Method register_callback

src/sql/src/session/vars.rs:1610–1620

Registers a closure that will get called when the value for the specified [`VarDefinition`] changes. The callback is guaranteed to be called at least once.

(
        &mut self,
        var: &VarDefinition,
        callback: Arc<dyn Fn(&SystemVars) + Send + Sync>,
    )

    ///
    /// The callback is guaranteed to be called at least once.
    pub fn register_callback(
        &mut self,
        var: &VarDefinition,
        callback: Arc<dyn Fn(&SystemVars) + Send + Sync>,
    ) {
        self.callbacks
            .entry(var.name().to_string())
            .or_default()
            .push(callback);
        self.notify_callbacks(var.name());
    }

    /// Notify any external components interested in this variable.
    fn notify_callbacks(&self, name: &str) {