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// gold-threads.h -- thread support for gold  -*- C++ -*-

// Copyright 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.

// Written by Ian Lance Taylor <iant@google.com>.

// This file is part of gold.

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

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation; either version 3 of the License, or

// (at your option) any later version.

// This program 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 for more details.

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

// along with this program; if not, write to the Free Software

// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,

// MA 02110-1301, USA.

// gold can be configured to support threads.  If threads are

// supported, the user can specify at runtime whether or not to

// support them.  This provides an interface to manage locking

// accordingly.

// Lock

//   A simple lock class.

#ifndef GOLD_THREADS_H

#define GOLD_THREADS_H

namespace gold

{

class Condvar;

class Once_initialize;

class Initialize_lock_once;

// The interface for the implementation of a Lock.

class Lock_impl

{

 public:

  Lock_impl()

  { }

  virtual

  ~Lock_impl()

  { }

  virtual void

  acquire() = 0;

  virtual void

  release() = 0;

};

// A simple lock class.

class Lock

{

 public:

  Lock();

  ~Lock();

  // Acquire the lock.

  void

  acquire()

  { this->lock_->acquire(); }

  // Release the lock.

  void

  release()

  { this->lock_->release(); }

 private:

  // This class can not be copied.

  Lock(const Lock&);

  Lock& operator=(const Lock&);

  friend class Condvar;

  Lock_impl*

  get_impl() const

  { return this->lock_; }

  Lock_impl* lock_;

};

// RAII for Lock.

class Hold_lock

{

 public:

  Hold_lock(Lock& lock)

    : lock_(lock)

  { this->lock_.acquire(); }

  ~Hold_lock()

  { this->lock_.release(); }

 private:

  // This class can not be copied.

  Hold_lock(const Hold_lock&);

  Hold_lock& operator=(const Hold_lock&);

  Lock& lock_;

};

class Hold_optional_lock

{

 public:

  Hold_optional_lock(Lock* lock)

    : lock_(lock)

  {

    if (this->lock_ != NULL)

      this->lock_->acquire();

  }

  ~Hold_optional_lock()

  {

    if (this->lock_ != NULL)

      this->lock_->release();

  }

 private:

  Hold_optional_lock(const Hold_optional_lock&);

  Hold_optional_lock& operator=(const Hold_optional_lock&);

  Lock* lock_;

};

// The interface for the implementation of a condition variable.

class Condvar_impl

{

 public:

  Condvar_impl()

  { }

  virtual

  ~Condvar_impl()

  { }

  virtual void

  wait(Lock_impl*) = 0;

  virtual void

  signal() = 0;

  virtual void

  broadcast() = 0;

};

// A simple condition variable class.  It is always associated with a

// specific lock.

class Condvar

{

 public:

  Condvar(Lock& lock);

  ~Condvar();

  // Wait for the condition variable to be signalled.  This should

  // only be called when the lock is held.

  void

  wait()

  { this->condvar_->wait(this->lock_.get_impl()); }

  // Signal the condition variable--wake up at least one thread

  // waiting on the condition variable.  This should only be called

  // when the lock is held.

  void

  signal()

  { this->condvar_->signal(); }

  // Broadcast the condition variable--wake up all threads waiting on

  // the condition variable.  This should only be called when the lock

  // is held.

  void

  broadcast()

  { this->condvar_->broadcast(); }

 private:

  // This class can not be copied.

  Condvar(const Condvar&);

  Condvar& operator=(const Condvar&);

  Lock& lock_;

  Condvar_impl* condvar_;

};

// A class used to do something once.  This is an abstract parent

// class; any actual use will involve a child of this.

class Once

{

 public:

  Once();

  virtual

  ~Once()

  { }

  // Call this function to do whatever it is.  We pass an argument

  // even though you have to use a child class because in some uses

  // setting the argument would itself require a Once class.

  void

  run_once(void* arg);

  // This is an internal function, which must be public because it is

  // run by an extern "C" function called via pthread_once.

  void

  internal_run(void* arg);

 protected:

  // This must be implemented by the child class.

  virtual void

  do_run_once(void* arg) = 0;

 private:

  // True if we have already run the function.

  bool was_run_;

  // Internal compare-and-swap lock on was_run_;

  uint32_t was_run_lock_;

  // The lock to run the function only once.

  Once_initialize* once_;

};

// A class used to initialize a lock exactly once, after the options

// have been read.  This is needed because the implementation of locks

// depends on whether we've seen the --threads option.  Before the

// options have been read, we know we are single-threaded, so we can

// get by without using a lock.  This class should be an instance

// variable of the class which has a lock which needs to be

// initialized.

class Initialize_lock : public Once

{

 public:

  // The class which uses this will have a pointer to a lock.  This

  // must be constructed with a pointer to that pointer.

  Initialize_lock(Lock** pplock)

    : pplock_(pplock)

  { }

  // Initialize the lock.  Return true if the lock is now initialized,

  // false if it is not (because the options have not yet been read).

  bool

  initialize();

 protected:

  void

  do_run_once(void*);

 private:

  // A pointer to the lock pointer which must be initialized.

  Lock** const pplock_;

};

} // End namespace gold.

#endif // !defined(GOLD_THREADS_H)