From 52b4e8f661c9db57677d4236a1f39c3cc028147b Mon Sep 17 00:00:00 2001
From: "A. S. Budden" <abudden@gmail.com>
Date: Sun, 12 Jun 2016 07:40:28 +0100
Subject: [PATCH] Added setStdIoUnbuffered for unbuffered stdio (fixes #2146).

---
 lib/system.nim                     | 3 +++
 lib/system/sysio.nim               | 5 +++++
 web/news/version_0_15_released.rst | 1 +
 3 files changed, 9 insertions(+)

diff --git a/lib/system.nim b/lib/system.nim
index d58d00ae9f37..504d215eaa1a 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -2708,6 +2708,9 @@ when not defined(JS): #and not defined(nimscript):
       ##
       ## Default mode is readonly. Returns true iff the file could be reopened.
 
+    proc setStdIoUnbuffered() {.tags: [], benign.}
+      ## Configures `stdin`, `stdout` and `stderr` to be unbuffered.
+
     proc close*(f: File) {.importc: "fclose", header: "<stdio.h>", tags: [].}
       ## Closes the file.
 
diff --git a/lib/system/sysio.nim b/lib/system/sysio.nim
index 2fcfd69d8eed..bf3be955dc59 100644
--- a/lib/system/sysio.nim
+++ b/lib/system/sysio.nim
@@ -354,4 +354,9 @@ proc writeFile(filename, content: string) =
   else:
     sysFatal(IOError, "cannot open: ", filename)
 
+proc setStdIoUnbuffered() =
+  discard setvbuf(stdout, nil, IONBF, 0)
+  discard setvbuf(stderr, nil, IONBF, 0)
+  discard setvbuf(stdin, nil, IONBF, 0)
+
 {.pop.}
diff --git a/web/news/version_0_15_released.rst b/web/news/version_0_15_released.rst
index 4cc5fb2a72f0..9ca8c3ec5707 100644
--- a/web/news/version_0_15_released.rst
+++ b/web/news/version_0_15_released.rst
@@ -14,6 +14,7 @@ Changes affecting backwards compatibility
 Library Additions
 -----------------
 
+- Added ``setStdIoUnbuffered`` proc to ``system.nim`` to enable unbuffered I/O.
 
 Compiler Additions
 ------------------