Dead Continuation cause resource leak?

[Alex Otenko]

Yes, but the JVM offers safety of try-finally. So finally is always
executed, if the enclosed block terminates. Implementing something of the
kind every time it is needed in CPS is not easy.

Alex

On Thu, 28 May 2020, 11:09 Ron Pressler, <ron.pressler at oracle.com> wrote:

> A continuation, or a virtual thread for that matter, that becomes
> unreachable before termination
> corresponds to an ordinary platform thread that sleeps forever. Neither
> the JDK nor the OS makes
> liveness guarantees about code.
>
> Having said that, a virtual thread can become unreachable before
> termination only due to a serious
> bug. When it is mounted, a reference to it is held by the scheduler or
> else it would be able to schedule
> it, and when blocked (and unmounted) a reference to it is held by the
> blocking construct, or else
> it would never be able to unblock it.
>
> — Ron
>
>
> On 28 May 2020 at 07:43:09, 施慧 (kalinshi at qq.com) wrote:
>
> Hi All,
>
>
> Trying to understand Loom continuation implementation. In following
> LeakTest,  Continuation Object is unreachable after first yield, but
> its runnable target is not finished yet.
> There might be some resources allcoated during continuation run (native
> memory in this test case and free in finally block --- not cleaner way),
> when continuation object is collected, these resources are not closed or
> freed.
>
>
> Is it possible to "clean up" a dead continuation which is not finished yet
> but collecting by GC? 
>
>
> Tested with code cloned from github today.
> javac --add-exports java.base/jdk.internal.ref=ALL-UNNAMED --add-exports
> java.base/jdk.internal.misc=ALL-UNNAMED  LeakTest.java
> java --add-exports java.base/jdk.internal.ref=ALL-UNNAMED --add-exports
> java.base/jdk.internal.misc=ALL-UNNAMED  LeakTest
> clean continuation
>
>
>
> import jdk.internal.ref.Cleaner;
> import jdk.internal.misc.Unsafe;
> public class LeakTest {
>     private static final Unsafe unsafe = Unsafe.getUnsafe();
>     static ContinuationScope scope = new
> ContinuationScope("scope");
>     public static void main(String[] args) throws Exception {
>         bar();
>         System.gc();
>         Thread.sleep(1000);
>         System.gc();
>         Thread.sleep(1000);
>     }
>
>
>     public static void bar() {
>         Continuation cont = new Continuation(scope, ()
> -> {
>             long mem = 0;
>             try {
>                 // open
> file/socket
>                 mem =
> unsafe.allocateMemory(100);
>                
> Continuation.yield(scope);
>             } finally {
>                
> unsafe.freeMemory(mem);
>                
> System.out.println("release memory");
>             }
>         });
>         Cleaner.create(cont, () -> {
> System.out.println("clean continuation");  });
>         cont.run();
>         //cont.run();
>     }
> }
>
>
>
> Regards
>