benchmarks/richards.js - v8/v8.git - Git at Google

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
 //     * Neither the name of Google Inc. nor the names of its
 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


 // This is a JavaScript implementation of the Richards
 // benchmark from:
 //
 //    http://www.cl.cam.ac.uk/~mr10/Bench.html
 //
 // The benchmark was originally implemented in BCPL by
 // Martin Richards.


 var Richards = new BenchmarkSuite('Richards', 35302, [
   new Benchmark("Richards", runRichards)
 ]);


 /**
  * The Richards benchmark simulates the task dispatcher of an
  * operating system.
  **/
 function runRichards() {
   var scheduler = new Scheduler();
   scheduler.addIdleTask(ID_IDLE, 0, null, COUNT);

   var queue = new Packet(null, ID_WORKER, KIND_WORK);
   queue = new Packet(queue,  ID_WORKER, KIND_WORK);
   scheduler.addWorkerTask(ID_WORKER, 1000, queue);

   queue = new Packet(null, ID_DEVICE_A, KIND_DEVICE);
   queue = new Packet(queue,  ID_DEVICE_A, KIND_DEVICE);
   queue = new Packet(queue,  ID_DEVICE_A, KIND_DEVICE);
   scheduler.addHandlerTask(ID_HANDLER_A, 2000, queue);

   queue = new Packet(null, ID_DEVICE_B, KIND_DEVICE);
   queue = new Packet(queue,  ID_DEVICE_B, KIND_DEVICE);
   queue = new Packet(queue,  ID_DEVICE_B, KIND_DEVICE);
   scheduler.addHandlerTask(ID_HANDLER_B, 3000, queue);

   scheduler.addDeviceTask(ID_DEVICE_A, 4000, null);

   scheduler.addDeviceTask(ID_DEVICE_B, 5000, null);

   scheduler.schedule();

   if (scheduler.queueCount != EXPECTED_QUEUE_COUNT ||
       scheduler.holdCount != EXPECTED_HOLD_COUNT) {
     var msg =
         "Error during execution: queueCount = " + scheduler.queueCount +
         ", holdCount = " + scheduler.holdCount + ".";
     throw new Error(msg);
   }
 }

 var COUNT = 1000;

 /**
  * These two constants specify how many times a packet is queued and
  * how many times a task is put on hold in a correct run of richards.
  * They don't have any meaning a such but are characteristic of a
  * correct run so if the actual queue or hold count is different from
  * the expected there must be a bug in the implementation.
  **/
 var EXPECTED_QUEUE_COUNT = 2322;
 var EXPECTED_HOLD_COUNT = 928;


 /**
  * A scheduler can be used to schedule a set of tasks based on their relative
  * priorities.  Scheduling is done by maintaining a list of task control blocks
  * which holds tasks and the data queue they are processing.
  * @constructor
  */
 function Scheduler() {
   this.queueCount = 0;
   this.holdCount = 0;
   this.blocks = new Array(NUMBER_OF_IDS);
   this.list = null;
   this.currentTcb = null;
   this.currentId = null;
 }

 var ID_IDLE       = 0;
 var ID_WORKER     = 1;
 var ID_HANDLER_A  = 2;
 var ID_HANDLER_B  = 3;
 var ID_DEVICE_A   = 4;
 var ID_DEVICE_B   = 5;
 var NUMBER_OF_IDS = 6;

 var KIND_DEVICE   = 0;
 var KIND_WORK     = 1;

 /**
  * Add an idle task to this scheduler.
  * @param {int} id the identity of the task
  * @param {int} priority the task's priority
  * @param {Packet} queue the queue of work to be processed by the task
  * @param {int} count the number of times to schedule the task
  */
 Scheduler.prototype.addIdleTask = function (id, priority, queue, count) {
   this.addRunningTask(id, priority, queue, new IdleTask(this, 1, count));
 };

 /**
  * Add a work task to this scheduler.
  * @param {int} id the identity of the task
  * @param {int} priority the task's priority
  * @param {Packet} queue the queue of work to be processed by the task
  */
 Scheduler.prototype.addWorkerTask = function (id, priority, queue) {
   this.addTask(id, priority, queue, new WorkerTask(this, ID_HANDLER_A, 0));
 };

 /**
  * Add a handler task to this scheduler.
  * @param {int} id the identity of the task
  * @param {int} priority the task's priority
  * @param {Packet} queue the queue of work to be processed by the task
  */
 Scheduler.prototype.addHandlerTask = function (id, priority, queue) {
   this.addTask(id, priority, queue, new HandlerTask(this));
 };

 /**
  * Add a handler task to this scheduler.
  * @param {int} id the identity of the task
  * @param {int} priority the task's priority
  * @param {Packet} queue the queue of work to be processed by the task
  */
 Scheduler.prototype.addDeviceTask = function (id, priority, queue) {
   this.addTask(id, priority, queue, new DeviceTask(this))
 };

 /**
  * Add the specified task and mark it as running.
  * @param {int} id the identity of the task
  * @param {int} priority the task's priority
  * @param {Packet} queue the queue of work to be processed by the task
  * @param {Task} task the task to add
  */
 Scheduler.prototype.addRunningTask = function (id, priority, queue, task) {
   this.addTask(id, priority, queue, task);
   this.currentTcb.setRunning();
 };

 /**
  * Add the specified task to this scheduler.
  * @param {int} id the identity of the task
  * @param {int} priority the task's priority
  * @param {Packet} queue the queue of work to be processed by the task
  * @param {Task} task the task to add
  */
 Scheduler.prototype.addTask = function (id, priority, queue, task) {
   this.currentTcb = new TaskControlBlock(this.list, id, priority, queue, task);
   this.list = this.currentTcb;
   this.blocks[id] = this.currentTcb;
 };

 /**
  * Execute the tasks managed by this scheduler.
  */
 Scheduler.prototype.schedule = function () {
   this.currentTcb = this.list;
   while (this.currentTcb != null) {
     if (this.currentTcb.isHeldOrSuspended()) {
       this.currentTcb = this.currentTcb.link;
     } else {
       this.currentId = this.currentTcb.id;
       this.currentTcb = this.currentTcb.run();
     }
   }
 };

 /**
  * Release a task that is currently blocked and return the next block to run.
  * @param {int} id the id of the task to suspend
  */
 Scheduler.prototype.release = function (id) {
   var tcb = this.blocks[id];
   if (tcb == null) return tcb;
   tcb.markAsNotHeld();
   if (tcb.priority > this.currentTcb.priority) {
     return tcb;
   } else {
     return this.currentTcb;
   }
 };

 /**
  * Block the currently executing task and return the next task control block
  * to run.  The blocked task will not be made runnable until it is explicitly
  * released, even if new work is added to it.
  */
 Scheduler.prototype.holdCurrent = function () {
   this.holdCount++;
   this.currentTcb.markAsHeld();
   return this.currentTcb.link;
 };

 /**
  * Suspend the currently executing task and return the next task control block
  * to run.  If new work is added to the suspended task it will be made runnable.
  */
 Scheduler.prototype.suspendCurrent = function () {
   this.currentTcb.markAsSuspended();
   return this.currentTcb;
 };

 /**
  * Add the specified packet to the end of the worklist used by the task
  * associated with the packet and make the task runnable if it is currently
  * suspended.
  * @param {Packet} packet the packet to add
  */
 Scheduler.prototype.queue = function (packet) {
   var t = this.blocks[packet.id];
   if (t == null) return t;
   this.queueCount++;
   packet.link = null;
   packet.id = this.currentId;
   return t.checkPriorityAdd(this.currentTcb, packet);
 };

 /**
  * A task control block manages a task and the queue of work packages associated
  * with it.
  * @param {TaskControlBlock} link the preceding block in the linked block list
  * @param {int} id the id of this block
  * @param {int} priority the priority of this block
  * @param {Packet} queue the queue of packages to be processed by the task
  * @param {Task} task the task
  * @constructor
  */
 function TaskControlBlock(link, id, priority, queue, task) {
   this.link = link;
   this.id = id;
   this.priority = priority;
   this.queue = queue;
   this.task = task;
   if (queue == null) {
     this.state = STATE_SUSPENDED;
   } else {
     this.state = STATE_SUSPENDED_RUNNABLE;
   }
 }

 /**
  * The task is running and is currently scheduled.
  */
 var STATE_RUNNING = 0;

 /**
  * The task has packets left to process.
  */
 var STATE_RUNNABLE = 1;

 /**
  * The task is not currently running.  The task is not blocked as such and may
 * be started by the scheduler.
  */
 var STATE_SUSPENDED = 2;

 /**
  * The task is blocked and cannot be run until it is explicitly released.
  */
 var STATE_HELD = 4;

 var STATE_SUSPENDED_RUNNABLE = STATE_SUSPENDED | STATE_RUNNABLE;
 var STATE_NOT_HELD = ~STATE_HELD;

 TaskControlBlock.prototype.setRunning = function () {
   this.state = STATE_RUNNING;
 };

 TaskControlBlock.prototype.markAsNotHeld = function () {
   this.state = this.state & STATE_NOT_HELD;
 };

 TaskControlBlock.prototype.markAsHeld = function () {
   this.state = this.state | STATE_HELD;
 };

 TaskControlBlock.prototype.isHeldOrSuspended = function () {
   return (this.state & STATE_HELD) != 0 || (this.state == STATE_SUSPENDED);
 };

 TaskControlBlock.prototype.markAsSuspended = function () {
   this.state = this.state | STATE_SUSPENDED;
 };

 TaskControlBlock.prototype.markAsRunnable = function () {
   this.state = this.state | STATE_RUNNABLE;
 };

 /**
  * Runs this task, if it is ready to be run, and returns the next task to run.
  */
 TaskControlBlock.prototype.run = function () {
   var packet;
   if (this.state == STATE_SUSPENDED_RUNNABLE) {
     packet = this.queue;
     this.queue = packet.link;
     if (this.queue == null) {
       this.state = STATE_RUNNING;
     } else {
       this.state = STATE_RUNNABLE;
     }
   } else {
     packet = null;
   }
   return this.task.run(packet);
 };

 /**
  * Adds a packet to the worklist of this block's task, marks this as runnable if
  * necessary, and returns the next runnable object to run (the one
  * with the highest priority).
  */
 TaskControlBlock.prototype.checkPriorityAdd = function (task, packet) {
   if (this.queue == null) {
     this.queue = packet;
     this.markAsRunnable();
     if (this.priority > task.priority) return this;
   } else {
     this.queue = packet.addTo(this.queue);
   }
   return task;
 };

 TaskControlBlock.prototype.toString = function () {
   return "tcb { " + this.task + "@" + this.state + " }";
 };

 /**
  * An idle task doesn't do any work itself but cycles control between the two
  * device tasks.
  * @param {Scheduler} scheduler the scheduler that manages this task
  * @param {int} v1 a seed value that controls how the device tasks are scheduled
  * @param {int} count the number of times this task should be scheduled
  * @constructor
  */
 function IdleTask(scheduler, v1, count) {
   this.scheduler = scheduler;
   this.v1 = v1;
   this.count = count;
 }

 IdleTask.prototype.run = function (packet) {
   this.count--;
   if (this.count == 0) return this.scheduler.holdCurrent();
   if ((this.v1 & 1) == 0) {
     this.v1 = this.v1 >> 1;
     return this.scheduler.release(ID_DEVICE_A);
   } else {
     this.v1 = (this.v1 >> 1) ^ 0xD008;
     return this.scheduler.release(ID_DEVICE_B);
   }
 };

 IdleTask.prototype.toString = function () {
   return "IdleTask"
 };

 /**
  * A task that suspends itself after each time it has been run to simulate
  * waiting for data from an external device.
  * @param {Scheduler} scheduler the scheduler that manages this task
  * @constructor
  */
 function DeviceTask(scheduler) {
   this.scheduler = scheduler;
   this.v1 = null;
 }

 DeviceTask.prototype.run = function (packet) {
   if (packet == null) {
     if (this.v1 == null) return this.scheduler.suspendCurrent();
     var v = this.v1;
     this.v1 = null;
     return this.scheduler.queue(v);
   } else {
     this.v1 = packet;
     return this.scheduler.holdCurrent();
   }
 };

 DeviceTask.prototype.toString = function () {
   return "DeviceTask";
 };

 /**
  * A task that manipulates work packets.
  * @param {Scheduler} scheduler the scheduler that manages this task
  * @param {int} v1 a seed used to specify how work packets are manipulated
  * @param {int} v2 another seed used to specify how work packets are manipulated
  * @constructor
  */
 function WorkerTask(scheduler, v1, v2) {
   this.scheduler = scheduler;
   this.v1 = v1;
   this.v2 = v2;
 }

 WorkerTask.prototype.run = function (packet) {
   if (packet == null) {
     return this.scheduler.suspendCurrent();
   } else {
     if (this.v1 == ID_HANDLER_A) {
       this.v1 = ID_HANDLER_B;
     } else {
       this.v1 = ID_HANDLER_A;
     }
     packet.id = this.v1;
     packet.a1 = 0;
     for (var i = 0; i < DATA_SIZE; i++) {
       this.v2++;
       if (this.v2 > 26) this.v2 = 1;
       packet.a2[i] = this.v2;
     }
     return this.scheduler.queue(packet);
   }
 };

 WorkerTask.prototype.toString = function () {
   return "WorkerTask";
 };

 /**
  * A task that manipulates work packets and then suspends itself.
  * @param {Scheduler} scheduler the scheduler that manages this task
  * @constructor
  */
 function HandlerTask(scheduler) {
   this.scheduler = scheduler;
   this.v1 = null;
   this.v2 = null;
 }

 HandlerTask.prototype.run = function (packet) {
   if (packet != null) {
     if (packet.kind == KIND_WORK) {
       this.v1 = packet.addTo(this.v1);
     } else {
       this.v2 = packet.addTo(this.v2);
     }
   }
   if (this.v1 != null) {
     var count = this.v1.a1;
     var v;
     if (count < DATA_SIZE) {
       if (this.v2 != null) {
         v = this.v2;
         this.v2 = this.v2.link;
         v.a1 = this.v1.a2[count];
         this.v1.a1 = count + 1;
         return this.scheduler.queue(v);
       }
     } else {
       v = this.v1;
       this.v1 = this.v1.link;
       return this.scheduler.queue(v);
     }
   }
   return this.scheduler.suspendCurrent();
 };

 HandlerTask.prototype.toString = function () {
   return "HandlerTask";
 };

 /* --- *
  * P a c k e t
  * --- */

 var DATA_SIZE = 4;

 /**
  * A simple package of data that is manipulated by the tasks.  The exact layout
  * of the payload data carried by a packet is not importaint, and neither is the
  * nature of the work performed on packets by the tasks.
  *
  * Besides carrying data, packets form linked lists and are hence used both as
  * data and worklists.
  * @param {Packet} link the tail of the linked list of packets
  * @param {int} id an ID for this packet
  * @param {int} kind the type of this packet
  * @constructor
  */
 function Packet(link, id, kind) {
   this.link = link;
   this.id = id;
   this.kind = kind;
   this.a1 = 0;
   this.a2 = new Array(DATA_SIZE);
 }

 /**
  * Add this packet to the end of a worklist, and return the worklist.
  * @param {Packet} queue the worklist to add this packet to
  */
 Packet.prototype.addTo = function (queue) {
   this.link = null;
   if (queue == null) return this;
   var peek, next = queue;
   while ((peek = next.link) != null)
     next = peek;
   next.link = this;
   return queue;
 };

 Packet.prototype.toString = function () {
   return "Packet";
 };
	// Copyright 2006-2008 the V8 project authors. All rights reserved.
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are
	// met:
	//
	// * Redistributions of source code must retain the above copyright
	// notice, this list of conditions and the following disclaimer.
	// * Redistributions in binary form must reproduce the above
	// copyright notice, this list of conditions and the following
	// disclaimer in the documentation and/or other materials provided
	// with the distribution.
	// * Neither the name of Google Inc. nor the names of its
	// contributors may be used to endorse or promote products derived
	// from this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


	// This is a JavaScript implementation of the Richards
	// benchmark from:
	//
	// http://www.cl.cam.ac.uk/~mr10/Bench.html
	//
	// The benchmark was originally implemented in BCPL by
	// Martin Richards.


	var Richards = new BenchmarkSuite('Richards', 35302, [
	new Benchmark("Richards", runRichards)
	]);


	/**
	* The Richards benchmark simulates the task dispatcher of an
	* operating system.
	**/
	function runRichards() {
	var scheduler = new Scheduler();
	scheduler.addIdleTask(ID_IDLE, 0, null, COUNT);

	var queue = new Packet(null, ID_WORKER, KIND_WORK);
	queue = new Packet(queue, ID_WORKER, KIND_WORK);
	scheduler.addWorkerTask(ID_WORKER, 1000, queue);

	queue = new Packet(null, ID_DEVICE_A, KIND_DEVICE);
	queue = new Packet(queue, ID_DEVICE_A, KIND_DEVICE);
	queue = new Packet(queue, ID_DEVICE_A, KIND_DEVICE);
	scheduler.addHandlerTask(ID_HANDLER_A, 2000, queue);

	queue = new Packet(null, ID_DEVICE_B, KIND_DEVICE);
	queue = new Packet(queue, ID_DEVICE_B, KIND_DEVICE);
	queue = new Packet(queue, ID_DEVICE_B, KIND_DEVICE);
	scheduler.addHandlerTask(ID_HANDLER_B, 3000, queue);

	scheduler.addDeviceTask(ID_DEVICE_A, 4000, null);

	scheduler.addDeviceTask(ID_DEVICE_B, 5000, null);

	scheduler.schedule();

	if (scheduler.queueCount != EXPECTED_QUEUE_COUNT \|\|
	scheduler.holdCount != EXPECTED_HOLD_COUNT) {
	var msg =
	"Error during execution: queueCount = " + scheduler.queueCount +
	", holdCount = " + scheduler.holdCount + ".";
	throw new Error(msg);
	}
	}

	var COUNT = 1000;

	/**
	* These two constants specify how many times a packet is queued and
	* how many times a task is put on hold in a correct run of richards.
	* They don't have any meaning a such but are characteristic of a
	* correct run so if the actual queue or hold count is different from
	* the expected there must be a bug in the implementation.
	**/
	var EXPECTED_QUEUE_COUNT = 2322;
	var EXPECTED_HOLD_COUNT = 928;


	/**
	* A scheduler can be used to schedule a set of tasks based on their relative
	* priorities. Scheduling is done by maintaining a list of task control blocks
	* which holds tasks and the data queue they are processing.
	* @constructor
	*/
	function Scheduler() {
	this.queueCount = 0;
	this.holdCount = 0;
	this.blocks = new Array(NUMBER_OF_IDS);
	this.list = null;
	this.currentTcb = null;
	this.currentId = null;
	}

	var ID_IDLE = 0;
	var ID_WORKER = 1;
	var ID_HANDLER_A = 2;
	var ID_HANDLER_B = 3;
	var ID_DEVICE_A = 4;
	var ID_DEVICE_B = 5;
	var NUMBER_OF_IDS = 6;

	var KIND_DEVICE = 0;
	var KIND_WORK = 1;

	/**
	* Add an idle task to this scheduler.
	* @param {int} id the identity of the task
	* @param {int} priority the task's priority
	* @param {Packet} queue the queue of work to be processed by the task
	* @param {int} count the number of times to schedule the task
	*/
	Scheduler.prototype.addIdleTask = function (id, priority, queue, count) {
	this.addRunningTask(id, priority, queue, new IdleTask(this, 1, count));
	};

	/**
	* Add a work task to this scheduler.
	* @param {int} id the identity of the task
	* @param {int} priority the task's priority
	* @param {Packet} queue the queue of work to be processed by the task
	*/
	Scheduler.prototype.addWorkerTask = function (id, priority, queue) {
	this.addTask(id, priority, queue, new WorkerTask(this, ID_HANDLER_A, 0));
	};

	/**
	* Add a handler task to this scheduler.
	* @param {int} id the identity of the task
	* @param {int} priority the task's priority
	* @param {Packet} queue the queue of work to be processed by the task
	*/
	Scheduler.prototype.addHandlerTask = function (id, priority, queue) {
	this.addTask(id, priority, queue, new HandlerTask(this));
	};

	/**
	* Add a handler task to this scheduler.
	* @param {int} id the identity of the task
	* @param {int} priority the task's priority
	* @param {Packet} queue the queue of work to be processed by the task
	*/
	Scheduler.prototype.addDeviceTask = function (id, priority, queue) {
	this.addTask(id, priority, queue, new DeviceTask(this))
	};

	/**
	* Add the specified task and mark it as running.
	* @param {int} id the identity of the task
	* @param {int} priority the task's priority
	* @param {Packet} queue the queue of work to be processed by the task
	* @param {Task} task the task to add
	*/
	Scheduler.prototype.addRunningTask = function (id, priority, queue, task) {
	this.addTask(id, priority, queue, task);
	this.currentTcb.setRunning();
	};

	/**
	* Add the specified task to this scheduler.
	* @param {int} id the identity of the task
	* @param {int} priority the task's priority
	* @param {Packet} queue the queue of work to be processed by the task
	* @param {Task} task the task to add
	*/
	Scheduler.prototype.addTask = function (id, priority, queue, task) {
	this.currentTcb = new TaskControlBlock(this.list, id, priority, queue, task);
	this.list = this.currentTcb;
	this.blocks[id] = this.currentTcb;
	};

	/**
	* Execute the tasks managed by this scheduler.
	*/
	Scheduler.prototype.schedule = function () {
	this.currentTcb = this.list;
	while (this.currentTcb != null) {
	if (this.currentTcb.isHeldOrSuspended()) {
	this.currentTcb = this.currentTcb.link;
	} else {
	this.currentId = this.currentTcb.id;
	this.currentTcb = this.currentTcb.run();
	}
	}
	};

	/**
	* Release a task that is currently blocked and return the next block to run.
	* @param {int} id the id of the task to suspend
	*/
	Scheduler.prototype.release = function (id) {
	var tcb = this.blocks[id];
	if (tcb == null) return tcb;
	tcb.markAsNotHeld();
	if (tcb.priority > this.currentTcb.priority) {
	return tcb;
	} else {
	return this.currentTcb;
	}
	};

	/**
	* Block the currently executing task and return the next task control block
	* to run. The blocked task will not be made runnable until it is explicitly
	* released, even if new work is added to it.
	*/
	Scheduler.prototype.holdCurrent = function () {
	this.holdCount++;
	this.currentTcb.markAsHeld();
	return this.currentTcb.link;
	};

	/**
	* Suspend the currently executing task and return the next task control block
	* to run. If new work is added to the suspended task it will be made runnable.
	*/
	Scheduler.prototype.suspendCurrent = function () {
	this.currentTcb.markAsSuspended();
	return this.currentTcb;
	};

	/**
	* Add the specified packet to the end of the worklist used by the task
	* associated with the packet and make the task runnable if it is currently
	* suspended.
	* @param {Packet} packet the packet to add
	*/
	Scheduler.prototype.queue = function (packet) {
	var t = this.blocks[packet.id];
	if (t == null) return t;
	this.queueCount++;
	packet.link = null;
	packet.id = this.currentId;
	return t.checkPriorityAdd(this.currentTcb, packet);
	};

	/**
	* A task control block manages a task and the queue of work packages associated
	* with it.
	* @param {TaskControlBlock} link the preceding block in the linked block list
	* @param {int} id the id of this block
	* @param {int} priority the priority of this block
	* @param {Packet} queue the queue of packages to be processed by the task
	* @param {Task} task the task
	* @constructor
	*/
	function TaskControlBlock(link, id, priority, queue, task) {
	this.link = link;
	this.id = id;
	this.priority = priority;
	this.queue = queue;
	this.task = task;
	if (queue == null) {
	this.state = STATE_SUSPENDED;
	} else {
	this.state = STATE_SUSPENDED_RUNNABLE;
	}
	}

	/**
	* The task is running and is currently scheduled.
	*/
	var STATE_RUNNING = 0;

	/**
	* The task has packets left to process.
	*/
	var STATE_RUNNABLE = 1;

	/**
	* The task is not currently running. The task is not blocked as such and may
	* be started by the scheduler.
	*/
	var STATE_SUSPENDED = 2;

	/**
	* The task is blocked and cannot be run until it is explicitly released.
	*/
	var STATE_HELD = 4;

	var STATE_SUSPENDED_RUNNABLE = STATE_SUSPENDED \| STATE_RUNNABLE;
	var STATE_NOT_HELD = ~STATE_HELD;

	TaskControlBlock.prototype.setRunning = function () {
	this.state = STATE_RUNNING;
	};

	TaskControlBlock.prototype.markAsNotHeld = function () {
	this.state = this.state & STATE_NOT_HELD;
	};

	TaskControlBlock.prototype.markAsHeld = function () {
	this.state = this.state \| STATE_HELD;
	};

	TaskControlBlock.prototype.isHeldOrSuspended = function () {
	return (this.state & STATE_HELD) != 0 \|\| (this.state == STATE_SUSPENDED);
	};

	TaskControlBlock.prototype.markAsSuspended = function () {
	this.state = this.state \| STATE_SUSPENDED;
	};

	TaskControlBlock.prototype.markAsRunnable = function () {
	this.state = this.state \| STATE_RUNNABLE;
	};

	/**
	* Runs this task, if it is ready to be run, and returns the next task to run.
	*/
	TaskControlBlock.prototype.run = function () {
	var packet;
	if (this.state == STATE_SUSPENDED_RUNNABLE) {
	packet = this.queue;
	this.queue = packet.link;
	if (this.queue == null) {
	this.state = STATE_RUNNING;
	} else {
	this.state = STATE_RUNNABLE;
	}
	} else {
	packet = null;
	}
	return this.task.run(packet);
	};

	/**
	* Adds a packet to the worklist of this block's task, marks this as runnable if
	* necessary, and returns the next runnable object to run (the one
	* with the highest priority).
	*/
	TaskControlBlock.prototype.checkPriorityAdd = function (task, packet) {
	if (this.queue == null) {
	this.queue = packet;
	this.markAsRunnable();
	if (this.priority > task.priority) return this;
	} else {
	this.queue = packet.addTo(this.queue);
	}
	return task;
	};

	TaskControlBlock.prototype.toString = function () {
	return "tcb { " + this.task + "@" + this.state + " }";
	};

	/**
	* An idle task doesn't do any work itself but cycles control between the two
	* device tasks.
	* @param {Scheduler} scheduler the scheduler that manages this task
	* @param {int} v1 a seed value that controls how the device tasks are scheduled
	* @param {int} count the number of times this task should be scheduled
	* @constructor
	*/
	function IdleTask(scheduler, v1, count) {
	this.scheduler = scheduler;
	this.v1 = v1;
	this.count = count;
	}

	IdleTask.prototype.run = function (packet) {
	this.count--;
	if (this.count == 0) return this.scheduler.holdCurrent();
	if ((this.v1 & 1) == 0) {
	this.v1 = this.v1 >> 1;
	return this.scheduler.release(ID_DEVICE_A);
	} else {
	this.v1 = (this.v1 >> 1) ^ 0xD008;
	return this.scheduler.release(ID_DEVICE_B);
	}
	};

	IdleTask.prototype.toString = function () {
	return "IdleTask"
	};

	/**
	* A task that suspends itself after each time it has been run to simulate
	* waiting for data from an external device.
	* @param {Scheduler} scheduler the scheduler that manages this task
	* @constructor
	*/
	function DeviceTask(scheduler) {
	this.scheduler = scheduler;
	this.v1 = null;
	}

	DeviceTask.prototype.run = function (packet) {
	if (packet == null) {
	if (this.v1 == null) return this.scheduler.suspendCurrent();
	var v = this.v1;
	this.v1 = null;
	return this.scheduler.queue(v);
	} else {
	this.v1 = packet;
	return this.scheduler.holdCurrent();
	}
	};

	DeviceTask.prototype.toString = function () {
	return "DeviceTask";
	};

	/**
	* A task that manipulates work packets.
	* @param {Scheduler} scheduler the scheduler that manages this task
	* @param {int} v1 a seed used to specify how work packets are manipulated
	* @param {int} v2 another seed used to specify how work packets are manipulated
	* @constructor
	*/
	function WorkerTask(scheduler, v1, v2) {
	this.scheduler = scheduler;
	this.v1 = v1;
	this.v2 = v2;
	}

	WorkerTask.prototype.run = function (packet) {
	if (packet == null) {
	return this.scheduler.suspendCurrent();
	} else {
	if (this.v1 == ID_HANDLER_A) {
	this.v1 = ID_HANDLER_B;
	} else {
	this.v1 = ID_HANDLER_A;
	}
	packet.id = this.v1;
	packet.a1 = 0;
	for (var i = 0; i < DATA_SIZE; i++) {
	this.v2++;
	if (this.v2 > 26) this.v2 = 1;
	packet.a2[i] = this.v2;
	}
	return this.scheduler.queue(packet);
	}
	};

	WorkerTask.prototype.toString = function () {
	return "WorkerTask";
	};

	/**
	* A task that manipulates work packets and then suspends itself.
	* @param {Scheduler} scheduler the scheduler that manages this task
	* @constructor
	*/
	function HandlerTask(scheduler) {
	this.scheduler = scheduler;
	this.v1 = null;
	this.v2 = null;
	}

	HandlerTask.prototype.run = function (packet) {
	if (packet != null) {
	if (packet.kind == KIND_WORK) {
	this.v1 = packet.addTo(this.v1);
	} else {
	this.v2 = packet.addTo(this.v2);
	}
	}
	if (this.v1 != null) {
	var count = this.v1.a1;
	var v;
	if (count < DATA_SIZE) {
	if (this.v2 != null) {
	v = this.v2;
	this.v2 = this.v2.link;
	v.a1 = this.v1.a2[count];
	this.v1.a1 = count + 1;
	return this.scheduler.queue(v);
	}
	} else {
	v = this.v1;
	this.v1 = this.v1.link;
	return this.scheduler.queue(v);
	}
	}
	return this.scheduler.suspendCurrent();
	};

	HandlerTask.prototype.toString = function () {
	return "HandlerTask";
	};

	/* --- *
	* P a c k e t
	* --- */

	var DATA_SIZE = 4;

	/**
	* A simple package of data that is manipulated by the tasks. The exact layout
	* of the payload data carried by a packet is not importaint, and neither is the
	* nature of the work performed on packets by the tasks.
	*
	* Besides carrying data, packets form linked lists and are hence used both as
	* data and worklists.
	* @param {Packet} link the tail of the linked list of packets
	* @param {int} id an ID for this packet
	* @param {int} kind the type of this packet
	* @constructor
	*/
	function Packet(link, id, kind) {
	this.link = link;
	this.id = id;
	this.kind = kind;
	this.a1 = 0;
	this.a2 = new Array(DATA_SIZE);
	}

	/**
	* Add this packet to the end of a worklist, and return the worklist.
	* @param {Packet} queue the worklist to add this packet to
	*/
	Packet.prototype.addTo = function (queue) {
	this.link = null;
	if (queue == null) return this;
	var peek, next = queue;
	while ((peek = next.link) != null)
	next = peek;
	next.link = this;
	return queue;
	};

	Packet.prototype.toString = function () {
	return "Packet";
	};