[armedbear-devel] Better multithreading support (was Re: [Bordeaux-threads-devel] [Updated4] Patch for ABCL against BORDEAUX-THREADS HEAD)

[Mark Evenson]

On 3/21/11 15:21 , Chun Tian (binghe) wrote:
> Hi, Mark
> 
> I'm interesting in your work.
> 
> First, I'd like to know, how to do a "condition variable wait with
> timeout" with your exist work,

It should be pretty easy, as THREADS:OBJECT-WAIT has an optional
parameter for TIMEOUT (see [the Java API for the semantics associated
with this value][1])

[1]:
http://download.oracle.com/javase/6/docs/api/java/lang/Object.html#wait%28long%29

So, one could naively extend my BORDEAUX-THREADS implementation as follows:

    (defun condition-wait (condition lock &optional timeout)
      (threads:synchronized-on condition
        (release-lock lock)
        (if timeout
          (threads:object-wait condition timeout)
          (threads:object-wait condition))
        (acquire-lock lock))

But then a wait on the condition variable which exceeded the timeout
would be the same as a thread which was notified, which probably isn't
what we want.

If you don't need to follow the B-T API, then I might go for an
encapsulation [of the actual Condition class][2] which returns a boolean
indicating whether the wait has returned because the timeout has expired.

[2]:
http://download.oracle.com/javase/6/docs/api/java/util/concurrent/locks/Condition.html#await%28long,%20java.util.concurrent.TimeUnit%29

I'm not sure of your comfort with ABCL's Java FFI, but I would be happy
to mentor you through an implementation that suits your needs, subject
to possible time delays on my part due to other tasks.

> Second, do you think it's possible to make ABCL supporting some
> atomic operations, something like ATOMIC-INCF or ATOMIC-PUSH, this
> can be very useful to implement some lockless algorithms.

Here, I would use the [atomic lock-free implementation in the JVM][3],
which could give us such things quite cheaply.

[3]:
http://download.oracle.com/javase/6/docs/api/java/util/concurrent/atomic/package-summary.html

Do you have a Lisp-side API to recommend?


-- 
"A screaming comes across the sky.  It has happened before, but there
is nothing to compare to it now."