This disentangles the following functions, which were previously all mixed together:
* 1) Waiting for jobs to terminate when shutting down
* 2) Handling signals in the Docker daemon
* 3) Per-subsystem cleanup handlers
* 4) pidfile management
Responsibilities are dispatched as follows:
* Signal traps are set in `main`, and trigger `engine.Shutdown`
* `engine.Shutdown` coordinates cleanup by waiting for jobs to complete, and calling shutdown handlers
* To perform cleanup at shutdown, each subsystem registers handlers with `engine.OnShutdown`
* `daemon` is one subsystem, so it registers cleanup via `engine.OnShutdown`.
* `daemon` owns the pidfile, which is used to lock access to `/var/lib/docker`. Part of its cleanup is to remove the pidfile.
Signed-off-by: Solomon Hykes <solomon@docker.com>
Upstream-commit: c9f3fd3fc7a4beb97de40ef8da7330b23397d9d3
Component: engine
727879ad53