examples: Build tiny-nghttpd only when epoll is available

configure.ac

@@ -476,6 +476,11 @@ AC_CHECK_FUNCS([ \
   timegm \
 ])
 
+# Checks for epoll availability, primarily for examples/tiny-nghttpd
+AX_HAVE_EPOLL([have_epoll=yes], [have_epoll=no])
+
+AM_CONDITIONAL([HAVE_EPOLL], [ test "x${have_epoll}" = "xyes" ])
+
 dnl Windows library for winsock2
 case "${host}" in
   *mingw*)

examples/Makefile.am

@@ -49,10 +49,14 @@ libevent_server_SOURCES = libevent-server.c
 
 deflate_SOURCES = deflate.c
 
+if HAVE_EPOLL
+
 noinst_PROGRAMS += tiny-nghttpd
 
 tiny_nghttpd_SOURCES = tiny-nghttpd.c
 
+endif # HAVE_EPOLL
+
 if ENABLE_ASIO_LIB
 
 noinst_PROGRAMS += asio-sv asio-sv2

m4/ax_have_epoll.m4

+# ===========================================================================
+#       http://www.gnu.org/software/autoconf-archive/ax_have_epoll.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_HAVE_EPOLL([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
+#   AX_HAVE_EPOLL_PWAIT([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
+#
+# DESCRIPTION
+#
+#   This macro determines whether the system supports the epoll I/O event
+#   interface. A neat usage example would be:
+#
+#     AX_HAVE_EPOLL(
+#       [AX_CONFIG_FEATURE_ENABLE(epoll)],
+#       [AX_CONFIG_FEATURE_DISABLE(epoll)])
+#     AX_CONFIG_FEATURE(
+#       [epoll], [This platform supports epoll(7)],
+#       [HAVE_EPOLL], [This platform supports epoll(7).])
+#
+#   The epoll interface was added to the Linux kernel in version 2.5.45, and
+#   the macro verifies that a kernel newer than this is installed. This
+#   check is somewhat unreliable if <linux/version.h> doesn't match the
+#   running kernel, but it is necessary regardless, because glibc comes with
+#   stubs for the epoll_create(), epoll_wait(), etc. that allow programs to
+#   compile and link even if the kernel is too old; the problem would then
+#   be detected only at runtime.
+#
+#   Linux kernel version 2.6.19 adds the epoll_pwait() call in addition to
+#   epoll_wait(). The availability of that function can be tested with the
+#   second macro. Generally speaking, it is safe to assume that
+#   AX_HAVE_EPOLL would succeed if AX_HAVE_EPOLL_PWAIT has, but not the
+#   other way round.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Peter Simons <simons@cryp.to>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved. This file is offered as-is, without any
+#   warranty.
+
+#serial 10
+
+AC_DEFUN([AX_HAVE_EPOLL], [dnl
+  ax_have_epoll_cppflags="${CPPFLAGS}"
+  AC_CHECK_HEADER([linux/version.h], [CPPFLAGS="${CPPFLAGS} -DHAVE_LINUX_VERSION_H"])
+  AC_MSG_CHECKING([for Linux epoll(7) interface])
+  AC_CACHE_VAL([ax_cv_have_epoll], [dnl
+    AC_LINK_IFELSE([dnl
+      AC_LANG_PROGRAM([dnl
+#include <sys/epoll.h>
+#ifdef HAVE_LINUX_VERSION_H
+#  include <linux/version.h>
+#  if LINUX_VERSION_CODE < KERNEL_VERSION(2,5,45)
+#    error linux kernel version is too old to have epoll
+#  endif
+#endif
+], [dnl
+int fd, rc;
+struct epoll_event ev;
+fd = epoll_create(128);
+rc = epoll_wait(fd, &ev, 1, 0);])],
+      [ax_cv_have_epoll=yes],
+      [ax_cv_have_epoll=no])])
+  CPPFLAGS="${ax_have_epoll_cppflags}"
+  AS_IF([test "${ax_cv_have_epoll}" = "yes"],
+    [AC_MSG_RESULT([yes])
+$1],[AC_MSG_RESULT([no])
+$2])
+])dnl
+
+AC_DEFUN([AX_HAVE_EPOLL_PWAIT], [dnl
+  ax_have_epoll_cppflags="${CPPFLAGS}"
+  AC_CHECK_HEADER([linux/version.h],
+    [CPPFLAGS="${CPPFLAGS} -DHAVE_LINUX_VERSION_H"])
+  AC_MSG_CHECKING([for Linux epoll(7) interface with signals extension])
+  AC_CACHE_VAL([ax_cv_have_epoll_pwait], [dnl
+    AC_LINK_IFELSE([dnl
+      AC_LANG_PROGRAM([dnl
+#ifdef HAVE_LINUX_VERSION_H
+#  include <linux/version.h>
+#  if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,19)
+#    error linux kernel version is too old to have epoll_pwait
+#  endif
+#endif
+#include <sys/epoll.h>
+#include <signal.h>
+], [dnl
+int fd, rc;
+struct epoll_event ev;
+fd = epoll_create(128);
+rc = epoll_wait(fd, &ev, 1, 0);
+rc = epoll_pwait(fd, &ev, 1, 0, (sigset_t const *)(0));])],
+      [ax_cv_have_epoll_pwait=yes],
+      [ax_cv_have_epoll_pwait=no])])
+  CPPFLAGS="${ax_have_epoll_cppflags}"
+  AS_IF([test "${ax_cv_have_epoll_pwait}" = "yes"],
+    [AC_MSG_RESULT([yes])
+$1],[AC_MSG_RESULT([no])
+$2])
+])dnl