1 /*
   2  * Copyright (c) 2014, 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 "gc_implementation/shared/suspendibleThreadSet.hpp"
  27 #include "runtime/mutexLocker.hpp"
  28 #include "runtime/thread.inline.hpp"
  29 
  30 uint   SuspendibleThreadSet::_nthreads          = 0;
  31 uint   SuspendibleThreadSet::_nthreads_stopped  = 0;
  32 bool   SuspendibleThreadSet::_suspend_all       = false;
  33 double SuspendibleThreadSet::_suspend_all_start = 0.0;
  34 
  35 void SuspendibleThreadSet::join() {
  36   MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
  37   while (_suspend_all) {
  38     ml.wait(Mutex::_no_safepoint_check_flag);
  39   }
  40   _nthreads++;
  41 }
  42 
  43 void SuspendibleThreadSet::leave() {
  44   MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
  45   assert(_nthreads > 0, "Invalid");
  46   _nthreads--;
  47   if (_suspend_all) {
  48     ml.notify_all();
  49   }
  50 }
  51 
  52 void SuspendibleThreadSet::yield() {
  53   if (_suspend_all) {
  54     MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
  55     if (_suspend_all) {
  56       _nthreads_stopped++;
  57       if (_nthreads_stopped == _nthreads) {
  58         if (ConcGCYieldTimeout > 0) {
  59           double now = os::elapsedTime();
  60           guarantee((now - _suspend_all_start) * 1000.0 < (double)ConcGCYieldTimeout, "Long delay");
  61         }
  62       }
  63       ml.notify_all();
  64       while (_suspend_all) {
  65         ml.wait(Mutex::_no_safepoint_check_flag);
  66       }
  67       assert(_nthreads_stopped > 0, "Invalid");
  68       _nthreads_stopped--;
  69       ml.notify_all();
  70     }
  71   }
  72 }
  73 
  74 void SuspendibleThreadSet::synchronize() {
  75   assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
  76   if (ConcGCYieldTimeout > 0) {
  77     _suspend_all_start = os::elapsedTime();
  78   }
  79   MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
  80   assert(!_suspend_all, "Only one at a time");
  81   _suspend_all = true;
  82   while (_nthreads_stopped < _nthreads) {
  83     ml.wait(Mutex::_no_safepoint_check_flag);
  84   }
  85 }
  86 
  87 void SuspendibleThreadSet::desynchronize() {
  88   assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
  89   MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
  90   assert(_nthreads_stopped == _nthreads, "Invalid");
  91   _suspend_all = false;
  92   ml.notify_all();
  93 }