| VFORK(2) | System Calls Manual | VFORK(2) |
vfork — spawn new
process and block parent
#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.
Same as for fork(2).
The 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.
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 ioctl(2) calls are
allowed and input attempts result in an end-of-file indication.
| September 10, 2015 | OpenBSD-current |