ln.skyscanner/threads/Pool.cs

using System;
using System.Threading;
using System.Collections.Generic;
using System.Linq.Expressions;
using ln.logging;
using System.Linq;
namespace ln.skyscanner.threads
{
    public delegate void JobDelegate();

    public enum PoolThreadState { READY, WORKING, EXITED }

    public class Pool :IDisposable
    {
        public PoolThread[] PoolThreads => poolThreads.ToArray();
        public int NumThreads
        {
            get => poolThreads.Count;
            set => setPoolThreads(value);
        }

        public PoolThreadState[] ThreadStates => poolThreads.Select((x) => x.State).ToArray();
        public int QueuedJobs => queuedJobs.Count;

        private List<PoolThread> poolThreads = new List<PoolThread>();
        private Queue<JobDelegate> queuedJobs = new Queue<JobDelegate>();

        private bool stopping;

        public Pool()
        {
            NumThreads = 4;
        }

        public void Close()
        {
            stopping = true;
            NumThreads = 0;
            stopping = false;
        }

        private void setPoolThreads(int count)
        {
            lock (poolThreads)
            {
                while (poolThreads.Count > count)
                {
                    poolThreads[poolThreads.Count - 1].Exit();
                }

                while (poolThreads.Count < count)
                {
                    poolThreads.Add(new PoolThread(this));
                }
            }
        }

        public void Enqueue(JobDelegate job)
        {
            if (stopping)
                return;

            lock (queuedJobs)
            {
                queuedJobs.Enqueue(job);
                Monitor.Pulse(queuedJobs);
            }
        }





        public class PoolThread
        {
            public Pool Pool { get; }
            public Thread Thread { get; }
            public PoolThreadState State { get; private set; }

            private bool exitCalled { get; set; }

            public PoolThread(Pool pool)
            {
                Pool = pool;
                Thread = new Thread(thread);

                WaitStarted();
            }

            private void WaitStarted()
            {
                lock (this)
                {
                    Thread.Start();
                    Monitor.Wait(this, 5000);
                }

            }

            private void thread()
            {
                lock (this)
                {
                    Monitor.Pulse(this);
                }

                while (!exitCalled)
                {
                    try
                    {
                        State = PoolThreadState.WORKING;
                        lock (Pool.queuedJobs)
                        {
                            while (!exitCalled && Pool.queuedJobs.Count > 0)
                            {
                                JobDelegate job = Pool.queuedJobs.Dequeue();
                                Monitor.Exit(Pool.queuedJobs);

                                Logging.Log(LogLevel.DEBUG, "PoolThread: starting next job {0}", job);

                                try
                                {
                                    job();
                                }
                                catch (Exception ie)
                                {
                                    Logging.Log(ie);
                                }
                                Monitor.Enter(Pool.queuedJobs);

                                State = PoolThreadState.READY;
                                Monitor.Wait(Pool.queuedJobs, 5000);
                                State = PoolThreadState.WORKING;
                            }
                        }
                    }
                    catch (Exception e)
                    {
                        Logging.Log(e);
                    }
                }
                lock (this)
                {
                    State = PoolThreadState.EXITED;
                    Monitor.Pulse(this);
                }

            }

            public void Exit()
            {
                lock (this)
                {
                    exitCalled = true;
                    Monitor.Pulse(this);
                    Monitor.Wait(this);
                    Pool.poolThreads.Remove(this);
                }
            }
        }


        public void Dispose()
        {
            Close();
        }
    }
}