cb_exit updates

[hasegaw]

I noticed cb_exit callbacks are not called if I hit Ctrl-C.
This change adds signal handler to catch exit events to resolve the issue.

in_serial plugin uses cb_exit to restore original termios.

[edsiper]

thanks for catching this, comments:

• for the engine modification I think the right way to do it is to implement the signal handlers on fluent-bit.c, otherwise when using fluent-bit in shared library mode we are setting a signal handler that commonly is set on the caller (e.g: examples/hello_world). So when the signal is trapped we can just dispatch a:

flb_lib_stop(config);

note: fluent-bit.c is not using the library API, it should.

[edsiper]

after a re-review of the current fluent-bit.c and lib mode..

fluent-bit.c should not use the library mode, because that one spawn a thread to make its job. So the only improvement would be to add the signal handler that implements a cleanup doing:

flb_engine_flush(config, NULL);
flb_input_exit_all(config);
flb_output_exit(config);

[hasegaw]

Aha, make sense to me. Thanks for the comment.