Client termination grace period should be configurable

[pdf]

Currently there is a hard-coded grace period of 2 seconds for a client to terminate, but some clients may require a longer period to cleanly shut down. The grace period should be configurable as a client option.

Current period is set at

go-plugin/client.go

Line 560 in 586d14f

case <-time.After(2 * time.Second):