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adds a bit of documentation
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@ -1,3 +1,22 @@
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//! This file implements a queue of searches to process and the ability to control how many searches can be run in parallel.
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//! We need this because we don't want to process more search requests than we have cores.
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//! That slows down everything and consumes RAM for no reason.
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//! The steps to do a search are to get the `SearchQueue` data structure and try to get a search permit.
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//! This can fail if the queue is full, and we need to drop your search request to register a new one.
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//!
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//! ### How to do a search request
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//!
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//! In order to do a search request you should try to get a search permit.
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//! Retrieve the `SearchQueue` structure from actix-web (`search_queue: Data<SearchQueue>`)
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//! and right before processing the search, calls the `SearchQueue::try_get_search_permit` method: `search_queue.try_get_search_permit().await?;`
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//!
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//! What is going to happen at this point is that you're going to send a oneshot::Sender over an async mpsc channel.
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//! Then, the queue/scheduler is going to either:
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//! - Drop your oneshot channel => that means there are too many searches going on, and yours won't be executed.
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//! You should exit and free all the RAM you use ASAP.
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//! - Sends you a Permit => that will unlock the method, and you will be able to process your search.
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//! And should drop the Permit only once you have freed all the RAM consumed by the method.
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use std::num::NonZeroUsize;
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use std::num::NonZeroUsize;
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use rand::rngs::StdRng;
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use rand::rngs::StdRng;
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@ -12,6 +31,8 @@ pub struct SearchQueue {
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capacity: usize,
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capacity: usize,
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}
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}
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/// You should only run search requests while holding this permit.
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/// Once it's dropped, a new search request will be able to process.
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#[derive(Debug)]
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#[derive(Debug)]
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pub struct Permit {
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pub struct Permit {
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sender: mpsc::Sender<()>,
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sender: mpsc::Sender<()>,
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@ -34,6 +55,10 @@ impl SearchQueue {
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Self { sender, capacity }
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Self { sender, capacity }
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}
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}
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/// This function is the main loop, it's in charge on scheduling which search request should execute first and
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/// how many should executes at the same time.
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///
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/// It **must never** panic or exit.
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async fn run(
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async fn run(
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capacity: usize,
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capacity: usize,
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parallelism: NonZeroUsize,
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parallelism: NonZeroUsize,
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@ -42,7 +67,7 @@ impl SearchQueue {
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let mut queue: Vec<oneshot::Sender<Permit>> = Default::default();
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let mut queue: Vec<oneshot::Sender<Permit>> = Default::default();
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let mut rng: StdRng = StdRng::from_entropy();
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let mut rng: StdRng = StdRng::from_entropy();
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let mut searches_running: usize = 0;
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let mut searches_running: usize = 0;
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// by having a capacity of parallelism we ensures that every time a search finish it can release its RAM asap
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// By having a capacity of parallelism we ensures that every time a search finish it can release its RAM asap
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let (sender, mut search_finished) = mpsc::channel(parallelism.into());
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let (sender, mut search_finished) = mpsc::channel(parallelism.into());
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loop {
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loop {
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@ -85,6 +110,8 @@ impl SearchQueue {
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}
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}
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}
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}
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/// Returns a search `Permit`.
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/// It should be dropped as soon as you've freed all the RAM associated with the search request being processed.
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pub async fn try_get_search_permit(&self) -> Result<Permit, MeilisearchHttpError> {
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pub async fn try_get_search_permit(&self) -> Result<Permit, MeilisearchHttpError> {
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let (sender, receiver) = oneshot::channel();
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let (sender, receiver) = oneshot::channel();
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self.sender.send(sender).await.map_err(|_| MeilisearchHttpError::SearchLimiterIsDown)?;
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self.sender.send(sender).await.map_err(|_| MeilisearchHttpError::SearchLimiterIsDown)?;
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