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Diffstat (limited to 'winsup/cygwin/how-vfork-works.txt')
| -rw-r--r-- | winsup/cygwin/how-vfork-works.txt | 36 |
1 files changed, 0 insertions, 36 deletions
diff --git a/winsup/cygwin/how-vfork-works.txt b/winsup/cygwin/how-vfork-works.txt deleted file mode 100644 index f249dab61..000000000 --- a/winsup/cygwin/how-vfork-works.txt +++ /dev/null @@ -1,36 +0,0 @@ -Copyright 2001 Red Hat Inc., Christopher Faylor - -How does vfork work? - -When a program calls vfork, cygwin attempts to short circuit its -normal, expensive fork mechanism. - -Vfork is mainly smoke and mirrors. A call to vfork contines to execute -in the current process but first it returns a pid of 0 so that process -will execute code intended for the child in a UNIX system. Before -returning the zero, vfork makes a copy of the current fd table so that -closing an fd in the "child" will not affect the "parent". - -Some of this info is stored in a per-thread structure but vfork is not -really thread-safe since it also stores the fd "backup" table in the -global fd table. - -The process continues to execute until it hits some type of exec call. -The exec call is essentially translated into a spawn NO_WAIT call and -the new process is started via this mechanism. After execing, the -"child" process no longer should exist, so the spawn code longjmps back -to the original vfork call. The previously opened fds are closed and -the parent's fd table is restored. vfork() then returns the pid of the -just-spawned process. - -Meanwhile, the just-spawned child notices that it has been spawned as -the result of a vfork and closes the extra file handles. - -This all relies on the fact that the child in a vfork call can affect -just about everything in the parent except for the parent's fds. -The assumption is that a vfork is always just used as a method for -starting a program. - -The assumption is also that all of this is much faster than the -slow method that cygwin uses to implement fork(). - |