[Turbopack] scale down process pool when module graph is finished

crates/next-api/src/project.rs

@@ -486,7 +486,7 @@
         self.project().hmr_identifiers()
     }
 
     /// Gets a source map for a particular `file_path`. If `dev` mode is
     /// disabled, this will always return [`OptionSourceMap::none`].
     #[turbo_tasks::function]
     pub fn get_source_map(
@@ -900,6 +900,15 @@
             let module_graphs_op = whole_app_module_graph_operation(self);
             let module_graphs_vc = module_graphs_op.connect().resolve().await?;
             let _ = module_graphs_op.take_issues_with_path().await?;
+
+            // At this point all modules have been computed and we can get rid of the node.js
+            // process pools
+            if self.await?.watch.enable {
+                turbopack_node::evaluate::scale_down();
+            } else {
+                turbopack_node::evaluate::scale_zero();
+            }
+
             Ok(module_graphs_vc)
         }
         .instrument(tracing::info_span!("module graph for app"))

turbopack/crates/turbopack-node/src/evaluate.rs

@@ -652,6 +652,14 @@ impl EvaluateContext for BasicEvaluateContext {
     }
 }
 
+pub fn scale_zero() {
+    NodeJsPool::scale_zero();
+}
+
+pub fn scale_down() {
+    NodeJsPool::scale_down();
+}
+
 async fn print_error(
     error: StructuredError,
     pool: &NodeJsPool,

turbopack/crates/turbopack-node/src/pool.rs

@@ -13,6 +13,7 @@ use std::{
 
 use anyhow::{bail, Context, Result};
 use futures::join;
+use once_cell::sync::Lazy;
 use owo_colors::{OwoColorize, Style};
 use parking_lot::Mutex;
 use rustc_hash::FxHashMap;
@@ -705,6 +706,12 @@ enum AcquiredPermits {
     },
 }
 
+type IdleProcessesList = Arc<Mutex<BinaryHeap<NodeJsPoolProcess>>>;
+
+/// All non-empty `IdleProcessesList`s of the whole application.
+/// This is used to scale down processes globally.
+static ACTIVE_POOLS: Lazy<Mutex<Vec<IdleProcessesList>>> = Lazy::new(Default::default);
+
 /// A pool of Node.js workers operating on [entrypoint] with specific [cwd] and
 /// [env].
 ///
@@ -793,7 +800,14 @@ impl NodeJsPool {
                 let idle_process_permit = idle_process_permit.context("acquiring idle process permit")?;
                 let process = {
                     let mut processes = self.processes.lock();
-                    processes.pop().unwrap()
+                    let process = processes.pop().unwrap();
+                    if processes.is_empty() {
+                        let mut pools = ACTIVE_POOLS.lock();
+                        if let Some(idx) = pools.iter().position(|p| Arc::ptr_eq(p, &self.processes)) {
+                            pools.swap_remove(idx);
+                        }
+                    }
+                    process
                 };
                 idle_process_permit.forget();
                 Ok((process, AcquiredPermits::Idle { concurrency_permit }))
@@ -849,6 +863,26 @@ impl NodeJsPool {
             allow_process_reuse: true,
         })
     }
+
+    pub fn scale_down() {
+        let pools = ACTIVE_POOLS.lock().clone();
+        for pool in pools {
+            let mut pool = pool.lock();
+            let best = pool.pop().unwrap();
+            pool.clear();
+            pool.push(best);
+            pool.shrink_to_fit();
+        }
+    }
+
+    pub fn scale_zero() {
+        let pools = take(&mut *ACTIVE_POOLS.lock());
+        for pool in pools {
+            let mut pool = pool.lock();
+            pool.clear();
+            pool.shrink_to_fit();
+        }
+    }
 }
 
 pub struct NodeJsOperation {
@@ -971,7 +1005,13 @@ impl Drop for NodeJsOperation {
             }
             if self.allow_process_reuse {
                 process.cpu_time_invested += elapsed;
-                self.processes.lock().push(process);
+                {
+                    let mut processes = self.processes.lock();
+                    if processes.is_empty() {
+                        ACTIVE_POOLS.lock().push(self.processes.clone());
+                    }
+                    processes.push(process);
+                }
                 self.idle_process_semaphore.add_permits(1);
             }
         }