subprocesses: don't bother saving descriptors.

* stream.c (fds_subst_nosave): New static function.
(fds_clobber): New static function. Like fds_swizzle,
without the saving.
(open_subprocess, run): Use fds_clobber instead of fds_swizzle
in the child process. It makes no sense to use fds_swizzle,
which saves duplicates of the old descriptors,
if fds_restore is not going to be called.

1 files changed, 21 insertions, 2 deletions

diff --git a/stream.c b/stream.c
index 7316972e..5a303685 100644
--- a/stream.c
+++ b/stream.c
@@ -4279,6 +4279,13 @@ static int fds_subst(int fd_sub, int fd_std, val self)
   }
 }
 
+static void fds_subst_nosave(int fd_sub, int fd_std)
+{
+  if (fd_sub == fd_std)
+    return;
+  dup2(fd_sub, fd_std);
+}
+
 static void fds_prepare(struct save_fds *fds, int flags, val self)
 {
   if ((flags & FDS_IN) != 0)
@@ -4321,6 +4328,18 @@ static void fds_restore(struct save_fds *fds)
   }
 }
 
+static void fds_clobber(struct save_fds *fds, int flags)
+{
+  if ((flags & FDS_IN) != 0)
+    fds_subst_nosave(fds->subin, STDIN_FILENO);
+
+  if ((flags & FDS_OUT) != 0)
+    fds_subst_nosave(fds->subout, STDOUT_FILENO);
+
+  if ((flags & FDS_ERR) != 0)
+    fds_subst_nosave(fds->suberr, STDERR_FILENO);
+}
+
 val open_command(val path, val mode_str)
 {
   val self = lit("open-command");
@@ -4418,7 +4437,7 @@ static val open_subprocess(val name, val mode_str, val args, val fun)
   }
 
   if (pid == 0) {
-    fds_swizzle(&sfds, fds_flags, self);
+    fds_clobber(&sfds, fds_flags);
 
     if (input) {
       dup2(fd[1], STDOUT_FILENO);
@@ -4726,7 +4745,7 @@ static val run(val name, val args)
   }
 
   if (pid == 0) {
-    fds_swizzle(&sfds, FDS_IN | FDS_OUT | FDS_ERR, self);
+    fds_clobber(&sfds, FDS_IN | FDS_OUT | FDS_ERR);
     execvp(argv[0], argv);
     _exit(errno);
   } else {