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// workqueue.h -- the work queue for gold   -*- C++ -*-

// Copyright 2006, 2007, 2008 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.

// After processing the command line, everything the linker does is

// driven from a work queue.  This permits us to parallelize the

// linker where possible.

#ifndef GOLD_WORKQUEUE_H

#define GOLD_WORKQUEUE_H

#include <string>

#include "gold-threads.h"

#include "token.h"

namespace gold

{

class General_options;

class Workqueue;

// The superclass for tasks to be placed on the workqueue.  Each

// specific task class will inherit from this one.

class Task

{

 public:

  Task()

    : list_next_(NULL), name_(), should_run_soon_(false)

  { }

  virtual ~Task()

  { }

  // Check whether the Task can be run now.  This method is only

  // called with the workqueue lock held.  If the Task can run, this

  // returns NULL.  Otherwise it returns a pointer to a token which

  // must be released before the Task can run.

  virtual Task_token*

  is_runnable() = 0;

  // Lock all the resources required by the Task, and store the locks

  // in a Task_locker.  This method does not need to do anything if no

  // locks are required.  This method is only called with the

  // workqueue lock held.

  virtual void

  locks(Task_locker*) = 0;

  // Run the task.

  virtual void

  run(Workqueue*) = 0;

  // Return whether this task should run soon.

  bool

  should_run_soon() const

  { return this->should_run_soon_; }

  // Note that this task should run soon.

  void

  set_should_run_soon()

  { this->should_run_soon_ = true; }

  // Get the next Task on the list of Tasks.  Called by Task_list.

  Task*

  list_next() const

  { return this->list_next_; }

  // Set the next Task on the list of Tasks.  Called by Task_list.

  void

  set_list_next(Task* t)

  {

    gold_assert(this->list_next_ == NULL);

    this->list_next_ = t;

  }

  // Clear the next Task on the list of Tasks.  Called by Task_list.

  void

  clear_list_next()

  { this->list_next_ = NULL; }

  // Return the name of the Task.  This is only used for debugging

  // purposes.

  const std::string&

  name()

  {

    if (this->name_.empty())

      this->name_ = this->get_name();

    return this->name_;

  }

 protected:

  // Get the name of the task.  This must be implemented by the child

  // class.

  virtual std::string

  get_name() const = 0;

 private:

  // Tasks may not be copied.

  Task(const Task&);

  Task& operator=(const Task&);

  // If this Task is on a list, this is a pointer to the next Task on

  // the list.  We use this simple list structure rather than building

  // a container, in order to avoid memory allocation while holding

  // the Workqueue lock.

  Task* list_next_;

  // Task name, for debugging purposes.

  std::string name_;

  // Whether this Task should be executed soon.  This is used for

  // Tasks which can be run after some data is read.

  bool should_run_soon_;

};

// An interface for Task_function.  This is a convenience class to run

// a single function.

class Task_function_runner

{

 public:

  virtual ~Task_function_runner()

  { }

  virtual void

  run(Workqueue*, const Task*) = 0;

};

// A simple task which waits for a blocker and then runs a function.

class Task_function : public Task

{

 public:

  // RUNNER and BLOCKER should be allocated using new, and will be

  // deleted after the task runs.

  Task_function(Task_function_runner* runner, Task_token* blocker,

                const char* name)

    : runner_(runner), blocker_(blocker), name_(name)

  { gold_assert(blocker != NULL); }

  ~Task_function()

  {

    delete this->runner_;

    delete this->blocker_;

  }

  // The standard task methods.

  // Wait until the task is unblocked.

  Task_token*

  is_runnable()

  { return this->blocker_->is_blocked() ? this->blocker_ : NULL; }

  // This type of task does not normally hold any locks.

  virtual void

  locks(Task_locker*)

  { }

  // Run the action.

  void

  run(Workqueue* workqueue)

  { this->runner_->run(workqueue, this); }

  // The debugging name.

  std::string

  get_name() const

  { return this->name_; }

 private:

  Task_function(const Task_function&);

  Task_function& operator=(const Task_function&);

  Task_function_runner* runner_;

  Task_token* blocker_;

  const char* name_;

};

// The workqueue itself.

class Workqueue_threader;

class Workqueue

{

 public:

  Workqueue(const General_options&);

  ~Workqueue();

  // Add a new task to the work queue.

  void

  queue(Task*);

  // Add a new task to the work queue which should run soon.  If the

  // task is ready, it will be run before any tasks added using

  // queue().

  void

  queue_soon(Task*);

  // Add a new task to the work queue which should run next if it is

  // ready.

  void

  queue_next(Task*);

  // Process all the tasks on the work queue.  This function runs

  // until all tasks have completed.  The argument is the thread

  // number, used only for debugging.

  void

  process(int);

  // Set the desired thread count--the number of threads we want to

  // have running.

  void

  set_thread_count(int);

  // Add a new blocker to an existing Task_token. This must be done

  // with the workqueue lock held.  This should not be done routinely,

  // only in special circumstances.

  void

  add_blocker(Task_token*);

 private:

  // This class can not be copied.

  Workqueue(const Workqueue&);

  Workqueue& operator=(const Workqueue&);

  // Add a task to a queue.

  void

  add_to_queue(Task_list* queue, Task* t, bool front);

  // Find a runnable task, or wait for one.

  Task*

  find_runnable_or_wait(int thread_number);

  // Find a runnable task.

  Task*

  find_runnable();

  // Find a runnable task in a list.

  Task*

  find_runnable_in_list(Task_list*);

  // Find an run a task.

  bool

  find_and_run_task(int);

  // Release the locks for a Task.  Return the next Task to run.

  Task*

  release_locks(Task*, Task_locker*);

  // Store T into *PRET, or queue it as appropriate.

  bool

  return_or_queue(Task* t, bool is_blocker, Task** pret);

  // Return whether to cancel this thread.

  bool

  should_cancel_thread();

  // Master Workqueue lock.  This controls access to the following

  // member variables.

  Lock lock_;

  // List of tasks to execute soon.

  Task_list first_tasks_;

  // List of tasks to execute after the ones in first_tasks_.

  Task_list tasks_;

  // Number of tasks currently running.

  int running_;

  // Number of tasks waiting for a lock to release.

  int waiting_;

  // Condition variable associated with lock_.  This is signalled when

  // there may be a new Task to execute.

  Condvar condvar_;

  // The threading implementation.  This is set at construction time

  // and not changed thereafter.

  Workqueue_threader* threader_;

};

} // End namespace gold.

#endif // !defined(GOLD_WORKQUEUE_H)