Apply modes

Every field has an apply mode (ApplyMode): LIVE (the default) or RESTART.

ConfigField.enumeration("storage-mode")
        .choice("yaml", "YAML file").choice("sqlite", "SQLite database")
        .restartRequired(),

What the owner seesCopy Anchor Link

The editor highlights restart fields and offers a Restart required filter. The review lists how many changes need a server restart before the owner applies.

What your apply returnsCopy Anchor Link

• ApplyContext.requiresRestart() tells you whether a changed field is declared restartRequired(), and each FieldChange in changes() carries its applyMode().
• When restart-only fields changed, return ApplyResult.savedRestartRequired(newRevision, message). The bridge fills restartRequired with the changed restartRequired() fields when you return it without paths.
• To name the paths that wait for a restart yourself, use savedRestartRequired(newRevision, message, paths).
• Return SAVED_RESTART_REQUIRED as well when the values were stored but the live reload failed, so they take effect only after a restart.

The demo saves a storage mode change and keeps the old storage active until the restart:

String proposedMode = context.proposed().getString("settings.storage-mode");
boolean storageChanged = !proposedMode.equals(context.current().get("settings.storage-mode"));
if (storageChanged && !proposedMode.equals(runtime.activeStorageMode())) {
    return ApplyResult.savedRestartRequired(newRevision, "Saved. The storage mode change to '"
            + proposedMode + "' takes effect after a restart; all other changes are active.",
            List.of("settings.storage-mode"));
}
return ApplyResult.applied(newRevision);

A restart-only change must never return APPLIED, and must not change the active value; see Outcomes.