Hello Stefan,
My personal opinion is that we continue with our release plans (whenever
we do it) instead of waiting for completing these changes. The virtual
threads feature is a preview feature in JDK 19, so I think as long as
our tests pass and Ant is usable in Java 19 with --enable-preview, I
think that's a good enough for an Ant release.
As for doing the actual changes, I think we will have to review these
call paths in core and individual tasks. Specifically, I think we need
to understand when/where a virtual thread might get used during a build
in a regular use case. The other thing I am hoping with our Ant release
is that we get actual users to start using the version with their own
builds/projects and tell us if/how the current release doesn't play well
(in terms of performance etc...) when it comes to virtual threads.
Given that this all boils down to "pinning" of the thread and since the
JEP 425 states:
"Pinning does not make an application incorrect, but it might hinder its
scalability. If a virtual thread performs a blocking operation such as
I/O or BlockingQueue.take() while it is pinned, then its carrier and the
underlying OS thread are blocked for the duration of the operation.
Frequent pinning for long durations can harm the scalability of an
application by capturing carriers.
The scheduler does not compensate for pinning by expanding its
parallelism. Instead, avoid frequent and long-lived pinning by revising
synchronized blocks or methods that run frequently and guard potentially
long I/O operations to use java.util.concurrent.locks.ReentrantLock
instead. There is no need to replace synchronized blocks and methods
that are used infrequently (e.g., only performed at startup) or that
guard in-memory operations. As always, strive to keep locking policies
simple and clear."
I think we should take our time to review these usages on a per use
basis (I realize 500 odd is too big to do on a per use basis, but I
think once we do the first few necessary changes, there should be more
clarity on which ones to focus on next).
-Jaikiran
On 06/06/22 4:19 pm, Stefan Bodewig wrote:
Hi
right now the Loom prototype doesn't play well with synchronized and the
recommended approach is to use ReentrantLock instead. A quick grep over
Ant's codebase turns up more than 500 hits for synchronized - many of
which in method declarations. So updating it will be a bigger task, in
particular if we wanted to take the time to think through the reasons
for synchronization and whether splitting read/write locks may be
useful.
Do you feel we should do this before the next release or should we defer
it? Another option might be to mechanically replace synchronized with
reentrantlock now and do the "read/write lock separation would be good"
assessment later.
Stefan
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