circular alert "new worker xxx seems to have failed to start"

[bohehe]

Hi, @lestrrat
[Mac OS & ubuntu env]
I was using following command to run my project:

$HOME/go/bin/start_server --pid-file ~/code/my_project/shared/pids/3000.pid -- ~/code/my_project/main 3000 &

everything looks fine until I run:

kill -HUP `cat ~/code/my_project/shared/pids/3000.pid`

And then I got circular alert as follow:

received HUP (num_old_workers=TODO)
spawning a new worker (num_old_workers=TODO)
starting new worker 31722
new worker 31722 seems to have failed to start
starting new worker 31729
new worker 31729 seems to have failed to start
starting new worker 31734
new worker 31734 seems to have failed to start

For the start_server of old version, it works fine.
Do you have any idea?