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Subject: Why jobtracker.jsp can safely call a non-thread-safe method of JT?
From: Min Zhou <coderplay@gmail.com>
To: mapreduce-dev@hadoop.apache.org, mapreduce-user@hadoop.apache.org
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Hi all,

Hadoop JobTracker's http info server provides running/failed/completed
job informations on the web through jobtracker.jsp.  Lines below show
the logic how the web retries those informations from JobTracker.

  JobTracker tracker = (JobTracker) application.getAttribute("job.tracker");
  ...
  Vector<JobInProgress> runningJobs = tracker.runningJobs();
  Vector<JobInProgress> completedJobs = tracker.completedJobs();
  Vector<JobInProgress> failedJobs = tracker.failedJobs();

Those three methods above are apparently non-thread-safe ones.  I am
confused,  why the web can safely call a non-thread-safe method of JT?

Thanks,
Min
-- 
My research interests are distributed systems, parallel computing and
bytecode based virtual machine.

My profile:
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