How can I do an atomic write/append in C#, or how do I get files opened with the FILE_APPEND_DATA flag?
Under most Unixes and Posix conforming operating systems performing an open() operating system call with the O_APPEND indicates to the OS that writes are to be atomic appen开发者_运维知识库d and write operations. With this behavior,for local filesystems when you do a write, you know it get appended to the end of the file.
The Windows operating systems support the same functionality by passing FILE_APPEND_DATA
in the appropriate parameter to the Win32 CreateFile() system call.
references:
http://www.google.com/search?q=msdn+createfile
or: http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx
http://www.google.com/search?q=msdn+IoCreateFileSpecifyDeviceObjectHint
or: http://www.google.com/search?q=msdn+IoCreateFileSpecifyDeviceObjectHint
My problem is this, I cannot determine how to get this behavior under C# using the Net Framework Libraries, is there a way to get such behavior using the Net Framework? I do not believe using FileMode.Append gives such behavior, by the way.
Use one of the overloads of the FileStream
constructor:
new FileStream(FileName, FileMode.Open, FileSystemRights.AppendData,
FileShare.Write, 4096, FileOptions.None)
FileSystemRights.AppendData
corresponds with FILE_APPEND_DATA
FileStream seems to insist on buffering, so make sure the buffer is large enough for each
write and call Flush()
after each write.
Tiny example:
private void button1_Click(object sender, EventArgs e) {
Thread t1 = new Thread(DoIt);
Thread t2 = new Thread(DoIt);
t1.Start("a");
t2.Start("b");
Thread.Sleep(2000);
Environment.Exit(0);
}
private void DoIt(object p) {
using (FileStream fs = new FileStream(FileName, FileMode.Open, FileSystemRights.AppendData,
FileShare.Write, 4096, FileOptions.None)) {
using (StreamWriter writer = new StreamWriter(fs)) {
writer.AutoFlush = true;
for (int i = 0; i < 20; ++i)
writer.WriteLine("{0}: {1:D3} {2:o} hello", p, i, DateTime.Now);
}
}
}
You can call CreateFile using PInvoke with the required parameters and pass the resulting handle to one of the FileStream Constructors which takes SafeFileHandle as a parameter.
Why can't you use
System.IO.File.AppendAllText("C:\\somefile.txt", "some content");
? That's a thread-safe/"atomic" call as well.
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