xronos /System.Xronos/Language/Threading/Transaction.cs

Language C# Lines 297
MD5 Hash 5b1d8d8aed1a185e13906954697fc176 Estimated Cost $5,721 (why?)
Repository https://bitbucket.org/stefanrusek/xronos View Raw File
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/* ****************************************************************************
 * 
 * Copyright (c) 2008 Stefan Rusek and Benjamin Pollack
 * 
 * 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.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Collections;

namespace System.Xronos.Language.Threading
{
    public enum TransactionState
    {
        Idle,
        Running,
        Commiting,
        Retry,
        Killed,
        Committed,
    }

    public class Transaction
    {
        static readonly int RetryLimit = 10000;
        static readonly TimeSpan OtherTransactionWaitTime = TimeSpan.FromMilliseconds(100);
        static readonly TimeSpan MinAgeToBarge = TimeSpan.FromMilliseconds(10);
        static readonly object RetryState = new object();

        [ThreadStatic]
        static Transaction _current;
        public static Transaction Current { get { return _current ?? (_current = new Transaction()); } }

        internal class RefState
        {
            public Ref Ref;
            public bool HasValue;
            public object Value;
            public List<Func<object, object>> Commutes;
        }

        DateTime startTime;
        public int StartPoint;
        public int ReadPoint;
        public int CommitPoint;
        int _state;
        IPersistentStack agentActions = null;
        object sync = new object();
        Thread thread = Thread.CurrentThread;

        public TransactionState State { get { return (TransactionState)_state; } }
        public bool IsRunning { get { return State == TransactionState.Running || State == TransactionState.Commiting; } }

        private Dictionary<Guid, RefState> refValues = new Dictionary<Guid, RefState>();

        internal bool TryGetRefValue(Guid id, out object result)
        {
            RefState state;
            bool rval;
            if (rval = refValues.TryGetValue(id, out state) && state.HasValue)
                result = state.Value;
            else
                result = default(object);
            return rval;
        }

        internal void SetValue(Guid id, Ref r, object value)
        {
            AssertNotIdle();

            RefState state;
            if (!refValues.TryGetValue(id, out state))
            {
                r.Enlist(this);
                refValues[id] = state = new RefState { Ref = r };
            }
            state.HasValue = true;
            state.Value = value;
        }

        internal void EnqueueCommute(Guid id, Ref r, object fn, ISequence args)
        {
            AssertNotIdle();

            RefState state;
            if (!refValues.TryGetValue(id, out state))
                refValues[id] = state = new RefState { Ref = r };

            Func<object, object> commute = old => FunctionHelper.Invoke<object>(fn, RT.Cons(old, args)); 

            Interlocked.CompareExchange(ref state.Commutes, new List<Func<object, object>>(), null);
            lock (state.Commutes)
                state.Commutes.Add(commute);

            state.Value = commute(state.HasValue ? state.Value : r.Value);
            state.HasValue = true;
        }

        private void AssertNotIdle()
        {
            if (State == TransactionState.Idle)
                throw new InvalidProgramException("No transaction running");
        }

        internal void Retry()
        {
            thread.Abort(RetryState);
        }

        internal void Abort()
        {
            Stop(TransactionState.Killed);
            thread.Abort();
        }

        internal static Transaction ResolveConflict(Action beforeStop, Transaction currentOwner, Transaction requestedOwner)
        {
            if (BargeIfNewer(currentOwner, requestedOwner))
                return requestedOwner;

            beforeStop();
            requestedOwner.Stop(TransactionState.Retry);

            lock (currentOwner.sync)
                Monitor.Wait(currentOwner.sync, OtherTransactionWaitTime);
            requestedOwner.Retry();

            return currentOwner;
        }

        private void Stop(TransactionState transactionState)
        {
            if (State != TransactionState.Idle)
            {
                lock (sync)
                {
                    _state = (int)transactionState;
                    Monitor.PulseAll(sync);
                }
                // right here all the waits that we just pulsed
                // will be able to read the new value of _state
                // when they are finished, then the code below
                // will execute.
                lock (sync)
                {
                    _state = 0;
                    refValues.Clear();
                }
            }
        }

        private static bool BargeIfNewer(Transaction current, Transaction requested)
        {
            if (DateTime.Now - requested.startTime < MinAgeToBarge || requested.StartPoint > current.StartPoint)
                return false;

            lock (current.sync)
            {
                var state = (TransactionState)Interlocked.CompareExchange(ref current._state, (int)TransactionState.Killed, (int)TransactionState.Running);
                if (state != TransactionState.Running)
                    return false;

                Monitor.PulseAll(current.sync);
                return true;
            }
        }

        public static object Run(object action){
            if (Current.IsRunning)
                return FunctionHelper.Invoke<object>(action);
            else
                return Current.InternalRun(action);
        }

        private object InternalRun(object action)
        {
            object result = null;
            bool success = false;
            List<RefState> lockedRefs = new List<RefState>();
            for (int i = 0; i < RetryLimit && !success; i++)
            {
                try
                {
                    ReadPoint = NewPoint();
                    if (i == 0)
                    {
                        StartPoint = ReadPoint;
                        startTime = DateTime.Now;
                    }
                    _state = (int)TransactionState.Running;
                    refValues.Clear();
                    result = Run(action);

                    if ((int)TransactionState.Running != Interlocked.CompareExchange(ref _state, (int)TransactionState.Commiting, (int)TransactionState.Running))
                        continue;

                    success = Commit(lockedRefs);
                }
                catch (ThreadAbortException taex)
                {
                    if (taex.ExceptionState != RetryState)
                        throw;
                    Thread.ResetAbort();
                }
                finally
                {
                    foreach (var item in lockedRefs)
                        item.Ref.Release();
                    lockedRefs.Clear();
                    Stop(success ? TransactionState.Committed : TransactionState.Retry);
                    if (success && agentActions != null)
                        foreach (IAgentItem item in (IEnumerable)agentActions)
                            item.Enqueue();
                    agentActions = null;
                }
            }
            _state = (int)TransactionState.Idle;
            if (!success)
                throw new InvalidOperationException("Transaction failed after reaching retry limit");
            return result;
        }

        private bool Commit(List<RefState> lockedRefs)
        {
            // lock all refs first
            List<RefState> refs = refValues.Values.ToList();
            foreach (var item in refs)
            {
                item.Ref.LockForCommit();
                lockedRefs.Add(item);
            }
            // apply commutes
            foreach (var item in refs)
                if (item.Commutes != null)
                    ApplyCommutes(item);
            // validate new values
            foreach (var item in refs)
            {
                item.Ref.Validate(item.Value);
            }
            // All of the above could fail, but from here on out we are cool
            foreach (var item in refs)
                item.Ref.Commit(this, item.Value);

            _state = (int)TransactionState.Committed;
            return true;
        }

        private void ApplyCommutes(RefState item)
        {
            if (item.Ref.CurrentOwner != this && item.Ref.CurrentOwner.IsRunning)
                if (!BargeIfNewer(item.Ref.CurrentOwner, this))
                    Retry();

            if (!item.HasValue)
            {
                item.Value = item.Ref.Value;
                item.HasValue = true;
            }

            foreach (var fn in item.Commutes)
                item.Value = fn(item.Value);
        }

        static int _lastPoint = 0;
        private static int NewPoint()
        {
            return Interlocked.Increment(ref _lastPoint);
        }

        internal void EnqueueAgent(IAgentItem item)
        {
            agentActions = (IPersistentStack)(agentActions ?? PersistentQueue.Empty).cons(item);
        }
    }
}
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