On Fri, 11 Jul 2008, Linus Torvalds wrote:
>
> If it's something that should be merged, and if it concerns code that I'm
> interested in, I want to know about it. It's that simple.
Btw, an example of where I think we need to look at both windows and unix
behavior and not try to make them two different camps is in that
"start_command()" thing.
It was changed to have a totally separate __MINGW32__ part, but the thing
is, the unix side could really be improved - and actually made more like
the MINGW32 code at the same time!
For example, on many systems it is rather noticeably faster to use
"vfork+execve" than it is to do "fork+execve", because you avoid a whole
"duplicate and tear down page tables" sequence. So the UNIX code would
actually be better off using "vfork()" instead of "fork()" there.
But it can't right now - because if "cmd->env" changes the environment, it
would change it both in the caller and in the result.
It turns out that Windows has the exact same issue (because it uses a
spawn thing), and already does a "copy_env() + change-in-copy + free"
model for that reason.
If that was shared, the UNIX side could just use vfork, I believe. In
fact, the following trivial - but horribly ugly - patch passes all the
tests, by doing the vfork() in all cases except when the environment
changes. But I don't know what coverage that has, though (maybe env is
effectively always set?).
And I suspect there are other cases where we'd actually be better off
trying to share things than having all the differences hidden away in
compat layers.
Linus
---
builtin-grep.c | 2 +-
run-command.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/builtin-grep.c b/builtin-grep.c
index ef29910..5d3053a 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -168,7 +168,7 @@ static int exec_grep(int argc, const char **argv)
int status;
argv[argc] = NULL;
- pid = fork();
+ pid = vfork();
if (pid < 0)
return pid;
if (!pid) {
diff --git a/run-command.c b/run-command.c
index 6e29fdf..200ba7b 100644
--- a/run-command.c
+++ b/run-command.c
@@ -68,7 +68,7 @@ int start_command(struct child_process *cmd)
trace_argv_printf(cmd->argv, "trace: run_command:");
#ifndef __MINGW32__
- cmd->pid = fork();
+ cmd->pid = cmd->env ? fork() : vfork();
if (!cmd->pid) {
if (cmd->no_stdin)
dup_devnull(0);
