1 /*

     2  * Copyright (c) 2001, 2019, 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_CMS_CONCURRENTMARKSWEEPTHREAD_HPP

    26 #define SHARE_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 

    45   enum CMS_flag_type {

    46     CMS_nil             = NoBits,

    47     CMS_cms_wants_token = nth_bit(0),

    48     CMS_cms_has_token   = nth_bit(1),

    49     CMS_vm_wants_token  = nth_bit(2),

    50     CMS_vm_has_token    = nth_bit(3)

    51   };

    52 

    53   static int _CMS_flag;

    54 

    55   static bool CMS_flag_is_set(int b)        { return (_CMS_flag & b) != 0;   }

    56   static bool set_CMS_flag(int b)           { return (_CMS_flag |= b) != 0;  }

    57   static bool clear_CMS_flag(int b)         { return (_CMS_flag &= ~b) != 0; }

    58   void sleepBeforeNextCycle();

    59 

    60   // CMS thread should yield for a young gen collection and direct allocations

    61   static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing

    62   static volatile jint _pending_yields;

    63   static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing

    64 

    65   // debugging

    66   void verify_ok_to_terminate() const PRODUCT_RETURN;

    67 

    68   void run_service();

    69   void stop_service();

    70 

    71  public:

    72   // Constructor

    73   ConcurrentMarkSweepThread(CMSCollector* collector);

    74 

    75   static void threads_do(ThreadClosure* tc);

    76 

    77   // Printing

    78   static void print_all_on(outputStream* st);

    79   static void print_all()                             { print_all_on(tty); }

    80 

    81   // Returns the CMS Thread

    82   static ConcurrentMarkSweepThread* cmst()    { return _cmst; }

    83   static CMSCollector*         collector()    { return _collector;  }

    84 

    85   // Create and start the CMS Thread, or stop it on shutdown

    86   static ConcurrentMarkSweepThread* start(CMSCollector* collector);

    87 

    88   // Synchronization using CMS token

    89   static void synchronize(bool is_cms_thread);

    90   static void desynchronize(bool is_cms_thread);

    91   static bool vm_thread_has_cms_token() {

    92     return CMS_flag_is_set(CMS_vm_has_token);

    93   }

    94   static bool cms_thread_has_cms_token() {

    95     return CMS_flag_is_set(CMS_cms_has_token);

    96   }

    97   static bool vm_thread_wants_cms_token() {

    98     return CMS_flag_is_set(CMS_vm_wants_token);

    99   }

   100   static bool cms_thread_wants_cms_token() {

   101     return CMS_flag_is_set(CMS_cms_wants_token);

   102   }

   103 

   104   // Wait on CMS lock until the next synchronous GC

   105   // or given timeout, whichever is earlier. A timeout value

   106   // of 0 indicates that there is no upper bound on the wait time.

   107   // A concurrent full gc request terminates the wait.

   108   void wait_on_cms_lock(long t_millis);

   109 

   110   // Wait on CMS lock until the next synchronous GC

   111   // or given timeout, whichever is earlier. A timeout value

   112   // of 0 indicates that there is no upper bound on the wait time.

   113   // A concurrent full gc request terminates the wait.

   114   void wait_on_cms_lock_for_scavenge(long t_millis);

   115 

   116   // The CMS thread will yield during the work portion of its cycle

   117   // only when requested to.

   118   // A synchronous request is used for young gen collections and

   119   // for direct allocations.  The requesting thread increments

   120   // _pending_yields at the beginning of an operation, and decrements

   121   // _pending_yields when that operation is completed.

   122   // In turn, the CMS thread yields when _pending_yields is positive,

   123   // and continues to yield until the value reverts to 0.

   124 

   125   static void increment_pending_yields()   {

   126     Atomic::inc(&_pending_yields);

   127     assert(_pending_yields >= 0, "can't be negative");

   128   }

   129   static void decrement_pending_yields()   {

   130     Atomic::dec(&_pending_yields);

   131     assert(_pending_yields >= 0, "can't be negative");

   132   }

   133   static bool should_yield()   { return _pending_yields > 0; }

   134 };

   135 

   136 // For scoped increment/decrement of (synchronous) yield requests

   137 class CMSSynchronousYieldRequest: public StackObj {

   138  public:

   139   CMSSynchronousYieldRequest() {

   140     ConcurrentMarkSweepThread::increment_pending_yields();

   141   }

   142   ~CMSSynchronousYieldRequest() {

   143     ConcurrentMarkSweepThread::decrement_pending_yields();

   144   }

   145 };

   146 

   147 // Used to emit a warning in case of unexpectedly excessive

   148 // looping (in "apparently endless loops") in CMS code.

   149 class CMSLoopCountWarn: public StackObj {

   150  private:

   151   const char* _src;

   152   const char* _msg;

   153   const intx  _threshold;

   154   intx        _ticks;

   155 

   156  public:

   157   inline CMSLoopCountWarn(const char* src, const char* msg,

   158                           const intx threshold) :

   159     _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }

   160 

   161   inline void tick() {

   162     _ticks++;

   163     if (CMSLoopWarn && _ticks % _threshold == 0) {

   164       log_warning(gc)("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);

   165     }

   166   }

   167 };

   168 

   169 #endif // SHARE_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP