Stream Reader process cannot access file because i

问题:

This question already has answers here:

How can I read a file even when getting an “in use by another process” exception? (4 answers)

Closed 3 years ago.

My application parses log files but when trying to parse the current day's file I get an error stating that the file is being used by another process. This log file is currently being written to and can be accessed through notepad but not through my application.

Current Code:

Stream stream = new FileStream(fileToRead, FileMode.Open, FileAccess.Read);
StreamReader sr = new StreamReader(stream);

Also tried this but had no luck:

Stream stream = new FileStream(fileToRead, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

What changes need to be to my code in order to READ a file that is being used by another process. Copying the log file is not a solution due to the size of the log and performance of my application

回答1:

We can use a different signature for opening the filestream with read/write access to other processes:

Stream stream = new FileStream(fileToRead, FileMode.Open, FileAccess.Read,
                        FileShare.ReadWrite);

or

Stream stream = File.Open(fileToRead, FileMode.Open, FileAccess.Read,
                        FileShare.ReadWrite);

The FileShare option determines how other processes can access the same file when this process opens the same file.

Your first code block will default to FileShare.None:

Stream stream = new FileStream(fileToRead, FileMode.Open, FileAccess.Read);

This would fail whilst the file is open as it's trying to obtain exclusive access to the file.

However, you would need this to occur in the log writer to allow your log reader to have read access.

Lastly, try running your log reader as an administrator, as there may be operating system permissions at play that are not obvious when you "open with notepad".

回答2:

Here is a code snippet

The problem is when another application opens it first and the file sharing is Read only (FileShare.Read) certainly you can't write onto the file but you can read, Or file sharing is Write only (FileShare.Write) you can't Read onto the file but still you can be write onto it.

 using (FileStream file = new FileStream("You File Name here", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite))
        {
            using (StreamReader sr = new (StreamReader (file))
            {
        //Do your codes here     
            }
        }

回答3:

I had a similar problem that was resolved by setting the file attributes.

File.SetAttributes(outputDirectory + fileName + ".txt", FileAttributes.Normal);

This was done after the file was created, though. The problem has to do with how the OS manages files that are being accessed by multiple processes. In my case, I deleted the file (you aren't always allowed to do this because you'll get the error you're seeing). The only real way to solve this is to track down the processes that are accessing the file and stop them. The easiest way I fix this is restarting my PC, but if you are working on a server, that isn't feasible to do.

I haven't done an extensive amount of testing, but if you wanted to get this to be used by multiple processes, maybe it might be a good idea to give the file read properties and/or attributes:

File.SetAttributes(outputDirectory + fileName + ".txt", FileAttributes.ReadOnly);

Good luck - hope this helps someone else out there (since this is already a year old!).