1 /*

     2  * Copyright (c) 2013, 2018, 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 "jfr/recorder/service/jfrPostBox.hpp"

    27 #include "jfr/utilities/jfrTryLock.hpp"

    28 #include "runtime/atomic.hpp"

    29 #include "runtime/orderAccess.inline.hpp"

    30 #include "runtime/thread.inline.hpp"

    31 

    32 #define MSG_IS_SYNCHRONOUS ( (MSGBIT(MSG_ROTATE)) |          \

    33                              (MSGBIT(MSG_STOP))   |          \

    34                              (MSGBIT(MSG_START))  |          \

    35                              (MSGBIT(MSG_CLONE_IN_MEMORY)) | \

    36                              (MSGBIT(MSG_VM_ERROR))          \

    37                            )

    38 

    39 static JfrPostBox* _instance = NULL;

    40 

    41 JfrPostBox& JfrPostBox::instance() {

    42   return *_instance;

    43 }

    44 

    45 JfrPostBox* JfrPostBox::create() {

    46   assert(_instance == NULL, "invariant");

    47   _instance = new JfrPostBox();

    48   return _instance;

    49 }

    50 

    51 void JfrPostBox::destroy() {

    52   assert(_instance != NULL, "invariant");

    53   delete _instance;

    54   _instance = NULL;

    55 }

    56 

    57 JfrPostBox::JfrPostBox() :

    58   _msg_read_serial(0),

    59   _msg_handled_serial(0),

    60   _messages(0),

    61   _has_waiters(false) {}

    62 

    63 static bool is_thread_lock_aversive() {

    64   Thread* const thread = Thread::current();

    65   return (thread->is_Java_thread() && ((JavaThread*)thread)->thread_state() != _thread_in_vm) || thread->is_VM_thread();

    66 }

    67 

    68 static bool is_synchronous(int messages) {

    69   return ((messages & MSG_IS_SYNCHRONOUS) != 0);

    70 }

    71 

    72 void JfrPostBox::post(JFR_Msg msg) {

    73   const int the_message = MSGBIT(msg);

    74   if (is_thread_lock_aversive()) {

    75     deposit(the_message);

    76     return;

    77   }

    78   if (!is_synchronous(the_message)) {

    79     asynchronous_post(the_message);

    80     return;

    81   }

    82   synchronous_post(the_message);

    83 }

    84 

    85 void JfrPostBox::deposit(int new_messages) {

    86   while (true) {

    87     const int current_msgs = OrderAccess::load_acquire(&_messages);

    88     // OR the new message

    89     const int exchange_value = current_msgs | new_messages;

    90     const int result = Atomic::cmpxchg(exchange_value, &_messages, current_msgs);

    91     if (result == current_msgs) {

    92       return;

    93     }

    94     /* Some other thread just set exactly what this thread wanted */

    95     if ((result & new_messages) == new_messages) {

    96       return;

    97     }

    98   }

    99 }

   100 

   101 void JfrPostBox::asynchronous_post(int msg) {

   102   assert(!is_synchronous(msg), "invariant");

   103   deposit(msg);

   104   JfrMonitorTryLock try_msg_lock(JfrMsg_lock);

   105   if (try_msg_lock.acquired()) {

   106     JfrMsg_lock->notify_all();

   107   }

   108 }

   109 

   110 void JfrPostBox::synchronous_post(int msg) {

   111   assert(is_synchronous(msg), "invariant");

   112   assert(!JfrMsg_lock->owned_by_self(), "should not hold JfrMsg_lock here!");

   113   MutexLockerEx msg_lock(JfrMsg_lock);

   114   deposit(msg);

   115   // serial_id is used to check when what we send in has been processed.

   116   // _msg_read_serial is read under JfrMsg_lock protection.

   117   const uintptr_t serial_id = OrderAccess::load_acquire(&_msg_read_serial) + 1;

   118   JfrMsg_lock->notify_all();

   119   while (!is_message_processed(serial_id)) {

   120     JfrMsg_lock->wait();

   121   }

   122 }

   123 

   124 /*

   125  * Check if a synchronous message has been processed.

   126  * We avoid racing on _msg_handled_serial by ensuring

   127  * that we are holding the JfrMsg_lock when checking

   128  * completion status.

   129  */

   130 bool JfrPostBox::is_message_processed(uintptr_t serial_id) const {

   131   assert(JfrMsg_lock->owned_by_self(), "_msg_handled_serial must be read under JfrMsg_lock protection");

   132   return serial_id <= OrderAccess::load_acquire(&_msg_handled_serial);

   133 }

   134 

   135 bool JfrPostBox::is_empty() const {

   136   assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");

   137   return OrderAccess::load_acquire(&_messages) == 0;

   138 }

   139 

   140 int JfrPostBox::collect() {

   141   // get pending and reset to 0

   142   const int messages = Atomic::xchg(0, &_messages);

   143   if (check_waiters(messages)) {

   144     _has_waiters = true;

   145     assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_read_serial is protected by JfrMsg_lock");

   146     // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.

   147     ++_msg_read_serial;

   148   }

   149   return messages;

   150 }

   151 

   152 bool JfrPostBox::check_waiters(int messages) const {

   153   assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");

   154   assert(!_has_waiters, "invariant");

   155   return is_synchronous(messages);

   156 }

   157 

   158 void JfrPostBox::notify_waiters() {

   159   if (!_has_waiters) {

   160     return;

   161   }

   162   _has_waiters = false;

   163   assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_handled_serial is protected by JfrMsg_lock.");

   164   // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.

   165   ++_msg_handled_serial;

   166   JfrMsg_lock->notify();

   167 }

   168 

   169 // safeguard to ensure no threads are left waiting

   170 void JfrPostBox::notify_collection_stop() {

   171   MutexLockerEx msg_lock(JfrMsg_lock);

   172   JfrMsg_lock->notify_all();

   173 }