing its frames.
This could be used for tracking the method invocations in Java.
Disadvantages:
But the stacks and it's frames not accessible from Java itself and it would be necessary to use an extension library written in C.
This is not acceptable, since it would go against the non-functional requirements and make the tracer platform dependent.
Java Stack Trace approach
Disadvantages:
- Slow (suboptimal implementation of getStackTrace())
- High memory consumption ( method calls can go very deep)
- There is a possibility that a JVM implementation does not provide this stack, since its not part of the JVM Specification.
Own Stack Trace approach
-großer Speicherverbrauch
-Langsam (pop push für jede Methode..)
Method Signature approach
Zusätzlicher Methodenparameter. - Viel aufwand um die nativen Methodensignaturen zu ändern.
Container approach
Einfach die bereits gesammelten daten mit schicken mit den RMI.
-Großer Speicher und Netzwerkverbrauch, da die mitgeschickten Daten sehr groß werden können.
Method-ID approach
Quote:
"Another possibility to realize the invocation tracer is to add unique identifiers to all available sensors, so that every sensor gets an additional thread Id and a continuous node number in a call tree. This way, the process of building a complete Context Call Tree is divided in several parts: the sensors provide small pieces of information and some kind of tree builder has to provide a basic functionality to connect the gathered values and build a complete context tree out of this multiple node information."---->Not sure if i understood it right...
Each thread gets an unique ID and an continuous number for each method invocation done by this thread. This way each invocation can be associated with its thread.
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Approach picket in the thesis for the prototype (mixed approach)
Each thread gets a stack, where current active methods are stored. Only monitored methods are considered for the stack.
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The invocation data is send to the server in small pieces, on every method entry and exit. This way there is no need to store the data until the method finishes, what reduce the stress on the target application. The network has to handle smaller packs, which is also good for the performance. Also the server has the possibility to process the data earlier and it can be displayed while the method is still executing.
- Die Aufrufinformationen werden beim Methodenstrart und end versendet.
- Ein Stack wird erschafft für jeden Thread, und die asynchronen Aufrufe werden damit verbunden.
Current solution:
Currently the sequence sensor is implemented as container, which collects all sensor(e.g. timer sensor) data starting from an defined start point (execution of a predefined method). This collected data is chronologically ordered, to allow to trace the invocation sequence.
But this is not suitable for asynchronous methods. TODO: Validate if this is the current state of the sequence sensor. Possibly there were improvements in the meantime.
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