Question

I have looked into the code of posix-spawn( https://github.com/rtomayko/posix-spawn), it seems that it uses vfork in the low level implementation.However, vfork is not encouraged to use in linux platform.Is it ok with posix-spawn module ?

Answer 1

vfork isn’t recommended because it heavily restricts what the new process can do (until it execs) and is consequently hard to use correctly. On Linux, fork uses copy-on-write semantics, so fork is going to be reasonably fast without needing to use vfork. Furthermore, vfork signal semantics are not at all standard across platforms. From man vfork:

It is rather unfortunate that Linux revived this specter from the past. The BSD man page states:

This system call will be eliminated when proper system sharing mechanisms are implemented. Users should not depend on the memory sharing semantics of vfork() as it will, in that case, be made synonymous to fork(2).

Details of the signal handling are obscure and differ between systems. The BSD man page states:

To avoid a possible deadlock situation, processes that are children in the middle of a vfork() are never sent SIGTTOU or SIGTTIN signals; rather, output or ioctls are allowed and input attempts result in an end-of-file indication.

That said, if used properly, vfork can be useful, and it will be faster on many other platforms. Linux does support it, so provided the code doesn’t do anything that is restricted by vfork, it should be just fine on Linux.