1 /*
   2  * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_RUNTIME_HANDSHAKE_HPP
  26 #define SHARE_RUNTIME_HANDSHAKE_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "memory/iterator.hpp"
  30 #include "runtime/flags/flagSetting.hpp"
  31 #include "runtime/semaphore.hpp"
  32 
  33 class JavaThread;
  34 
  35 // A handshake closure is a callback that is executed for each JavaThread
  36 // while that thread is in a safepoint safe state. The callback is executed
  37 // either by the thread itself or by the VM thread while keeping the thread
  38 // in a blocked state. A handshake can be performed with a single
  39 // JavaThread as well.
  40 class HandshakeClosure : public ThreadClosure {
  41   const char* const _name;
  42  public:
  43   HandshakeClosure(const char* name) : _name(name) {}
  44   const char* name() const {
  45     return _name;
  46   }
  47   virtual void do_thread(Thread* thread) = 0;
  48 };
  49 
  50 class Handshake : public AllStatic {
  51  public:
  52   // Execution of handshake operation
  53   static void execute(HandshakeClosure* hs_cl);
  54   static bool execute(HandshakeClosure* hs_cl, JavaThread* target);
  55 };
  56 
  57 class HandshakeOperation;
  58 
  59 // The HandshakeState keep tracks of an ongoing handshake for one JavaThread.
  60 // VM thread and JavaThread are serialized with the semaphore making sure
  61 // the operation is only done by either VM thread on behalf of the JavaThread
  62 // or the JavaThread itself.
  63 class HandshakeState {
  64   HandshakeOperation* volatile _operation;
  65 
  66   Semaphore _semaphore;
  67   bool _thread_in_process_handshake;
  68 
  69   bool claim_handshake_for_vmthread();
  70   bool vmthread_can_process_handshake(JavaThread* target);
  71 
  72   void clear_handshake(JavaThread* thread);
  73 
  74   void process_self_inner(JavaThread* thread);
  75 public:
  76   HandshakeState();
  77 
  78   void set_operation(JavaThread* thread, HandshakeOperation* op);
  79 
  80   bool has_operation() const {
  81     return _operation != NULL;
  82   }
  83 
  84   void process_by_self(JavaThread* thread) {
  85     if (!_thread_in_process_handshake) {
  86       FlagSetting fs(_thread_in_process_handshake, true);
  87       process_self_inner(thread);
  88     }
  89   }
  90 
  91   void process_by_vmthread(JavaThread* target);
  92 };
  93 
  94 #endif // SHARE_RUNTIME_HANDSHAKE_HPP