If you’ve wanted to combine parallel / multi-threading and also writing to files, you’ve probably experienced the issue of a file being locked when another process is writing at the same time. Something like:
An unhandled exception of type ‘System.IO.IOException’ occurred in mscorlib.dll
Additional information: The process cannot access the file ‘c:\yourfile’ because it is being used by another process.
One of the ways to get around this is utilize the “lock” statement.
In my below example, I’m running parallel tasks (including the optional MaxDegreeOfParallelism) and writing to a file. I also added a stopwatch and a .sleep to add time and debugging to the method. If you were to remove the lock() from the below, you should experience the ioexception.
Hope this helps as you create parallel tasks (so many great uses) and write files (maybe some simple logging, etc.)
You can also download the sample here.
using System;
using System.Diagnostics;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
namespace parallelTasks_Example
{
//custom object for passing to queue task
public class UpdateFile
{
public string lineData { get; set; }
public string filePath { get; set; }
public long timeTaken { get; set; }
}
internal class Program
{
//set an update to use a lock
private static object fileLock = new object();
private static void Main(string[] args)
{
//just for testing
Stopwatch timer = new Stopwatch();
timer.Reset();
//get some data
string[] contacts = { "jon", "jon2", "aaron", "efren", "diedrich", "tina", "sandy", "haylie", "trevor", "shondrella" };
//do something with the data
timer.Start();
Parallel.ForEach(contacts, new ParallelOptions { MaxDegreeOfParallelism = 3 }, contact =>
{
//do the task
Console.WriteLine(contact + " " + timer.ElapsedMilliseconds);
//create an object to past to the queue item
UpdateFile fileupdate = new UpdateFile { filePath = @"c:\temp\temp.txt", lineData = contact, timeTaken = timer.ElapsedMilliseconds };
//add the queue item
ThreadPool.QueueUserWorkItem(UpdateFile, fileupdate);
});
Console.ReadLine();
}
private static void UpdateFile(object fileData)
{
//set object to be locked
lock (fileLock)
{
//get the file
using (var fw = File.AppendText(((UpdateFile)fileData).filePath))
{
//write the data
fw.WriteLine(((UpdateFile)fileData).lineData + ": " + ((UpdateFile)fileData).timeTaken.ToString());
//make process take long (for example)
System.Threading.Thread.Sleep(100);
}
}
}
}
}
Chris Bitting 