merge revision(s) 44643: [Backport #9039]

	* 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/branches/ruby_1_9_3@44943 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

4 files changed, 20 insertions, 4 deletions

diff --git a/ext/socket/basicsocket.c b/ext/socket/basicsocket.c
index 6f942e3a55..1530d677a3 100644
--- a/ext/socket/basicsocket.c
+++ b/ext/socket/basicsocket.c
@@ -566,7 +566,7 @@ 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 54452e4b99..8e418230be 100644
--- a/ext/socket/init.c
+++ b/ext/socket/init.c
@@ -129,7 +129,7 @@ rsock_s_recvfrom(VALUE sock, int argc, VALUE *argv, enum sock_recv_type from)
     RBASIC(str)->klass = 0;
 
     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)");
@@ -503,7 +503,7 @@ 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 ab05270be6..9a5f15c542 100644
--- a/ext/socket/rubysocket.h
+++ b/ext/socket/rubysocket.h
@@ -306,4 +306,20 @@ void rsock_init_addrinfo(void);
 void rsock_init_sockopt(void);
 void rsock_init_socket_init(void);
 
+/*
+ * 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 0ba4371f1a..b66c45dee4 100644
--- a/ext/socket/udpsocket.c
+++ b/ext/socket/udpsocket.c
@@ -176,7 +176,7 @@ 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);