The Autoconf macro AC_USE_SYSTEM_EXTENSIONS defines preprocessor macros
which turn on extensions to C and POSIX. The macro also makes it easier
for developers to use the extensions without needing (or forgetting) to
define them manually.
The macro can be safely used because it was introduced in Autoconf 2.60
and Tor requires Autoconf 2.63 and above.
If the returned value of read/recv is 0 (meaning EOF), we'll end up in an
infinite loop (active wait) until something is written on the pipe which is
not really what we want here especially because those functions are called
from the main thread.
Signed-off-by: David Goulet <dgoulet@ev0ke.net>
This way we can use the linux eventfd extension where available.
Using EVFILT_USER on the BSDs will be a teeny bit trickier, and will
require libevent hacking.
Also, re-enable the #if'd out condition-variable code.
Work queues are going to make us hack on all of this stuff a bit more
closely, so it might not be a terrible idea to make it easier to hack.
