1 /*
2  * Copyright (c) 2019, 2021, 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
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23  */
24 
25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.hpp"
27 #include "classfile/vmClasses.hpp"
28 #include "memory/universe.hpp"
29 #include "runtime/interfaceSupport.inline.hpp"
30 #include "runtime/java.hpp"
31 #include "runtime/javaCalls.hpp"
32 #include "runtime/notificationThread.hpp"
33 #include "services/diagnosticArgument.hpp"
34 #include "services/diagnosticFramework.hpp"
35 #include "services/gcNotifier.hpp"
36 #include "services/lowMemoryDetector.hpp"
37 
38 NotificationThread* NotificationThread::_instance = NULL;
39 
initialize()40 void NotificationThread::initialize() {
41   EXCEPTION_MARK;
42 
43   const char* name = "Notification Thread";
44   Handle string = java_lang_String::create_from_str(name, CHECK);
45 
46   // Initialize thread_oop to put it into the system threadGroup
47   Handle thread_group (THREAD, Universe::system_thread_group());
48   Handle thread_oop = JavaCalls::construct_new_instance(
49                           vmClasses::Thread_klass(),
50                           vmSymbols::threadgroup_string_void_signature(),
51                           thread_group,
52                           string,
53                           CHECK);
54 
55   Klass* group = vmClasses::ThreadGroup_klass();
56   JavaValue result(T_VOID);
57   JavaCalls::call_special(&result,
58                           thread_group,
59                           group,
60                           vmSymbols::add_method_name(),
61                           vmSymbols::thread_void_signature(),
62                           thread_oop,
63                           THREAD);
64   {
65     MutexLocker mu(THREAD, Threads_lock);
66     NotificationThread* thread =  new NotificationThread(&notification_thread_entry);
67 
68     // At this point it may be possible that no osthread was created for the
69     // JavaThread due to lack of memory. We would have to throw an exception
70     // in that case. However, since this must work and we do not allow
71     // exceptions anyway, check and abort if this fails.
72     if (thread == NULL || thread->osthread() == NULL) {
73       vm_exit_during_initialization("java.lang.OutOfMemoryError",
74                                     os::native_thread_creation_failed_msg());
75     }
76 
77     java_lang_Thread::set_thread(thread_oop(), thread);
78     java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);
79     java_lang_Thread::set_daemon(thread_oop());
80     thread->set_threadObj(thread_oop());
81     _instance = thread;
82 
83     Threads::add(thread);
84     Thread::start(thread);
85   }
86 }
87 
88 
89 
notification_thread_entry(JavaThread * jt,TRAPS)90 void NotificationThread::notification_thread_entry(JavaThread* jt, TRAPS) {
91   while (true) {
92     bool sensors_changed = false;
93     bool has_dcmd_notification_event = false;
94     bool has_gc_notification_event = false;
95     {
96       // Need state transition ThreadBlockInVM so that this thread
97       // will be handled by safepoint correctly when this thread is
98       // notified at a safepoint.
99 
100       ThreadBlockInVM tbivm(jt);
101 
102       MonitorLocker ml(Notification_lock, Mutex::_no_safepoint_check_flag);
103       // Process all available work on each (outer) iteration, rather than
104       // only the first recognized bit of work, to avoid frequently true early
105       // tests from potentially starving later work.  Hence the use of
106       // arithmetic-or to combine results; we don't want short-circuiting.
107       while (((sensors_changed = LowMemoryDetector::has_pending_requests()) |
108               (has_dcmd_notification_event = DCmdFactory::has_pending_jmx_notification()) |
109               (has_gc_notification_event = GCNotifier::has_event()))
110              == 0) {
111         // Wait until notified that there is some work to do.
112         ml.wait(0);
113       }
114 
115     }
116 
117     if (sensors_changed) {
118       LowMemoryDetector::process_sensor_changes(jt);
119     }
120 
121     if(has_gc_notification_event) {
122       GCNotifier::sendNotification(CHECK);
123     }
124 
125     if(has_dcmd_notification_event) {
126       DCmdFactory::send_notification(CHECK);
127     }
128 
129   }
130 }
131 
132