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.hpp"
28 #include "runtime/atomic.hpp"
29 #include "runtime/thread.inline.hpp"
30
31 #define MSG_IS_SYNCHRONOUS ( (MSGBIT(MSG_ROTATE)) | \
32 (MSGBIT(MSG_STOP)) | \
33 (MSGBIT(MSG_START)) | \
34 (MSGBIT(MSG_CLONE_IN_MEMORY)) | \
35 (MSGBIT(MSG_VM_ERROR)) | \
36 (MSGBIT(MSG_FLUSHPOINT)) \
37 )
38
39 static JfrPostBox* _instance = NULL;
40
instance()41 JfrPostBox& JfrPostBox::instance() {
42 return *_instance;
43 }
44
create()45 JfrPostBox* JfrPostBox::create() {
46 assert(_instance == NULL, "invariant");
47 _instance = new JfrPostBox();
48 return _instance;
49 }
50
destroy()51 void JfrPostBox::destroy() {
52 assert(_instance != NULL, "invariant");
53 delete _instance;
54 _instance = NULL;
55 }
56
JfrPostBox()57 JfrPostBox::JfrPostBox() :
58 _msg_read_serial(0),
59 _msg_handled_serial(0),
60 _messages(0),
61 _has_waiters(false) {}
62
is_thread_lock_aversive()63 static bool is_thread_lock_aversive() {
64 Thread* const thread = Thread::current();
65 return (thread->is_Java_thread() && ((JavaThread*)thread)->thread_state() != _thread_in_vm) || thread->is_VM_thread();
66 }
67
is_synchronous(int messages)68 static bool is_synchronous(int messages) {
69 return ((messages & MSG_IS_SYNCHRONOUS) != 0);
70 }
71
post(JFR_Msg msg)72 void JfrPostBox::post(JFR_Msg msg) {
73 const int the_message = MSGBIT(msg);
74 if (is_thread_lock_aversive()) {
75 deposit(the_message);
76 return;
77 }
78 if (!is_synchronous(the_message)) {
79 asynchronous_post(the_message);
80 return;
81 }
82 synchronous_post(the_message);
83 }
84
deposit(int new_messages)85 void JfrPostBox::deposit(int new_messages) {
86 while (true) {
87 const int current_msgs = Atomic::load(&_messages);
88 // OR the new message
89 const int exchange_value = current_msgs | new_messages;
90 const int result = Atomic::cmpxchg(&_messages, current_msgs, exchange_value);
91 if (result == current_msgs) {
92 return;
93 }
94 /* Some other thread just set exactly what this thread wanted */
95 if ((result & new_messages) == new_messages) {
96 return;
97 }
98 }
99 }
100
asynchronous_post(int msg)101 void JfrPostBox::asynchronous_post(int msg) {
102 assert(!is_synchronous(msg), "invariant");
103 deposit(msg);
104 JfrMonitorTryLock try_msg_lock(JfrMsg_lock);
105 if (try_msg_lock.acquired()) {
106 JfrMsg_lock->notify_all();
107 }
108 }
109
synchronous_post(int msg)110 void JfrPostBox::synchronous_post(int msg) {
111 assert(is_synchronous(msg), "invariant");
112 assert(!JfrMsg_lock->owned_by_self(), "should not hold JfrMsg_lock here!");
113 MonitorLocker msg_lock(JfrMsg_lock);
114 deposit(msg);
115 // serial_id is used to check when what we send in has been processed.
116 // _msg_read_serial is read under JfrMsg_lock protection.
117 const uintptr_t serial_id = Atomic::load(&_msg_read_serial) + 1;
118 msg_lock.notify_all();
119 while (!is_message_processed(serial_id)) {
120 msg_lock.wait();
121 }
122 }
123
124 /*
125 * Check if a synchronous message has been processed.
126 * We avoid racing on _msg_handled_serial by ensuring
127 * that we are holding the JfrMsg_lock when checking
128 * completion status.
129 */
is_message_processed(uintptr_t serial_id) const130 bool JfrPostBox::is_message_processed(uintptr_t serial_id) const {
131 assert(JfrMsg_lock->owned_by_self(), "_msg_handled_serial must be read under JfrMsg_lock protection");
132 return serial_id <= Atomic::load(&_msg_handled_serial);
133 }
134
is_empty() const135 bool JfrPostBox::is_empty() const {
136 assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");
137 return Atomic::load(&_messages) == 0;
138 }
139
collect()140 int JfrPostBox::collect() {
141 // get pending and reset to 0
142 const int messages = Atomic::xchg(&_messages, 0);
143 if (check_waiters(messages)) {
144 _has_waiters = true;
145 assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_read_serial is protected by JfrMsg_lock");
146 // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.
147 ++_msg_read_serial;
148 }
149 return messages;
150 }
151
check_waiters(int messages) const152 bool JfrPostBox::check_waiters(int messages) const {
153 assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");
154 assert(!_has_waiters, "invariant");
155 return is_synchronous(messages);
156 }
157
notify_waiters()158 void JfrPostBox::notify_waiters() {
159 if (!_has_waiters) {
160 return;
161 }
162 _has_waiters = false;
163 assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_handled_serial is protected by JfrMsg_lock.");
164 // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.
165 ++_msg_handled_serial;
166 JfrMsg_lock->notify();
167 }
168
169 // safeguard to ensure no threads are left waiting
notify_collection_stop()170 void JfrPostBox::notify_collection_stop() {
171 MutexLocker msg_lock(JfrMsg_lock);
172 JfrMsg_lock->notify_all();
173 }
174