Only load LOCAL_STREAMS if they are being used

SergioBenitez · SergioBenitez · commit db15596c5747 · 2020-10-22T18:15:48.000-07:00
diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs
@@ -963,6 +963,11 @@ pub fn set_print(sink: Option<Box<dyn LocalOutput>>) -> Option<Box<dyn LocalOutp
 }
 
 pub(crate) fn clone_io() -> (Option<Box<dyn LocalOutput>>, Option<Box<dyn LocalOutput>>) {
+    // Don't waste time when LOCAL_{STDOUT,STDERR} are definitely None.
+    if !LOCAL_STREAMS.load(Ordering::Relaxed) {
+        return (None, None);
+    }
+
     LOCAL_STDOUT.with(|stdout| {
         LOCAL_STDERR.with(|stderr| {
             (

Original file line number	Diff line number	Diff line change
`@@ -963,6 +963,11 @@ pub fn set_print(sink: Option<Box<dyn LocalOutput>>) -> Option<Box<dyn LocalOutp`
`963`	`963`	`}`
`964`	`964`
`965`	`965`	`pub(crate) fn clone_io() -> (Option<Box<dyn LocalOutput>>, Option<Box<dyn LocalOutput>>) {`
	`966`	`+ // Don't waste time when LOCAL_{STDOUT,STDERR} are definitely None.`
	`967`	`+ if !LOCAL_STREAMS.load(Ordering::Relaxed) {`
	`968`	`+ return (None, None);`
	`969`	`+ }`
	`970`	`+`
`966`	`971`	`LOCAL_STDOUT.with(\|stdout\| {`
`967`	`972`	`LOCAL_STDERR.with(\|stderr\| {`
`968`	`973`	`(`