1 /*
2  * Copyright (c) 2019, 2020, 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
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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
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24 
25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.hpp"
27 #include "memory/universe.hpp"
28 #include "runtime/interfaceSupport.inline.hpp"
29 #include "runtime/javaCalls.hpp"
30 #include "runtime/notificationThread.hpp"
31 #include "services/diagnosticArgument.hpp"
32 #include "services/diagnosticFramework.hpp"
33 #include "services/gcNotifier.hpp"
34 #include "services/lowMemoryDetector.hpp"
35 
36 NotificationThread* NotificationThread::_instance = NULL;
37 
initialize()38 void NotificationThread::initialize() {
39   EXCEPTION_MARK;
40 
41   const char* name = "Notification Thread";
42   Handle string = java_lang_String::create_from_str(name, CHECK);
43 
44   // Initialize thread_oop to put it into the system threadGroup
45   Handle thread_group (THREAD, Universe::system_thread_group());
46   Handle thread_oop = JavaCalls::construct_new_instance(
47                           SystemDictionary::Thread_klass(),
48                           vmSymbols::threadgroup_string_void_signature(),
49                           thread_group,
50                           string,
51                           CHECK);
52 
53   Klass* group = SystemDictionary::ThreadGroup_klass();
54   JavaValue result(T_VOID);
55   JavaCalls::call_special(&result,
56                           thread_group,
57                           group,
58                           vmSymbols::add_method_name(),
59                           vmSymbols::thread_void_signature(),
60                           thread_oop,
61                           THREAD);
62   {
63     MutexLocker mu(THREAD, Threads_lock);
64     NotificationThread* thread =  new NotificationThread(&notification_thread_entry);
65 
66     // At this point it may be possible that no osthread was created for the
67     // JavaThread due to lack of memory. We would have to throw an exception
68     // in that case. However, since this must work and we do not allow
69     // exceptions anyway, check and abort if this fails.
70     if (thread == NULL || thread->osthread() == NULL) {
71       vm_exit_during_initialization("java.lang.OutOfMemoryError",
72                                     os::native_thread_creation_failed_msg());
73     }
74 
75     java_lang_Thread::set_thread(thread_oop(), thread);
76     java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);
77     java_lang_Thread::set_daemon(thread_oop());
78     thread->set_threadObj(thread_oop());
79     _instance = thread;
80 
81     Threads::add(thread);
82     Thread::start(thread);
83   }
84 }
85 
86 
87 
notification_thread_entry(JavaThread * jt,TRAPS)88 void NotificationThread::notification_thread_entry(JavaThread* jt, TRAPS) {
89   while (true) {
90     bool sensors_changed = false;
91     bool has_dcmd_notification_event = false;
92     bool has_gc_notification_event = false;
93     {
94       // Need state transition ThreadBlockInVM so that this thread
95       // will be handled by safepoint correctly when this thread is
96       // notified at a safepoint.
97 
98       ThreadBlockInVM tbivm(jt);
99 
100       MonitorLocker ml(Notification_lock, Mutex::_no_safepoint_check_flag);
101       // Process all available work on each (outer) iteration, rather than
102       // only the first recognized bit of work, to avoid frequently true early
103       // tests from potentially starving later work.  Hence the use of
104       // arithmetic-or to combine results; we don't want short-circuiting.
105       while (((sensors_changed = LowMemoryDetector::has_pending_requests()) |
106               (has_dcmd_notification_event = DCmdFactory::has_pending_jmx_notification()) |
107               (has_gc_notification_event = GCNotifier::has_event()))
108              == 0) {
109         // Wait as a suspend equalent until notified that there is some work to do.
110         ml.wait(0, true);
111       }
112 
113     }
114 
115     if (sensors_changed) {
116       LowMemoryDetector::process_sensor_changes(jt);
117     }
118 
119     if(has_gc_notification_event) {
120       GCNotifier::sendNotification(CHECK);
121     }
122 
123     if(has_dcmd_notification_event) {
124       DCmdFactory::send_notification(CHECK);
125     }
126 
127   }
128 }
129 
130