quiet spurious wakeups for accept() in Thread* models

Under all MRI 1.8, a blocking Socket#accept Ruby method (needs
to[1]) translate to a non-blocking accept(2) system call that may
wake up threads/processes unnecessarily.  Unfortunately, we
failed to trap and ignore EAGAIN in those cases.

This issue did not affect Ruby 1.9 running under modern Linux
kernels where a _blocking_ accept(2) system call is not (easily,
at least) susceptible to spurious wakeups.  Non-Linux systems
running Ruby 1.9 may be affected.

[1] - using a blocking accept(2) on a shared socket with
      green threads is dangerous, as noted in
      commit ee7fe220ccbc991e1e7cbe982caf48e3303274c7
      (and commit 451ca6997b4f298b436605b7f0af75f369320425)

1 files changed, 41 insertions, 0 deletions

diff --git a/t/t0012-spurious-wakeups-quiet.sh b/t/t0012-spurious-wakeups-quiet.sh
new file mode 100755
index 0000000..23557b7
--- /dev/null
+++ b/t/t0012-spurious-wakeups-quiet.sh
@@ -0,0 +1,41 @@
+#!/bin/sh
+nr=${nr-4}
+. ./test-lib.sh
+
+# ApacheBench (ab) is commonly installed in the sbin paths in Debian-based
+# systems...
+AB="$(which ab 2>/dev/null || :)"
+if test -z "$AB"
+then
+        AB=$(PATH=/usr/local/sbin:/usr/sbin:$PATH which ab 2>/dev/null || :)
+fi
+
+if test -z "$AB"
+then
+        t_info "skipping $T since 'ab' could not be found"
+        exit 0
+fi
+
+t_plan 4 "quiet spurious wakeups for $model"
+
+t_begin "setup and start" && {
+        rainbows_setup $model
+        echo "preload_app true" >> $unicorn_config
+        echo "worker_processes $nr" >> $unicorn_config
+        rainbows -D env.ru -c $unicorn_config -E none
+        rainbows_wait_start
+}
+
+t_begin "spam the server with requests" && {
+        $AB -c1 -n100 http://$listen/
+}
+
+t_begin "killing succeeds" && {
+        kill -QUIT $rainbows_pid
+}
+
+t_begin "check stderr" && {
+        check_stderr
+}
+
+t_done