| 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 |