This rewrites the shutdown logic to simplify the shutdown signalling.
All cleanup is now run from deferred functions in the main function and
channels are used to signal shutdown either from OS signals or from
other subsystems such as the RPC server and windows service controller.
The RPC server has been modified to use a new channel for signalling
shutdown that is exposed via the RequestedProcessShutdown function
instead of directly calling Stop on the server as it previously did.
Finally, it adds a few checks for early termination during the main
start sequence so the process can be stopped without starting all the
subsystems if desired.
This is a backport of the equivalent logic from Decred with a few slight
modifications. Credits go to @jrick.
When an OS reboots or shuts down, it sends all processes SIGTERM before
sending SIGKILL. This allows btcd to do a proper shutdown which most
importantly closes the database.
This commit prevents a race that could happen on shutdown if a sigint was
received between adding the first the interrupt handler and and future
handlers. This code is loosely based on initial pull request #154 which
was not accepted due to introducing a race of its own.
Thanks to @tuxcanfly for the intial pull request and finding the issue.
Also, make every subsystem within btcd use its own logger instance so each
subsystem can have its own level specified independent of the others.
This is work towards #48.
Since the main SIGINT handler is running as a goroutine, the main
goroutine must be kept active long enough for it to finish or it will be
nuked when the main goroutine exits. This commit makes that happen by
slightly modifying how it waits for shutdown.
Rather than having the main goroutine only wait for the server to
shutdown, there is now a shutdown channel that is used to signal the main
goroutine to shutdown for all cases such as a graceful shutdown, a
scheduled shutdown, an RPC stop, or a SIGINT.
While here, also add a few prints to indicate a SIGINT was received and
the shutdown progress.
