I was just about to post a comment with : "Me: But there are other forms of concurrency. Processes that communicate using files, pipes, sockets, or even shared

I was just about to post a comment with : "Me: But there are other forms of concurrency. Processes that communicate using files, pipes, sockets, or even shared memory." You are spot on with the problem itself being hard. As I understand it, the distinction between a process and a thread is that threads share memory. If you don't want to use the shared address space, simply don't use it - thread local variables are fine. The issue is that there are multiple threads of execution happening concurrently, and therefore communicating data is difficult. It's hard to believe that taking away the shared memory will do anything but make things harder. Like ajross says, parallel algorithms are just hard.