[Java] Add Plasma Free to Java code path (#2802)

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

@@ -0,0 +1,53 @@
+package org.ray.api.test;
+
+import com.google.common.collect.ImmutableList;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.Assert;
+import org.junit.Assume;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.ray.api.Ray;
+import org.ray.api.RayObject;
+import org.ray.api.WaitResult;
+import org.ray.api.annotation.RayRemote;
+import org.ray.api.id.UniqueId;
+import org.ray.core.AbstractRayRuntime;
+
+
+@RunWith(MyRunner.class)
+public class PlasmaFreeTest {
+
+  @RayRemote
+  private static String hello() {
+    return "hello";
+  }
+
+  @Test
+  public void test() {
+    Assume.assumeTrue(AbstractRayRuntime.getParams().use_raylet);
+    RayObject<String> helloId = Ray.call(PlasmaFreeTest::hello);
+    String helloString = helloId.get();
+    Assert.assertEquals("hello", helloString);
+    List<RayObject<String>> waitFor = ImmutableList.of(helloId);
+    WaitResult<String> waitResult = Ray.wait(waitFor, 1, 2 * 1000);
+    List<RayObject<String>> readyOnes = waitResult.getReady();
+    List<RayObject<String>> unreadyOnes = waitResult.getUnready();
+    Assert.assertEquals(1, readyOnes.size());
+    Assert.assertEquals(0, unreadyOnes.size());
+
+    List<UniqueId> freeList = new ArrayList<>();
+    freeList.add(helloId.getId());
+    Ray.internal().free(freeList, true);
+    // Flush: trigger the release function because Plasma Client has cache.
+    for (int i = 0; i < 128; i++) {
+      Ray.call(PlasmaFreeTest::hello).get();
+    }
+
+    waitResult = Ray.wait(waitFor, 1, 2 * 1000);
+    readyOnes = waitResult.getReady();
+    unreadyOnes = waitResult.getUnready();
+    Assert.assertEquals(0, readyOnes.size());
+    Assert.assertEquals(1, unreadyOnes.size());
+  }
+}