'jdb' - The Java Debugger

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(Continued from previous part...)

main[1] stop in PrimeNumberSeeker.run
Set breakpoint PrimeNumberSeeker.run

main[1] cont
Period, Current int, # primes
1, 2, 0
>
Breakpoint hit: "thread=Thread-0", PrimeNumberSeeker.run(), line=28
28          primes = new int[ceiling];

Thread-0[1] threads
Group system:
  (java.lang.ref.Reference$ReferenceHandler)0xe2 Reference Handler
  (java.lang.ref.Finalizer$FinalizerThread)0xe1  Finalizer        
  (java.lang.Thread)0xe0                         Signal Dispatcher
Group main:
  (java.lang.Thread)0x1         main          running
  (PrimeNumberSeeker)0x118      Thread-0      running (at breakpoint)

Ok. What I have done so far:

• Started the debugging session with the first breakpoint at the beginning of the main() method, which cause the execution to stop at line 13.
• Then I created the second breakpoint at the beginning of the run() method in order to catch the sub thread.
• Then I issued the "cont" command. My application continued with the sub thread created stopped at the breakpoint at line 28. The main thread also stopped.
• Noticed that the debugger prompt is changed from "main[1]" to "Thread-0[1]". This is to inform you that you are currently in the sub thread, no longer in the main thread.
• The I used the "threads" command to list all threads. I saw two thread groups: "system" and "main". Of course, I am not interested in the "system" group at this point. The "main" shows two threads: "main" (my monitoring thread) and "Thread-0" (my sub thread working on the calculation).
• Thread "Thread-0" status shows "running (at breakpoint)". But the word "running" is referring to the thread execution mode, not the current execution status.
• Notice that tread "main" is also stopped at this moment. As a general rule, if one thread is stopped, all other threads are stopped also.

2. Stepping through the sub thread:

Thread-0[1] where all
Signal Dispatcher:
Finalizer:
  [1] java.lang.Object.wait (native method)
  [2] java.lang.ref.ReferenceQueue.remove (ReferenceQueue.java:111)
  [3] java.lang.ref.ReferenceQueue.remove (ReferenceQueue.java:127)
  [4] java.lang.ref.Finalizer$FinalizerThread.run (Finalizer.java:...
Reference Handler:
  [1] java.lang.Object.wait (native method)
  [2] java.lang.Object.wait (Object.java:429)
  [3] java.lang.ref.Reference$ReferenceHandler.run (Reference.java...
main:
  [1] java.lang.Thread.sleep (native method)
  [2] PrimeNumberSeeker.main (PrimeNumberSeeker.java:21)
Thread-0:
  [1] PrimeNumberSeeker.run (PrimeNumberSeeker.java:28)

Thread-0[1] next
2, 2, 0
>
Step completed: "thread=Thread-0", PrimeNumberSeeker.run(), line=29
29          while (count < ceiling) {

Thread-0[1] where all
...
main:
  [1] java.lang.Thread.sleep (native method)
  [2] PrimeNumberSeeker.main (PrimeNumberSeeker.java:21)
Thread-0:
  [1] PrimeNumberSeeker.run (PrimeNumberSeeker.java:29)

Thread-0[1] next
3, 2, 0
>
30             current++;

Thread-0[1] next
4, 3, 0
>
31             int j = 2;

(Continued on next part...)

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