2007-12-15 03:00:21 +08:00
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// token.h -- lock tokens for gold -*- C++ -*-
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2010-02-11 15:42:17 +08:00
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// Copyright 2006, 2007, 2008, 2010 Free Software Foundation, Inc.
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2007-12-15 03:00:21 +08:00
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// Written by Ian Lance Taylor <iant@google.com>.
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// This file is part of gold.
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3 of the License, or
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// (at your option) any later version.
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
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// MA 02110-1301, USA.
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#ifndef GOLD_TOKEN_H
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#define GOLD_TOKEN_H
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namespace gold
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{
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class Condvar;
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class Task;
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// A list of Tasks, managed through the next_locked_ field in the
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// class Task. We define this class here because we need it in
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// Task_token.
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class Task_list
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{
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public:
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Task_list()
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: head_(NULL), tail_(NULL)
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{ }
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~Task_list()
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{ gold_assert(this->head_ == NULL && this->tail_ == NULL); }
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// Return whether the list is empty.
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bool
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empty() const
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{ return this->head_ == NULL; }
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2008-02-29 03:46:06 +08:00
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// Add T to the head of the list.
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void
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push_front(Task* t);
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2007-12-15 03:00:21 +08:00
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// Add T to the end of the list.
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void
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push_back(Task* t);
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// Remove the first Task on the list and return it. Return NULL if
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// the list is empty.
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Task*
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pop_front();
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private:
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// The start of the list. NULL if the list is empty.
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Task* head_;
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// The end of the list. NULL if the list is empty.
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Task* tail_;
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};
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// We support two basic types of locks, which are both implemented
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// using the single class Task_token.
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// A write lock may be held by a single Task at a time. This is used
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// to control access to a single shared resource such as an Object.
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// A blocker is used to indicate that a Task A must be run after some
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// set of Tasks B. For each of the Tasks B, we increment the blocker
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// when the Task is created, and decrement it when the Task is
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// completed. When the count goes to 0, the task A is ready to run.
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// There are no shared read locks. We always read and write objects
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// in predictable patterns. The purpose of the locks is to permit
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// some flexibility for the threading system, for cases where the
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// execution order does not matter.
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// These tokens are only manipulated when the workqueue lock is held
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// or when they are first created. They do not require any locking
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// themselves.
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class Task_token
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{
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public:
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Task_token(bool is_blocker)
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: is_blocker_(is_blocker), blockers_(0), writer_(NULL), waiting_()
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{ }
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~Task_token()
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{
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gold_assert(this->blockers_ == 0);
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gold_assert(this->writer_ == NULL);
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}
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// Return whether this is a blocker.
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bool
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is_blocker() const
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{ return this->is_blocker_; }
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// A write lock token uses these methods.
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// Is the token writable?
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bool
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is_writable() const
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{
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gold_assert(!this->is_blocker_);
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return this->writer_ == NULL;
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}
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// Add the task as the token's writer (there may only be one
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// writer).
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void
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add_writer(const Task* t)
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{
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gold_assert(!this->is_blocker_ && this->writer_ == NULL);
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this->writer_ = t;
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}
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// Remove the task as the token's writer.
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void
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remove_writer(const Task* t)
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{
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gold_assert(!this->is_blocker_ && this->writer_ == t);
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this->writer_ = NULL;
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}
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// A blocker token uses these methods.
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// Add a blocker to the token.
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void
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add_blocker()
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{
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gold_assert(this->is_blocker_);
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++this->blockers_;
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this->writer_ = NULL;
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2010-02-11 15:42:17 +08:00
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}
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// Add some number of blockers to the token.
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void
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add_blockers(int c)
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{
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gold_assert(this->is_blocker_);
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this->blockers_ += c;
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this->writer_ = NULL;
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2007-12-15 03:00:21 +08:00
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}
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// Remove a blocker from the token. Returns true if block count
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// drops to zero.
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bool
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remove_blocker()
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{
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gold_assert(this->is_blocker_ && this->blockers_ > 0);
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--this->blockers_;
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this->writer_ = NULL;
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return this->blockers_ == 0;
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}
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// Is the token currently blocked?
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bool
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is_blocked() const
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{
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gold_assert(this->is_blocker_);
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return this->blockers_ > 0;
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}
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// Both blocker and write lock tokens use these methods.
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// Add T to the list of tasks waiting for this token to be released.
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void
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add_waiting(Task* t)
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{ this->waiting_.push_back(t); }
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2008-02-29 03:46:06 +08:00
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// Add T to the front of the list of tasks waiting for this token to
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// be released.
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void
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add_waiting_front(Task* t)
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{ this->waiting_.push_front(t); }
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2007-12-15 03:00:21 +08:00
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// Remove the first Task waiting for this token to be released, and
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// return it. Return NULL if no Tasks are waiting.
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Task*
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remove_first_waiting()
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{ return this->waiting_.pop_front(); }
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private:
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// It makes no sense to copy these.
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Task_token(const Task_token&);
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Task_token& operator=(const Task_token&);
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// Whether this is a blocker token.
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bool is_blocker_;
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// The number of blockers.
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int blockers_;
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// The single writer.
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const Task* writer_;
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// The list of Tasks waiting for this token to be released.
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Task_list waiting_;
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};
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// In order to support tokens more reliably, we provide objects which
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// handle them using RAII.
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// RAII class to get a write lock on a token. This requires
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// specifying the task which is doing the lock.
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class Task_write_token
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{
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public:
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Task_write_token(Task_token* token, const Task* task)
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: token_(token), task_(task)
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{ this->token_->add_writer(this->task_); }
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~Task_write_token()
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{ this->token_->remove_writer(this->task_); }
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private:
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Task_write_token(const Task_write_token&);
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Task_write_token& operator=(const Task_write_token&);
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Task_token* token_;
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const Task* task_;
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};
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// RAII class for a blocker.
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class Task_block_token
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{
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public:
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// The blocker count must be incremented when the task is created.
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// This object is created when the task is run, so we don't do
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// anything in the constructor.
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Task_block_token(Task_token* token)
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: token_(token)
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{ gold_assert(this->token_->is_blocked()); }
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~Task_block_token()
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{ this->token_->remove_blocker(); }
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private:
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Task_block_token(const Task_block_token&);
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Task_block_token& operator=(const Task_block_token&);
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Task_token* token_;
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};
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// An object which implements an RAII lock for any object which
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// supports lock and unlock methods.
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template<typename Obj>
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class Task_lock_obj
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{
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public:
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Task_lock_obj(const Task* task, Obj* obj)
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: task_(task), obj_(obj)
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{ this->obj_->lock(task); }
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~Task_lock_obj()
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{ this->obj_->unlock(this->task_); }
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private:
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Task_lock_obj(const Task_lock_obj&);
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Task_lock_obj& operator=(const Task_lock_obj&);
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const Task* task_;
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Obj* obj_;
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};
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// A class which holds the set of Task_tokens which must be locked for
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// a Task. No Task requires more than four Task_tokens, so we set
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// that as a limit.
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class Task_locker
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{
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public:
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static const int max_task_count = 4;
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Task_locker()
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: count_(0)
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{ }
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~Task_locker()
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{ }
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// Clear the locker.
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void
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clear()
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{ this->count_ = 0; }
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// Add a token to the locker.
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void
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add(Task* t, Task_token* token)
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{
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gold_assert(this->count_ < max_task_count);
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this->tokens_[this->count_] = token;
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++this->count_;
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// A blocker will have been incremented when the task is created.
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// A writer we need to lock now.
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if (!token->is_blocker())
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token->add_writer(t);
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}
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// Iterate over the tokens.
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typedef Task_token** iterator;
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iterator
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begin()
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{ return &this->tokens_[0]; }
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iterator
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end()
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{ return &this->tokens_[this->count_]; }
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private:
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Task_locker(const Task_locker&);
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Task_locker& operator=(const Task_locker&);
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// The number of tokens.
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int count_;
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// The tokens.
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Task_token* tokens_[max_task_count];
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};
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} // End namespace gold.
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#endif // !defined(GOLD_TOKEN_H)
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