1 /*
   2  * Copyright (c) 2014, 2017, 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 #ifndef SHARE_GC_COMMON_SUSPENDIBLETHREADSET_HPP
  26 #define SHARE_GC_COMMON_SUSPENDIBLETHREADSET_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 
  30 // A SuspendibleThreadSet is a set of threads that can be suspended.
  31 // A thread can join and later leave the set, and periodically yield.
  32 // If some thread (not in the set) requests, via synchronize(), that
  33 // the threads be suspended, then the requesting thread is blocked
  34 // until all the threads in the set have yielded or left the set. Threads
  35 // may not enter the set when an attempted suspension is in progress. The
  36 // suspending thread later calls desynchronize(), allowing the suspended
  37 // threads to continue.
  38 class SuspendibleThreadSet : public AllStatic {
  39   friend class SuspendibleThreadSetJoiner;
  40   friend class SuspendibleThreadSetLeaver;
  41 
  42 private:
  43   static uint   _nthreads;
  44   static uint   _nthreads_stopped;
  45   static bool   _suspend_all;
  46   static double _suspend_all_start;
  47 
  48   static bool is_synchronized();
  49 
  50   // Add the current thread to the set. May block if a suspension is in progress.
  51   static void join();
  52 
  53   // Removes the current thread from the set.
  54   static void leave();
  55 
  56 public:
  57   // Returns true if an suspension is in progress.
  58   static bool should_yield() { return _suspend_all; }
  59 
  60   // Suspends the current thread if a suspension is in progress.
  61   static void yield();
  62 
  63   // Returns when all threads in the set are suspended.
  64   static void synchronize();
  65 
  66   // Resumes all suspended threads in the set.
  67   static void desynchronize();
  68 };
  69 
  70 class SuspendibleThreadSetJoiner : public StackObj {
  71 private:
  72   bool _active;
  73 
  74 public:
  75   SuspendibleThreadSetJoiner(bool active = true) : _active(active) {
  76     if (_active) {
  77       SuspendibleThreadSet::join();
  78     }
  79   }
  80 
  81   ~SuspendibleThreadSetJoiner() {
  82     if (_active) {
  83       SuspendibleThreadSet::leave();
  84     }
  85   }
  86 
  87   bool should_yield() {
  88     if (_active) {
  89       return SuspendibleThreadSet::should_yield();
  90     } else {
  91       return false;
  92     }
  93   }
  94 
  95   void yield() {
  96     assert(_active, "Thread has not joined the suspendible thread set");
  97     SuspendibleThreadSet::yield();
  98   }
  99 };
 100 
 101 class SuspendibleThreadSetLeaver : public StackObj {
 102 private:
 103   bool _active;
 104 
 105 public:
 106   SuspendibleThreadSetLeaver(bool active = true) : _active(active) {
 107     if (_active) {
 108       SuspendibleThreadSet::leave();
 109     }
 110   }
 111 
 112   ~SuspendibleThreadSetLeaver() {
 113     if (_active) {
 114       SuspendibleThreadSet::join();
 115     }
 116   }
 117 };
 118 
 119 #endif // SHARE_GC_COMMON_SUSPENDIBLETHREADSET_HPP