FiberTaskScheduler.cs

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/*

Author: Aaron Oneal, http://aarononeal.info

Copyright (c) 2012 Spicy Pixel, http://spicypixel.com

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

*/
using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace SpicyPixel.Threading.Tasks
{
    public sealed class FiberTaskScheduler : TaskScheduler, IDisposable
    {   
        FiberScheduler scheduler;
        
        public CancellationToken CancellationToken
        {
            get { return scheduler.CancellationToken; }
        }
  
        public FiberTaskScheduler () : this(FiberScheduler.Current)
        {     
        }
        
        public FiberTaskScheduler (FiberScheduler scheduler)
        {             
            this.scheduler = scheduler == null ? FiberScheduler.Current : scheduler;            
        }
        
        public FiberScheduler FiberScheduler
        {
            get { return scheduler; }
        }
        
        protected override void QueueTask (Task task)
        {   
            // Start a fiber to run the task
            Fiber.Factory.StartNew(ExecuteTask(task), scheduler);
        }
                
        protected override bool TryExecuteTaskInline (Task task, bool taskWasPreviouslyQueued)
        {
            // 1. Tasks using fiber schedulers have thread affinity and must run on the thread the scheduler was created on.
            // 2. Fiber tasks cannot run inline here because they may yield which is only handled when queued.
            //
            // That being said, the fiber scheduler may choose to inline anyway when
            // queueing occurs on the scheduler thread, it just doesn't happen in this method.
            if(scheduler.SchedulerThread != Thread.CurrentThread || task is YieldableTask)
                return false;
            
            return TryExecuteTask(task);
        }

        #region implemented abstract members of System.Threading.Tasks.TaskScheduler                
        
        protected override bool TryDequeue (Task task)
        {
            return false;
        }
        
        protected override IEnumerable<Task> GetScheduledTasks ()
        {
            return null;
        }
        
        #endregion
        
        private IEnumerator ExecuteTask (Task task)
        {
            // Execute yieldable actions using the MonoBehavior.
            //
            // The continuation will execute the task itself 
            // via TryExecuteTask(). That task action will
            // rethrow any exceptions caught during the yieldable
            // action invocation and TryExecuteTask() will set
            // the final state.
            //
            // The downside to this approach is that yieldable tasks
            // aren't considered running until they have already
            // completed because TryExecuteTask() is what sets state.
            var yieldableTask = task as YieldableTask;
            if(yieldableTask != null)
                yield return Fiber.Factory.StartNew(ExecuteYieldableTask(yieldableTask), scheduler);
            
            // Run the action
            TryExecuteTask(task);
        }
        
        private IEnumerator ExecuteYieldableTask(YieldableTask task)
        {
            object fiberResult = null;

            // TODO: Cleanup
            //
            // This uses internal setters to fake starting the fiber
            // and then uses internal Execute(). It should be possible to
            // use public APIs instead to:
            //   1. Set a fiber property to associate the task
            //   2. Set an exception handler on the FiberScheduler
            //   3. Retrieve the task in the handler from the fiber and set
            //      the exeption
            //   4. Return from the handler without rethrowing
            //
            // This method could be removed then and the internal setters
            // removed as well.
            task.Fiber.Scheduler = scheduler;
            task.Fiber.Status = FiberStatus.Running;
            
            while(true)
            {
                try
                {
                    // Throw here because the scheduler is disposed and will not
                    // run anything else. No further access is valid.
                    CancellationToken.ThrowIfCancellationRequested();
                    
                    fiberResult = task.Fiber.Execute();
                    
                    if(fiberResult is StopInstruction) {
                        // Check for exceptions
                        if (task.Fiber.IsFaulted) {
                            task.FiberException = task.Fiber.Exception;
                        }

                        yield break;
                    }
                }
                catch(System.Threading.OperationCanceledException ex)
                {
                    // Fiber execution does not throw so the only exception
                    // expected is the cancellation above.
                    task.FiberException = ex;
                    yield break;
                }

                yield return fiberResult;
            }
        }
                
        #region IDisposable implementation
        
        ~FiberTaskScheduler()
        {
            Dispose(false);
        }
        
        private bool isDisposed = false;
        
        public void Dispose() 
        {           
            Dispose(true);
            GC.SuppressFinalize(this); 
        }
        
        private /*protected virtual*/ void Dispose(bool disposing) 
        {
            // Do nothing if already called
            if(isDisposed)
                return;
                        
            if(disposing) 
            {
                // Free other state (managed objects).
                scheduler.Dispose();
            }
            
            // Free your own state (unmanaged objects).
            // Set large fields to null.
            
            // Mark disposed
            isDisposed = true;          
        }
        #endregion
    }
}