enable id reusing (vercel/turborepo#2895)

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

crates/turbo-tasks/Cargo.toml

@@ -20,6 +20,7 @@ any_key = "0.1.1"
 anyhow = "1.0.47"
 auto-hash-map = { path = "../auto-hash-map" }
 bitflags = "1.3.2"
+concurrent-queue = "1.2.2"
 dashmap = "5.4.0"
 erased-serde = "0.3.20"
 event-listener = "2.5.3"

crates/turbo-tasks/src/id_factory.rs

@@ -4,10 +4,12 @@ use std::{
     sync::atomic::{AtomicUsize, Ordering},
 };
 
+use concurrent_queue::ConcurrentQueue;
+use once_cell::sync::Lazy;
+
 pub struct IdFactory<T> {
     next_id: AtomicUsize,
-    // TODO
-    // free_ids: AtomicPtr<...>
+    free_ids: Lazy<ConcurrentQueue<T>>,
     phantom_data: PhantomData<T>,
 }
 
@@ -21,18 +23,22 @@ impl<T: From<usize> + Deref<Target = usize>> IdFactory<T> {
     pub const fn new() -> Self {
         Self {
             next_id: AtomicUsize::new(1),
+            free_ids: Lazy::new(|| ConcurrentQueue::unbounded()),
             phantom_data: PhantomData,
         }
     }
 
     pub fn get(&self) -> T {
+        if let Ok(id) = self.free_ids.pop() {
+            return id;
+        }
         self.next_id.fetch_add(1, Ordering::Relaxed).into()
     }
 
     /// # Safety
     ///
     /// It must be ensured that the id is no longer used
-    pub unsafe fn reuse(&self, _id: T) {
-        // TODO
+    pub unsafe fn reuse(&self, id: T) {
+        let _ = self.free_ids.push(id);
     }
 }