You should avoid ThreadStatic (especially for a stateful object like a hash code provider) when you don't control the Thread creation. Underneath, you have no idea if you are going to be run on a thread for each loop, or shared across a pool of worker threads.
Perhaps I'm missing something, but why isn't this as simple as newing up a new provider as a local at the start of the action, and disposing it at the end? From: [email protected] [mailto:[email protected]] On Behalf Of Corneliu I. Tusnea Sent: Friday, February 15, 2013 4:49 PM To: ozDotNet Subject: Re: Crypto hash in a Parallel.ForEach Wal, That does not really work properly. You have to dispose the object as well plus (I've tried it) every now and then it hits some odd error. I don't think [ThreadStatic] is safe to use with Parallel.ForEach. Corneliu,. On Fri, Feb 15, 2013 at 10:45 PM, Wallace Turner <[email protected]<mailto:[email protected]>> wrote: It should work fine... the following code does what its supposed to do :) [ThreadStatic] private static object _hasher; var items = Enumerable.Range(1, 50); Parallel.ForEach(items, (i, state) => { if (_hasher == null) { _hasher = new object(); Console.WriteLine("new hasher for thread " + Thread.CurrentThread.ManagedThreadId); } Console.WriteLine(i + " " + Thread.CurrentThread.ManagedThreadId); }); On Fri, Feb 15, 2013 at 7:37 PM, Wallace Turner <[email protected]<mailto:[email protected]>> wrote: attribute your hasher with [ThreadStatic] ? (and obviously move the init check into the loop which would only be done once per thread) http://msdn.microsoft.com/en-us/library/system.threadstaticattribute.aspx On Fri, Feb 15, 2013 at 7:00 PM, Corneliu I. Tusnea <[email protected]<mailto:[email protected]>> wrote: I hit exactly the same issue with calculating hashes. I don't think it's threadsafe to do it. Just initialize it in each thread. I found the performance to be acceptable (at least for my use). However if you do find a better way I'd like to know :) On Fri, Feb 15, 2013 at 8:38 PM, mike smith <[email protected]<mailto:[email protected]>> wrote: SOme of the stuff around here about TLS? http://msdn.microsoft.com/en-us/library/6sby1byh.aspx On Fri, Feb 15, 2013 at 7:25 PM, Greg Keogh <[email protected]<mailto:[email protected]>> wrote: Folks, I can't remember if I've asked about this before. I think I year ago when I hit this I gave up and worked around it ... but now I want it solved! I have a Parallel.ForEach loop over EnumerateFiles which is blazing fast, but then I added to code to make an MD5 hash of the files and it dies because of "Hash not valid for use in specified state". I have a single static MD5 hasher which lives for the life of the app, but calling it from many threads is not allowed. I have a suspicion there is an overload of Parallel.ForEach that allows each thread to start/use/finish its own resources. In theory I need each thread needs to make its own MD5 and dispose at the end. There are so many overloads in the Threading Tasks namespace that I'm confused at first and I'll have to plod through Jeffrey Richter's book overnight to find a possible example. Are there any Task ninjas out there who know how to do this sort of thing? Greg K P.S. I just went to pat the cat and on the way back I picked up Richter's CLR via C# and I found a skeleton example on page 742 where he adds up the sizes of all files in a folder. However, the example is very terse and I'll need to stare at it for a while to grok it. I will need to check that this example behaves consistently under all conditions such as cancellation, unhandled crash, etc. If I find anything useful I'll let you know. -- Meski http://courteous.ly/aAOZcv "Going to Starbucks for coffee is like going to prison for sex. Sure, you'll get it, but it's going to be rough" - Adam Hills
