[jerf]

A "library" that wants to have a process of some sort continuously running encounters the problem that the more cross-language generic you try to make the library, the less possible it is to work out a threading model that can be used by everyone, and the less language-generic you make it, the smaller your target audience is, which has non-linear affects on the usage and development resources it can attract. Languages that include a "blessed" runtime model like Node or Go can easily ship such "daemonized libraries", but then they are generally impossible to bind to for anybody else. Using POSIX threads, by contrast, will lock a lot of other languages out that have very sophisticated runtimes, be very difficult to use in others, and, even in C, when you get right down to it, there's no guarantee that they'll play nicely with the rest of the C program.

Distributing a service invokes the sort of lowest-common-denominator solution to this problem, which is "OS process". Everyone can talk to an OS process.

(This is an explanation, not advocacy or celebration.)