Late cleanup of stack objects

[Arnaud Masson]

> I will check if C2 helps, but afaik since it’s triggered when method is
> used often (not because the method consumes significant memory), it’s
> not ideal to count on it anyway. Moreover, I suspect it’s not documented
> public behavior while lambda capture is well defined.


I have checked the following example with (no debugger)

--enable-preview
-XX:-TieredCompilation
-Xbatch
-Xcomp
-Xlog:nmethod+install

… to force C2, but the bigBuffer is still retained.

(Won’t C2 clear a stack ref only if it can be reused in the same scope for another java var?)

Thanks
Arnaud


import java.lang.management.ManagementFactory;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;

public class Main1 {
   public static void main(String[] args) throws ExecutionException, InterruptedException {
      var timer = new Timer();
      var memBean = ManagementFactory.getMemoryMXBean();
      timer.schedule(new TimerTask() {
            @Override
            public void run() {
               System.gc();
               System.out.println("--- " + memBean.getHeapMemoryUsage());
            }
         }, 10*1000, 10*1000);
      myApp();
   }

   private static void myApp() throws ExecutionException, InterruptedException {
      var executor = Executors.newVirtualThreadPerTaskExecutor();
      var future = executor.submit(() -> {
         try {
            System.out.println("Starting work");
            var bigBuffer = new byte[1024 * 1024 * 1024];
            System.out.println("bigBuffer size: " + bigBuffer.length);
            // bigBuffer = null;
            slowIO();
         } catch (InterruptedException e) {
            throw new RuntimeException(e);
         }
      });
      future.get();
   }

   private static void slowIO() throws InterruptedException {
      System.out.println("Starting slowIO");
      Thread.sleep(Long.MAX_VALUE);
   }
}

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