--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/runtime/handshake.hpp	Thu Aug 31 10:00:28 2017 +0200
@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2017, 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.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_VM_RUNTIME_HANDSHAKE_HPP
+#define SHARE_VM_RUNTIME_HANDSHAKE_HPP
+
+#include "memory/allocation.hpp"
+#include "runtime/semaphore.hpp"
+
+class ThreadClosure;
+class JavaThread;
+
+// A handshake operation 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.
+class Handshake : public AllStatic {
+ public:
+  // Execution of handshake operation
+  static void execute(ThreadClosure* thread_cl);
+  static bool execute(ThreadClosure* thread_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.
+class HandshakeState VALUE_OBJ_CLASS_SPEC {
+  HandshakeOperation* volatile _operation;
+
+  Semaphore _semaphore;
+  bool _vmthread_holds_semaphore;
+  bool _thread_in_process_handshake;
+
+  bool claim_handshake_for_vmthread();
+  bool vmthread_can_process_handshake(JavaThread* target);
+
+  void clear_handshake(JavaThread* thread);
+  void cancel_inner(JavaThread* thread);
+
+  void process_self_inner(JavaThread* thread);
+public:
+  HandshakeState();
+
+  void set_operation(JavaThread* thread, HandshakeOperation* op);
+
+  bool has_operation() const {
+    return _operation != NULL;
+  }
+
+  void cancel(JavaThread* thread) {
+    if (!_thread_in_process_handshake) {
+      FlagSetting fs(_thread_in_process_handshake, true);
+      cancel_inner(thread);
+    }
+  }
+
+  void process_by_self(JavaThread* thread) {
+    if (!_thread_in_process_handshake) {
+      FlagSetting fs(_thread_in_process_handshake, true);
+      process_self_inner(thread);
+    }
+  }
+  void process_by_vmthread(JavaThread* target);
+};
+
+#endif // SHARE_VM_RUNTIME_HANDSHAKE_HPP