Recently I was needed to read context of some log file that's in use by another process when I trying to read from it.
It seems that there is no way to do it with System.IO.StreamReader. The stuff like:
using( System.IO.StreamReader logReader = new System.IO.StreamReader(logPath) )
{
System.String errorFileContext = updateErrorFileReader.ReadToEnd();
}
will cause System.IO.IOException with Message saying "The process cannot access the file ... because it is being used by another process."
My obvious guess was that System.IO.StreamReader doesn't have a constructor specifying the file sharing mode, so I switched to System.IO.FileStream:
using( System.IO.FileStream logReader = new System.IO.FileStream(
logFilePath, System.IO.FileMode.Open,
System.IO.FileAccess.Read, System.IO.FileShare.Read ) )
{
// In my case it always the case, o/w you can read file line-by-line
const int maxFileSize = 10*1024;
byte[] fileBytes = new byte[maxFileSize];
int amountOfBytes = updateErrorFileReader.Read(fileBytes, 0, maxFileSize);
System.Text.UTF7Encoding utf7 = new System.Text.UTF7Encoding();
System.String errorFileContext = utf7.GetString(fileBytes, 0, amountOfBytes);
}
MSDN documentation states that setting last parameter of System.IO.FileStream constructor to System.IO.FileShare.Read:
"Allows subsequent opening of the file for reading.
If this flag is not specified, any request to open the file
for reading (by this process or another process) will fail
until the file is closed. However, if this flag is specified
additional permissions might still be needed to access the file."
Well, that's was exactly what I was going to do and ... imagine my surprise when I got the same thing again:
System.IO.IOException with "The process cannot access the file ... because it is being used by another process.".
Solution came after playing a bit around. What you need to do - is to put last parameter to
System.IO.FileShare.ReadWrite
It was quite surprising and took me some time to found it, since MSDN says that it "Allows subsequent opening of the file for reading or writing." while I was need reading only. Any way it just works...
