Re: RFR (M): 8231595 [TEST] develop a test case for SuspendThreadList including current thread

[serguei . spitsyn]

Hi Chris,

On 10/8/19 12:56 PM, Chris Plummer wrote:
Hi Serguei,
The just seems like an odd coding pattern to me:

  // Block until the suspender thread competes the tested threads 
suspension
  agent_lock(jni);
  agent_unlock(jni);

I do not consider it as odd but normal.
We have similar coding patterns in the jdwp agent.
The agent_unlock(jni) call can be moved to the end of the function if 
you like.
It does not matter in this particular case but will look "better".

Wouldn't you normally use wait/notify in this situation? Some like:

  agent_lock(jni);
  if (!suspenderDone) {
    agent_wait(jni);
  }
  agent_unlock(jni);

The above will make synchronization more complex.

I think maybe you left out the middle part because you know that this 
code will never grab the agent_lock before the suspender thread does, 
and therefore once this code gets the lock you know the suspender 
thread is done (is that actually the case?).
Yes, it is the case.

Thanks,
Serguei


thanks,

Chris

On 10/8/19 11:50 AM, serguei.spit...@oracle.com wrote:
Ping...

Thanks,
Serguei

On 10/7/19 5:25 PM, serguei.spit...@oracle.com wrote:
On 10/7/19 17:14, serguei.spit...@oracle.com wrote:
Hi Alex, Chris and David,

The mach5 testing in 100 runs loop on all platform discovered a 
race in new test.
It is between the native suspendTestedThreads() called on the 
suspender thread
and the checkSuspendedStatus() calling native 
checkTestedThreadsSuspended().

It occurred that the iteration count and sleep time in 
checkSuspendedStatus() can be not enough:
  100     private boolean checkSuspendedStatus(ThreadToSuspend[] threads) 
throws RuntimeException  {
  101         boolean success = false;
  102
  103         log("Main: checking all tested threads have been suspended");
  104
  105         // wait for tested threads to reach suspended status
  106         for (int i = 0; !success && i < 20; i++) {
  107             try {
  108                 Thread.sleep(10);
  109             } catch (InterruptedException e) {
  110               throw new RuntimeException("Main: sleep was 
interrupted\n\t" + e);
  111             }
  112             success = checkTestedThreadsSuspended();
  113         }
  114         return success;
  115     }

So, I've decided to refactor/update the test a little bit:

1. Now the checkSuspendedStatus() is:
  100     private boolean checkSuspendedStatus() throws RuntimeException  {
  101         log("Main: checking all tested threads have been suspended");
  102         return checkTestedThreadsSuspended();
  103     }
2. A raw monitor agent_monitor is added to the native agent.
   It is created and locked in the Java_ThreadToSuspend_init() 
function called at
   the beginning of the ThreadToSuspend.run() execution of the 
suspender thread
   and unlocked at the end of 
Java_ThreadToSuspend_suspendTestedThreads().

   The Java_SuspendWithCurrentThread_checkTestedThreadsSuspended() 
grabs the agent_monitor
   on the Main thread to wait until the suspendTestedThreads() 
completes its work.

3. Also, the results[] array is always created and used locally in 
the functions
   where it is needed: suspendTestedThreads() and 
resumeTestedThreads().

Forgot to tell about one more change:

4. The releaseTestedThreads() is renamed to 
releaseTestedThreadsInfo() and moved
   to the end of the Main thread run() method.

Also wanted to thank Alex for sharing good suggestions on the sync 
approaches.

Thanks,
Serguei


Updated webrev version:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2019/8231595-jvmti-susp-tlist.4/


Testing:
  One mach5 run with 100 rep counter successfully passed.
  To be more confident, I've submitted one more mach5 job which is 
in progress.

Thanks,
Serguei