Implement graceful in Passenger Standalone (builtin)

[FooBarWidget]

Passenger Standalone does not currently support graceful shutdown. We should implement support for this. This may require changes in daemon_controller.

• When using the Nginx engine, this can be made to work by sending SIGQUIT instead of SIGTERM.
• I have not yet investigated how this can be made to work with the builtin engine. Having said that, the ServerKit::HttpServer class supports graceful shutdown. We may not have properly integrated this in CoreMain.cpp or in the Watchdog.

[meoooh]

Any changes?

[CamJN]

No, there haven't been any changes on this front yet.

[PikachuEXE]

When will this be implemented...

[PikachuEXE]

Also SIGQUIT seems being used for printing

passenger/doc/users_guide_snippets/analysis_and_system_maintenance.txt

Line 35 in 62a4d72

In case of Ruby applications, you can also send the 'SIGQUIT' signal to have it print

a backtrace without aborting

Edit:
And SIGQUIT cannot be used by JRuby:

passenger/CHANGELOG

Line 1725 in 8cfa5bc

* Sending SIGBART to a Ruby process will now trigger the same behavior

Edit 2:
Also looking at

passenger/src/ruby_supportlib/phusion_passenger/standalone/start_command.rb

Line 526 in 632cfc4

def trapsafe_shutdown_and_cleanup(error_occurred)

I am not sure if it's implemented already or not

[PikachuEXE]

Please look at #1956 for possible implementation for Nginx engine

[CamJN]

Added in 5.1.6