// ----------------------------------------------------------------------------
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ----------------------------------------------------------------------------

using System;
using System.Collections;
using System.Threading;

using Microsoft.Contracts;

namespace Microsoft.Singularity.FileSystem
{
    public class FSThreadPool {
        private int numThreads;
        private readonly Queue workQueue = new Queue();
        private readonly FSThreadPoolCallback workCallback;
        private bool keepGoing = true;

        [NotDelayed]
        public FSThreadPool(int threads, FSThreadPoolCallback callback) {
            numThreads = threads;
            workCallback = callback;
            
            while (threads > 0) {
                Thread t = new Thread(new ThreadStart(DoWork));
                t.Start();
                threads--;
            }
        }
        
        public void KillPool() {
            Monitor.Enter(workQueue);
            keepGoing = false;
            Monitor.PulseAll(workQueue);
            while (numThreads > 0) {
                Monitor.Wait(workQueue);
            }
            Monitor.Exit(workQueue);
        }
        
        public void EnqueueItem(FSRequestInfo request) {
            Monitor.Enter(workQueue);
            workQueue.Enqueue(request);
            Monitor.Pulse(workQueue);
            Monitor.Exit(workQueue);
        }
        
        private void DoWork() {
            while (true) {
                Monitor.Enter(workQueue);
                while (workQueue.Count == 0 && keepGoing) {
                    Monitor.Wait(workQueue);
                }
                
                if (!keepGoing && workQueue.Count == 0) {
                    numThreads--;
                    Monitor.PulseAll(workQueue);
                    Monitor.Exit(workQueue);
                    break;
                }
                
                FSRequestInfo request = (FSRequestInfo)workQueue.Dequeue();
                
                Monitor.Exit(workQueue);
                
                workCallback(request);
            }
        }
    }
}