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Comment by dkersten | Hacker News Reader

Threads are not that hard.

I wouldn't quite say that, but perhaps rephrase it to Multicore is not that hard. Or maybe Concurrency is not that hard. (Basically, threads are just one abstraction for multicore/concurrent programming and I think its harder than some of the alternatives - its certainly a lower-level approach than others).

In any case, it isn't that hard. The problem is we're being educated to program sequentially and very little effort (relatively speaking) is being put into educating programmers to program concurrent/parallel multicore software. You cannot simply write a sequential program and then magically make it multi threaded. Good sequential algorithms are not good multicore algorithms and vice versa.

My response to the previous time this was posted to HN (linked in my other comment) explains what I mean.

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Exactly. For example, process forks are much lighter in overhead than they used to be (depending on the platform), and for long running processes their initiation and termination is insignificant compared to the overall task time. Processes are conceptually easier for people to get started with when starting development of concurrent software.

My current quad core is running about 550 processes at near-idle. Their workload is distributed across cores with no effort. Most Apache implementations use multiple processes for the workers, as an example.

The idea that multi-core code has to have threading actually slows development, because it's a more difficult concept to implement correctly. Multiple processes get the job done as well in many instances, and since each process is single threaded it's easier to implement and maintain.

Whether memory is shared by default (threads) or explicitly (processes) is a little bit of a red herring. The thing that makes parallelized designs hard happens at a higher level: it's that whatever your shared resources are (files, databases, shared memory, in-core databases hanging off message listeners, etc), you have to find a design that allows things to be shared and correct, and that's a hard balance to strike.

You are assuming shared memory as the communication medium. When using processes, you can use sockets for IPC for example. The advantage is that the application can then scale beyond a single system with no change - something that's impossible to do with threads. It's easier to implement and more scalable. Far from a red herring, the persistent focus on threads for concurrency imposes limitations that are unnecessary in modern systems, and slows development.

Pretty sure you and I just said the same thing, though let me just add that just because you hang something off a socket doesn't mean your design can't serialize around it. Having 100 concurrent workers doesn't help if all of them are just lining up waiting for another program to answer their messages.

Of course, this is the exact same problem you have when you try to make a naive design concurrent by wrapping all the global variables in mutexes.

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