Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 class ConcurrentMarkSweepGeneration;

 class CMSCollector;

 // The Concurrent Mark Sweep GC Thread (could be several in the future).

 class ConcurrentMarkSweepThread: public ConcurrentGCThread {

   friend class VMStructs;

   friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship

   friend class CMSCollector;

  public:

   virtual void run();

  private:

   static ConcurrentMarkSweepThread*     _cmst;

   static CMSCollector*                  _collector;

   static SurrogateLockerThread*         _slt;

   static SurrogateLockerThread::SLT_msg_type _sltBuffer;

   static Monitor*                       _sltMonitor;

   ConcurrentMarkSweepThread*            _next;

   static bool _should_terminate;

   enum CMS_flag_type {

     CMS_nil             = NoBits,

     CMS_cms_wants_token = nth_bit(0),

     CMS_cms_has_token   = nth_bit(1),

     CMS_vm_wants_token  = nth_bit(2),

     CMS_vm_has_token    = nth_bit(3)

   };

   static int _CMS_flag;

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

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

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

   void sleepBeforeNextCycle();

   // CMS thread should yield for a young gen collection, direct allocation,

   // and iCMS activity.

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

   static volatile jint _pending_yields;

   static volatile jint _pending_decrements; // decrements to _pending_yields

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

   // Tracing messages, enabled by CMSTraceThreadState.

   static inline void trace_state(const char* desc);

   static volatile bool _icms_enabled;   // iCMS enabled?

   static volatile bool _should_run;     // iCMS may run

   static volatile bool _should_stop;    // iCMS should stop

   // debugging

   void verify_ok_to_terminate() const PRODUCT_RETURN;

  public:

   // Constructor

   ConcurrentMarkSweepThread(CMSCollector* collector);

   static void makeSurrogateLockerThread(TRAPS);

   static SurrogateLockerThread* slt() { return _slt; }

   // Tester

   bool is_ConcurrentGC_thread() const { return true;       }

   static void threads_do(ThreadClosure* tc);

   // Printing

   void print_on(outputStream* st) const;

   void print() const                                  { print_on(tty); }

   static void print_all_on(outputStream* st);

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

   // Returns the CMS Thread

   static ConcurrentMarkSweepThread* cmst()    { return _cmst; }

   static CMSCollector*         collector()    { return _collector;  }

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

   static ConcurrentMarkSweepThread* start(CMSCollector* collector);

   static void stop();

   static bool should_terminate() { return _should_terminate; }

   // Synchronization using CMS token

   static void synchronize(bool is_cms_thread);

   static void desynchronize(bool is_cms_thread);

   static bool vm_thread_has_cms_token() {

     return CMS_flag_is_set(CMS_vm_has_token);

   }

   static bool cms_thread_has_cms_token() {

     return CMS_flag_is_set(CMS_cms_has_token);

   }

   static bool vm_thread_wants_cms_token() {

     return CMS_flag_is_set(CMS_vm_wants_token);

   }

   static bool cms_thread_wants_cms_token() {

     return CMS_flag_is_set(CMS_cms_wants_token);

   }

   // Wait on CMS lock until the next synchronous GC

   // or given timeout, whichever is earlier.

   void    wait_on_cms_lock(long t); // milliseconds

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

   // only when requested to.  Both synchronous and asychronous requests

   // are provided:

   // (1) A synchronous request is used for young gen collections and

   //     for direct allocations.  The requesting thread increments

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

   //     _pending_yields when that operation is completed.

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

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

   // (2) An asynchronous request, on the other hand, is used by iCMS

   //     for the stop_icms() operation. A single yield satisfies all of

   //     the outstanding asynch yield requests, of which there may

   //     occasionally be several in close succession. To accomplish

   //     this, an asynch-requesting thread atomically increments both

   //     _pending_yields and _pending_decrements. An asynchr requesting

   //     thread does not wait and "acknowledge" completion of an operation

   //     and deregister the request, like the synchronous version described

   //     above does. In turn, after yielding, the CMS thread decrements both

   //     _pending_yields and _pending_decrements by the value seen in

   //     _pending_decrements before the decrement.

   //  NOTE: The above scheme is isomorphic to having two request counters,

   //  one for async requests and one for sync requests, and for the CMS thread

   //  to check the sum of the two counters to decide whether it should yield

   //  and to clear only the async counter when it yields. However, it turns out

   //  to be more efficient for CMS code to just check a single counter

   //  _pending_yields that holds the sum (of both sync and async requests), and

   //  a second counter _pending_decrements that only holds the async requests,

   //  for greater efficiency, since in a typical CMS run, there are many more

   //  pontential (i.e. static) yield points than there are actual

   //  (i.e. dynamic) yields because of requests, which are few and far between.

   //

   // Note that, while "_pending_yields >= _pending_decrements" is an invariant,

   // we cannot easily test that invariant, since the counters are manipulated via

   // atomic instructions without explicit locking and we cannot read

   // the two counters atomically together: one suggestion is to

   // use (for example) 16-bit counters so as to be able to read the

   // two counters atomically even on 32-bit platforms. Notice that

   // the second assert in acknowledge_yield_request() below does indeed

   // check a form of the above invariant, albeit indirectly.

   static void increment_pending_yields()   {

     Atomic::inc(&_pending_yields);

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

   }

   static void decrement_pending_yields()   {

     Atomic::dec(&_pending_yields);

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

   }

   static void asynchronous_yield_request() {

     assert(CMSIncrementalMode, "Currently only used w/iCMS");

     increment_pending_yields();

     Atomic::inc(&_pending_decrements);

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

   }

   static void acknowledge_yield_request() {

     jint decrement = _pending_decrements;

     if (decrement > 0) {

       assert(CMSIncrementalMode, "Currently only used w/iCMS");

       // Order important to preserve: _pending_yields >= _pending_decrements

       Atomic::add(-decrement, &_pending_decrements);

       Atomic::add(-decrement, &_pending_yields);

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

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

     }

   }

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

   // CMS incremental mode.

   static void start_icms(); // notify thread to start a quantum of work

   static void stop_icms();  // request thread to stop working

   void icms_wait();         // if asked to stop, wait until notified to start

   // Incremental mode is enabled globally by the flag CMSIncrementalMode.  It

   // must also be enabled/disabled dynamically to allow foreground collections.

   static inline void enable_icms()              { _icms_enabled = true; }

   static inline void disable_icms()             { _icms_enabled = false; }

   static inline void set_icms_enabled(bool val) { _icms_enabled = val; }

   static inline bool icms_enabled()             { return _icms_enabled; }

 };

 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {

   if (CMSTraceThreadState) {

     char buf[128];

     TimeStamp& ts = gclog_or_tty->time_stamp();

     if (!ts.is_updated()) {

       ts.update();

     }

     jio_snprintf(buf, sizeof(buf), " [%.3f:  CMSThread %s] ",

                  ts.seconds(), desc);

     buf[sizeof(buf) - 1] = '\0';

     gclog_or_tty->print(buf);

   }

 }

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

 class CMSSynchronousYieldRequest: public StackObj {

  public:

   CMSSynchronousYieldRequest() {

     ConcurrentMarkSweepThread::increment_pending_yields();

   }

   ~CMSSynchronousYieldRequest() {

     ConcurrentMarkSweepThread::decrement_pending_yields();

   }

 };

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

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

 class CMSLoopCountWarn: public StackObj {

  private:

   const char* _src;

   const char* _msg;

   const intx  _threshold;

   intx        _ticks;

  public:

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

                           const intx threshold) :

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

   inline void tick() {

     _ticks++;

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

       warning("%s has looped %d times %s", _src, _ticks, _msg);

     }

   }

 };