Remove once_cell dependency

Cargo.toml

@@ -9,14 +9,13 @@ repository = "https://github.com/Amanieu/thread_local-rs"
 readme = "README.md"
 keywords = ["thread_local", "concurrent", "thread"]
 edition = "2021"
-rust-version = "1.61"
+rust-version = "1.63"
 
 [features]
 # this feature provides performance improvements using nightly features
 nightly = []
 
 [dependencies]
-once_cell = "1.5.2"
 # this is required to gate `nightly` related code paths
 cfg-if = "1.0.0"
 

README.md

@@ -21,7 +21,7 @@ thread_local = "1.1"
 
 ## Minimum Rust version
 
-This crate's minimum supported Rust version (MSRV) is 1.61.0.
+This crate's minimum supported Rust version (MSRV) is 1.63.0.
 
 ## License
 

src/thread_id.rs

@@ -6,7 +6,6 @@
 // copied, modified, or distributed except according to those terms.
 
 use crate::POINTER_WIDTH;
-use once_cell::sync::Lazy;
 use std::cell::Cell;
 use std::cmp::Reverse;
 use std::collections::BinaryHeap;
@@ -17,17 +16,19 @@ use std::sync::Mutex;
 /// indefinitely when it is used by many short-lived threads.
 struct ThreadIdManager {
     free_from: usize,
-    free_list: BinaryHeap<Reverse<usize>>,
+    free_list: Option<BinaryHeap<Reverse<usize>>>,
 }
+
 impl ThreadIdManager {
-    fn new() -> Self {
+    const fn new() -> Self {
         Self {
             free_from: 0,
-            free_list: BinaryHeap::new(),
+            free_list: None,
         }
     }
+
     fn alloc(&mut self) -> usize {
-        if let Some(id) = self.free_list.pop() {
+        if let Some(id) = self.free_list.as_mut().and_then(|heap| heap.pop()) {
             id.0
         } else {
             // `free_from` can't overflow as each thread takes up at least 2 bytes of memory and
@@ -38,12 +39,15 @@ impl ThreadIdManager {
             id
         }
     }
+
     fn free(&mut self, id: usize) {
-        self.free_list.push(Reverse(id));
+        self.free_list
+            .get_or_insert_with(BinaryHeap::new)
+            .push(Reverse(id));
     }
 }
-static THREAD_ID_MANAGER: Lazy<Mutex<ThreadIdManager>> =
-    Lazy::new(|| Mutex::new(ThreadIdManager::new()));
+
+static THREAD_ID_MANAGER: Mutex<ThreadIdManager> = Mutex::new(ThreadIdManager::new());
 
 /// Data which is unique to the current thread while it is running.
 /// A thread ID may be reused after a thread exits.