erts: Accept sockets non-blocking with accept4

Passing SOCK_NONBLOCK to accept4() makes the SET_NONBLOCKING
call on every accepted socket redundant, saving a syscall per
accept on platforms that have accept4().

Author: lpgauth

erts/config.h.in

@@ -462,6 +462,9 @@
 /* Define to 1 if _Float16 can be converted from/to double. */
 #undef FLOAT16_IS_CONVERTIBLE
 
+/* Define to 1 if you have the 'accept4' function. */
+#undef HAVE_ACCEPT4
+
 /* Define to 1 if you have the <arpa/nameser.h> header file. */
 #undef HAVE_ARPA_NAMESER_H
 

erts/configure

@@ -21341,6 +21341,14 @@ fi
      ;;
 esac
 
+ac_fn_c_check_func "$LINENO" "accept4" "ac_cv_func_accept4"
+if test "x$ac_cv_func_accept4" = xyes
+then :
+  printf "%s\n" "#define HAVE_ACCEPT4 1" >>confdefs.h
+
+fi
+
+
 
 
 saved_cppflags=$CPPFLAGS

erts/configure.ac

@@ -2243,6 +2243,10 @@ AS_CASE([$host_os],
                         [[#include <sys/socket.h>]])
         ])
 
+dnl Check for accept4, which accepts a socket and sets it non-blocking
+dnl and close-on-exec in one call
+AC_CHECK_FUNCS([accept4])
+
 
 dnl ----------------------------------------------------------------------
 dnl Checks for library functions.

erts/emulator/nifs/unix/unix_socket_syncio.c

@@ -195,10 +195,11 @@
  * ======================================================================== *
  */
 
-#ifdef HAS_ACCEPT4
-// We have to figure out what the flags are...
+#if defined(HAVE_ACCEPT4) && defined(SOCK_CLOEXEC) && defined(SOCK_NONBLOCK)
 #define sock_accept(s, addr, len)       \
-    accept4((s), (addr), (len), (SOCK_CLOEXEC))
+    accept4((s), (addr), (len), (SOCK_CLOEXEC | SOCK_NONBLOCK))
+/* The accepted socket is already non-blocking */
+#define ESSIO_ACCEPTED_NONBLOCK 1
 #else
 #define sock_accept(s, addr, len)       accept((s), (addr), (len))
 #endif
@@ -2863,7 +2864,9 @@ BOOLEAN_T essio_accept_accepted(ErlNifEnv*       env,
                        &accDescP->ctrlPid,
                        &accDescP->ctrlMon) == 0 );
 
+#ifndef ESSIO_ACCEPTED_NONBLOCK
     SET_NONBLOCKING(accDescP->sock);
+#endif
 
     accDescP->writeState |= ESOCK_STATE_CONNECTED;