1 /*
   2  * Copyright (c) 2011, 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 "runtime/interfaceSupport.hpp"
  27 #include "runtime/javaCalls.hpp"
  28 #include "runtime/serviceThread.hpp"
  29 #include "runtime/mutexLocker.hpp"
  30 #include "prims/jvmtiImpl.hpp"
  31 
  32 void ServiceThread::initialize() {
  33   EXCEPTION_MARK;
  34 
  35   instanceKlassHandle klass (THREAD,  SystemDictionary::Thread_klass());
  36   instanceHandle thread_oop = klass->allocate_instance_handle(CHECK);
  37 
  38   const char thread_name[] = "Service Thread";
  39   Handle string = java_lang_String::create_from_str(thread_name, CHECK);
  40 
  41   // Initialize thread_oop to put it into the system threadGroup
  42   Handle thread_group (THREAD, Universe::system_thread_group());
  43   JavaValue result(T_VOID);
  44   JavaCalls::call_special(&result, thread_oop,
  45                           klass,
  46                           vmSymbolHandles::object_initializer_name(),
  47                           vmSymbolHandles::threadgroup_string_void_signature(),
  48                           thread_group,
  49                           string,
  50                           CHECK);
  51 
  52   {
  53     MutexLocker mu(Threads_lock);
  54     ServiceThread* thread =  new ServiceThread(&service_thread_entry);
  55 
  56     // At this point it may be possible that no osthread was created for the
  57     // JavaThread due to lack of memory. We would have to throw an exception
  58     // in that case. However, since this must work and we do not allow
  59     // exceptions anyway, check and abort if this fails.
  60     if (thread == NULL || thread->osthread() == NULL) {
  61       vm_exit_during_initialization("java.lang.OutOfMemoryError",
  62                                     "unable to create new native thread");
  63     }
  64 
  65     java_lang_Thread::set_thread(thread_oop(), thread);
  66     java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);
  67     java_lang_Thread::set_daemon(thread_oop());
  68     thread->set_threadObj(thread_oop());
  69 
  70     Threads::add(thread);
  71     Thread::start(thread);
  72   }
  73 }
  74 
  75 void ServiceThread::service_thread_entry(JavaThread* jt, TRAPS) {
  76   while (true) {
  77     bool sensors_changed = false;
  78     bool has_jvmti_events = false;
  79     JvmtiDeferredEvent jvmti_event = JvmtiDeferredEvent::null_event();
  80     {
  81       // _no_safepoint_check_flag is used here as Service_lock is a
  82       // special lock and the VMThread may acquire this lock at safepoint.
  83       // Need state transition ThreadBlockInVM so that this thread
  84       // will be handled by safepoint correctly when this thread is
  85       // notified at a safepoint.
  86 
  87       // This ThreadBlockInVM object is not also considered to be
  88       // suspend-equivalent because ServiceThread is not visible to
  89       // external suspension.
  90 
  91       ThreadBlockInVM tbivm(jt);
  92 
  93       MutexLockerEx ml(Service_lock, Mutex::_no_safepoint_check_flag);
  94       while (!(sensors_changed = LowMemoryDetector::has_pending_requests()) &&
  95              !(has_jvmti_events = JvmtiDeferredEventQueue::has_events())) {
  96         // wait until one of the sensors has pending requests, or there is a
  97         // pending JVMTI event to post
  98         Service_lock->wait(Mutex::_no_safepoint_check_flag);
  99       }
 100 
 101       if (has_jvmti_events) {
 102         // We dequeue the event here while holding Service_lock but post it
 103         // after releasing the lock.
 104         jvmti_event = JvmtiDeferredEventQueue::dequeue();
 105       }
 106     }
 107 
 108     if (sensors_changed) {
 109       LowMemoryDetector::process_sensor_changes(jt);
 110     }
 111 
 112     if (has_jvmti_events) {
 113       jvmti_event.post();
 114     }
 115   }
 116 }