Re: Using ReentrantLock

Knute Johnson <>
Fri, 21 Aug 2009 14:36:18 -0700
markspace wrote:

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

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

and make it final too.

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

  public void writeStuff() {

        try {
        catch (Exception e) {
        finally {
          if (null != lockObject) {

  } // writeStuff
} // class MyOutputStream


Knute Johnson
email s/nospam/knute2009/

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