1 /*
   2  * Copyright (c) 2003, 2015, 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/atomic.hpp"
  27 #include "runtime/globalSynchronizer.hpp"
  28 #include "runtime/thread.inline.hpp"
  29 
  30 #ifndef MIN
  31 #define MIN(x, y) (((x) < (y)) ? (x) : (y))
  32 #endif
  33 
  34 volatile int GlobalSynchronizer::_global_serialized_memory_version = 0;
  35 volatile int GlobalSynchronizer::_latest_global_serialized_memory_version = 0;
  36 
  37 int GlobalSynchronizer::global_serialized_memory_version() {
  38   return _global_serialized_memory_version;
  39 }
  40 
  41 GlobalSynchronizer::GlobalSynchronizer(UrgencyLevel start_urgency, UrgencyLevel max_urgency)
  42   : _current_urgency(start_urgency), _max_urgency(max_urgency) {
  43   assert(max_urgency >= start_urgency, "sanity");
  44   assert(start_urgency >= UrgencyLevel1 && start_urgency <= UrgencyLevelMax, "sanity");
  45 }
  46 
  47 GlobalSynchronizer::~GlobalSynchronizer() {
  48 }
  49 
  50 void GlobalSynchronizer::start_synchronizing() {
  51   assert(ThreadLocalSafepoints, "sanity");
  52   _local_serialized_memory_version = Atomic::add(1, &_global_serialized_memory_version);
  53 }
  54 
  55 bool GlobalSynchronizer::increase_urgency() {
  56   if (_current_urgency + 1 < _max_urgency) {
  57     _current_urgency = (UrgencyLevel)(int(_current_urgency) + 1);
  58     return true;
  59   } else {
  60     return false;
  61   }
  62 }
  63 
  64 void GlobalSynchronizer::maximize_urgency() {
  65   _current_urgency = _max_urgency;
  66 }
  67 
  68 void GlobalSynchronizer::threads_do(ThreadClosure *cl) {
  69   Threads::java_threads_do_fast(cl, Thread::current());
  70 }
  71 
  72 class GSHasFinishedThreadClosure : public ThreadClosure {
  73 private:
  74   int _needed_version;
  75   int _min_agreed_version;
  76   bool _check_thread_state;
  77 
  78 public:
  79   GSHasFinishedThreadClosure(int version, bool check_thread_state) : _needed_version(version), _min_agreed_version(INT_MAX), _check_thread_state(check_thread_state) {}
  80 
  81   virtual void do_thread(Thread *thread) {
  82     JavaThread *jthread = reinterpret_cast<JavaThread*>(thread);
  83     int thread_version = jthread->serialized_memory_version();
  84     if (thread_version < _needed_version) {
  85       if (!jthread->is_online_vm()) _min_agreed_version = MIN(_needed_version, _min_agreed_version);
  86       else if (_check_thread_state && !jthread->is_online_os()) _min_agreed_version = MIN(_needed_version, _min_agreed_version);
  87       else _min_agreed_version = MIN(thread_version, _min_agreed_version);
  88     } else {
  89       _min_agreed_version = MIN(thread_version, _min_agreed_version);
  90     }
  91   }
  92 
  93   bool did_synchronize() { return _min_agreed_version >= _needed_version; }
  94   void fixup_global_version() {
  95     int global_version = GlobalSynchronizer::_latest_global_serialized_memory_version;
  96     if (global_version < _min_agreed_version) {
  97       (void) Atomic::cmpxchg(_min_agreed_version, &GlobalSynchronizer::_latest_global_serialized_memory_version, global_version);
  98     }
  99   }
 100 };
 101 
 102 class GSSetYieldpointThreadClosure : public ThreadClosure {
 103   const int  _target_version;
 104   const bool _force_yields;
 105 public:
 106   GSSetYieldpointThreadClosure(bool force_yields, int target_version) : _force_yields(force_yields), _target_version(target_version) {}
 107 
 108   virtual void do_thread(Thread *thread) {
 109     JavaThread *const jthread = (JavaThread*)thread;
 110     if (jthread->serialized_memory_version() >= _target_version) return;
 111     if (_force_yields) jthread->set_force_yield();
 112     jthread->set_yieldpoint(true);
 113   }
 114 };
 115 
 116 bool GlobalSynchronizer::try_synchronize() {
 117   Thread *thread = Thread::current();
 118   if (thread->is_Java_thread()) {
 119     JavaThread *jthread = reinterpret_cast<JavaThread*>(thread);
 120     jthread->update_serialized_memory_version();
 121   }
 122 
 123   if (_latest_global_serialized_memory_version >= _local_serialized_memory_version) {
 124     return true;
 125   }
 126 
 127   GSHasFinishedThreadClosure cl(_local_serialized_memory_version, /* check_thread_state */ _current_urgency >= UrgencyLevel2);
 128   threads_do(&cl);
 129   if (cl.did_synchronize()) {
 130     cl.fixup_global_version();
 131     return true;
 132   }
 133 
 134   switch (_current_urgency) {
 135   case UrgencyLevel3:
 136   case UrgencyLevel4: {
 137     GSSetYieldpointThreadClosure cl(false, _local_serialized_memory_version);
 138     threads_do(&cl);
 139     return false;
 140   }
 141   default: return false;
 142   }
 143 }
 144 
 145 void GlobalSynchronizer::synchronize() {
 146   while (!try_synchronize()) os::naked_yield();
 147 }