RFR: 8284161: Implementation of Virtual Threads (Preview) [v8]

[Erik Gahlin]

On Wed, 27 Apr 2022 14:24:20 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> This is the implementation of JEP 425: Virtual Threads (Preview); TBD which JDK version to target.
>> 
>> We will refresh this PR periodically to pick up changes and fixes from the loom repo.
>> 
>> Most of the new mechanisms in the HotSpot VM are disabled by default and require running with `--enable-preview` to enable.
>> 
>> The patch has support for x64 and aarch64 on the usual operating systems (Linux, macOS, and Windows). There are stubs (calling Unimplemented) for zero and some of the other ports. Additional ports can be contributed via PRs against the fibers branch in the loom repo.
>> 
>> There are changes in many areas. To reduce notifications/mails, the labels have been trimmed down for now to hotspot, serviceability and core-libs. We'll add the complete set of labels when the PR is further along.
>> 
>> The changes include a refresh of java.util.concurrent and ForkJoinPool from Doug Lea's CVS. These changes will probably be proposed and integrated in advance of this PR.
>> 
>> The changes include some non-exposed and low-level infrastructure to support the (in draft) JEPs for Structured Concurrency and Scope Locals. This is to make life a bit easier and avoid having to separate VM changes and juggle branches at this time.
>
> Alan Bateman has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Refresh 7965cc6b168e567ac2596f2fbc3b00a7d99b7e1e

src/hotspot/share/jfr/leakprofiler/sampling/objectSampler.cpp line 168:

> 166:   assert(!tl->is_excluded(), "invariant");
> 167:   if (virtual_thread) {
> 168:     // TODO: blob cache for virtual threads

Fix this now or after integration?

src/hotspot/share/jfr/metadata/metadata.xml line 121:

> 119:     thread="true" stackTrace="true">
> 120:     <Field type="Thread" name="carrierThread" label="Carrier Thread" description="Thread enlisted as a carrier" />
> 121:     <Field type="Class" name="contClass" label="Continuation class" description="Class of the continuation" />

"Continuation class" = >" Continuation Class"
numFrames = frames
numRefs = references
"Number of interpreted frames" => "Interpreted Frames"
"Number of references" => "References"
"Stack size in bytes" => "Stack Size" contentType"bytes"

src/hotspot/share/jfr/metadata/metadata.xml line 130:

> 128:     thread="true" stackTrace="true">
> 129:     <Field type="Thread" name="carrierThread" label="Carrier Thread" description="Thread enlisted as a carrier" />
> 130:     <Field type="Class" name="contClass" label="Continuation class" description="Class of the continuation" />

contClass => continuationClass
"Continuation class" => "Continuation Class"
"Class of the continuation" Remove (not needed)
"Number of interpreted frames" => "Interpreted Frames"
numFrames => frames
"Number of references" => "References"
numRefs => references
"Stack size in bytes" => "Stack Size" contentType="bytes"

src/hotspot/share/jfr/metadata/metadata.xml line 138:

> 136:   <Event name="ContinuationFreezeYoung" experimental="true" category="Java Virtual Machine" label="Continuation Freeze Young" thread="true" stackTrace="false" startTime="false">
> 137:     <Field type="ulong" name="id" label="Continuation ID" />
> 138:     <Field type="uint" name="size" label="Size" />

"Allocated new" => "Allocated New"

src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointManager.cpp line 94:

> 92: static const size_t global_buffer_size = 512 * K;
> 93: 
> 94: static const size_t thread_local_buffer_prealloc_count = 32;

Why is more memory needed? Moore's law or something specific to virtual threads?

src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointWriter.cpp line 81:

> 79:   be_writer.write(size);
> 80:   be_writer.write(time);
> 81:   be_writer.write(JfrTicks::now().value() - time);

Why is this changed?

src/jdk.jfr/share/classes/jdk/jfr/events/VirtualThreadEndEvent.java line 35:

> 33: 
> 34: @Category({"Java Runtime"})
> 35: @Label("Virtual thread end")

"Virtual thread end" => "Virtual Thread End"
Remove description.

src/jdk.jfr/share/classes/jdk/jfr/events/VirtualThreadPinnedEvent.java line 35:

> 33: 
> 34: @Category({"Java Runtime"})
> 35: @Label("Virtual thread pinned")

"Virtual thread pinned" => "Virtual Thread Pinned"
Remove description

src/jdk.jfr/share/classes/jdk/jfr/events/VirtualThreadStartEvent.java line 35:

> 33: 
> 34: @Category({"Java Runtime"})
> 35: @Label("Virtual thread start")

"virtual thread start" => "Virtual Thread Start"
Remove description

src/jdk.jfr/share/classes/jdk/jfr/events/VirtualThreadSubmitFailedEvent.java line 35:

> 33: 
> 34: @Category({"Java Runtime"})
> 35: @Label("Virtual thread submit task failed")

The label is a bit a long, would "Virtual Thread Submit Failed" work?

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PR: https://git.openjdk.java.net/jdk/pull/8166