[RFC] use MSG_NOSIGNAL under Linux 2.2+

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

I don't consider this a serious patch because it only affects
rare error handling paths and is not going to make a difference
in real-world use.  But oh well, I'm low on caffeine right now :x

MSG_NOSIGNAL exists on any machine that supports MSG_DONTWAIT.
While Ruby itself ignore SIGPIPE, this can save a few cycles
inside the kernel by avoiding the no-op signal delivery
in the first place.
---
 ext/kgio/read.c  | 10 ++++++++--
 ext/kgio/write.c |  2 +-
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/ext/kgio/read.c b/ext/kgio/read.c
index 472a592..76b1638 100644
--- a/ext/kgio/read.c
+++ b/ext/kgio/read.c
@@ -5,8 +5,14 @@
 #include "nonblock.h"
 static VALUE sym_wait_readable;
 
+/*
+ * MSG_NOSIGNAL exists on any machine that supports MSG_DONTWAIT.
+ * While Ruby itself ignore SIGPIPE, this can save a few cycles
+ * inside the kernel by avoiding the no-op signal delivery
+ * in the first place.
+ */
 #ifdef USE_MSG_DONTWAIT
-static const int peek_flags = MSG_DONTWAIT|MSG_PEEK;
+static const int peek_flags = MSG_DONTWAIT|MSG_PEEK|MSG_NOSIGNAL;
 
 /* we don't need these variants, we call kgio_autopush_recv directly */
 static inline void kgio_autopush_read(VALUE io) { }
@@ -162,7 +168,7 @@ static VALUE my_recv(int io_wait, int argc, VALUE *argv, VALUE io)
 
 	if (a.len > 0) {
 retry:
-		n = (long)recv(a.fd, a.ptr, a.len, MSG_DONTWAIT);
+		n = (long)recv(a.fd, a.ptr, a.len, MSG_DONTWAIT|MSG_NOSIGNAL);
 		if (read_check(&a, n, "recv", io_wait) != 0)
 			goto retry;
 	}
diff --git a/ext/kgio/write.c b/ext/kgio/write.c
index ce4aa75..c97b049 100644
--- a/ext/kgio/write.c
+++ b/ext/kgio/write.c
@@ -123,7 +123,7 @@ static VALUE my_send(VALUE io, VALUE str, int io_wait)
 
 	prepare_write(&a, io, str);
 retry:
-	n = (long)send(a.fd, a.ptr, a.len, MSG_DONTWAIT);
+	n = (long)send(a.fd, a.ptr, a.len, MSG_DONTWAIT|MSG_NOSIGNAL);
 	if (write_check(&a, n, "send", io_wait) != 0)
 		goto retry;
 	if (TYPE(a.buf) != T_SYMBOL)
-- 
EW