1 /*
2 * Copyright (c) 2013, 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 #include "precompiled.hpp"
26 #include "jfr/recorder/service/jfrPostBox.hpp"
27 #include "jfr/utilities/jfrTryLock.inline.hpp"
28 #include "runtime/atomic.hpp"
29 #include "runtime/mutexLocker.inline.hpp"
30 #include "runtime/orderAccess.hpp"
31 #include "runtime/thread.inline.hpp"
32
33 #define MSG_IS_SYNCHRONOUS ( (MSGBIT(MSG_ROTATE)) | \
34 (MSGBIT(MSG_STOP)) | \
35 (MSGBIT(MSG_START)) | \
36 (MSGBIT(MSG_CLONE_IN_MEMORY)) | \
37 (MSGBIT(MSG_VM_ERROR)) \
38 )
39
40 static JfrPostBox* _instance = NULL;
41
42 JfrPostBox& JfrPostBox::instance() {
43 return *_instance;
44 }
45
46 JfrPostBox* JfrPostBox::create() {
47 assert(_instance == NULL, "invariant");
48 _instance = new JfrPostBox();
49 return _instance;
50 }
51
52 void JfrPostBox::destroy() {
53 assert(_instance != NULL, "invariant");
54 delete _instance;
55 _instance = NULL;
56 }
57
58 JfrPostBox::JfrPostBox() :
59 _msg_read_serial(0),
60 _msg_handled_serial(0),
61 _messages(0),
62 _has_waiters(false) {}
63
64 static bool is_thread_lock_aversive() {
65 Thread* const thread = Thread::current();
66 return (thread->is_Java_thread() && ((JavaThread*)thread)->thread_state() != _thread_in_vm) || thread->is_VM_thread();
67 }
68
69 static bool is_synchronous(int messages) {
70 return ((messages & MSG_IS_SYNCHRONOUS) != 0);
71 }
72
73 void JfrPostBox::post(JFR_Msg msg) {
74 const int the_message = MSGBIT(msg);
75 if (is_thread_lock_aversive()) {
76 deposit(the_message);
77 return;
78 }
79 if (!is_synchronous(the_message)) {
80 asynchronous_post(the_message);
81 return;
82 }
83 synchronous_post(the_message);
84 }
85
86 void JfrPostBox::deposit(int new_messages) {
87 while (true) {
88 const int current_msgs = OrderAccess::load_acquire(&_messages);
89 // OR the new message
90 const int exchange_value = current_msgs | new_messages;
91 const int result = Atomic::cmpxchg(exchange_value, &_messages, current_msgs);
92 if (result == current_msgs) {
93 return;
94 }
95 /* Some other thread just set exactly what this thread wanted */
96 if ((result & new_messages) == new_messages) {
97 return;
98 }
99 }
100 }
101
102 void JfrPostBox::asynchronous_post(int msg) {
103 assert(!is_synchronous(msg), "invariant");
104 deposit(msg);
105 JfrMonitorTryLock try_msg_lock(JfrMsg_lock);
106 if (try_msg_lock.acquired()) {
107 JfrMsg_lock->notify_all();
108 }
109 }
110
111 void JfrPostBox::synchronous_post(int msg) {
112 assert(is_synchronous(msg), "invariant");
113 assert(!JfrMsg_lock->owned_by_self(), "should not hold JfrMsg_lock here!");
114 MonitorLocker msg_lock(JfrMsg_lock);
115 deposit(msg);
116 // serial_id is used to check when what we send in has been processed.
117 // _msg_read_serial is read under JfrMsg_lock protection.
118 const uintptr_t serial_id = OrderAccess::load_acquire(&_msg_read_serial) + 1;
119 msg_lock.notify_all();
120 while (!is_message_processed(serial_id)) {
121 msg_lock.wait();
122 }
123 }
124
125 /*
126 * Check if a synchronous message has been processed.
127 * We avoid racing on _msg_handled_serial by ensuring
128 * that we are holding the JfrMsg_lock when checking
129 * completion status.
130 */
131 bool JfrPostBox::is_message_processed(uintptr_t serial_id) const {
132 assert(JfrMsg_lock->owned_by_self(), "_msg_handled_serial must be read under JfrMsg_lock protection");
133 return serial_id <= OrderAccess::load_acquire(&_msg_handled_serial);
134 }
135
136 bool JfrPostBox::is_empty() const {
137 assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");
138 return OrderAccess::load_acquire(&_messages) == 0;
139 }
140
141 int JfrPostBox::collect() {
142 // get pending and reset to 0
143 const int messages = Atomic::xchg(0, &_messages);
144 if (check_waiters(messages)) {
145 _has_waiters = true;
146 assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_read_serial is protected by JfrMsg_lock");
147 // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.
148 ++_msg_read_serial;
149 }
150 return messages;
151 }
152
153 bool JfrPostBox::check_waiters(int messages) const {
154 assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");
155 assert(!_has_waiters, "invariant");
156 return is_synchronous(messages);
157 }
158
159 void JfrPostBox::notify_waiters() {
160 if (!_has_waiters) {
161 return;
162 }
163 _has_waiters = false;
164 assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_handled_serial is protected by JfrMsg_lock.");
165 // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.
166 ++_msg_handled_serial;
167 JfrMsg_lock->notify();
168 }
169
170 // safeguard to ensure no threads are left waiting
171 void JfrPostBox::notify_collection_stop() {
172 MutexLocker msg_lock(JfrMsg_lock);
173 JfrMsg_lock->notify_all();
174 }