feat(downloads): interleave the downloads with their installations

Even though downloads are done concurrently, the installations are done
sequentially. This means that, as downloads complete, they are in a
queue (an mpsc channel) waiting to be consumed by the future responsible
for the (sequential) installations.

There was a need to relax some test cases to allow for uninstall to
happen before the downloads.

Author: FranciscoTGouveia

src/dist/manifestation.rs

@@ -6,10 +6,10 @@ mod tests;
 
 use std::path::Path;
 
-use anyhow::{Context, Result, anyhow, bail};
+use anyhow::{Context, Error, Result, anyhow, bail};
 use futures_util::stream::StreamExt;
 use std::sync::Arc;
-use tokio::sync::Semaphore;
+use tokio::sync::{Semaphore, mpsc};
 use tracing::info;
 use url::Url;
 
@@ -154,8 +154,7 @@ impl Manifestation {
         let altered = tmp_cx.dist_server != DEFAULT_DIST_SERVER;
 
         // Download component packages and validate hashes
-        let mut things_to_install = Vec::new();
-        let mut things_downloaded = Vec::new();
+        let mut things_downloaded: Vec<String> = Vec::new();
         let components = update.components_urls_and_hashes(new_manifest)?;
         let components_len = components.len();
 
@@ -173,49 +172,7 @@ impl Manifestation {
             .and_then(|s| s.parse().ok())
             .unwrap_or(DEFAULT_MAX_RETRIES);
 
-        info!("downloading component(s)");
-        for bin in &components {
-            (download_cfg.notify_handler)(Notification::DownloadingComponent(
-                &bin.component.short_name(new_manifest),
-                &self.target_triple,
-                bin.component.target.as_ref(),
-                &bin.binary.url,
-            ));
-        }
-
-        let semaphore = Arc::new(Semaphore::new(concurrent_downloads));
-        let component_stream = tokio_stream::iter(components.into_iter()).map(|bin| {
-            let sem = semaphore.clone();
-            async move {
-                let _permit = sem.acquire().await.unwrap();
-                let url = if altered {
-                    utils::parse_url(
-                        &bin.binary
-                            .url
-                            .replace(DEFAULT_DIST_SERVER, tmp_cx.dist_server.as_str()),
-                    )?
-                } else {
-                    utils::parse_url(&bin.binary.url)?
-                };
-
-                bin.download(&url, download_cfg, max_retries, new_manifest)
-                    .await
-                    .map(|downloaded| (bin, downloaded))
-            }
-        });
-        if components_len > 0 {
-            let results = component_stream
-                .buffered(components_len)
-                .collect::<Vec<_>>()
-                .await;
-            for result in results {
-                let (bin, downloaded_file) = result?;
-                things_downloaded.push(bin.binary.hash.clone());
-                things_to_install.push((bin, downloaded_file));
-            }
-        }
-
-        // Begin transaction
+        // Begin transaction before the downloads, as installations are interleaved with those
         let mut tx = Transaction::new(
             prefix.clone(),
             tmp_cx,
@@ -227,6 +184,16 @@ impl Manifestation {
         // to uninstall it first.
         tx = self.maybe_handle_v2_upgrade(&config, tx, download_cfg.process)?;
 
+        info!("downloading component(s)");
+        for bin in &components {
+            (download_cfg.notify_handler)(Notification::DownloadingComponent(
+                &bin.component.short_name(new_manifest),
+                &self.target_triple,
+                bin.component.target.as_ref(),
+                &bin.binary.url,
+            ));
+        }
+
         // Uninstall components
         for component in &update.components_to_uninstall {
             let notification = if implicit_modify {
@@ -249,16 +216,77 @@ impl Manifestation {
             )?;
         }
 
-        // Install components
-        for (component_bin, installer_file) in things_to_install {
-            tx = self.install_component(
-                component_bin,
-                installer_file,
-                tmp_cx,
-                download_cfg,
-                new_manifest,
-                tx,
-            )?;
+        if components_len > 0 {
+            // Create a channel to communicate whenever a download is done and the component can be installed
+            // The `mpsc` channel was used as we need to send many messages from one producer (download's thread) to one consumer (install's thread)
+            // This is recommended in the official docs: https://docs.rs/tokio/latest/tokio/sync/index.html#mpsc-channel
+            let total_components = components.len();
+            let (download_tx, mut download_rx) =
+                mpsc::channel::<Result<(ComponentBinary<'_>, File)>>(total_components);
+
+            let semaphore = Arc::new(Semaphore::new(concurrent_downloads));
+            let component_stream = tokio_stream::iter(components.into_iter()).map(|bin| {
+                let sem = semaphore.clone();
+                let download_tx = download_tx.clone();
+                async move {
+                    let _permit = sem.acquire().await.unwrap();
+                    let url = if altered {
+                        utils::parse_url(
+                            &bin.binary
+                                .url
+                                .replace(DEFAULT_DIST_SERVER, tmp_cx.dist_server.as_str()),
+                        )?
+                    } else {
+                        utils::parse_url(&bin.binary.url)?
+                    };
+
+                    let installer_file = bin
+                        .download(&url, download_cfg, max_retries, new_manifest)
+                        .await?;
+                    let hash = bin.binary.hash.clone();
+                    let _ = download_tx.send(Ok((bin, installer_file))).await;
+                    Ok(hash)
+                }
+            });
+
+            let mut stream = component_stream.buffered(components_len);
+            let download_handle = async {
+                let mut hashes = Vec::new();
+                while let Some(result) = stream.next().await {
+                    match result {
+                        Ok(hash) => {
+                            hashes.push(hash);
+                        }
+                        Err(e) => {
+                            let _ = download_tx.send(Err(e)).await;
+                        }
+                    }
+                }
+                hashes
+            };
+            let install_handle = async {
+                let mut current_tx = tx;
+                let mut counter = 0;
+                while counter < total_components
+                    && let Some(message) = download_rx.recv().await
+                {
+                    let (component_bin, installer_file) = message?;
+                    current_tx = self.install_component(
+                        component_bin,
+                        installer_file,
+                        tmp_cx,
+                        download_cfg,
+                        new_manifest,
+                        current_tx,
+                    )?;
+                    counter += 1;
+                }
+                Ok::<_, Error>(current_tx)
+            };
+
+            let (download_results, install_result) = tokio::join!(download_handle, install_handle);
+            things_downloaded = download_results;
+            tx = install_result?;
         }
 
         // Install new distribution manifest

tests/suite/cli_rustup.rs

@@ -35,7 +35,6 @@ async fn rustup_stable() {
         .with_stderr(snapbox::str![[r#"
 info: syncing channel updates for 'stable-[HOST_TRIPLE]'
 info: latest update on 2015-01-02, rust version 1.1.0 (hash-stable-1.1.0)
-info: downloading component[..]
 ...
 info: cleaning up downloads & tmp directories
 
@@ -131,15 +130,12 @@ async fn rustup_all_channels() {
         .with_stderr(snapbox::str![[r#"
 info: syncing channel updates for 'stable-[HOST_TRIPLE]'
 info: latest update on 2015-01-02, rust version 1.1.0 (hash-stable-1.1.0)
-info: downloading component[..]
 ...
 info: syncing channel updates for 'beta-[HOST_TRIPLE]'
 info: latest update on 2015-01-02, rust version 1.2.0 (hash-beta-1.2.0)
-info: downloading component[..]
 ...
 info: syncing channel updates for 'nightly-[HOST_TRIPLE]'
 info: latest update on 2015-01-02, rust version 1.3.0 (hash-nightly-2)
-info: downloading component[..]
 ...
 info: cleaning up downloads & tmp directories
 
@@ -208,12 +204,10 @@ async fn rustup_some_channels_up_to_date() {
         .with_stderr(snapbox::str![[r#"
 info: syncing channel updates for 'stable-[HOST_TRIPLE]'
 info: latest update on 2015-01-02, rust version 1.1.0 (hash-stable-1.1.0)
-info: downloading component[..]
 ...
 info: syncing channel updates for 'beta-[HOST_TRIPLE]'
 info: syncing channel updates for 'nightly-[HOST_TRIPLE]'
 info: latest update on 2015-01-02, rust version 1.3.0 (hash-nightly-2)
-info: downloading component[..]
 ...
 info: cleaning up downloads & tmp directories