eventmachine: wait for deferred actions to finish em-deferred

Since EventMachine 1.0.0 in 2012, the EM.defers_finish? API
exists to check for the existence of deferred actions.
Support it if it exists in the running version of EM and
update the note in our SIGNALS document.

Thanks to <alex0375@gmail.com> on the mailing list for bringing
this up:
https://bogomips.org/rainbows-public/CAKwvcL-VH3we4qA1pkNAstTmWvqNA=Rir2N_YiWztV_qbaLQvA@mail.gmail.com/

1 files changed, 7 insertions, 1 deletions

diff --git a/t/app_deferred.ru b/t/app_deferred.ru
index a70b33b..b3d7ff1 100644
--- a/t/app_deferred.ru
+++ b/t/app_deferred.ru
@@ -6,12 +6,18 @@
 
 class DeferredApp < Struct.new(:app)
   def deferred?(env)
-    env["PATH_INFO"] == "/deferred"
+    env["PATH_INFO"] =~ %r{\A/deferred}
   end
 
   def call(env)
     env["rack.multithread"] or raise RuntimeError, "rack.multithread not true"
     body = "#{Thread.current.inspect}\n"
+    if env["PATH_INFO"] =~ %r{\A/deferred(\d+)}
+      delay = $1.to_i
+      File.open(ENV['fifo'], 'w') { |fp| fp.write "sleeping #{delay}s\n" }
+      body = "deferred sleep\n"
+      sleep(delay)
+    end
     headers = {
       "Content-Type" => "text/plain",
       "Content-Length" => body.size.to_s,