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 ServiceThread* ServiceThread::_instance = NULL;

    33 

    34 void ServiceThread::initialize() {

    35   EXCEPTION_MARK;

    36 

    37   instanceKlassHandle klass (THREAD,  SystemDictionary::Thread_klass());

    38   instanceHandle thread_oop = klass->allocate_instance_handle(CHECK);

    39 

    40   const char* name = JDK_Version::is_gte_jdk17x_version() ?

    41       "Service Thread" : "Low Memory Detector";

    42 

    43   Handle string = java_lang_String::create_from_str(name, CHECK);

    44 

    45   // Initialize thread_oop to put it into the system threadGroup

    46   Handle thread_group (THREAD, Universe::system_thread_group());

    47   JavaValue result(T_VOID);

    48   JavaCalls::call_special(&result, thread_oop,

    49                           klass,

    50                           vmSymbols::object_initializer_name(),

    51                           vmSymbols::threadgroup_string_void_signature(),

    52                           thread_group,

    53                           string,

    54                           CHECK);

    55 

    56   {

    57     MutexLocker mu(Threads_lock);

    58     ServiceThread* thread =  new ServiceThread(&service_thread_entry);

    59 

    60     // At this point it may be possible that no osthread was created for the

    61     // JavaThread due to lack of memory. We would have to throw an exception

    62     // in that case. However, since this must work and we do not allow

    63     // exceptions anyway, check and abort if this fails.

    64     if (thread == NULL || thread->osthread() == NULL) {

    65       vm_exit_during_initialization("java.lang.OutOfMemoryError",

    66                                     "unable to create new native thread");

    67     }

    68 

    69     java_lang_Thread::set_thread(thread_oop(), thread);

    70     java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);

    71     java_lang_Thread::set_daemon(thread_oop());

    72     thread->set_threadObj(thread_oop());

    73 

    74     Threads::add(thread);

    75     Thread::start(thread);

    76 

    77     _instance = thread;

    78   }

    79 }

    80 

    81 void ServiceThread::service_thread_entry(JavaThread* jt, TRAPS) {

    82   while (true) {

    83     bool sensors_changed = false;

    84     bool has_jvmti_events = false;

    85     JvmtiDeferredEvent jvmti_event;

    86     {

    87       // Need state transition ThreadBlockInVM so that this thread

    88       // will be handled by safepoint correctly when this thread is

    89       // notified at a safepoint.

    90 

    91       // This ThreadBlockInVM object is not also considered to be

    92       // suspend-equivalent because ServiceThread is not visible to

    93       // external suspension.

    94 

    95       ThreadBlockInVM tbivm(jt);

    96 

    97       MutexLockerEx ml(Service_lock, Mutex::_no_safepoint_check_flag);

    98       while (!(sensors_changed = LowMemoryDetector::has_pending_requests()) &&

    99              !(has_jvmti_events = JvmtiDeferredEventQueue::has_events())) {

   100         // wait until one of the sensors has pending requests, or there is a

   101         // pending JVMTI event to post

   102         Service_lock->wait(Mutex::_no_safepoint_check_flag);

   103       }

   104 

   105       if (has_jvmti_events) {

   106         jvmti_event = JvmtiDeferredEventQueue::dequeue();

   107       }

   108     }

   109 

   110     if (has_jvmti_events) {

   111       jvmti_event.post();

   112     }

   113 

   114     if (sensors_changed) {

   115       LowMemoryDetector::process_sensor_changes(jt);

   116     }

   117   }

   118 }

   119 

   120 bool ServiceThread::is_service_thread(Thread* thread) {

   121   return thread == _instance;

   122 }