Use global semaphores for concurrency limits (#18156)

Avoid problems such as https://github.com/astral-sh/uv/issues/15307,
follow-up to https://github.com/astral-sh/uv/pull/18054. See also
https://github.com/astral-sh/uv/pull/17633, for which this should be
helpful.

Cargo.lock

@@ -6171,6 +6171,7 @@ dependencies = [
  "serde-untagged",
  "serde_json",
  "thiserror 2.0.18",
+ "tokio",
  "tracing",
  "url",
  "uv-auth",

crates/uv-bench/benches/uv.rs

@@ -203,7 +203,7 @@ mod resolver {
             exclude_newer,
             sources,
             workspace_cache,
-            concurrency,
+            concurrency.clone(),
             Preview::default(),
         );
 
@@ -226,7 +226,11 @@ mod resolver {
             &hashes,
             &build_context,
             installed_packages,
-            DistributionDatabase::new(client, &build_context, concurrency.downloads),
+            DistributionDatabase::new(
+                client,
+                &build_context,
+                concurrency.downloads_semaphore.clone(),
+            ),
         )?;
 
         Ok(resolver.resolve().await?)

crates/uv-build-frontend/src/lib.rs

@@ -223,11 +223,11 @@ pub struct SourceBuildContext {
 }
 
 impl SourceBuildContext {
-    /// Create a [`SourceBuildContext`] with the given concurrent build limit.
-    pub fn new(concurrent_builds: usize) -> Self {
+    /// Create a [`SourceBuildContext`] with the given shared concurrency semaphore.
+    pub fn new(concurrent_build_slots: Arc<Semaphore>) -> Self {
         Self {
             default_resolution: Arc::default(),
-            concurrent_build_slots: Arc::new(Semaphore::new(concurrent_builds)),
+            concurrent_build_slots,
         }
     }
 }

crates/uv-configuration/Cargo.toml

@@ -37,6 +37,7 @@ rustc-hash = { workspace = true }
 same-file = { workspace = true }
 schemars = { workspace = true, optional = true }
 serde = { workspace = true }
+tokio = { workspace = true }
 serde-untagged = { workspace = true }
 thiserror = { workspace = true }
 tracing = { workspace = true }

crates/uv-configuration/src/concurrency.rs

@@ -1,7 +1,12 @@
+use std::fmt;
 use std::num::NonZeroUsize;
+use std::sync::Arc;
+
+use tokio::sync::Semaphore;
 
 /// Concurrency limit settings.
-#[derive(Copy, Clone, Debug)]
+// TODO(konsti): We should find a pattern that doesn't require having both semaphores and counts.
+#[derive(Clone)]
 pub struct Concurrency {
     /// The maximum number of concurrent downloads.
     ///
@@ -15,15 +20,27 @@ pub struct Concurrency {
     ///
     /// Note this value must be non-zero.
     pub installs: usize,
+    /// A global semaphore to limit the number of concurrent downloads.
+    pub downloads_semaphore: Arc<Semaphore>,
+    /// A global semaphore to limit the number of concurrent builds.
+    pub builds_semaphore: Arc<Semaphore>,
+}
+
+/// Custom `Debug` to hide semaphore fields from `--show-settings` output.
+#[expect(clippy::missing_fields_in_debug)]
+impl fmt::Debug for Concurrency {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Concurrency")
+            .field("downloads", &self.downloads)
+            .field("builds", &self.builds)
+            .field("installs", &self.installs)
+            .finish()
+    }
 }
 
 impl Default for Concurrency {
     fn default() -> Self {
-        Self {
-            downloads: Self::DEFAULT_DOWNLOADS,
-            builds: Self::threads(),
-            installs: Self::threads(),
-        }
+        Self::new(Self::DEFAULT_DOWNLOADS, Self::threads(), Self::threads())
     }
 }
 
@@ -31,6 +48,17 @@ impl Concurrency {
     // The default concurrent downloads limit.
     pub const DEFAULT_DOWNLOADS: usize = 50;
 
+    /// Create a new [`Concurrency`] with the given limits.
+    pub fn new(downloads: usize, builds: usize, installs: usize) -> Self {
+        Self {
+            downloads,
+            builds,
+            installs,
+            downloads_semaphore: Arc::new(Semaphore::new(downloads)),
+            builds_semaphore: Arc::new(Semaphore::new(builds)),
+        }
+    }
+
     // The default concurrent builds and install limit.
     pub fn threads() -> usize {
         std::thread::available_parallelism()

crates/uv-dispatch/src/lib.rs

@@ -147,7 +147,7 @@ impl<'a> BuildDispatch<'a> {
             build_options,
             hasher,
             exclude_newer,
-            source_build_context: SourceBuildContext::new(concurrency.builds),
+            source_build_context: SourceBuildContext::new(concurrency.builds_semaphore.clone()),
             build_extra_env_vars: FxHashMap::default(),
             sources,
             workspace_cache,
@@ -264,8 +264,12 @@ impl BuildContext for BuildDispatch<'_> {
             self.hasher,
             self,
             EmptyInstalledPackages,
-            DistributionDatabase::new(self.client, self, self.concurrency.downloads)
-                .with_build_stack(build_stack),
+            DistributionDatabase::new(
+                self.client,
+                self,
+                self.concurrency.downloads_semaphore.clone(),
+            )
+            .with_build_stack(build_stack),
         )?;
         let resolution = Resolution::from(resolver.resolve().await.with_context(|| {
             format!(
@@ -353,8 +357,12 @@ impl BuildContext for BuildDispatch<'_> {
                 tags,
                 self.hasher,
                 self.build_options,
-                DistributionDatabase::new(self.client, self, self.concurrency.downloads)
-                    .with_build_stack(build_stack),
+                DistributionDatabase::new(
+                    self.client,
+                    self,
+                    self.concurrency.downloads_semaphore.clone(),
+                )
+                .with_build_stack(build_stack),
             );
 
             debug!(

crates/uv-distribution/src/distribution_database.rs

@@ -58,12 +58,12 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
     pub fn new(
         client: &'a RegistryClient,
         build_context: &'a Context,
-        concurrent_downloads: usize,
+        downloads_semaphore: Arc<Semaphore>,
     ) -> Self {
         Self {
             build_context,
             builder: SourceDistributionBuilder::new(build_context),
-            client: ManagedClient::new(client, concurrent_downloads),
+            client: ManagedClient::new(client, downloads_semaphore),
             reporter: None,
         }
     }
@@ -1151,15 +1151,15 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
 /// A wrapper around `RegistryClient` that manages a concurrency limit.
 pub struct ManagedClient<'a> {
     pub unmanaged: &'a RegistryClient,
-    control: Semaphore,
+    control: Arc<Semaphore>,
 }
 
 impl<'a> ManagedClient<'a> {
-    /// Create a new `ManagedClient` using the given client and concurrency limit.
-    fn new(client: &'a RegistryClient, concurrency: usize) -> Self {
+    /// Create a new `ManagedClient` using the given client and concurrency semaphore.
+    fn new(client: &'a RegistryClient, control: Arc<Semaphore>) -> Self {
         ManagedClient {
             unmanaged: client,
-            control: Semaphore::new(concurrency),
+            control,
         }
     }
 

crates/uv/src/commands/build_frontend.rs

@@ -146,7 +146,7 @@ pub(crate) async fn build_frontend(
         no_config,
         python_preference,
         python_downloads,
-        concurrency,
+        &concurrency,
         cache,
         printer,
         preview,
@@ -193,7 +193,7 @@ async fn build_impl(
     no_config: bool,
     python_preference: PythonPreference,
     python_downloads: PythonDownloads,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     printer: Printer,
     preview: Preview,
@@ -469,7 +469,7 @@ async fn build_package(
     keyring_provider: KeyringProviderType,
     exclude_newer: ExcludeNewer,
     sources: NoSources,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     build_options: &BuildOptions,
     sdist: bool,
     wheel: bool,
@@ -630,7 +630,7 @@ async fn build_package(
         exclude_newer,
         sources.clone(),
         workspace_cache,
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 

crates/uv/src/commands/pip/compile.rs

@@ -540,7 +540,7 @@ pub(crate) async fn pip_compile(
         exclude_newer.clone(),
         sources,
         WorkspaceCache::default(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -580,7 +580,7 @@ pub(crate) async fn pip_compile(
         &flat_index,
         &top_level_index,
         &build_dispatch,
-        concurrency,
+        &concurrency,
         options,
         Box::new(DefaultResolveLogger),
         printer,

crates/uv/src/commands/pip/install.rs

@@ -486,7 +486,7 @@ pub(crate) async fn pip_install(
         exclude_newer.clone(),
         sources.clone(),
         WorkspaceCache::default(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -595,7 +595,7 @@ pub(crate) async fn pip_install(
             &flat_index,
             state.index(),
             &build_dispatch,
-            concurrency,
+            &concurrency,
             options,
             Box::new(DefaultResolveLogger),
             printer,
@@ -640,7 +640,7 @@ pub(crate) async fn pip_install(
         exclude_newer.clone(),
         sources,
         WorkspaceCache::default(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -658,7 +658,7 @@ pub(crate) async fn pip_install(
         &tags,
         &client,
         state.in_flight(),
-        concurrency,
+        &concurrency,
         &build_dispatch,
         &cache,
         &environment,

crates/uv/src/commands/pip/list.rs

@@ -7,7 +7,6 @@ use itertools::Itertools;
 use owo_colors::OwoColorize;
 use rustc_hash::{FxHashMap, FxHashSet};
 use serde::Serialize;
-use tokio::sync::Semaphore;
 use tracing::debug;
 use unicode_width::UnicodeWidthStr;
 
@@ -117,7 +116,7 @@ pub(crate) async fn pip_list(
         .markers(environment.interpreter().markers())
         .platform(environment.interpreter().platform())
         .build();
-        let download_concurrency = Semaphore::new(concurrency.downloads);
+        let download_concurrency = concurrency.downloads_semaphore.clone();
 
         // Determine the platform tags.
         let interpreter = environment.interpreter();

crates/uv/src/commands/pip/operations.rs

@@ -128,7 +128,7 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
     flat_index: &FlatIndex,
     index: &InMemoryIndex,
     build_dispatch: &BuildDispatch<'_>,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     options: Options,
     logger: Box<dyn ResolveLogger>,
     printer: Printer,
@@ -156,7 +156,11 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
                 NamedRequirementsResolver::new(
                     hasher,
                     index,
-                    DistributionDatabase::new(client, build_dispatch, concurrency.downloads),
+                    DistributionDatabase::new(
+                        client,
+                        build_dispatch,
+                        concurrency.downloads_semaphore.clone(),
+                    ),
                 )
                 .with_reporter(Arc::new(ResolverReporter::from(printer)))
                 .resolve(unnamed.into_iter())
@@ -170,7 +174,11 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
                 extras,
                 hasher,
                 index,
-                DistributionDatabase::new(client, build_dispatch, concurrency.downloads),
+                DistributionDatabase::new(
+                    client,
+                    build_dispatch,
+                    concurrency.downloads_semaphore.clone(),
+                ),
             )
             .with_reporter(Arc::new(ResolverReporter::from(printer)))
             .resolve(source_trees.iter())
@@ -278,7 +286,11 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
                 NamedRequirementsResolver::new(
                     hasher,
                     index,
-                    DistributionDatabase::new(client, build_dispatch, concurrency.downloads),
+                    DistributionDatabase::new(
+                        client,
+                        build_dispatch,
+                        concurrency.downloads_semaphore.clone(),
+                    ),
                 )
                 .with_reporter(Arc::new(ResolverReporter::from(printer)))
                 .resolve(unnamed.into_iter())
@@ -309,7 +321,11 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
                 &overrides,
                 hasher,
                 index,
-                DistributionDatabase::new(client, build_dispatch, concurrency.downloads),
+                DistributionDatabase::new(
+                    client,
+                    build_dispatch,
+                    concurrency.downloads_semaphore.clone(),
+                ),
             )
             .with_reporter(Arc::new(ResolverReporter::from(printer)))
             .resolve(&resolver_env)
@@ -357,7 +373,11 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
             hasher,
             build_dispatch,
             installed_packages,
-            DistributionDatabase::new(client, build_dispatch, concurrency.downloads),
+            DistributionDatabase::new(
+                client,
+                build_dispatch,
+                concurrency.downloads_semaphore.clone(),
+            ),
         )?
         .with_reporter(Arc::new(reporter));
 
@@ -544,7 +564,7 @@ pub(crate) async fn install(
     tags: &Tags,
     client: &RegistryClient,
     in_flight: &InFlight,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     build_dispatch: &BuildDispatch<'_>,
     cache: &Cache,
     venv: &PythonEnvironment,
@@ -685,7 +705,7 @@ pub(crate) async fn install(
     }
 
     if compile {
-        compile_bytecode(venv, &concurrency, cache, printer).await?;
+        compile_bytecode(venv, concurrency, cache, printer).await?;
     }
 
     // Construct a summary of the changes made to the environment.
@@ -722,7 +742,7 @@ async fn execute_plan(
     tags: &Tags,
     client: &RegistryClient,
     in_flight: &InFlight,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     build_dispatch: &BuildDispatch<'_>,
     cache: &Cache,
     venv: &PythonEnvironment,
@@ -749,7 +769,11 @@ async fn execute_plan(
             tags,
             hasher,
             build_options,
-            DistributionDatabase::new(client, build_dispatch, concurrency.downloads),
+            DistributionDatabase::new(
+                client,
+                build_dispatch,
+                concurrency.downloads_semaphore.clone(),
+            ),
         )
         .with_reporter(Arc::new(
             PrepareReporter::from(printer).with_length(remote.len() as u64),

crates/uv/src/commands/pip/sync.rs

@@ -393,7 +393,7 @@ pub(crate) async fn pip_sync(
         exclude_newer.clone(),
         sources.clone(),
         WorkspaceCache::default(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -486,7 +486,7 @@ pub(crate) async fn pip_sync(
             &flat_index,
             state.index(),
             &build_dispatch,
-            concurrency,
+            &concurrency,
             options,
             Box::new(DefaultResolveLogger),
             printer,
@@ -531,7 +531,7 @@ pub(crate) async fn pip_sync(
         exclude_newer.clone(),
         sources,
         WorkspaceCache::default(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -549,7 +549,7 @@ pub(crate) async fn pip_sync(
         &tags,
         &client,
         state.in_flight(),
-        concurrency,
+        &concurrency,
         &build_dispatch,
         &cache,
         &environment,

crates/uv/src/commands/pip/tree.rs

@@ -9,7 +9,6 @@ use petgraph::Direction;
 use petgraph::graph::{EdgeIndex, NodeIndex};
 use petgraph::prelude::EdgeRef;
 use rustc_hash::{FxHashMap, FxHashSet};
-use tokio::sync::Semaphore;
 
 use uv_cache::{Cache, Refresh};
 use uv_cache_info::Timestamp;
@@ -100,7 +99,7 @@ pub(crate) async fn pip_tree(
         .markers(environment.interpreter().markers())
         .platform(environment.interpreter().platform())
         .build();
-        let download_concurrency = Semaphore::new(concurrency.downloads);
+        let download_concurrency = concurrency.downloads_semaphore.clone();
 
         // Determine the platform tags.
         let interpreter = environment.interpreter();

crates/uv/src/commands/project/add.rs

@@ -459,7 +459,7 @@ pub(crate) async fn add(
                 sources,
                 // No workspace caching since `uv add` changes the workspace definition.
                 WorkspaceCache::default(),
-                concurrency,
+                concurrency.clone(),
                 preview,
             );
 
@@ -467,7 +467,11 @@ pub(crate) async fn add(
                 NamedRequirementsResolver::new(
                     &hasher,
                     state.index(),
-                    DistributionDatabase::new(&client, &build_dispatch, concurrency.downloads),
+                    DistributionDatabase::new(
+                        &client,
+                        &build_dispatch,
+                        concurrency.downloads_semaphore.clone(),
+                    ),
                 )
                 .with_reporter(Arc::new(ResolverReporter::from(printer)))
                 .resolve(unnamed.into_iter())
@@ -750,7 +754,7 @@ pub(crate) async fn add(
         &settings,
         &client_builder,
         installer_metadata,
-        concurrency,
+        &concurrency,
         cache,
         printer,
         preview,
@@ -992,7 +996,7 @@ async fn lock_and_sync(
     settings: &ResolverInstallerSettings,
     client_builder: &BaseClientBuilder<'_>,
     installer_metadata: bool,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     printer: Printer,
     preview: Preview,

crates/uv/src/commands/project/environment.rs

@@ -119,7 +119,7 @@ impl CachedEnvironment {
         resolve: Box<dyn ResolveLogger>,
         install: Box<dyn InstallLogger>,
         installer_metadata: bool,
-        concurrency: Concurrency,
+        concurrency: &Concurrency,
         cache: &Cache,
         printer: Printer,
         preview: Preview,

crates/uv/src/commands/project/export.rs

@@ -208,7 +208,7 @@ pub(crate) async fn export(
             &client_builder,
             &state,
             Box::new(DefaultResolveLogger),
-            concurrency,
+            &concurrency,
             cache,
             &workspace_cache,
             printer,

crates/uv/src/commands/project/lock.rs

@@ -196,7 +196,7 @@ pub(crate) async fn lock(
             &client_builder,
             &state,
             Box::new(DefaultResolveLogger),
-            concurrency,
+            &concurrency,
             cache,
             &workspace_cache,
             printer,
@@ -288,7 +288,7 @@ pub(super) struct LockOperation<'env> {
     client_builder: &'env BaseClientBuilder<'env>,
     state: &'env UniversalState,
     logger: Box<dyn ResolveLogger>,
-    concurrency: Concurrency,
+    concurrency: &'env Concurrency,
     cache: &'env Cache,
     workspace_cache: &'env WorkspaceCache,
     printer: Printer,
@@ -303,7 +303,7 @@ impl<'env> LockOperation<'env> {
         client_builder: &'env BaseClientBuilder<'env>,
         state: &'env UniversalState,
         logger: Box<dyn ResolveLogger>,
-        concurrency: Concurrency,
+        concurrency: &'env Concurrency,
         cache: &'env Cache,
         workspace_cache: &'env WorkspaceCache,
         printer: Printer,
@@ -459,7 +459,7 @@ async fn do_lock(
     client_builder: &BaseClientBuilder<'_>,
     state: &UniversalState,
     logger: Box<dyn ResolveLogger>,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     workspace_cache: &WorkspaceCache,
     printer: Printer,
@@ -783,11 +783,15 @@ async fn do_lock(
         exclude_newer.clone(),
         sources.clone(),
         workspace_cache.clone(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
-    let database = DistributionDatabase::new(&client, &build_dispatch, concurrency.downloads);
+    let database = DistributionDatabase::new(
+        &client,
+        &build_dispatch,
+        concurrency.downloads_semaphore.clone(),
+    );
 
     // If any of the resolution-determining settings changed, invalidate the lock.
     let existing_lock = if let Some(existing_lock) = existing_lock {

crates/uv/src/commands/project/mod.rs

@@ -1793,7 +1793,7 @@ pub(crate) async fn resolve_names(
     settings: &ResolverInstallerSettings,
     client_builder: &BaseClientBuilder<'_>,
     state: &SharedState,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     workspace_cache: &WorkspaceCache,
     printer: Printer,
@@ -1919,7 +1919,7 @@ pub(crate) async fn resolve_names(
         exclude_newer.clone(),
         sources.clone(),
         workspace_cache.clone(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -1928,7 +1928,11 @@ pub(crate) async fn resolve_names(
         NamedRequirementsResolver::new(
             &hasher,
             state.index(),
-            DistributionDatabase::new(&client, &build_dispatch, concurrency.downloads),
+            DistributionDatabase::new(
+                &client,
+                &build_dispatch,
+                concurrency.downloads_semaphore.clone(),
+            ),
         )
         .with_reporter(Arc::new(ResolverReporter::from(printer)))
         .resolve(unnamed.into_iter())
@@ -1987,7 +1991,7 @@ pub(crate) async fn resolve_environment(
     client_builder: &BaseClientBuilder<'_>,
     state: &PlatformState,
     logger: Box<dyn ResolveLogger>,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     printer: Printer,
     preview: Preview,
@@ -2155,7 +2159,7 @@ pub(crate) async fn resolve_environment(
         exclude_newer.clone(),
         sources.clone(),
         workspace_cache,
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -2203,7 +2207,7 @@ pub(crate) async fn sync_environment(
     state: &PlatformState,
     logger: Box<dyn InstallLogger>,
     installer_metadata: bool,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     printer: Printer,
     preview: Preview,
@@ -2294,7 +2298,7 @@ pub(crate) async fn sync_environment(
         exclude_newer.clone(),
         sources,
         workspace_cache,
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 
@@ -2360,7 +2364,7 @@ pub(crate) async fn update_environment(
     resolve: Box<dyn ResolveLogger>,
     install: Box<dyn InstallLogger>,
     installer_metadata: bool,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     workspace_cache: WorkspaceCache,
     dry_run: DryRun,
@@ -2550,7 +2554,7 @@ pub(crate) async fn update_environment(
         exclude_newer.clone(),
         sources.clone(),
         workspace_cache,
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 

crates/uv/src/commands/project/remove.rs

@@ -307,7 +307,7 @@ pub(crate) async fn remove(
             &client_builder,
             &state,
             Box::new(DefaultResolveLogger),
-            concurrency,
+            &concurrency,
             cache,
             &WorkspaceCache::default(),
             printer,
@@ -365,7 +365,7 @@ pub(crate) async fn remove(
         &state,
         Box::new(DefaultInstallLogger),
         installer_metadata,
-        concurrency,
+        &concurrency,
         cache,
         WorkspaceCache::default(),
         DryRun::Disabled,

crates/uv/src/commands/project/run.rs

@@ -282,7 +282,7 @@ hint: If you are running a script with `{}` in the shebang, you may need to incl
                     } else {
                         Box::new(SummaryResolveLogger)
                     },
-                    concurrency,
+                    &concurrency,
                     &cache,
                     &workspace_cache,
                     printer,
@@ -330,7 +330,7 @@ hint: If you are running a script with `{}` in the shebang, you may need to incl
                     Box::new(SummaryInstallLogger)
                 },
                 installer_metadata,
-                concurrency,
+                &concurrency,
                 &cache,
                 workspace_cache.clone(),
                 DryRun::Disabled,
@@ -447,7 +447,7 @@ hint: If you are running a script with `{}` in the shebang, you may need to incl
                         Box::new(SummaryInstallLogger)
                     },
                     installer_metadata,
-                    concurrency,
+                    &concurrency,
                     &cache,
                     workspace_cache.clone(),
                     DryRun::Disabled,
@@ -784,7 +784,7 @@ hint: If you are running a script with `{}` in the shebang, you may need to incl
                         } else {
                             Box::new(SummaryResolveLogger)
                         },
-                        concurrency,
+                        &concurrency,
                         &cache,
                         &workspace_cache,
                         printer,
@@ -873,7 +873,7 @@ hint: If you are running a script with `{}` in the shebang, you may need to incl
                         Box::new(SummaryInstallLogger)
                     },
                     installer_metadata,
-                    concurrency,
+                    &concurrency,
                     &cache,
                     workspace_cache.clone(),
                     DryRun::Disabled,
@@ -1028,7 +1028,7 @@ hint: If you are running a script with `{}` in the shebang, you may need to incl
                     Box::new(SummaryInstallLogger)
                 },
                 installer_metadata,
-                concurrency,
+                &concurrency,
                 &cache,
                 printer,
                 preview,

crates/uv/src/commands/project/sync.rs

@@ -283,7 +283,7 @@ pub(crate) async fn sync(
                 Box::new(DefaultResolveLogger),
                 Box::new(DefaultInstallLogger),
                 installer_metadata,
-                concurrency,
+                &concurrency,
                 cache,
                 workspace_cache.clone(),
                 dry_run,
@@ -350,7 +350,7 @@ pub(crate) async fn sync(
             &client_builder,
             &state,
             Box::new(DefaultResolveLogger),
-            concurrency,
+            &concurrency,
             cache,
             &workspace_cache,
             printer,
@@ -410,7 +410,7 @@ pub(crate) async fn sync(
         &state,
         Box::new(DefaultInstallLogger),
         installer_metadata,
-        concurrency,
+        &concurrency,
         cache,
         workspace_cache,
         dry_run,
@@ -613,7 +613,7 @@ pub(super) async fn do_sync(
     state: &PlatformState,
     logger: Box<dyn InstallLogger>,
     installer_metadata: bool,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     workspace_cache: WorkspaceCache,
     dry_run: DryRun,
@@ -815,7 +815,7 @@ pub(super) async fn do_sync(
         exclude_newer.clone(),
         sources.clone(),
         workspace_cache.clone(),
-        concurrency,
+        concurrency.clone(),
         preview,
     );
 

crates/uv/src/commands/project/tree.rs

@@ -3,7 +3,6 @@ use std::path::Path;
 use anstream::print;
 use anyhow::{Error, Result};
 use futures::StreamExt;
-use tokio::sync::Semaphore;
 use uv_cache::{Cache, Refresh};
 use uv_cache_info::Timestamp;
 use uv_client::{BaseClientBuilder, RegistryClientBuilder};
@@ -147,7 +146,7 @@ pub(crate) async fn tree(
             client_builder,
             &state,
             Box::new(DefaultResolveLogger),
-            concurrency,
+            &concurrency,
             cache,
             &WorkspaceCache::default(),
             printer,
@@ -226,7 +225,7 @@ pub(crate) async fn tree(
             .index_locations(index_locations.clone())
             .keyring(*keyring_provider)
             .build();
-            let download_concurrency = Semaphore::new(concurrency.downloads);
+            let download_concurrency = concurrency.downloads_semaphore.clone();
 
             // Initialize the client to fetch the latest version of each package.
             let client = LatestClient {

crates/uv/src/commands/project/version.rs

@@ -107,7 +107,7 @@ pub(crate) async fn project_version(
                 client_builder,
                 python_preference,
                 python_downloads,
-                concurrency,
+                &concurrency,
                 no_config,
                 cache,
                 short,
@@ -328,7 +328,7 @@ pub(crate) async fn project_version(
             python_preference,
             python_downloads,
             installer_metadata,
-            concurrency,
+            &concurrency,
             no_config,
             cache,
             printer,
@@ -437,7 +437,7 @@ async fn print_frozen_version(
     client_builder: BaseClientBuilder<'_>,
     python_preference: PythonPreference,
     python_downloads: PythonDownloads,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     no_config: bool,
     cache: &Cache,
     short: bool,
@@ -535,7 +535,7 @@ async fn lock_and_sync(
     python_preference: PythonPreference,
     python_downloads: PythonDownloads,
     installer_metadata: bool,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     no_config: bool,
     cache: &Cache,
     printer: Printer,

crates/uv/src/commands/tool/install.rs

@@ -3,7 +3,6 @@ use std::str::FromStr;
 
 use anyhow::{Result, bail};
 use owo_colors::OwoColorize;
-use tokio::sync::Semaphore;
 use tracing::{debug, trace};
 
 use uv_cache::{Cache, Refresh};
@@ -174,7 +173,7 @@ pub(crate) async fn install(
                 &settings,
                 &client_builder,
                 &state,
-                concurrency,
+                &concurrency,
                 &cache,
                 &workspace_cache,
                 printer,
@@ -275,7 +274,7 @@ pub(crate) async fn install(
 
         // Initialize the capabilities.
         let capabilities = IndexCapabilities::default();
-        let download_concurrency = Semaphore::new(concurrency.downloads);
+        let download_concurrency = concurrency.downloads_semaphore.clone();
 
         // Initialize the client to fetch the latest version.
         let latest_client = LatestClient {
@@ -362,7 +361,7 @@ pub(crate) async fn install(
                 &settings,
                 &client_builder,
                 &state,
-                concurrency,
+                &concurrency,
                 &cache,
                 &workspace_cache,
                 printer,
@@ -388,7 +387,7 @@ pub(crate) async fn install(
         &settings,
         &client_builder,
         &state,
-        concurrency,
+        &concurrency,
         &cache,
         &workspace_cache,
         printer,
@@ -578,7 +577,7 @@ pub(crate) async fn install(
             Box::new(DefaultResolveLogger),
             Box::new(DefaultInstallLogger),
             installer_metadata,
-            concurrency,
+            &concurrency,
             &cache,
             workspace_cache,
             DryRun::Disabled,
@@ -619,7 +618,7 @@ pub(crate) async fn install(
             &client_builder,
             &state,
             Box::new(DefaultResolveLogger),
-            concurrency,
+            &concurrency,
             &cache,
             printer,
             preview,
@@ -674,7 +673,7 @@ pub(crate) async fn install(
                         &client_builder,
                         &state,
                         Box::new(DefaultResolveLogger),
-                        concurrency,
+                        &concurrency,
                         &cache,
                         printer,
                         preview,
@@ -715,7 +714,7 @@ pub(crate) async fn install(
             &state,
             Box::new(DefaultInstallLogger),
             installer_metadata,
-            concurrency,
+            &concurrency,
             &cache,
             printer,
             preview,

crates/uv/src/commands/tool/run.rs

@@ -10,7 +10,6 @@ use console::Term;
 use itertools::Itertools;
 use owo_colors::OwoColorize;
 use tokio::process::Command;
-use tokio::sync::Semaphore;
 use tracing::{debug, warn};
 
 use uv_cache::{Cache, Refresh};
@@ -304,7 +303,7 @@ pub(crate) async fn run(
         python_preference,
         python_downloads,
         installer_metadata,
-        concurrency,
+        &concurrency,
         &cache,
         printer,
         preview,
@@ -736,7 +735,7 @@ async fn get_or_create_environment(
     python_preference: PythonPreference,
     python_downloads: PythonDownloads,
     installer_metadata: bool,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     cache: &Cache,
     printer: Printer,
     preview: Preview,
@@ -929,7 +928,7 @@ async fn get_or_create_environment(
 
         // Initialize the capabilities.
         let capabilities = IndexCapabilities::default();
-        let download_concurrency = Semaphore::new(concurrency.downloads);
+        let download_concurrency = concurrency.downloads_semaphore.clone();
 
         // Initialize the client to fetch the latest version.
         let latest_client = LatestClient {

crates/uv/src/commands/tool/upgrade.rs

@@ -133,7 +133,7 @@ pub(crate) async fn upgrade(
             cache,
             &filesystem,
             installer_metadata,
-            concurrency,
+            &concurrency,
             preview,
         ))
         .await;
@@ -268,7 +268,7 @@ async fn upgrade_tool(
     cache: &Cache,
     filesystem: &ResolverInstallerOptions,
     installer_metadata: bool,
-    concurrency: Concurrency,
+    concurrency: &Concurrency,
     preview: Preview,
 ) -> Result<UpgradeReport> {
     // Ensure the tool is installed.

crates/uv/src/settings.rs

@@ -123,26 +123,26 @@ impl GlobalSettings {
                 ColorChoice::Auto
             },
             network_settings,
-            concurrency: Concurrency {
-                downloads: environment
+            concurrency: Concurrency::new(
+                environment
                     .concurrency
                     .downloads
                     .combine(workspace.and_then(|workspace| workspace.globals.concurrent_downloads))
                     .map(NonZeroUsize::get)
                     .unwrap_or(Concurrency::DEFAULT_DOWNLOADS),
-                builds: environment
+                environment
                     .concurrency
                     .builds
                     .combine(workspace.and_then(|workspace| workspace.globals.concurrent_builds))
                     .map(NonZeroUsize::get)
                     .unwrap_or_else(Concurrency::threads),
-                installs: environment
+                environment
                     .concurrency
                     .installs
                     .combine(workspace.and_then(|workspace| workspace.globals.concurrent_installs))
                     .map(NonZeroUsize::get)
                     .unwrap_or_else(Concurrency::threads),
-            },
+            ),
             show_settings: args.show_settings,
             preview: Preview::from_args(
                 resolve_preview(args, workspace, environment),