[PATCH] use non-blocking stdin for interactive mode

[Eric Wong <e@80x24.org>]

When accepting keyboard input, it is possible for select() to
return a false-positive with spurious wakeups from inside the
update_status callback.

Using the FIONREAD ioctl in place of select is also a possibility,
but may be less portable.
---
 src/sox.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/sox.c b/src/sox.c
index bab0f45..fdb7616 100644
--- a/src/sox.c
+++ b/src/sox.c
@@ -1789,6 +1789,18 @@ static int process(void)
     tcsetattr(fileno(stdin), TCSANOW, &modified_termios);
   }
 #endif
+#if defined(F_GETFL) && defined(F_SETFL) && defined(O_NONBLOCK)
+  if (interactive) {
+    int fd = fileno(stdin);
+    int flags = fcntl(fd, F_GETFL);
+    if (flags == -1) {
+      lsx_warn("error getting flags on stdin descriptor: %s", strerror(errno));
+    } else if (!(flags & O_NONBLOCK)) {
+      if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
+        lsx_warn("error setting non-blocking on stdin: %s", strerror(errno));
+    }
+  }
+#endif
 
   signal(SIGTERM, sigint); /* Stop gracefully, as soon as we possibly can. */
   signal(SIGINT , sigint); /* Either skip current input or behave as SIGTERM. */
-- 
2.5.0.rc1.33.g9b79a96