Call to fork in Sys.command

[smondet]

The explict call to fork is guarded here: fork.c#L28:

if (caml_domain_is_multicore()) {
  caml_failwith
    ("Unix.fork may not be called while other domains were created");
}

But in runtime/sys.c:L497 there is a call to int system(const char *command) whose manpage says:

 The system() library function uses fork(2) to create a child
 process that executes the shell command specified in command
 using execl(3) […]

Should this one also failwith?

[xavierleroy]

If there are multiple domains running, in the child process created by fork there is only one domain running and the OCaml runtime system is in an inconsistent state. So, the child cannot run OCaml code, and that's why Unix.fork must fail in multi-domain programs.

However, the child process can still run C code, esp. if the C code does little more than calling exec, as in the case for the system C standard library function.

Plus, this man page is misleading: system can also be implemented with posix_spawn, which in turn may not involve a full fork.