C# in Depth

Life in a parallel universe357ArrayList filteredUsers = new ArrayList();foreach (User user in SampleData.AllUsers){if (user.UserType==UserType.Developer){filteredUsers.Add(user);}}filteredUsers.Sort(new UserNameComparer());ArrayList upperCasedNames = new ArrayList();foreach (User user in filteredUsers){upperCasedNames.Add(user.Name.ToUpper());}Each step is clear, but it’s relatively hard to understand exactly what’s going on! Theversion we saw earlier with the explicit calls to Enumerable was shorter, but the evaluationorder still made it difficult to read. C# 3 hides exactly how and where the filtering,sorting, and projection is taking place—even after translating the query expressioninto method calls—but the overall purpose of the code is much more obvious.Usually this type of readability is a good thing, but it does mean you need to keepyour wits about you. For instance, capturing local variables makes it a lot easier towrite query expressions—but you need to understand that if you change the values ofthose local variables after creating the query expression, those changes will applywhen you execute the query expression.One of the aims of this book has been to make you sufficiently comfortable withthe mechanics of C# 3 that you can make use of the magic without finding it hard tounderstand what’s going on when you need to dig into it—as well as warning you ofsome of the potential hazards you might run into.So far these have all been somewhat inward-looking aspects of development—changes that could have happened at any time. The next point is very much due towhat a biologist might call an “external stimulus.”13.4 Life in a parallel universeIn chapter 12 we looked briefly at Parallel LINQ, and I mentioned that it is part of awider project called Parallel Extensions. This is Microsoft’s next attempt to make concurrencyeasier. I don’t expect it to be the final word on such a daunting topic, but it’sexciting nonetheless.As I write this, most computers still have just a few cores. Some servers have eightor possibly even 16 (within the x86/x64 space—other architectures already supportfar more than this). Given how everything in the industry is progressing, it may not belong before that looks like small fry, with genuine massively parallel chips becomingpart of everyday life. Concurrency is at the tipping point between “nice to have” and“must have” as a developer skill.We’ve already seen how the functional aspects of C# 3 and LINQ enable some concurrencyscenarios—parallelism is often a matter of breaking down a big task into lotsLicensed to Rhona Hadida