Change phases of WebServer start-stop and graceful shutdown lifecycles to allow other smart lifecycles to run before graceful shutdown

[jGleitz]

Use case: We would like to add some logic that runs on shutdown, but before the web server is shut down. To do so, we want to implement a SmartLifecycle with a phase that’s higher than WebServerGracefulShutdownLifecycle’s.

Our concrete use case is that we want to have the application wait some time before actually shutting down, as in #20995. However, the proposed solution in #20995 relies on hanging the thread that sends out the context closed event. We think that using the SmartLifecycle interface is more appropriate. However, since WebServerGracefulShutdownLifecycle’s phase is hard-coded to Integer.MAX_VALUE, we can’t do that.

Proposal: Add a property server.shutdown-phase to configure the SmartLifecycle phase of all WebServerGracefulShutdownLifecycles. Default the value to Integer.MAX_VALUE.

Alternative: Set the hard-coded phase of WebServerGracefulShutdownLifecycle to something lower than Integer.MAX_VALUE to allow using a higher phase. This is slightly less work, but is not strictly backwards-compatible, as it may influence the order in relation to other SmartLifecycles.

We would be happy to provide a pull request if one of the proposals is accepted.

[wilkinsona]

We discussed this today and we'd prefer not to make the phase externally configurable as the phases of WebServerGracefulShutdownLifecycle and WebServerStartStopLifecycle need to be configured correctly in relation to each other. Instead, we'd prefer to change the defaults. Rather than using MAX_VALUE and MAX_VALUE - 1, we think it would be better to use something like MAX_VALUE - 5 and MAX_VALUE - 10.

[jGleitz]

Hi, and thank you for considering this.

Some feedback: if this is implemented by changing the hard-coded values, I’d suggest giving more headroom than just 5. In my experience, a lot of Lifecycles are configured to run one after the other, which can quickly fill up just 5 slots. I’d suggest something like MAX-VALUE - 32, or even less.