src/hotspot/share/runtime/handshake.hpp

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.

@@ -28,17 +28,21 @@
 #include "memory/allocation.hpp"
 #include "memory/iterator.hpp"
 #include "runtime/flags/flagSetting.hpp"
 #include "runtime/semaphore.hpp"
 
+class HandshakeOperation;
 class JavaThread;
 
 // A handshake closure is a callback that is executed for each JavaThread
 // while that thread is in a safepoint safe state. The callback is executed
-// either by the thread itself or by the VM thread while keeping the thread
-// in a blocked state. A handshake can be performed with a single
-// JavaThread as well.
+// either by the target JavaThread itself or by the VMThread while keeping
+// the target thread in a blocked state. A handshake can be performed with a
+// single JavaThread as well. In that case, the callback is executed either
+// by the target JavaThread itself or, depending on whether the operation is
+// a direct handshake or not, by the JavaThread that requested the handshake
+// or the VMThread respectively.
 class HandshakeClosure : public ThreadClosure {
   const char* const _name;
  public:
   HandshakeClosure(const char* name) : _name(name) {}
   const char* name() const {

@@ -50,51 +54,55 @@
 class Handshake : public AllStatic {
  public:
   // Execution of handshake operation
   static void execute(HandshakeClosure* hs_cl);
   static bool execute(HandshakeClosure* hs_cl, JavaThread* target);
+  static bool execute_direct(HandshakeClosure* hs_cl, JavaThread* target);
 };
 
-class HandshakeOperation;
-
-// The HandshakeState keep tracks of an ongoing handshake for one JavaThread.
-// VM thread and JavaThread are serialized with the semaphore making sure
-// the operation is only done by either VM thread on behalf of the JavaThread
-// or the JavaThread itself.
+// The HandshakeState keeps track of an ongoing handshake for this JavaThread.
+// VMThread/Handshaker and JavaThread are serialized with semaphore _processing_sem
+// making sure the operation is only done by either VMThread/Handshaker on behalf
+// of the JavaThread or by the target JavaThread itself.
 class HandshakeState {
+  JavaThread* _handshakee;
   HandshakeOperation* volatile _operation;
+  HandshakeOperation* volatile _operation_direct;
 
-  Semaphore _semaphore;
+  Semaphore _handshake_turn_sem;  // Used to serialize direct handshakes for this JavaThread.
+  Semaphore _processing_sem;
   bool _thread_in_process_handshake;
 
-  bool claim_handshake_for_vmthread();
-  bool vmthread_can_process_handshake(JavaThread* target);
+  bool claim_handshake(bool is_direct);
+  bool possibly_can_process_handshake();
+  bool can_process_handshake();
+  void clear_handshake(bool is_direct);
 
-  void clear_handshake(JavaThread* thread);
+  void process_self_inner();
 
-  void process_self_inner(JavaThread* thread);
 public:
   HandshakeState();
 
-  void set_operation(JavaThread* thread, HandshakeOperation* op);
+  void set_handshakee(JavaThread* thread) { _handshakee = thread; }
 
-  bool has_operation() const {
-    return _operation != NULL;
+  void set_operation(HandshakeOperation* op);
+  bool has_operation() const { return _operation != NULL || _operation_direct != NULL; }
+  bool has_specific_operation(bool is_direct) const {
+    return is_direct ? _operation_direct != NULL : _operation != NULL;
   }
 
-  void process_by_self(JavaThread* thread) {
+  void process_by_self() {
     if (!_thread_in_process_handshake) {
       FlagSetting fs(_thread_in_process_handshake, true);
-      process_self_inner(thread);
+      process_self_inner();
     }
   }
-
-  bool try_process_by_vmThread(JavaThread* target);
+  bool try_process(HandshakeOperation* op);
 
 #ifdef ASSERT
-  bool _vmthread_processing_handshake;
-  bool is_vmthread_processing_handshake() const { return _vmthread_processing_handshake; }
+  Thread* _active_handshaker;
+  Thread* active_handshaker() const { return _active_handshaker; }
 #endif
 
 };
 
 #endif // SHARE_RUNTIME_HANDSHAKE_HPP