Merge pull request #272 from antifuchs/better-subprocess-handling

Better subprocess handling

rubygem/lib/zeus.rb

@@ -58,15 +58,26 @@ def go(identifier=:boot)
       Thread.new { notify_features(feature_pipe_w, features) }
 
       # We are now 'connected'. From this point, we may receive requests to fork.
+      children = Set.new
       loop do
         messages = local.recv(2**16)
+
+        # Reap any child runners or slaves that might have exited in
+        # the meantime. Note that reaping them like this can leave <=1
+        # zombie process per slave around while the slave waits for a
+        # new command.
+        children.each do |pid|
+          children.delete(pid) if Process.waitpid(pid, Process::WNOHANG)
+        end
+
         messages.split("\0").each do |new_identifier|
           new_identifier =~ /^(.):(.*)/
           code, ident = $1, $2
+          pid = nil
           if code == "S"
-            fork { go(ident.to_sym) }
+            children << fork { go(ident.to_sym) }
           else
-            fork { command(ident.to_sym, local) }
+            children << fork { command(ident.to_sym, local) }
           end
         end
       end
@@ -107,14 +118,17 @@ def command(identifier, sock)
 
       kill_command_if_client_quits!(pid, client_pid)
 
-      at_exit{ Process.kill(:TERM, client_pid) }
-
       Process.wait(pid)
       code = $?.exitstatus || 0
 
       local.write "#{code}\0"
 
       local.close
+    rescue Exception
+      # If anything at all went wrong, kill the client - if anything
+      # went wrong before the runner can clean up, it might hang
+      # around forever.
+      Process.kill(:TERM, client_pid)
     end
 
     def kill_command_if_client_quits!(command_pid, client_pid)