mz_timely_util/activator.rs
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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License in the LICENSE file at the
// root of this repository, or online at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! Utilities to activate dataflows based on external triggers.
use std::cell::RefCell;
use std::rc::Rc;
use timely::dataflow::Scope;
use timely::scheduling::Activator;
/// Generic activator behavior
pub trait ActivatorTrait {
/// Trigger an activation of operators behind this activator.
fn activate(&self);
/// Acknowledge the receipt of activations from within an operator.
fn ack(&self);
/// Register a new operator with its path with this activator.
fn register<S: Scope>(&self, scope: &mut S, path: Rc<[usize]>);
}
/// An shared handle to multiple activators with support for triggering and acknowledging
/// activations.
///
/// Activations are only triggered once the `activate` function has been called at least `threshold`
/// times, and then not again until `ack` is called. This way, the [RcActivator] ensures two
/// properties:
/// * It does not enqueue more than one activation per activator, if there is only one activator
/// registered with this [RcActivator]. Once multiple activators are registered, any ack will
/// enable more activations.
/// * The threshold to activation avoids activations purely caused by previous activations. Each
/// scheduling of a logging dataflow potentially creates additional log data, which needs to be
/// processed. The threshold should ensure that multiple activations under no load cause the
/// dataflow to be scheduled. For Materialize's log dataflows, this number seems to be larger than
/// 32, below we might risk that we do not cause monotonically decreasing work. A value of 64 or
/// larger is recommended, as there is no harm in bigger values. The log dataflow will still pick
/// up all its inputs once every introspection interval, and this activator only creates
/// additional activations.
#[derive(Debug, Clone)]
pub struct RcActivator {
inner: Rc<RefCell<ActivatorInner>>,
}
impl RcActivator {
/// Construct a new [RcActivator] with the given name and threshold.
///
/// The threshold determines now many activations to ignore until scheduling the activation.
pub fn new(name: String, threshold: usize) -> Self {
let inner = ActivatorInner::new(name, threshold);
Self {
inner: Rc::new(RefCell::new(inner)),
}
}
/// Register an additional [Activator] with this [RcActivator].
pub fn register(&self, activator: Activator) {
self.inner.borrow_mut().register(activator)
}
/// Activate all contained activators.
///
/// The implementation is free to ignore activations and only release them once a sufficient
/// volume has been accumulated.
pub fn activate(&self) {
self.inner.borrow_mut().activate()
}
/// Acknowledge the activation, which enables new activations to be scheduled.
pub fn ack(&self) {
self.inner.borrow_mut().ack()
}
}
impl ActivatorTrait for RcActivator {
fn activate(&self) {
self.activate()
}
fn ack(&self) {
self.ack()
}
fn register<S: Scope>(&self, scope: &mut S, path: Rc<[usize]>) {
self.register(scope.activator_for(path))
}
}
#[derive(Debug)]
struct ActivatorInner {
activated: usize,
activators: Vec<Activator>,
_name: String,
threshold: usize,
}
impl ActivatorInner {
fn new(name: String, threshold: usize) -> Self {
Self {
_name: name,
threshold,
activated: 0,
activators: Vec::new(),
}
}
fn register(&mut self, activator: Activator) {
self.activators.push(activator)
}
fn activate(&mut self) {
if self.activators.is_empty() {
return;
}
self.activated += 1;
if self.activated == self.threshold {
for activator in &self.activators {
activator.activate();
}
}
}
fn ack(&mut self) {
self.activated = 0;
}
}