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 "runtime/flags/flagSetting.hpp" 30 #include "runtime/semaphore.hpp" 31 32 class JavaThread; 33 34 // A handshake operation is a callback that is executed for each JavaThread 35 // while that thread is in a safepoint safe state. The callback is executed 36 // either by the thread itself or by the VM thread while keeping the thread 37 // in a blocked state. A handshake can be performed with a single 38 // JavaThread as well. 39 class HandshakeOperation: public StackObj { 40 static Semaphore _done; 41 const char* _name; 42 bool _executed; 43 public: 44 HandshakeOperation(const char* name) : _name(name), _executed(false) {} 45 46 void do_handshake(JavaThread* thread); 47 bool thread_has_completed() { return _done.trywait(); } 48 bool executed() const { return _executed; } 49 const char* name() { return _name; }; 50 51 #ifdef ASSERT 52 void check_state() { 53 assert(!_done.trywait(), "Must be zero"); 54 } 55 #endif 56 57 // Impl 58 virtual void do_thread(JavaThread* thread) = 0; 59 }; 60 61 class Handshake : public AllStatic { 62 public: 63 // Execution of handshake operation 64 static void execute(HandshakeOperation* hs_op); 65 static bool execute(HandshakeOperation* hs_op, JavaThread* target); 66 }; 67 68 // The HandshakeState keep tracks of an ongoing handshake for one JavaThread. 69 // VM thread and JavaThread are serialized with the semaphore making sure 70 // the operation is only done by either VM thread on behalf of the JavaThread 71 // or the JavaThread itself. 72 class HandshakeState { 73 HandshakeOperation* volatile _operation; 74 75 Semaphore _semaphore; 76 bool _thread_in_process_handshake; 77 78 bool claim_handshake_for_vmthread(); 79 bool vmthread_can_process_handshake(JavaThread* target); 80 81 void clear_handshake(JavaThread* thread); 82 83 void process_self_inner(JavaThread* thread); 84 public: 85 HandshakeState(); 86 87 void set_operation(JavaThread* thread, HandshakeOperation* op); 88 89 bool has_operation() const { 90 return _operation != NULL; 91 } 92 93 void process_by_self(JavaThread* thread) { 94 if (!_thread_in_process_handshake) { 95 FlagSetting fs(_thread_in_process_handshake, true); 96 process_self_inner(thread); 97 } 98 } 99 100 bool process_by_vmthread(JavaThread* target); 101 }; 102 103 #endif // SHARE_RUNTIME_HANDSHAKE_HPP