Hi Robbin,
On 7/05/2019 4:50 pm, Robbin Ehn wrote:
Hi David,
On 5/7/19 12:40 AM, David Holmes wrote:
Hi Robbin,
I have a few concerns here.
First I can't see how you are actually integrating the SA with the
ThreadSMR. You've exposed the _java_thread_list for it to iterate but
IIRC that list can be updated when threads are added/removed and I'm
not seeing how the SA is left iterating a valid list - we'd normally
using a ThreadsListHandle for that ?? (I may need a refresher on how
this list is actually maintained.)
The processes must be paused. If the processes would be running the
linked list is also broken since if we unlink and delete a JavaThread
and then later SA follows that _next pointer.
Ah good point. Thanks for clarifying.
The conversion from external iteration of the list (the for loop) to
internal iteration (passing a lambda to JavaThreadsDo) is also
problematic. First I'd be very wary about introducing lambda
expressions into the SA code - lambda drags in a lot of supporting
code that could have an impact on the way SA functions. There are
places where we have to avoid lambdas due to
bootstrapping/initialization issues and I think the SA may be an area
where we also want to keep the code extremely simple.
There are already several usages of lambdas in SA code, e.g.
LinuxDebuggerLocal.java. SA is not a core module, it's an application,
there is not a bootstrap issue or so.
Hmm okay. Lambda carries a lot of baggage. But if its already being used ...
Second by using lambda's with internal iteration you've lost the
ability to terminate the iteration loop! In the existing code if we
have a return in the for-loop then we not only terminate the loop but
the enclosing method. With the lambda the "return" just ends the
current iteration and JavaThreadsDo will then continue with the next
thread - so we don't even terminate the iteration let alone the method
performing the iteration. So for places were we want to process one
thread, for example, we will continue to iterate all remaining threads
and just do nothing with them. That's very inefficient.
That's why I only used the internal iteration where we didn't have early
returns.
src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/CommandProcessor.java
- original code:
1556 new Command("where", "where { -a | id }", false) {
1557 public void doit(Tokens t) {
...
1564 for (JavaThread thread = threads.first();
thread != null; thread = thread.next()) {
1565 ByteArrayOutputStream bos = new
ByteArrayOutputStream();
1566 thread.printThreadIDOn(new PrintStream(bos));
1567 if (all || bos.toString().equals(name)) {
1568 out.println("Thread " + bos.toString()
+ " Address: " + thread.getAddress());
...
1577 }
1578 if (!all) return;
That looks like an early return to me.
Cheers,
David
-----
Thanks, Robbin
Thanks,
David
On 6/05/2019 5:31 pm, Robbin Ehn wrote:
Hi, please review.
Old threads linked list remove and updated SA to use ThreadsList
array instead.
Issue:
https://bugs.openjdk.java.net/browse/JDK-8223306
Webrev:
http://cr.openjdk.java.net/~rehn/8223306/webrev/
Passes t1-3 (which includes SA tests).
Thanks, Robbin
