Virtual thread hang and all threads stop running on JDK21

[robert engels]

What are you trying to do? I am pretty sure the current scheduler is tied directly to the implementation and if you change it, I am not surprised that things don’t work. The default scheduler creates instances of CarrierThread which has special properties. It is doubtful yours does.

> On Jun 4, 2024, at 8:29 AM, 何品(虎鸣) <hepin.p at alibaba-inc.com> wrote:
> 
> 
> Hi, we are using Virtual threads on JDK21.0.2, and find it can stop running, all threads stopped/hung, and we can't even call thread dump.
> We try to separate the Virtual Thread's scheduler with reflections. but that does not work too.
> 
> Our userbase are pretty simple:
> A: VT Executor backing by 128-sized ThreadPoolExecutor for running java code with `CompletableFuture.get`
> B: VT Executor backing by 64-sized ThreadPoolExecutor for retrieving data with HTTP client, with max concurrency to 3000 (virtual threads)
> 
> Even if A and B are using Different backing ThreadPool, they all stop responding。
> 
> 
> 
> ```java
>     public static Executor virtualize(final String prefix,
>                                       final boolean enabled,
>                                       final Executor executor) {
>         if (!enabled) {
>             return executor;
>         }
>         try {
>             final var builder = Thread.ofVirtual();
>             if (executor != null) {
>                 final var clazz = builder.getClass();
>                 final var privateLookup = MethodHandles.privateLookupIn(clazz, lookup);
>                 final var schedulerFieldSetter = privateLookup.findSetter(clazz, "scheduler", Executor.class);
>                 schedulerFieldSetter.invoke(builder, executor);
>             }
>             builder.name(prefix + "-virtual-thread-", 0L);
>             final var factory = builder.factory();
>             return Executors.newThreadPerTaskExecutor(factory);
>         } catch (Throwable e) {
>             log.error("Error when virtualize a executor", e);
>             return executor;
>         }
>     }
> 

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