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Use OnceLock in crate::threads

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Verified that std::sync::OnceLock<T> compiles to the same assembly at the
*access* site as the Option<T> we were using. The additional overhead upon init
is fine. No need for extra Box<T> indirection for IO_THREAD_POOL.
This commit is contained in:
Mahmoud Al-Qudsi 2024-05-24 12:46:47 -05:00
parent b49e9b906f
commit cf4ab20055
1 changed files with 9 additions and 21 deletions
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30
src/threads.rs
View File

@ -3,26 +3,17 @@
use crate::flog::{FloggableDebug, FLOG};
use crate::reader::ReaderData;
use once_cell::race::OnceBox;
use std::marker::PhantomData;
use std::num::NonZeroU64;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Mutex};
use std::sync::{Arc, Mutex, OnceLock};
use std::thread::{self, ThreadId};
use std::time::{Duration, Instant};
impl FloggableDebug for ThreadId {}
// We don't want to use a full-blown Lazy<T> for the cached main thread id, but we can't use
// AtomicU64 since std::thread::ThreadId::as_u64() is a nightly-only feature (issue #67939,
// thread_id_value). We also can't safely transmute `ThreadId` to `NonZeroU64` because there's no
// guarantee that's what the underlying type will always be on all platforms and in all cases,
// `ThreadId` isn't marked `#[repr(transparent)]`. We could generate our own thread-local value, but
// `#[thread_local]` is nightly-only while the stable `thread_local!()` macro doesn't generate
// efficient/fast/low-overhead code.
/// The thread id of the main thread, as set by [`init()`] at startup.
static mut MAIN_THREAD_ID: Option<ThreadId> = None;
static MAIN_THREAD_ID: OnceLock<ThreadId> = OnceLock::new();
/// Used to bypass thread assertions when testing.
const THREAD_ASSERTS_CFG_FOR_TESTING: bool = cfg!(test);
/// This allows us to notice when we've forked.
@ -37,7 +28,7 @@ const IO_WAIT_FOR_WORK_DURATION: Duration = Duration::from_millis(500);
/// The iothreads [`ThreadPool`] singleton. Used to lift I/O off of the main thread and used for
/// completions, etc.
static IO_THREAD_POOL: OnceBox<Mutex<ThreadPool>> = OnceBox::new();
static IO_THREAD_POOL: OnceLock<Mutex<ThreadPool>> = OnceLock::new();
/// The event signaller singleton used for completions and queued main thread requests.
static NOTIFY_SIGNALLER: once_cell::sync::Lazy<crate::fd_monitor::FdEventSignaller> =
@ -63,12 +54,9 @@ static MAIN_THREAD_QUEUE: Mutex<Vec<DebounceCallback>> = Mutex::new(Vec::new());
/// Initialize some global static variables. Must be called at startup from the main thread.
pub fn init() {
unsafe {
if MAIN_THREAD_ID.is_some() {
panic!("threads::init() must only be called once (at startup)!");
}
MAIN_THREAD_ID = Some(thread::current().id());
}
MAIN_THREAD_ID
.set(thread::current().id())
.expect("threads::init() must only be called once (at startup)!");
extern "C" fn child_post_fork() {
IS_FORKED_PROC.store(true, Ordering::Relaxed);
@ -79,7 +67,7 @@ pub fn init() {
}
IO_THREAD_POOL
.set(Box::new(Mutex::new(ThreadPool::new(1, IO_MAX_THREADS))))
.set(Mutex::new(ThreadPool::new(1, IO_MAX_THREADS)))
.expect("IO_THREAD_POOL has already been initialized!");
}
@ -90,9 +78,9 @@ fn main_thread_id() -> ThreadId {
panic!("threads::init() was not called at startup!");
}
match unsafe { MAIN_THREAD_ID } {
match MAIN_THREAD_ID.get() {
None => init_not_called(),
Some(id) => id,
Some(id) => *id,
}
}