1 /*
   2  * Copyright (c) 2016, 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 "classfile/javaClasses.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "gc/shared/collectedHeap.hpp"
  29 #include "gc/shared/referencePendingListLocker.hpp"
  30 #include "memory/universe.hpp"
  31 #include "runtime/javaCalls.hpp"
  32 #include "utilities/preserveException.hpp"
  33 
  34 ReferencePendingListLockerThread::ReferencePendingListLockerThread() :
  35   JavaThread(&start),
  36   _monitor(Monitor::nonleaf, "ReferencePendingListLocker", false, Monitor::_safepoint_check_sometimes),
  37   _message(NONE) {}
  38 
  39 ReferencePendingListLockerThread* ReferencePendingListLockerThread::create(TRAPS) {
  40   // Create Java thread objects
  41   instanceKlassHandle thread_klass = SystemDictionary::resolve_or_fail(vmSymbols::java_lang_Thread(), true, CHECK_NULL);
  42   instanceHandle thread_object = thread_klass->allocate_instance_handle(CHECK_NULL);
  43   Handle thread_name = java_lang_String::create_from_str("Reference Pending List Locker", CHECK_NULL);
  44   Handle thread_group = Universe::system_thread_group();
  45   JavaValue result(T_VOID);
  46   JavaCalls::call_special(&result,
  47                           thread_object,
  48                           thread_klass,
  49                           vmSymbols::object_initializer_name(),
  50                           vmSymbols::threadgroup_string_void_signature(),
  51                           thread_group,
  52                           thread_name,
  53                           CHECK_NULL);
  54 
  55   {
  56     MutexLocker ml(Threads_lock);
  57 
  58     // Allocate thread
  59     ReferencePendingListLockerThread* thread = new ReferencePendingListLockerThread();
  60     if (thread == NULL || thread->osthread() == NULL) {
  61       vm_exit_during_initialization("java.lang.OutOfMemoryError",
  62                                     os::native_thread_creation_failed_msg());
  63     }
  64 
  65     // Initialize thread
  66     java_lang_Thread::set_thread(thread_object(), thread);
  67     java_lang_Thread::set_priority(thread_object(), NearMaxPriority);
  68     java_lang_Thread::set_daemon(thread_object());
  69     thread->set_threadObj(thread_object());
  70 
  71     // Start thread
  72     Threads::add(thread);
  73     Thread::start(thread);
  74 
  75     return thread;
  76   }
  77 }
  78 
  79 void ReferencePendingListLockerThread::start(JavaThread* thread, TRAPS) {
  80   ReferencePendingListLockerThread* locker_thread = static_cast<ReferencePendingListLockerThread*>(thread);
  81   locker_thread->receive_and_handle_messages();
  82 }
  83 
  84 bool ReferencePendingListLockerThread::is_hidden_from_external_view() const {
  85   return true;
  86 }
  87 
  88 void ReferencePendingListLockerThread::send_message(Message message) {
  89   assert(message != NONE, "Should not be none");
  90   MonitorLockerEx ml(&_monitor, Monitor::_no_safepoint_check_flag);
  91 
  92   // Wait for completion of current message
  93   while (_message != NONE) {
  94     ml.wait(Monitor::_no_safepoint_check_flag);
  95   }
  96 
  97   // Send new message
  98   _message = message;
  99   ml.notify_all();
 100 
 101   // Wait for completion of new message
 102   while (_message != NONE) {
 103     ml.wait(Monitor::_no_safepoint_check_flag);
 104   }
 105 }
 106 
 107 void ReferencePendingListLockerThread::receive_and_handle_messages() {
 108   ReferencePendingListLocker pending_list_locker;
 109   MonitorLockerEx ml(&_monitor);
 110 
 111   // Main loop, never terminates
 112   for (;;) {
 113     // Wait for message
 114     while (_message == NONE) {
 115       ml.wait();
 116     }
 117 
 118     // Handle message
 119     if (_message == LOCK) {
 120       pending_list_locker.lock();
 121     } else if (_message == UNLOCK) {
 122       pending_list_locker.unlock();
 123     } else {
 124       ShouldNotReachHere();
 125     }
 126 
 127     // Clear message
 128     _message = NONE;
 129     ml.notify_all();
 130   }
 131 }
 132 
 133 void ReferencePendingListLockerThread::lock() {
 134   send_message(LOCK);
 135 }
 136 
 137 void ReferencePendingListLockerThread::unlock() {
 138   send_message(UNLOCK);
 139 }
 140 
 141 bool ReferencePendingListLocker::_is_initialized = false;
 142 ReferencePendingListLockerThread* ReferencePendingListLocker::_locker_thread = NULL;
 143 
 144 void ReferencePendingListLocker::initialize(bool needs_locker_thread, TRAPS) {
 145   if (needs_locker_thread) {
 146     _locker_thread = ReferencePendingListLockerThread::create(CHECK);
 147   }
 148 
 149   _is_initialized = true;
 150 }
 151 
 152 bool ReferencePendingListLocker::is_initialized() {
 153   return _is_initialized;
 154 }
 155 
 156 bool ReferencePendingListLocker::is_locked_by_self() {
 157   oop pending_list_lock = java_lang_ref_Reference::pending_list_lock();
 158   if (pending_list_lock == NULL) {
 159     return false;
 160   }
 161 
 162   JavaThread* thread = JavaThread::current();
 163   Handle handle(thread, pending_list_lock);
 164   return ObjectSynchronizer::current_thread_holds_lock(thread, handle);
 165 }
 166 
 167 void ReferencePendingListLocker::lock() {
 168   assert(!Heap_lock->owned_by_self(), "Heap_lock must not be owned by requesting thread");
 169 
 170   if (Thread::current()->is_Java_thread()) {
 171     assert(java_lang_ref_Reference::pending_list_lock() != NULL, "Not initialized");
 172 
 173     // We may enter this with a pending exception
 174     PRESERVE_EXCEPTION_MARK;
 175 
 176     HandleMark hm;
 177     Handle handle(THREAD, java_lang_ref_Reference::pending_list_lock());
 178 
 179     assert(!is_locked_by_self(), "Should not be locked by self");
 180 
 181     // Lock
 182     ObjectSynchronizer::fast_enter(handle, &_basic_lock, false, THREAD);
 183 
 184     assert(is_locked_by_self(), "Locking failed");
 185 
 186     if (HAS_PENDING_EXCEPTION) {
 187       CLEAR_PENDING_EXCEPTION;
 188     }
 189   } else {
 190     // Delegate operation to locker thread
 191     assert(_locker_thread != NULL, "Locker thread not created");
 192     _locker_thread->lock();
 193   }
 194 }
 195 
 196 void ReferencePendingListLocker::unlock() {
 197   if (Thread::current()->is_Java_thread()) {
 198     assert(java_lang_ref_Reference::pending_list_lock() != NULL, "Not initialized");
 199 
 200     // We may enter this with a pending exception
 201     PRESERVE_EXCEPTION_MARK;
 202 
 203     HandleMark hm;
 204     Handle handle(THREAD, java_lang_ref_Reference::pending_list_lock());
 205 
 206     assert(is_locked_by_self(), "Should be locked by self");
 207 
 208     // Notify waiters if the pending list is non-empty
 209     if (java_lang_ref_Reference::pending_list() != NULL) {
 210       ObjectSynchronizer::notifyall(handle, THREAD);
 211     }
 212 
 213     // Unlock
 214     ObjectSynchronizer::fast_exit(handle(), &_basic_lock, THREAD);
 215 
 216     assert(!is_locked_by_self(), "Unlocking failed");
 217 
 218     if (HAS_PENDING_EXCEPTION) {
 219       CLEAR_PENDING_EXCEPTION;
 220     }
 221   } else {
 222     // Delegate operation to locker thread
 223     assert(_locker_thread != NULL, "Locker thread not created");
 224     _locker_thread->unlock();
 225   }
 226 }