jdk/hotspot/src/share/vm/gc_implementation/shared/concurrentGCThread.hpp

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
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 * 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.
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#ifndef SHARE_VM_GC_IMPLEMENTATION_SHARED_CONCURRENTGCTHREAD_HPP
#define SHARE_VM_GC_IMPLEMENTATION_SHARED_CONCURRENTGCTHREAD_HPP

#ifndef SERIALGC
#include "runtime/thread.hpp"
#endif

class VoidClosure;

// A SuspendibleThreadSet is (obviously) a set of threads that can be
// suspended.  A thread can join and later leave the set, and periodically
// yield.  If some thread (not in the set) requests, via suspend_all, that
// the threads be suspended, then the requesting thread is blocked until
// all the threads in the set have yielded or left the set.  (Threads may
// not enter the set when an attempted suspension is in progress.)  The
// suspending thread later calls resume_all, allowing the suspended threads
// to continue.

class SuspendibleThreadSet {
  Monitor* _m;
  int      _async;
  bool     _async_stop;
  int      _async_stopped;
  bool     _initialized;
  double   _suspend_all_start;

  void initialize_work();

 public:
  SuspendibleThreadSet() : _initialized(false) {}

  // Add the current thread to the set.  May block if a suspension
  // is in progress.
  void join();
  // Removes the current thread from the set.
  void leave();
  // Returns "true" iff an suspension is in progress.
  bool should_yield() { return _async_stop; }
  // Suspends the current thread if a suspension is in progress (for
  // the duration of the suspension.)
  void yield(const char* id);
  // Return when all threads in the set are suspended.
  void suspend_all();
  // Allow suspended threads to resume.
  void resume_all();
  // Redundant initializations okay.
  void initialize() {
    // Double-check dirty read idiom.
    if (!_initialized) initialize_work();
  }
};


class ConcurrentGCThread: public NamedThread {
  friend class VMStructs;

protected:
  bool _should_terminate;
  bool _has_terminated;

  enum CGC_flag_type {
    CGC_nil           = 0x0,
    CGC_dont_suspend  = 0x1,
    CGC_CGC_safepoint = 0x2,
    CGC_VM_safepoint  = 0x4
  };

  static int _CGC_flag;

  static bool CGC_flag_is_set(int b)       { return (_CGC_flag & b) != 0; }
  static int set_CGC_flag(int b)           { return _CGC_flag |= b; }
  static int reset_CGC_flag(int b)         { return _CGC_flag &= ~b; }

  // All instances share this one set.
  static SuspendibleThreadSet _sts;

  // Create and start the thread (setting it's priority high.)
  void create_and_start();

  // Do initialization steps in the thread: record stack base and size,
  // init thread local storage, set JNI handle block.
  void initialize_in_thread();

  // Wait until Universe::is_fully_initialized();
  void wait_for_universe_init();

  // Record that the current thread is terminating, and will do more
  // concurrent work.
  void terminate();

public:
  // Constructor

  ConcurrentGCThread();
  ~ConcurrentGCThread() {} // Exists to call NamedThread destructor.

  // Tester
  bool is_ConcurrentGC_thread() const          { return true;       }

  static void safepoint_synchronize();
  static void safepoint_desynchronize();

  // All overridings should probably do _sts::yield, but we allow
  // overriding for distinguished debugging messages.  Default is to do
  // nothing.
  virtual void yield() {}

  bool should_yield() { return _sts.should_yield(); }

  // they are prefixed by sts since there are already yield() and
  // should_yield() (non-static) methods in this class and it was an
  // easy way to differentiate them.
  static void stsYield(const char* id);
  static bool stsShouldYield();
  static void stsJoin();
  static void stsLeave();

};

// The SurrogateLockerThread is used by concurrent GC threads for
// manipulating Java monitors, in particular, currently for
// manipulating the pending_list_lock. XXX
class SurrogateLockerThread: public JavaThread {
  friend class VMStructs;
 public:
  enum SLT_msg_type {
    empty = 0,           // no message
    acquirePLL,          // acquire pending list lock
    releaseAndNotifyPLL  // notify and release pending list lock
  };
 private:
  // the following are shared with the CMSThread
  SLT_msg_type  _buffer;  // communication buffer
  Monitor       _monitor; // monitor controlling buffer
  BasicLock     _basicLock; // used for PLL locking

 public:
  static SurrogateLockerThread* make(TRAPS);

  SurrogateLockerThread();

  bool is_hidden_from_external_view() const     { return true; }

  void loop(); // main method

  void manipulatePLL(SLT_msg_type msg);

};

#endif // SHARE_VM_GC_IMPLEMENTATION_SHARED_CONCURRENTGCTHREAD_HPP