zlacker

Because fork() was very simple and conceptually "easy" to do when it first was introduced, and is now massively complex and has huge implications on every part of the system. It's not compositional, isn't thread safe, insecure by default (inherits env/fds), and it's also slow with all the state it must copy. And at a conceptual level it doesn't work in environments where the nature of a "process" and "address space" aren't synonymous. For instance if your application uses a hardware accelerator (NIC, GPU, whatever) fork() isn't ever viable or sensible, since the hardware resources can't be duplicated safely. And it'll never work in a design like WebAssembly (just an example of this idea, but WASM isn't the only one), again "process" and "virtual memory address space" are not the same. Consider that posix_spawn can make reasonable sense in WebAssembly at a first guess ("launch this wasm module"), but fork() in contrast is much more difficult when it implies COW semantics.

The reality is fork() is pretty much exclusively used to launch new processes these days, outside a few specific cases. Today, it's a poor fit for that problem. And the answer is what Windows has been doing (and POSIX has now had) for a long time: explicitly launching processes by giving a handle/pathname to an executable like posix_spawn. That's the first solution, anyway; a better one would be more capability-oriented design where you have to supply a new address space with all its resources yourself.

This HotOS paper is a pretty good detailed coverage of the argument; I find it very convincing. If fork() went away, I honestly wouldn't miss it, I think. https://www.microsoft.com/en-us/research/uploads/prod/2019/0...

>>aseipp+(OP)
> It's not compositional

What does that mean?

> isn't thread safe

True but it's not meant to be. I'm not sure there are many if any valid use cases for forking and not immediately exec-ing and using threads together in the same application.

> insecure by default (inherits env/fds)

Inherits env and open file descriptors by design. It's pretty much always been understood that if you fork in most scenarios you immediately exec. You can set file to close on exec and set a new env if desired, and not do that if it's not.

> and it's also slow with all the state it must copy.

I thought it was mostly COW?

> And at a conceptual level it doesn't work in environments where the nature of a "process" and "address space" aren't synonymous.

Yeah valid argument. posix_spawn man page says:

> "The posix_spawn() and posix_spawnp() functions are used to create a new child process that executes a specified file. These functions were specified by POSIX to provide a standardized method of creating new processes on machines that lack the capability to support the fork(2) system call. These machines are generally small, embedded systems lacking MMU support.".

posix_spawn is POSIX and has existed along side fork since POSIX.2001. So your saying you want every application ever written to be automatically portable to systems the can't support fork, therefore get rid of fork entirely? I guess.