Support multiple core workers in one process (#7623)

java/api/src/main/java/org/ray/api/Ray.java

@@ -44,7 +44,7 @@ public final class Ray extends RayCall {
   /**
    * Shutdown Ray runtime.
    */
-  public static void shutdown() {
+  public static synchronized void shutdown() {
     if (runtime != null) {
       runtime.shutdown();
       runtime = null;
@@ -137,6 +137,11 @@ public final class Ray extends RayCall {
     runtime.setAsyncContext(asyncContext);
   }
 
+  // TODO (kfstorm): add the `rollbackAsyncContext` API to allow rollbacking the async context of
+  // the current thread to the one before `setAsyncContext` is called.
+
+  // TODO (kfstorm): unify the `wrap*` methods.
+
   /**
    * If users want to use Ray API in their own threads, they should wrap their {@link Runnable}
    * objects with this method.
@@ -155,7 +160,7 @@ public final class Ray extends RayCall {
    * @param callable The callable to wrap.
    * @return The wrapped callable.
    */
-  public static Callable wrapCallable(Callable callable) {
+  public static <T> Callable<T> wrapCallable(Callable<T> callable) {
     return runtime.wrapCallable(callable);
   }
 

java/api/src/main/java/org/ray/api/runtime/RayRuntime.java

@@ -159,6 +159,7 @@ public interface RayRuntime {
 
   /**
    * Wrap a {@link Runnable} with necessary context capture.
+   *
    * @param runnable The runnable to wrap.
    * @return The wrapped runnable.
    */
@@ -166,8 +167,9 @@ public interface RayRuntime {
 
   /**
    * Wrap a {@link Callable} with necessary context capture.
+   *
    * @param callable The callable to wrap.
    * @return The wrapped callable.
    */
-  Callable wrapCallable(Callable callable);
+  <T> Callable<T> wrapCallable(Callable<T> callable);
 }