Re: [SCM] master: Avoid spurious waits in CountDownLatch.await

Re: [SCM] master: Avoid spurious waits in CountDownLatch.await

[Mark Wielaard]

Hi Tim,

On Thu, 2007-11-22 at 20:53 +0000, moore@sourceware.org wrote:
>     2007-11-22  Tim Moore  <timoore@redhat.com>
>     
>     	* CountDownLatch.java (await): Loop to avoid spurious wakeup.

Using wait() and notify() are such a pain :{
Good you caught this one.
Using higher order concurrent primitives is good.

There are some other non-guarded wait()s in some of the stepping command
(StepInstructionCommand, StepNextCommand, StepNextiCommand), which all
have something like:

      synchronized (cli.steppingObserver.getMonitor())
        {
          try
            {
              //XXX This looks racy.
              cli.steppingObserver.getMonitor().wait();
            }
          catch (InterruptedException ie) {}
        }

The XXX comment is right :{

If you are cleaning this up anyway you might want to abstract away all
the logic about guarding the mutex into the steppingObserver.

Cheers,

Mark

Re: [SCM] master: Avoid spurious waits in CountDownLatch.await

[Mark Wielaard]

Hi Tim,

On Fri, 2007-11-23 at 10:40 +0100, Mark Wielaard wrote:
> On Thu, 2007-11-22 at 20:53 +0000, moore@sourceware.org wrote:
> >     2007-11-22  Tim Moore  <timoore@redhat.com>
> >     
> >     	* CountDownLatch.java (await): Loop to avoid spurious wakeup.
> 
> Using wait() and notify() are such a pain :{
> Good you caught this one.
> Using higher order concurrent primitives is good.

I did find a bug though (just by running make check in frysk-core).
await need to be synchronized if you call wait() on this otherwise you
will get "current thread not owner" exceptions.

You might want to look into the public domain implementation of
CountDownLatch maybe to double check you got all the corner cases:
http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/main/java/util/concurrent/CountDownLatch.java

Cheers,

Mark

diff --git a/frysk-core/frysk/util/CountDownLatch.java
b/frysk-core/frysk/util/C
index b191782..f9d548f 100644
--- a/frysk-core/frysk/util/CountDownLatch.java
+++ b/frysk-core/frysk/util/CountDownLatch.java
@@ -53,7 +53,7 @@ public class CountDownLatch {
         this.count = count;
     }
 
-    public void await()
+    public synchronized void await()
         throws InterruptedException {
         while (count != 0) {
             try {