| VFORK(2) | System Calls Manual | VFORK(2) |
vfork —
#include <unistd.h>
pid_t
vfork(void);
vfork() was originally used to create new processes
without fully copying the address space of the old process, which is
horrendously inefficient in a paged environment. It was useful when the
purpose of fork(2) would have been to create
a new system context for an execve(2).
Since fork(2) is now efficient, even in the
above case, the need for vfork() has diminished.
vfork() differs from
fork(2) in that the parent is suspended until
the child makes a call to execve(2) or an
exit (either by a call to _exit(2) or
abnormally). In addition, fork handlers established using
pthread_atfork(3) are not called
when a multithreaded program calls vfork().
vfork() returns 0 in the child's context
and (later) the PID of the child in the parent's context.
vfork() function call appeared in
3.0BSD with the additional semantics that the child
process ran in the memory of the parent until it called
execve(2) or exited. That sharing of memory
was removed in 4.4BSD, leaving just the semantics of
blocking the parent until the child calls
execve(2) or exits. On many other systems
the original behavior has been restored, making this interface particularly
unportable.
vfork() are never sent
SIGTTOU or SIGTTIN signals;
rather, output or ioctl(2) calls are allowed
and input attempts result in an end-of-file indication.
| September 10, 2015 | OpenBSD-current |