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

[Serguei Spitsyn]

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

test/hotspot/jtreg/serviceability/jvmti/events/Breakpoint/breakpoint01/libbreakpoint01.cpp line 139:

> 137:            thr_info.name,        (jni->IsVirtualThread(thread) == JNI_TRUE) ? "virtual" : "kernel",
> 138:         (thr_info.is_daemon == JNI_TRUE) ? "deamon" : "user");
> 139:   }

I'd suggest to add locals (their names are up to you):
   const char* thr_virtual_tag = jni->IsVirtualThread(thread) == JNI_TRUE ? "virtual" : "kernel";
   const char* thr_daemon_tag == JNI_TRUE) ? "deamon" : "user";

It is better to place togeter lines: 129+130.
Line 137 is not aligned, and there are many unneeded spaces.
The '()' around conditions are not needed. At least, I do not see them increasing readability.

test/hotspot/jtreg/serviceability/jvmti/events/Breakpoint/breakpoint01/libbreakpoint01.cpp line 167:

> 165:     result = checkStatus = STATUS_FAILED;
> 166:     LOG(
> 167:         "TEST FAILED: Breakpoint event with unexpected class signature:\n"

Combine lines 166+167.

test/hotspot/jtreg/serviceability/jvmti/events/Breakpoint/breakpoint01/libbreakpoint01.cpp line 187:

> 185:       jboolean isVirtual = jni->IsVirtualThread(thread);
> 186:       if (isVirtual != METHODS_ATTRS[i]) {
> 187:         LOG("TEST FAILED: IsVirtualThread check failed with unexpected result %d  when expected is %d\n", isVirtual, METHODS_ATTRS[i]);

Line 187 is too long and can be splitted.

test/hotspot/jtreg/serviceability/jvmti/events/Breakpoint/breakpoint01/libbreakpoint01.cpp line 231:

> 229:       result = STATUS_FAILED;
> 230:       LOG(
> 231:           "TEST FAILED: wrong number of Breakpoint events\n"

Combine 230+231.

test/hotspot/jtreg/serviceability/jvmti/events/Breakpoint/breakpoint01/libbreakpoint01.cpp line 307:

> 305:   if (agent_lock == NULL) {
> 306:     return JNI_ERR;
> 307:   }

Better to also use same style with curly brackets in fragments: 293, 296, 299.

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