From 971ef822679dfa6ee63ff83a47b4e4d1aa60d146 Mon Sep 17 00:00:00 2001
From: akr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sat, 18 Jan 2014 14:13:22 +0000
Subject: * ext/socket: Avoid unnecessary ppoll/select on Linux.   Patch by
 Eric Wong.  [ruby-core:57950] [Bug #9039]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44643 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ext/socket/basicsocket.c |  2 +-
 ext/socket/init.c        |  4 ++--
 ext/socket/rubysocket.h  | 16 ++++++++++++++++
 ext/socket/udpsocket.c   |  2 +-
 4 files changed, 20 insertions(+), 4 deletions(-)

(limited to 'ext/socket')

diff --git a/ext/socket/basicsocket.c b/ext/socket/basicsocket.c
index bce085b632..088234aa85 100644
--- a/ext/socket/basicsocket.c
+++ b/ext/socket/basicsocket.c
@@ -563,7 +563,7 @@ rsock_bsock_send(int argc, VALUE *argv, VALUE sock)
     GetOpenFile(sock, fptr);
     arg.fd = fptr->fd;
     arg.flags = NUM2INT(flags);
-    while (rb_thread_fd_writable(arg.fd),
+    while (rsock_maybe_fd_writable(arg.fd),
 	   (n = (int)BLOCKING_REGION_FD(func, &arg)) < 0) {
 	if (rb_io_wait_writable(arg.fd)) {
 	    continue;
diff --git a/ext/socket/init.c b/ext/socket/init.c
index 6d98a66d6e..a69d2e7904 100644
--- a/ext/socket/init.c
+++ b/ext/socket/init.c
@@ -135,7 +135,7 @@ rsock_s_recvfrom(VALUE sock, int argc, VALUE *argv, enum sock_recv_type from)
     rb_obj_hide(str);
 
     while (rb_io_check_closed(fptr),
-	   rb_thread_wait_fd(arg.fd),
+	   rsock_maybe_wait_fd(arg.fd),
 	   (slen = BLOCKING_REGION_FD(recvfrom_blocking, &arg)) < 0) {
         if (!rb_io_wait_readable(fptr->fd)) {
             rb_sys_fail("recvfrom(2)");
@@ -575,7 +575,7 @@ rsock_s_accept(VALUE klass, int fd, struct sockaddr *sockaddr, socklen_t *len)
     arg.sockaddr = sockaddr;
     arg.len = len;
   retry:
-    rb_thread_wait_fd(fd);
+    rsock_maybe_wait_fd(fd);
     fd2 = (int)BLOCKING_REGION_FD(accept_blocking, &arg);
     if (fd2 < 0) {
 	switch (errno) {
diff --git a/ext/socket/rubysocket.h b/ext/socket/rubysocket.h
index c74fb326ec..2f8ce9d084 100644
--- a/ext/socket/rubysocket.h
+++ b/ext/socket/rubysocket.h
@@ -386,4 +386,20 @@ NORETURN(void rsock_sys_fail_sockaddr(const char *, struct sockaddr *addr, sockl
 NORETURN(void rsock_sys_fail_raddrinfo(const char *, VALUE rai));
 NORETURN(void rsock_sys_fail_raddrinfo_or_sockaddr(const char *, VALUE addr, VALUE rai));
 
+/*
+ * It is safe on Linux to attempt using a socket without waiting on it in
+ * all cases.  For some syscalls (e.g. accept/accept4), blocking on the
+ * syscall instead of relying on select/poll allows the kernel to use
+ * "wake-one" behavior and avoid the thundering herd problem.
+ * This is likely safe on all other *nix-like systems, so this whitelist
+ * can be expanded by interested parties.
+ */
+#if defined(__linux__)
+static inline int rsock_maybe_fd_writable(int fd) { return 1; }
+static inline void rsock_maybe_wait_fd(int fd) { }
+#else /* some systems (mswin/mingw) need these.  ref: r36946 */
+#  define rsock_maybe_fd_writable(fd) rb_thread_fd_writable((fd))
+#  define rsock_maybe_wait_fd(fd) rb_thread_wait_fd((fd))
+#endif
+
 #endif
diff --git a/ext/socket/udpsocket.c b/ext/socket/udpsocket.c
index a89c453239..7a40d9aa23 100644
--- a/ext/socket/udpsocket.c
+++ b/ext/socket/udpsocket.c
@@ -177,7 +177,7 @@ udp_send(int argc, VALUE *argv, VALUE sock)
       retry:
 	arg.to = res->ai_addr;
 	arg.tolen = res->ai_addrlen;
-	rb_thread_fd_writable(arg.fd);
+	rsock_maybe_fd_writable(arg.fd);
 	n = (int)BLOCKING_REGION_FD(rsock_sendto_blocking, &arg);
 	if (n >= 0) {
 	    freeaddrinfo(res0);
-- 
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