[C++] Add option to disable atfork handlers

[pitrou]

Describe the enhancement requested

The atfork handlers we register in Arrow C++ are generally useful if the Arrow APIs are meant to be used from the child process, but they also have the unfortunate effect of executing non-async-signal-safe code in the child process even if Arrow is not be used there. That is not allowed by POSIX if the parent process is multi-threaded.

There are situations where fork() is only called just before exec(), and therefore it is not necessary to run any atfork handler. We could add an option to disable our atfork handlers for this kind of situation.

Component(s)

C++