core: handle sigint (ctrl+c)

[sitano]

This patch makes YCSB to print measurement
results when the process receives a SIGINT
(CTRL+C) signal to output results before exit.

It is useful for all who don't want to wait
for the process to finish requested load amount
and don't want to lose measured results.

[sitano]

@busbey ^^
example_output.txt
It was useful for me when I was running tests. Decided to contribute with CTRL+C handler.

[sitano]

@busbey ping

[allanbank]

If you move the TerminatorThread created on line 396 up here can you then reuse the instance? You would still only start the thread on 361 if there is a maxExecutionTime > 0 but always create it for the hook.

[sitano]

I was lazy last time to make stopWorkload static, so I had to create an instance. This time a made it static.

[allanbank]

I am not a big fan of the multiple l.countDown(). Ideally there would be only a single call in a finally block but that would require yet another try block and this method is already try block heavy.

I think the nested try blocks on line 378/379 and then again on 405/406 can be merged. Maybe then add an outer try block with all of the exceptions and the finally for the latch? Something like:

try {
   // code...
    try (final TraceScope span = tracer.newScope(CLIENT_WORKLOAD_SPAN)) {
      // code...
    }
    try (final TraceScope span = tracer.newScope(CLIENT_CLEANUP_SPAN)) {
      // code...
    }
    try (final TraceScope span = tracer.newScope(CLIENT_EXPORT_MEASUREMENTS_SPAN)) {
      // code...
    }
} catch (WorkloadException e) {
  e.printStackTrace();
  e.printStackTrace(System.out);
  System.exit(0);
} catch (IOException e) {
  System.err.println("Could not export measurements, error: " + e.getMessage());
  e.printStackTrace();
  System.exit(-1);
} finally {
   l.countDown();
}

[sitano]

Done

[allanbank]

The use of the CountDownLatch I think obscures what is it doing. I'd suggest moving to a Semaphore.

Here would be:

final Semaphore done = new Semaphore(1);
done.acquire();

Below it would be:

done.release();

Then in the hook:

if( ! done.tryAquire() ) {
  // ...stopWorkload()
  try {
    if( ! done.tryAquire(5, TimeUnit.SECONDS) ) {
     System.err.println("Shutdown await timeout. Exit.");
    }
  } catch (InterruptedException timeout) {
  }
}

Extra credit to move this to a Phaser where things can then track the progress of the run (init, workload, cleanup, export measurement). In this case, as an example, you probably don't want to trigger the hook if we are already in the export phase.

[sitano]

Done. I am sorry I didnt have time this time to port it to Phaser.

[allanbank]

This message should be in the run() method.

[sitano]

Fixed

[sitano]

@allanbank ping