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// Copyright 2017 Amanieu d'Antras
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.
use std::collections::BinaryHeap;
use std::sync::Mutex;
use std::usize;
// Thread ID manager which allocates thread IDs. It attempts to aggressively
// reuse thread IDs where possible to avoid cases where a ThreadLocal grows
// indefinitely when it is used by many short-lived threads.
struct ThreadIdManager {
limit: usize,
free_list: BinaryHeap<usize>,
}
impl ThreadIdManager {
fn new() -> ThreadIdManager {
ThreadIdManager {
limit: usize::MAX,
free_list: BinaryHeap::new(),
}
}
fn alloc(&mut self) -> usize {
if let Some(id) = self.free_list.pop() {
id
} else {
let id = self.limit;
self.limit = self.limit.checked_sub(1).expect("Ran out of thread IDs");
id
}
}
fn free(&mut self, id: usize) {
self.free_list.push(id);
}
}
lazy_static! {
static ref THREAD_ID_MANAGER: Mutex<ThreadIdManager> = Mutex::new(ThreadIdManager::new());
}
// Non-zero integer which is unique to the current thread while it is running.
// A thread ID may be reused after a thread exits.
struct ThreadId(usize);
impl ThreadId {
fn new() -> ThreadId {
ThreadId(THREAD_ID_MANAGER.lock().unwrap().alloc())
}
}
impl Drop for ThreadId {
fn drop(&mut self) {
THREAD_ID_MANAGER.lock().unwrap().free(self.0);
}
}
thread_local!(static THREAD_ID: ThreadId = ThreadId::new());
/// Returns a non-zero ID for the current thread
pub fn get() -> usize {
THREAD_ID.with(|x| x.0)
}
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