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 #ifndef SHARE_VM_GC_IMPLEMENTATION_SHARED_SUSPENDIBLETHREADSET_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_SHARED_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 private:
  40   static uint   _nthreads;
  41   static uint   _nthreads_stopped;
  42   static bool   _suspend_all;
  43   static double _suspend_all_start;
  44 
  45 public:
  46   // Add the current thread to the set. May block if a suspension is in progress.
  47   static void join();
  48 
  49   // Removes the current thread from the set.
  50   static void leave();
  51 
  52   // Returns true if an suspension is in progress.
  53   static bool should_yield() { return _suspend_all; }
  54 
  55   // Suspends the current thread if a suspension is in progress.
  56   static void yield();
  57 
  58   // Returns when all threads in the set are suspended.
  59   static void synchronize();
  60 
  61   // Resumes all suspended threads in the set.
  62   static void desynchronize();
  63 };
  64 
  65 class SuspendibleThreadSetJoiner : public StackObj {
  66 public:
  67   SuspendibleThreadSetJoiner() {
  68     SuspendibleThreadSet::join();
  69   }
  70 
  71   ~SuspendibleThreadSetJoiner() {
  72     SuspendibleThreadSet::leave();
  73   }
  74 
  75   bool should_yield() {
  76     return SuspendibleThreadSet::should_yield();
  77   }
  78 
  79   void yield() {
  80     SuspendibleThreadSet::yield();
  81   }
  82 };
  83 
  84 #endif // SHARE_VM_GC_IMPLEMENTATION_SHARED_SUSPENDIBLETHREADSET_HPP