1 /*
   2  * Copyright (c) 2001, 2016, 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_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
  26 #define SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
  27 
  28 #include "gc/cms/concurrentMarkSweepGeneration.hpp"
  29 #include "gc/shared/concurrentGCThread.hpp"
  30 #include "runtime/thread.hpp"
  31 
  32 class ConcurrentMarkSweepGeneration;
  33 class CMSCollector;
  34 
  35 // The Concurrent Mark Sweep GC Thread
  36 class ConcurrentMarkSweepThread: public ConcurrentGCThread {
  37   friend class VMStructs;
  38   friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship
  39   friend class CMSCollector;
  40 
  41  private:
  42   static ConcurrentMarkSweepThread*     _cmst;
  43   static CMSCollector*                  _collector;
  44   static SurrogateLockerThread*         _slt;
  45   static SurrogateLockerThread::SLT_msg_type _sltBuffer;
  46   static Monitor*                       _sltMonitor;
  47 
  48   enum CMS_flag_type {
  49     CMS_nil             = NoBits,
  50     CMS_cms_wants_token = nth_bit(0),
  51     CMS_cms_has_token   = nth_bit(1),
  52     CMS_vm_wants_token  = nth_bit(2),
  53     CMS_vm_has_token    = nth_bit(3)
  54   };
  55 
  56   static int _CMS_flag;
  57 
  58   static bool CMS_flag_is_set(int b)        { return (_CMS_flag & b) != 0;   }
  59   static bool set_CMS_flag(int b)           { return (_CMS_flag |= b) != 0;  }
  60   static bool clear_CMS_flag(int b)         { return (_CMS_flag &= ~b) != 0; }
  61   void sleepBeforeNextCycle();
  62 
  63   // CMS thread should yield for a young gen collection and direct allocations
  64   static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing
  65   static volatile jint _pending_yields;
  66   static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing
  67 
  68   // debugging
  69   void verify_ok_to_terminate() const PRODUCT_RETURN;
  70 
  71   void run_service();
  72   void stop_service();
  73 
  74  public:
  75   // Constructor
  76   ConcurrentMarkSweepThread(CMSCollector* collector);
  77 
  78   static void makeSurrogateLockerThread(TRAPS);
  79   static SurrogateLockerThread* slt() { return _slt; }
  80 
  81   static void threads_do(ThreadClosure* tc);
  82 
  83   // Printing
  84   static void print_all_on(outputStream* st);
  85   static void print_all()                             { print_all_on(tty); }
  86 
  87   // Returns the CMS Thread
  88   inline static ConcurrentMarkSweepThread* cmst() {
  89     if (_cmst != NULL && !_cmst->_has_terminated) {
  90       return _cmst;
  91     }
  92     return NULL;
  93   }
  94 
  95   static CMSCollector*         collector()    { return _collector;  }
  96 
  97   // Create and start the CMS Thread, or stop it on shutdown
  98   static ConcurrentMarkSweepThread* start(CMSCollector* collector);
  99   static void stop_all();
 100   static bool should_terminate() { return _cmst != NULL && _cmst->_should_terminate; }
 101 
 102   // Synchronization using CMS token
 103   static void synchronize(bool is_cms_thread);
 104   static void desynchronize(bool is_cms_thread);
 105   static bool vm_thread_has_cms_token() {
 106     return CMS_flag_is_set(CMS_vm_has_token);
 107   }
 108   static bool cms_thread_has_cms_token() {
 109     return CMS_flag_is_set(CMS_cms_has_token);
 110   }
 111   static bool vm_thread_wants_cms_token() {
 112     return CMS_flag_is_set(CMS_vm_wants_token);
 113   }
 114   static bool cms_thread_wants_cms_token() {
 115     return CMS_flag_is_set(CMS_cms_wants_token);
 116   }
 117 
 118   // Wait on CMS lock until the next synchronous GC
 119   // or given timeout, whichever is earlier. A timeout value
 120   // of 0 indicates that there is no upper bound on the wait time.
 121   // A concurrent full gc request terminates the wait.
 122   void wait_on_cms_lock(long t_millis);
 123 
 124   // Wait on CMS lock until the next synchronous GC
 125   // or given timeout, whichever is earlier. A timeout value
 126   // of 0 indicates that there is no upper bound on the wait time.
 127   // A concurrent full gc request terminates the wait.
 128   void wait_on_cms_lock_for_scavenge(long t_millis);
 129 
 130   // The CMS thread will yield during the work portion of its cycle
 131   // only when requested to.
 132   // A synchronous request is used for young gen collections and
 133   // for direct allocations.  The requesting thread increments
 134   // _pending_yields at the beginning of an operation, and decrements
 135   // _pending_yields when that operation is completed.
 136   // In turn, the CMS thread yields when _pending_yields is positive,
 137   // and continues to yield until the value reverts to 0.
 138 
 139   static void increment_pending_yields()   {
 140     Atomic::inc(&_pending_yields);
 141     assert(_pending_yields >= 0, "can't be negative");
 142   }
 143   static void decrement_pending_yields()   {
 144     Atomic::dec(&_pending_yields);
 145     assert(_pending_yields >= 0, "can't be negative");
 146   }
 147   static bool should_yield()   { return _pending_yields > 0; }
 148 };
 149 
 150 // For scoped increment/decrement of (synchronous) yield requests
 151 class CMSSynchronousYieldRequest: public StackObj {
 152  public:
 153   CMSSynchronousYieldRequest() {
 154     ConcurrentMarkSweepThread::increment_pending_yields();
 155   }
 156   ~CMSSynchronousYieldRequest() {
 157     ConcurrentMarkSweepThread::decrement_pending_yields();
 158   }
 159 };
 160 
 161 // Used to emit a warning in case of unexpectedly excessive
 162 // looping (in "apparently endless loops") in CMS code.
 163 class CMSLoopCountWarn: public StackObj {
 164  private:
 165   const char* _src;
 166   const char* _msg;
 167   const intx  _threshold;
 168   intx        _ticks;
 169 
 170  public:
 171   inline CMSLoopCountWarn(const char* src, const char* msg,
 172                           const intx threshold) :
 173     _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
 174 
 175   inline void tick() {
 176     _ticks++;
 177     if (CMSLoopWarn && _ticks % _threshold == 0) {
 178       warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
 179     }
 180   }
 181 };
 182 
 183 #endif // SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP