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POAccess List<T> elements in multiple threads and report progress
 

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  1. POAccess List<T> elements in multiple threads and report progress
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    <p>Inside my application I have list of persons from my database. For every person I must call 5 (for now) services to search for some informations. If service returns info I' adding it to that person (list of orders for specific person)<br> Because services work independent I thought I could try to run them parallel. I've created my code as so:</p> <pre><code>using System; using System.Collections.Generic; using System.Threading; namespace Testy { internal class Program { internal class Person { public int Id { get; set; } public string Name { get; set; } public List&lt;string&gt; Orders { get; private set; } public Person() { // thanks for tip @juharr Orders = new List&lt;string&gt;(); } public void AddOrder(string order) { lock (Orders) //access across threads { Orders.Add(order); } } } internal class Service { public int Id { get; private set; } public Service(int id) { Id = id; } //I get error when I use IList instead of List public void Search(ref List&lt;Person&gt; list) { foreach (Person p in list) { lock (p) //should I lock Person here? and like this??? { Search(p); } } } private void Search(Person p) { Thread.Sleep(50); p.AddOrder(string.Format("test order from {0,2}", Thread.CurrentThread.ManagedThreadId)); Thread.Sleep(100); } } private static void Main() { //here I load my services from external dll's var services = new List&lt;Service&gt;(); for (int i = 1; i &lt;= 5; i++) { services.Add(new Service(i)); } //sample data load from db var persons = new List&lt;Person&gt;(); for (int i = 1; i &lt;= 10; i++) { persons.Add( new Person {Id = i, Name = string.Format("Test {0}", i)}); } Console.WriteLine("Number of services: {0}", services.Count); Console.WriteLine("Number of persons: {0}", persons.Count); ManualResetEvent resetEvent = new ManualResetEvent(false); int toProcess = services.Count; foreach (Service service in services) { new Thread(() =&gt; { service.Search(ref persons); if (Interlocked.Decrement(ref toProcess) == 0) resetEvent.Set(); } ).Start(); } // Wait for workers. resetEvent.WaitOne(); foreach (Person p in persons) { Console.WriteLine("{0,2} Person name: {1}",p.Id,p.Name); if (null != p.Orders) { Console.WriteLine(" Orders:"); foreach (string order in p.Orders) { Console.WriteLine(" Order: {0}", order); } } else { Console.WriteLine(" No orders!"); } } Console.ReadLine(); } } } </code></pre> <p>I have 2 problems with my code:</p> <ol> <li><s> When I run my app I should get list of 10 persons and for every person 5 orders, but from time to time (ones for 3-5 runs) for first person I get only 4 orders. <strong>How I can prevent such behaviour?</strong></s><br> <strong>solved! thanks to @juharr</strong></li> <li>How can I report progress from my threads? What I would like to get is one Function from my Program class that will be called every time order is added from service - I need that to show some kind of progress for every report. <br>I was trying solution described here: <a href="https://stackoverflow.com/a/3874184/965722">https://stackoverflow.com/a/3874184/965722</a>, but I'm wondering if there is an easier way. Ideally I would like to add delegate to <code>Service</code> class and place all Thread code there.<br> <strong>How should I add event and delegate to <code>Service</code> class and how to subscribe to it in Main method?</strong> </li> </ol> <hr> <p><strong>I'm using .NET 3.5</strong></p> <p>I've added this code to be able to get progress reports:</p> <pre><code>using System; using System.Collections.Generic; using System.Threading; namespace Testy { internal class Program { public class ServiceEventArgs : EventArgs { public ServiceEventArgs(int sId, int progress) { SId = sId; Progress = progress; } public int SId { get; private set; } public int Progress { get; private set; } } internal class Person { private static readonly object ordersLock = new object(); public int Id { get; set; } public string Name { get; set; } public List&lt;string&gt; Orders { get; private set; } public Person() { Orders = new List&lt;string&gt;(); } public void AddOrder(string order) { lock (ordersLock) //access across threads { Orders.Add(order); } } } internal class Service { public event EventHandler&lt;ServiceEventArgs&gt; ReportProgress; public int Id { get; private set; } public string Name { get; private set; } private int counter; public Service(int id, string name) { Id = id; Name = name; } public void Search(List&lt;Person&gt; list) //I get error when I use IList instead of List { counter = 0; foreach (Person p in list) { counter++; Search(p); Thread.Sleep(3000); } } private void Search(Person p) { p.AddOrder(string.Format("Order from {0,2}", Thread.CurrentThread.ManagedThreadId)); EventHandler&lt;ServiceEventArgs&gt; handler = ReportProgress; if (handler != null) { var e = new ServiceEventArgs(Id, counter); handler(this, e); } } } private static void Main() { const int count = 5; var services = new List&lt;Service&gt;(); for (int i = 1; i &lt;= count; i++) { services.Add(new Service(i, "Service " + i)); } var persons = new List&lt;Person&gt;(); for (int i = 1; i &lt;= 10; i++) { persons.Add(new Person {Id = i, Name = string.Format("Test {0}", i)}); } Console.WriteLine("Number of services: {0}", services.Count); Console.WriteLine("Number of persons: {0}", persons.Count); Console.WriteLine("Press ENTER to start..."); Console.ReadLine(); ManualResetEvent resetEvent = new ManualResetEvent(false); int toProcess = services.Count; foreach (Service service in services) { new Thread(() =&gt; { service.ReportProgress += service_ReportProgress; service.Search(persons); if (Interlocked.Decrement(ref toProcess) == 0) resetEvent.Set(); } ).Start(); } // Wait for workers. resetEvent.WaitOne(); foreach (Person p in persons) { if (p.Orders.Count != count) Console.WriteLine("{0,2} Person name: {1}, orders: {2}", p.Id, p.Name, p.Orders.Count); } Console.WriteLine("END :)"); Console.ReadLine(); } private static void service_ReportProgress(object sender, ServiceEventArgs e) { Console.CursorLeft = 0; Console.CursorTop = e.SId; Console.WriteLine("Id: {0,2}, Name: {1,2} - Progress: {2,2}", e.SId, ((Service) sender).Name, e.Progress); } } } </code></pre> <p>I've added custom EventArgs, event for Service class. In this configuration I should have 5 services running, but only 3 of them report progress.<br> I imagined that if I have 5 services I should have 5 events (5 lines showing progress).<br> This is probably because of threads, but I have no ideas how to solve this.</p> <p>Sample output now looks like this:</p> <pre><code>Number of services: 5 Number of persons: 10 Press ENTER to start... Id: 3, Name: Service 3 - Progress: 10 Id: 4, Name: Service 4 - Progress: 10 Id: 5, Name: Service 5 - Progress: 19 END :) </code></pre> <p>It should look like this:</p> <pre><code>Number of services: 5 Number of persons: 10 Press ENTER to start... Id: 1, Name: Service 1 - Progress: 10 Id: 2, Name: Service 2 - Progress: 10 Id: 3, Name: Service 3 - Progress: 10 Id: 4, Name: Service 4 - Progress: 10 Id: 5, Name: Service 5 - Progress: 10 END :) </code></pre> <hr> <p><strong>Last edit</strong><br> I've moved all my thread creation to separate class <code>ServiceManager</code> now my code looks like so:</p> <pre><code>using System; using System.Collections.Generic; using System.Threading; namespace Testy { internal class Program { public class ServiceEventArgs : EventArgs { public ServiceEventArgs(int sId, int progress) { SId = sId; Progress = progress; } public int SId { get; private set; } // service id public int Progress { get; private set; } } internal class Person { private static readonly object ordersLock = new object(); public int Id { get; set; } public string Name { get; set; } public List&lt;string&gt; Orders { get; private set; } public Person() { Orders = new List&lt;string&gt;(); } public void AddOrder(string order) { lock (ordersLock) //access across threads { Orders.Add(order); } } } internal class Service { public event EventHandler&lt;ServiceEventArgs&gt; ReportProgress; public int Id { get; private set; } public string Name { get; private set; } public Service(int id, string name) { Id = id; Name = name; } public void Search(List&lt;Person&gt; list) { int counter = 0; foreach (Person p in list) { counter++; Search(p); var e = new ServiceEventArgs(Id, counter); OnReportProgress(e); } } private void Search(Person p) { p.AddOrder(string.Format("Order from {0,2}", Thread.CurrentThread.ManagedThreadId)); Thread.Sleep(50*Id); } protected virtual void OnReportProgress(ServiceEventArgs e) { var handler = ReportProgress; if (handler != null) { handler(this, e); } } } internal static class ServiceManager { private static IList&lt;Service&gt; _services; public static IList&lt;Service&gt; Services { get { if (null == _services) Reload(); return _services; } } public static void RunAll(List&lt;Person&gt; persons) { ManualResetEvent resetEvent = new ManualResetEvent(false); int toProcess = _services.Count; foreach (Service service in _services) { var local = service; local.ReportProgress += ServiceReportProgress; new Thread(() =&gt; { local.Search(persons); if (Interlocked.Decrement(ref toProcess) == 0) resetEvent.Set(); } ).Start(); } // Wait for workers. resetEvent.WaitOne(); } private static readonly object consoleLock = new object(); private static void ServiceReportProgress(object sender, ServiceEventArgs e) { lock (consoleLock) { Console.CursorTop = 1 + (e.SId - 1)*2; int progress = (100*e.Progress)/100; RenderConsoleProgress(progress, '■', ConsoleColor.Cyan, String.Format("{0} - {1,3}%", ((Service) sender).Name, progress)); } } private static void ConsoleMessage(string message) { Console.CursorLeft = 0; int maxCharacterWidth = Console.WindowWidth - 1; if (message.Length &gt; maxCharacterWidth) { message = message.Substring(0, maxCharacterWidth - 3) + "..."; } message = message + new string(' ', maxCharacterWidth - message.Length); Console.Write(message); } private static void RenderConsoleProgress(int percentage, char progressBarCharacter, ConsoleColor color, string message) { ConsoleColor originalColor = Console.ForegroundColor; Console.ForegroundColor = color; Console.CursorLeft = 0; int width = Console.WindowWidth - 1; var newWidth = (int) ((width*percentage)/100d); string progBar = new string(progressBarCharacter, newWidth) + new string(' ', width - newWidth); Console.Write(progBar); if (!String.IsNullOrEmpty(message)) { Console.CursorTop++; ConsoleMessage(message); Console.CursorTop--; } Console.ForegroundColor = originalColor; } private static void Reload() { if (null == _services) _services = new List&lt;Service&gt;(); else _services.Clear(); for (int i = 1; i &lt;= 5; i++) { _services.Add(new Service(i, "Service " + i)); } } } private static void Main() { var services = ServiceManager.Services; int count = services.Count; var persons = new List&lt;Person&gt;(); for (int i = 1; i &lt;= 100; i++) { persons.Add(new Person {Id = i, Name = string.Format("Test {0}", i)}); } Console.WriteLine("Services: {0}, Persons: {1}", services.Count, persons.Count); Console.WriteLine("Press ENTER to start..."); Console.ReadLine(); Console.Clear(); Console.CursorVisible = false; ServiceManager.RunAll(persons); foreach (Person p in persons) { if (p.Orders.Count != count) Console.WriteLine("{0,2} Person name: {1}, orders: {2}", p.Id, p.Name, p.Orders.Count); } Console.CursorTop = 12; Console.CursorLeft = 0; Console.WriteLine("END :)"); Console.CursorVisible = true; Console.ReadLine(); } } } </code></pre>
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    1. COYour null check and creation of the Order list should be inside the lock, or better yet inside a Person constructor.
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    2. CO@juharr - thanks for that tip :) I'll modify and check my code right away!
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