Log.cs

/* *********************************************************************
 * This Source Code Form is copyright of 51Degrees Mobile Experts Limited. 
 * Copyright © 2017 51Degrees Mobile Experts Limited, 5 Charlotte Close,
 * Caversham, Reading, Berkshire, United Kingdom RG4 7BY
 * 
 * This Source Code Form is the subject of the following patents and patent 
 * applications, owned by 51Degrees Mobile Experts Limited of 5 Charlotte
 * Close, Caversham, Reading, Berkshire, United Kingdom RG4 7BY: 
 * European Patent No. 2871816;
 * European Patent Application No. 17184134.9;
 * United States Patent Nos. 9,332,086 and 9,350,823; and
 * United States Patent Application No. 15/686,066.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0.
 * 
 * If a copy of the MPL was not distributed with this file, You can obtain
 * one at http://mozilla.org/MPL/2.0/.
 * 
 * This Source Code Form is “Incompatible With Secondary Licenses”, as
 * defined by the Mozilla Public License, v. 2.0.
 * ********************************************************************* */

#region Usings

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;

#endregion

using System.Threading.Tasks;

#if AZURE

using Microsoft.WindowsAzure;
using Microsoft.WindowsAzure.StorageClient;
using System.Text.RegularExpressions;

#endif

namespace FiftyOne
{
    /// <summary>
    /// This is the base class for recording messages in text files. The write operation to
    /// file occurs outside of the current thread ensuring minimal impact on performance.
    /// If the process completes before the thread has finished writing it is possible that
    /// some messages will not be written. This is by design.
    /// </summary>
    /// <remarks>
    /// This class should not be used in developers code.
    /// </remarks>
    public abstract class Log
    {
        #region Fields

        /// <summary>
        /// An internal object used for synchronising access to the message queue.
        /// </summary>
        protected internal static object _syncQueue = new object();

        /// <summary>
        /// An internal object used to synchronising access to the log file.
        /// </summary>
        protected internal static object _syncWait = new object();

        /// <summary>
        /// The message queue to use to record log entries.
        /// </summary>
        private readonly Queue<string> _queue = new Queue<string>();

        /// <summary>
        /// Set to true if the message writing thread is running.
        /// </summary>
        private bool _running;

        #endregion

        #region Abstract Methods

        /// <summary>
        /// Returns the full path to the file to be written to.
        /// </summary>
        protected abstract string LogFile { get; }

        #endregion

        #region Methods

#if AZURE

        /// <summary>
        /// The main loop for the log table service thread.
        /// </summary>
        protected void Run(Object stateInfo)
        {
            // Initialise the Azure table service creating the table if it does not exist.
            var storageAccount = CloudStorageAccount.Parse(Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment.GetConfigurationSettingValue(FiftyOne.Foundation.Mobile.Constants.AZURE_STORAGE_NAME));
            var serviceContext = new TableServiceContext(storageAccount.TableEndpoint.ToString(), storageAccount.Credentials);
            var tableName = Regex.Replace(LogFile, "[^A-Za-z]+", String.Empty);
            storageAccount.CreateCloudTableClient().CreateTableIfNotExist(tableName);

            while (IsQueueEmpty() == false)
            {
                try
                {
                    while (IsQueueEmpty() == false)
                    {
                        lock (_syncQueue)
                        {
                            string message = _queue.Peek();
                            if (message != null)
                            {
                                var entity = new LogMessageEntity(message);
                                serviceContext.AddObject(tableName, entity);
                                _queue.Dequeue();
                            }
                        }
                    }
                    // Commit the new log entries to the database.
                    serviceContext.SaveChanges();
                }
                catch
                {
                    // End the thread and wait until another message comes
                    // arrives to resume writing.
                    _running = false;
                    return;
                }

                // Sleep for 50ms incase any new messages come in.
                Thread.Sleep(50);
            }
            _running = false;
        }

#else

        /// <summary>
        /// The main loop for the log file thread.
        /// </summary>
        protected void Run(Object stateInfo)
        {
            while (IsQueueEmpty() == false)
            {
                try
                {
                    if (String.IsNullOrEmpty(LogFile) == false)
                    {
                        try
                        {
                            using (var writer = new StreamWriter(
                                File.Open(LogFile, FileMode.Append, FileAccess.Write, FileShare.ReadWrite)))
                            {
                                while (IsQueueEmpty() == false)
                                {
                                    lock (_syncQueue)
                                    {
                                        string message = _queue.Peek();
                                        if (message != null)
                                        {
                                            writer.WriteLine(message);
                                            _queue.Dequeue();
                                        }
                                    }
                                }
                            }
                        }
                        catch
                        {
                            // End the thread and wait until another message
                            // arrives to resume writing.
                            _running = false;
                            return;
                        }
                    }
                }
                catch
                {
                    // End the thread and wait until another message comes
                    // arrives to resume writing.
                    _running = false;
                    return;
                }
                // Sleep for 50ms incase any new messages come in.
                Thread.Sleep(50);
            }
            _running = false;
        }

#endif

        /// <summary>
        /// Returns true if the message queue is empty.
        /// </summary>
        /// <returns></returns>
        private bool IsQueueEmpty()
        {
            return (_queue.Count == 0);
        }

        /// <summary>
        /// Makes sure the logging thread is running and then writes the message
        /// to the queue of messages to be serviced.
        /// </summary>
        /// <param name="message">The message to be written to the log file.</param>
        protected internal void Write(string message)
        {
            // If the queue is very large sleep for 10ms and
            // give it time to reduce.
            // This should never happen if debug is disabled.
            if (_queue.Count > 100 && _running)
            {
                lock (_syncWait)
                {
                    if (_queue.Count > 100 && _running)
                    {
                        Thread.Sleep(10);
                    }
                }
            }

            // Add this entry to the queue for writing.
            lock (_syncQueue)
            {
                _queue.Enqueue(message);
            }

            // Check the thread is running.
            if (_running == false)
            {
                lock (_syncQueue)
                {
                    if (_running == false)
                    {
                        _running = true;
                        Task.Factory.StartNew(() => Run(null));
                    }
                }
            }
        }

        #endregion
    }
}