CODEWITHSUNDEEP
javamultithreadingaspectjaop
Arani
Arani

Reputation: 400

How to track Java parent thread id using aspectj?

I am trying to track to obtain the parent thread id of each new thread created in a program using AspectJ. Since a new thread starts execution using the start() method, I thought the following technique should work:

aspect getParentThread {
    pointcut threadStarting(): call(public void start());
    Object around(): threadStarting() {
         long parentThread = Thread.currentThread().getId();
         Object ret = proceed();
         long newThread = Thread.currentThread().getId();
         if (parentThread != newThread) {
              /*Store parentThread id in data structure */
         }
         return ret;
     }
}

But this simply does not work. Although the advice executes, even after proceed() completes there is just a single thread id. So what am I getting wrong here?

Upvotes: 0

Views: 1298

Answers (2)

kriegaex
kriegaex

Reputation: 67417

Warren Dew is right, but I want to add some sample code in order to show how you can easily do it with AspectJ. You do not even need an around() advice, a simple before() is enough.

Driver application:

package de.scrum_master.app;

public class Application {
    public static void main(String[] args) {
        new Thread(
            new Runnable() {
                @Override
                public void run() {}
            },
            "first thread"
        ).start();
        new Thread(
            new Runnable() {
                @Override
                public void run() {}
            },
            "second thread"
        ).start();
    }
}

Aspect:

package de.scrum_master.aspect;

public aspect ThreadStartInterceptor {
    before(Thread childThread) :
        call(public void Thread+.start()) &&
        target(childThread)
    {
        System.out.printf(
            "%s%n  Parent thread: %3d -> %s%n  Child thread:  %3d -> %s%n",
            thisJoinPoint,
            Thread.currentThread().getId(),
            Thread.currentThread().getName(),
            childThread.getId(),
            childThread.getName()
        );
    }
}
  • As you can see, I am limiting method interception to Thread+, i.e. to Thread and subclass instances. I am doing this explicitly even though it is not strictly necessary because the next point already does it implicitly:
  • I am also binding the child thread to a variable which can be used neatly from within the aspect.

Console log:

call(void java.lang.Thread.start())
  Parent thread:   1 -> main
  Child thread:   11 -> first thread
call(void java.lang.Thread.start())
  Parent thread:   1 -> main
  Child thread:   12 -> second thread

Upvotes: 2

Warren Dew
Warren Dew

Reputation: 8938

The issue is that all of your code executes in the parent thread, including the code after the child thread starts, because the start() method is called from and executes in the parent thread.

You could try getting the ID of the new thread from the Thread object on which the start() method is called.

Upvotes: 1

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