different thread accessing MemoryStream
- by Wayne
There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately.
This code works purposes 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem is that the memory.Position property suddenly returns zero instead of the appropriate value.
However, code was added that checks for the 0 and throws an exception which include log of the MemoryStream properties like Position and Length in a separate method. Those return the correct value. Further addition shows that when this rare condition occurs, the memory.Position only has zero inside this particular method.
Okay. Obviously, this must be a threading issue. But this code is well locked. However, the nature of this software is that it's organized by "tasks" with a scheduler and so any one of several actual O/S thread may run this code at any give time--but never more than one at a time.
So it's my guess that ordinarily it so happens that the same thread keeps getting used for this method and then on a rare occasion a different thread get used.
Then due to compiler optimizations, the different thread never gets the correct value. It gets a "stale" value.
Ordinarily in a situation like this I would apply a "volatile" keyword to the variable in question. But that (those) variables are inside the MemoryStream object.
Does anyone have any other idea? Or does this mean we have to implement our own MemoryStream object? (Just like we end up having to do with practically every collection in .NET?) It's a shame to have such an awesome platform as .NET and have virtually the entire system useless as-is for seriously parallelized applications.
If I'm wrong or you have other ideas, please advise.
Sincerely,
Wayne
