CODEWITHSUNDEEP
.netfileioexists
Matt W
Matt W

Reputation: 12424

Is File.Exists an expensive operation?

Re: http://msdn.microsoft.com/en-us/library/system.io.file.exists.aspx

Does anyone know if this is a particularly slow or locking operation which could impact server performance in a large environment?

Upvotes: 23

Views: 15671

Answers (5)

t3chb0t
t3chb0t

Reputation: 18694

In year 2016 it doesn't seem to be very expensive and there also seem to be no real difference between File.Exists and PathFileExists (Why is File.Exists() much slower when the file does not exist?). The only difference I could measure is that it's faster to check for a non-existing file then an existing one:

(Tested on an SSD)

[DllImport("Shlwapi.dll", SetLastError = true, CharSet = CharSet.Auto)]
private extern static bool PathFileExists(StringBuilder path);

void Main()
{
    var sw = Stopwatch.StartNew();
    for (int i = 0; i < 10000; i++)
    {
        File.Exists(@"c:\Home\Temp\test_.log");
    }
    sw.Stop();
    sw.Dump("File.Exists = false");

    sw = Stopwatch.StartNew();
    for (int i = 0; i < 10000; i++)
    {
        File.Exists(@"c:\Home\Temp\test.log");
    }
    sw.Stop();
    sw.Dump("File.Exists = true");

    var sb = new StringBuilder(@"c:\Home\Temp\test_.log");
    sw = Stopwatch.StartNew();
    for (int i = 0; i < 10000; i++)
    {
        PathFileExists(sb);
    }
    sw.Stop();
    sw.Dump("PathFileExists = false");

    sb = new StringBuilder(@"c:\Home\Temp\test.log");
    sw = Stopwatch.StartNew();
    for (int i = 0; i < 10000; i++)
    {
        PathFileExists(sb);
    }
    sw.Stop();
    sw.Dump("PathFileExists = true");

}

Results

Upvotes: 13

Brian Knoblauch
Brian Knoblauch

Reputation: 21389

Locking no. Slow, depends on what you're comparing it to. It's fairly cheap as far as I/O goes, but I/O is generally slow overall compared to other operations. So, if you must use it, it won't hurt too bad. However, I'd try not to call it more times than is truly necessary! :-)

Upvotes: 8

Damon Achey
Damon Achey

Reputation: 182

Best would be to run some tests in your environment. I have an app that can do 10,000+ per second without a hiccup to my systems. I consider that pretty fast.

Upvotes: 2

Mike Chaliy
Mike Chaliy

Reputation: 26698

File.Exisits with kernel32.dll FindFirstFile open handler to the file. If resulting handle is invalid, it return false. If valid it fill data structure with all stuff like LastAccessTime, CreationTime, file size and so on. And then return true. Nothing blocking.

Upvotes: 2

Yann Schwartz
Yann Schwartz

Reputation: 5994

I don't think it is (file operations are heavily optimized and cached on most OS's) and most of the other operations are more likely to be culprits here (sockets, DB access, general processing, etc). But, as usual, the best way is to actually profile your application and see if it's an hotspot.

Upvotes: 7

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