std: Don't always create stdin for children

For example if `Command::output` or `Command::status` is used then stdin is just
immediately closed. Add an option for this so as an optimization we can avoid
creating pipes entirely.

This should help reduce the number of active file descriptors when spawning
processes on Unix and the number of active handles on Windows.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/libstd/process.rs b/src/libstd/process.rs
index ec86dd062b5..fe5e49ecb09 100644
--- a/src/libstd/process.rs
+++ b/src/libstd/process.rs
@@ -295,7 +295,7 @@ impl Command {
     /// By default, stdin, stdout and stderr are inherited from the parent.
     #[stable(feature = "process", since = "1.0.0")]
     pub fn spawn(&mut self) -> io::Result<Child> {
-        self.inner.spawn(imp::Stdio::Inherit).map(Child::from_inner)
+        self.inner.spawn(imp::Stdio::Inherit, true).map(Child::from_inner)
     }
 
     /// Executes the command as a child process, waiting for it to finish and
@@ -318,7 +318,7 @@ impl Command {
     /// ```
     #[stable(feature = "process", since = "1.0.0")]
     pub fn output(&mut self) -> io::Result<Output> {
-        self.inner.spawn(imp::Stdio::MakePipe).map(Child::from_inner)
+        self.inner.spawn(imp::Stdio::MakePipe, false).map(Child::from_inner)
             .and_then(|p| p.wait_with_output())
     }
 
@@ -340,7 +340,8 @@ impl Command {
     /// ```
     #[stable(feature = "process", since = "1.0.0")]
     pub fn status(&mut self) -> io::Result<ExitStatus> {
-        self.spawn().and_then(|mut p| p.wait())
+        self.inner.spawn(imp::Stdio::Inherit, false).map(Child::from_inner)
+                  .and_then(|mut p| p.wait())
     }
 }