Re: Using ReentrantLock

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Newsgroups:

comp.lang.java.programmer

Date:

Fri, 21 Aug 2009 14:05:40 -0700

Message-ID:

<h6n277$v21$1@news.eternal-september.org>

RVic wrote:

if (null != response) {
I haev an output stream passed to a thread wherein I wish to write to
the outputstream, but have anyone else locked out from writing to it
while the particular handed-off-to thread writes to it.

I am a little unsure about using ReentrantLock to do this. In my code
below, which compiles (so what!) can anyone tell if I am using it
correctly or incorrectly or what I might have that's incorrect or
missing? Thanks, Rvince

ReentrantLock lockObject = new ReentrantLock(false);

I don't think this can work because you allocate a new lock each time.
Each invocation will get a new lock, which is unlocked, and then just
lock it. Hence there's no co-ordination between the various different
users.

Use an instance variable instead. Make one lock, and make sure everyone
(all callers) use the same lock object.

public class MyOutputStream implements OutputStream
{
ReentrantLock lockObject = new ReentrantLock(false);

public void writeStuff() {

        try {
          lockObject.lock();
          output.write(merchLinklengthBytes(response));
          output.write(headerControl);
          output.write(response.getBytes());
        }
        catch (Exception e) {
              e.printStackTrace();
        }
        finally {
          if (null != lockObject) {
            lockObject.unlock();
          }
        }
      }

} // writeStuff
} // class MyOutputStream