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POMulti-threaded application interaction with logger thread
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copied!<p>Here I am again with questions about multi-threading and an exercise of my <strong>Concurrent Programming</strong> class.</p> <p>I have a multi-threaded server - implemented using .NET <em>Asynchronous Programming Model</em> - with <code>GET</code> (<em>download</em>) and <code>PUT</code> (<em>upload</em>) file services. This part is done and tested.</p> <p>It happens that the statement of the problem says this server must have <em>logging</em> activity with the minimum impact on the server response time, and it should be supported by a low priority <em>thread</em> - <em>logger thread</em> - created for this effect. All <em>logging</em> messages shall be passed by the <em>threads</em> that produce them to this <em>logger thread</em>, using a communication mechanism that <strong>may not</strong> lock the <em>thread</em> that invokes it (besides the necessary locking to ensure mutual exclusion) and assuming that some <em>logging messages</em> may be ignored.</p> <p>Here is my current solution, please help validating if this stands as a solution to the stated problem:</p> <pre><code>using System; using System.IO; using System.Threading; // Multi-threaded Logger public class Logger { // textwriter to use as logging output protected readonly TextWriter _output; // logger thread protected Thread _loggerThread; // logger thread wait timeout protected int _timeOut = 500; //500ms // amount of log requests attended protected volatile int reqNr = 0; // logging queue protected readonly object[] _queue; protected struct LogObj { public DateTime _start; public string _msg; public LogObj(string msg) { _start = DateTime.Now; _msg = msg; } public LogObj(DateTime start, string msg) { _start = start; _msg = msg; } public override string ToString() { return String.Format("{0}: {1}", _start, _msg); } } public Logger(int dimension,TextWriter output) { /// initialize queue with parameterized dimension this._queue = new object[dimension]; // initialize logging output this._output = output; // initialize logger thread Start(); } public Logger() { // initialize queue with 10 positions this._queue = new object[10]; // initialize logging output to use console output this._output = Console.Out; // initialize logger thread Start(); } public void Log(string msg) { lock (this) { for (int i = 0; i < _queue.Length; i++) { // seek for the first available position on queue if (_queue[i] == null) { // insert pending log into queue position _queue[i] = new LogObj(DateTime.Now, msg); // notify logger thread for a pending log on the queue Monitor.Pulse(this); break; } // if there aren't any available positions on logging queue, this // log is not considered and the thread returns } } } public void GetLog() { lock (this) { while(true) { for (int i = 0; i < _queue.Length; i++) { // seek all occupied positions on queue (those who have logs) if (_queue[i] != null) { // log LogObj obj = (LogObj)_queue[i]; // makes this position available _queue[i] = null; // print log into output stream _output.WriteLine(String.Format("[Thread #{0} | {1}ms] {2}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.Subtract(obj._start).TotalMilliseconds, obj.ToString())); } } // after printing all pending log's (or if there aren't any pending log's), // the thread waits until another log arrives //Monitor.Wait(this, _timeOut); Monitor.Wait(this); } } } // Starts logger thread activity public void Start() { // Create the thread object, passing in the Logger.Start method // via a ThreadStart delegate. This does not start the thread. _loggerThread = new Thread(this.GetLog); _loggerThread.Priority = ThreadPriority.Lowest; _loggerThread.Start(); } // Stops logger thread activity public void Stop() { _loggerThread.Abort(); _loggerThread = null; } // Increments number of attended log requests public void IncReq() { reqNr++; } } </code></pre> <p>Basically, here are the main points of this code:</p> <ol> <li>Start a low priority <em>thread</em> that loops the <em>logging queue</em> and prints pending <em>logs</em> to the output. After this, the <em>thread</em> is suspended till new <em>log</em> arrives;</li> <li>When a log arrives, the logger thread is awaken and does it's work.</li> </ol> <p>Is this solution <em>thread-safe</em>? I have been reading <em>Producers-Consumers</em> problem and solution algorithm, but in this problem although I have multiple producers, I only have one reader.</p> <p>Thanks in advance for all your attention.</p>

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