Turbopack: add manual worker count override (#84454)

Cargo.toml

@@ -254,6 +254,10 @@ inherits = "release"
 debug-assertions = true
 overflow-checks = true
 
+[profile.release-with-debug]
+inherits = "release"
+debug = true
+
 [workspace.dependencies]
 # Workspace crates
 next-api = { path = "crates/next-api" }

turbopack/crates/turbopack-cli/benches/small_apps.rs

@@ -74,6 +74,7 @@ fn bench_small_apps(c: &mut Criterion) {
                                 log_detail: false,
                                 full_stats: false,
                                 target: None,
+                                worker_threads: None,
                             },
                             no_sourcemap: false,
                             no_minify: false,

turbopack/crates/turbopack-cli/src/arguments.rs

@@ -25,6 +25,14 @@ impl Arguments {
             Arguments::Dev(args) => args.common.dir.as_deref(),
         }
     }
+
+    /// The number of worker threads to use. see [CommonArguments]::worker_threads
+    pub fn worker_threads(&self) -> Option<usize> {
+        match self {
+            Arguments::Build(args) => args.common.worker_threads,
+            Arguments::Dev(args) => args.common.worker_threads,
+        }
+    }
 }
 
 #[derive(
@@ -80,13 +88,17 @@ pub struct CommonArguments {
     #[clap(long)]
     pub full_stats: bool,
 
+    /// Whether to build for the `browser` or `node`
+    #[clap(long)]
+    pub target: Option<Target>,
+
+    /// Number of worker threads to use for parallel processing
+    #[clap(long)]
+    pub worker_threads: Option<usize>,
     // Enable experimental garbage collection with the provided memory limit in
     // MB.
     // #[clap(long)]
     // pub memory_limit: Option<usize>,
-    /// Whether to build for the `browser` or `node``
-    #[clap(long)]
-    pub target: Option<Target>,
 }
 
 #[derive(Debug, Args)]

turbopack/crates/turbopack-cli/src/main.rs

@@ -42,7 +42,18 @@ fn main() {
             });
         });
 
-    let worker_threads = available_parallelism().map(|n| n.get()).unwrap_or(1);
+    let args = Arguments::parse();
+
+    let worker_threads = args
+        .worker_threads()
+        .map(|v| {
+            if v == 0 {
+                panic!("--worker-threads=0 is invalid, you must use at least one thread.");
+            } else {
+                v
+            }
+        })
+        .unwrap_or_else(|| available_parallelism().map(|n| n.get()).unwrap_or(1));
 
     rt.worker_threads(worker_threads);
     rt.max_blocking_threads(usize::MAX - worker_threads);
@@ -50,7 +61,6 @@ fn main() {
     #[cfg(not(codspeed))]
     rt.disable_lifo_slot();
 
-    let args = Arguments::parse();
     rt.build().unwrap().block_on(main_inner(args)).unwrap();
 }