I feel kind of stupid posting this, but it seems like a genuine issue that I've made sufficiently simple so as to demonstrate that it should not fail. As part of my work I am responsible for maintaining build systems that take files under version control, and copy them to other locations. Sounds simple, but I've constantly experienced file access violations when attempting to copy files that I've supposedly already set as 'Normal'.
The code sample below simply creates a set of test files, makes them read only, and then copies them over to another folder. If the files already exist in the destination folder, the RO attribute is cleared so that the file copy will not fail.
The code works to a point, but at seemingly random points an exception is thrown when the file copy is attempted. The code is all single threaded, so unless .NET is doing something under the hood that causes a delay on the setting of attributes I can't really explain the problem.
If anyone can explain why this is happening I'd be interested. I'm not looking for a solution unless there is something I am definitely doing wrong, as I've handled the issue already, I'm just curious as no one else seems to have reported anything related to this.
After a few iterations I get something like:
A first chance exception of type 'System.UnauthorizedAccessException' occurred in mscorlib.dll Additional information: Access to the path 'C:\TempFolderB\TEMPFILENAME8903.txt' is denied.
One other fact, if you get the file attributes BEFORE the file copy, the resulting state says the file attributes indeed Normal, yet examination of the local file shows it as Read Only.
/// <summary>
/// Test copying multiple files from one folder to another while resetting RO attr
/// </summary>
static void MultiFileCopyTest()
{
/// Temp folders for our test files
string folderA = @"C:\TempFolderA";
string folderB = @"C:\TempFolderB";
/// Number of files to create
const int fileCount = 10000;
/// If the test folders do not exist populate them with some test files
if (System.IO.Directory.Exists(folderA) == false)
{
const int bufferSize = 32768;
System.IO.Directory.CreateDirectory(folderA);
System.IO.Directory.CreateDirectory(folderB);
byte[] tempBuffer = new byte[bufferSize];
/// Create a bunch of files and make them all Read Only
for (int i = 0; i < fileCount; i++)
{
string filename = folderA + "\\" + "TEMPFILENAME" + i.ToString() + ".txt";
if (System.IO.File.Exists(filename) == false)
{
System.IO.FileStream str = System.IO.File.Create(filename);
str.Write(tempBuffer, 0, bufferSize);
str.Close();
}
/// Ensure files are Read Only
System.IO.File.SetAttributes(filename, System.IO.FileAttributes.ReadOnly);
}
}
/// Number of iterations around the folders
const int maxIterations = 100;
for (int idx = 0; idx < maxIterations; idx++)
{
Console.WriteLine("Iteration {0}", idx);
/// Loop for copying all files after resetting the RO attribute
for (int i = 0; i < fileCount; i++)
{
string filenameA = folderA + "\\" + "TEMPFILENAME" + i.ToString() + ".txt";
string filenameB = folderB + "\\" + "TEMPFILENAME" + i.ToString() + ".txt";
try
{
if (System.IO.File.Exists(filenameB) == true)
{
System.IO.File.SetAttributes(filenameB, System.IO.FileAttributes.Normal);
}
System.IO.File.Copy(filenameA, filenameB, true);
}
catch (System.UnauthorizedAccessException ex)
{
Console.WriteLine(ex.Message);
}
}
}
}
