[xray] Implement Actor Reconstruction (#3332)

* Implement Actor Reconstruction

* fix

* fix actor handle __del__

* fix lint

* add comment

* Remove actorCreationDummyObjectId

* address comments

* fix

* address comments

* avoid copy

* change log to debug

* fix error name

java/test/src/main/java/org/ray/api/test/ActorReconstructionTest.java

@@ -0,0 +1,69 @@
+package org.ray.api.test;
+
+import static org.ray.runtime.util.SystemUtil.pid;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.concurrent.TimeUnit;
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.ray.api.Ray;
+import org.ray.api.RayActor;
+import org.ray.api.annotation.RayRemote;
+import org.ray.api.options.ActorCreationOptions;
+
+@RunWith(MyRunner.class)
+public class ActorReconstructionTest {
+
+  @RayRemote()
+  public static class Counter {
+
+    private int value = 0;
+
+    public int increase(int delta) {
+      value += delta;
+      return value;
+    }
+
+    public int getPid() {
+      return pid();
+    }
+  }
+
+  @Test
+  public void testActorReconstruction() throws InterruptedException, IOException {
+    ActorCreationOptions options = new ActorCreationOptions(new HashMap<>(), 1);
+    RayActor<Counter> actor = Ray.createActor(Counter::new, options);
+    // Call increase 3 times.
+    for (int i = 0; i < 3; i++) {
+      Ray.call(Counter::increase, actor, 1).get();
+    }
+
+    // Kill the actor process.
+    int pid = Ray.call(Counter::getPid, actor).get();
+    Runtime.getRuntime().exec("kill -9 " + pid);
+    // Wait for the actor to be killed.
+    TimeUnit.SECONDS.sleep(1);
+
+    // Try calling increase on this actor again and check the value is now 4.
+    int value = Ray.call(Counter::increase, actor, 1).get();
+    Assert.assertEquals(value, 4);
+
+    // Kill the actor process again.
+    pid = Ray.call(Counter::getPid, actor).get();
+    Runtime.getRuntime().exec("kill -9 " + pid);
+    TimeUnit.SECONDS.sleep(1);
+
+    // Try calling increase on this actor again and this should fail.
+    try {
+      Ray.call(Counter::increase, actor, 1).get();
+      Assert.fail("The above task didn't fail.");
+    } catch (StringIndexOutOfBoundsException e) {
+      // Raylet backend will put invalid data in task's result to indicate the task has failed.
+      // Thus, Java deserialization will fail and throw `StringIndexOutOfBoundsException`.
+      // TODO(hchen): we should use object's metadata to indicate task failure,
+      // instead of throwing this exception.
+    }
+  }
+}