fix event lost

[ningmingxiao]

sometimes if listener chan is full,event will lost.
@fsouza @bufdev
can you review my pr? thank you

[bufdev]

@ningmingxiao I have not been involved in this repo for about a decade, it's not really professional to tag people here. Will leave this to others.

[ningmingxiao]

sory,but thank you anyway.

[fsouza]

Thanks for contributing! This is a big change that can lead to slow consumers hanging. I recommend either making sure your caller is always fast enough to consume the events, or putting the new behavior behind a knob.

[ningmingxiao]

sometimes I can't make sure consumers run faster, if run plenty of containers, will generate many events, channel will be filled. At least we should let user know event is dropped when chan is filled.