> the problem with threads is that everything is shared all of the time, which makes it incredibly difficult to enforce invariants.
Your entire commet comes down to this, and my point is that this is not a problem. Design your threaded code around a simple principle: one thread's code must never touch another thread's data. Now you have safe threaded code. If you want to add some limited well-documented cases where you break that golden rule, go for it and reap the performance benefits.
There are some things that some threading models can be criticized for. For example, POSIX threads cannot be killed if they get stuck. However, threads are a powerful tool. The idea that you can share the in-memory code between all your threads is great. Additionally, you can share state and you control how and when it is shared. Want complete isolation? Communicate via queues! Want some shared state for performance reasons? Go for it! Want complete and utter chaos that will blow up as soon as you look at it funny? Let threads access other thread's data at will.
Your argument is similar to one that table saws are terrible because one cannot guarantee that they will never cut off your fingers.
Edit: one other problem with callbacks. AFAIK, no implementation of callback-based concurrency is able to take advantage of multiple hardware cores for true parallelism. In the meantime OS schedulers already take care of distributing OS threads between CPU cores, and some green thread implementations do this as well.
So, you're not wrong ... but the table-saw argument is a straw-man.
There's a company that sells a revolutionary table saw with intelligent saw stop precisely because experienced, skilled practitioners regularly cut off their fingers.
In general "be smarter / do better" is not a reasonable prescription for large numbers of people. Empirically, if people are fucking up, it makes sense to analyze why and to give them automatic solutions to their fuck-ups.
I don't see it as a straw-man as I see threads as a tool. Existence of the actor model does not detract from the value that OS threads provide, the same way that existence of Common Lisp does not detract from the value that C provides. They are both tools. It's just that some tools are more dangerous than others. In other words, I don't believe that threads are a "worse is better" approach. There are things that can be improved about the specific implementations of threading, but on the whole, the paradigm is far from broken.
> Empirically, if people are fucking up, it makes sense to analyze why and to give them automatic solutions to their fuck-ups.
The problem is that other implementations of concurrency are not as widely adopted and people tend to fall back on threads (especially OS threads) when they really don't need them. But when you really do need threads, very few things are a good substitute.
P.S.: I am aware of the table saw you refer to, and this is the kind of improvement that tooling around threads could use. Note that this new table saw does not completely re-design how you interact with the blade in order to provide the safety.
>Your entire commet comes down to this, and my point is that this is not a problem. Design your threaded code around a simple principle: one thread's code must never touch another thread's data. Now you have safe threaded code. If you want to add some limited well-documented cases where you break that golden rule, go for it and reap the performance benefits.
How do you know which code is touching which data, particularly if you're using libraries? Heck, we can't even reliably keep track of which data another piece of data belongs to - even with code written and audited by experts, memory leaks get found all the time. Just as memory management is too hard to do in complex programs without language support, isolating data to the appropriate threads is too hard to do in complex programs without language support.
Bullshit. You know that you are not violating your one golden rule by only having the one golden rule. Break fingers of any developers that violate it. Testing is important but there is a certain level at which mistrust of your code becomes paranoia. How do you know that your code is not littering the disk with debug files, declaring global variables, adding rogue macros, etc.?
As for libraries, don't use ones where you have not seen the source or good docs that make the guarantees that satisfy you. Thread safety is one of many reasons for this.
As for memory management being too complex for large projects, see Linux kernel, BSD kernels, nginx, apache, and a million other large projects written in C.
The only thing I agree with you on is that often times language support makes things easier. However, using "unsafe" languages does not make large projects impossible.
> How do you know that your code is not littering the disk with debug files, declaring global variables, adding rogue macros, etc.?
I use a language in which functions that perform disk I/O look different (and are typed differently, so this is not just convention but compiler-enforced) from functions that don't, functions that mutate state look different from functions that don't, and macros don't exist.
Yes, you can forcibly cast around these things. But you have to do so explicitly. Whereas in most threaded languages, access to a variable that's owned by another thread looks exactly like access to a variable that's owned by the current thread.
> As for memory management being too complex for large projects, see Linux kernel, BSD kernels, nginx, apache, and a million other large projects written in C.
I do. I watch the growing list of security advisories for each of them with a mixture of amusement and frustration.
Your entire commet comes down to this, and my point is that this is not a problem. Design your threaded code around a simple principle: one thread's code must never touch another thread's data. Now you have safe threaded code. If you want to add some limited well-documented cases where you break that golden rule, go for it and reap the performance benefits.
There are some things that some threading models can be criticized for. For example, POSIX threads cannot be killed if they get stuck. However, threads are a powerful tool. The idea that you can share the in-memory code between all your threads is great. Additionally, you can share state and you control how and when it is shared. Want complete isolation? Communicate via queues! Want some shared state for performance reasons? Go for it! Want complete and utter chaos that will blow up as soon as you look at it funny? Let threads access other thread's data at will.
Your argument is similar to one that table saws are terrible because one cannot guarantee that they will never cut off your fingers.
Edit: one other problem with callbacks. AFAIK, no implementation of callback-based concurrency is able to take advantage of multiple hardware cores for true parallelism. In the meantime OS schedulers already take care of distributing OS threads between CPU cores, and some green thread implementations do this as well.