chore: vendor once_cell

.github/workflows/ci.yml

@@ -298,7 +298,8 @@ jobs:
           override: true
       - uses: Swatinem/rust-cache@v1
       - name: "test --workspace --all-features"
-        run: cargo check --workspace --all-features
+        # todo remove the exclude whenever we bump clippy to 1.56 (MSRV will fail rn)
+        run: cargo check --workspace --all-features --exclude examples --exclude tokio-stream
 
   minimal-versions:
     name: minimal-versions

tokio/Cargo.toml

@@ -63,7 +63,7 @@ net = [
 ]
 process = [
   "bytes",
-  "once_cell",
+  "parking_lot_core",
   "libc",
   "mio/os-poll",
   "mio/os-ext",
@@ -77,13 +77,13 @@ process = [
   "winapi/winnt",
 ]
 # Includes basic task execution capabilities
-rt = ["once_cell"]
+rt = ["parking_lot_core"]
 rt-multi-thread = [
   "num_cpus",
   "rt",
 ]
 signal = [
-  "once_cell",
+  "parking_lot_core",
   "libc",
   "mio/os-poll",
   "mio/net",
@@ -112,11 +112,11 @@ pin-project-lite = "0.2.0"
 
 # Everything else is optional...
 bytes = { version = "1.0.0", optional = true }
-once_cell = { version = "1.5.2", optional = true }
 memchr = { version = "2.2", optional = true }
 mio = { version = "0.8.4", optional = true }
 num_cpus = { version = "1.8.0", optional = true }
 parking_lot = { version = "0.12.0", optional = true }
+parking_lot_core = { version = "0.9.3", optional = true }
 
 [target.'cfg(not(any(target_arch = "wasm32", target_arch = "wasm64")))'.dependencies]
 socket2 = { version = "0.4.4", optional = true, features = [ "all" ] }

tokio/src/process/unix/mod.rs

@@ -35,9 +35,9 @@ use crate::process::SpawnedChild;
 use crate::signal::unix::driver::Handle as SignalHandle;
 use crate::signal::unix::{signal, Signal, SignalKind};
 
+use crate::util::once_cell::sync::Lazy;
 use mio::event::Source;
 use mio::unix::SourceFd;
-use once_cell::sync::Lazy;
 use std::fmt;
 use std::fs::File;
 use std::future::Future;

tokio/src/runtime/task/mod.rs

@@ -508,7 +508,7 @@ impl Id {
 
     cfg_not_has_atomic_u64! {
         pub(crate) fn next() -> Self {
-            use once_cell::sync::Lazy;
+            use crate::util::once_cell::sync::Lazy;
             use crate::loom::sync::Mutex;
 
             static NEXT_ID: Lazy<Mutex<u64>> = Lazy::new(|| Mutex::new(1));

tokio/src/signal/registry.rs

@@ -4,7 +4,7 @@ use crate::signal::os::{OsExtraData, OsStorage};
 
 use crate::sync::watch;
 
-use once_cell::sync::Lazy;
+use crate::util::once_cell::sync::Lazy;
 use std::ops;
 use std::pin::Pin;
 use std::sync::atomic::{AtomicBool, Ordering};

tokio/src/util/mod.rs

@@ -6,6 +6,10 @@ cfg_io_driver! {
 #[cfg(feature = "rt")]
 pub(crate) mod atomic_cell;
 
+/// Vendored from [here](https://github.com/matklad/once_cell/tree/v1.14.0)
+#[cfg(any(feature = "process", feature = "rt", feature = "signal"))]
+pub(crate) mod once_cell;
+
 #[cfg(any(
     // io driver uses `WakeList` directly
     feature = "net",

tokio/src/util/once_cell/imp_pl.rs

@@ -0,0 +1,173 @@
+use std::{
+    cell::UnsafeCell,
+    hint,
+    panic::{RefUnwindSafe, UnwindSafe},
+    sync::atomic::{AtomicU8, Ordering},
+};
+
+pub(crate) struct OnceCell<T> {
+    state: AtomicU8,
+    value: UnsafeCell<Option<T>>,
+}
+
+const INCOMPLETE: u8 = 0x0;
+const RUNNING: u8 = 0x1;
+const COMPLETE: u8 = 0x2;
+
+// Why do we need `T: Send`?
+// Thread A creates a `OnceCell` and shares it with
+// scoped thread B, which fills the cell, which is
+// then destroyed by A. That is, destructor observes
+// a sent value.
+unsafe impl<T: Sync + Send> Sync for OnceCell<T> {}
+unsafe impl<T: Send> Send for OnceCell<T> {}
+
+impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceCell<T> {}
+impl<T: UnwindSafe> UnwindSafe for OnceCell<T> {}
+
+impl<T> OnceCell<T> {
+    pub(crate) const fn new() -> OnceCell<T> {
+        OnceCell {
+            state: AtomicU8::new(INCOMPLETE),
+            value: UnsafeCell::new(None),
+        }
+    }
+
+    pub(crate) const fn with_value(value: T) -> OnceCell<T> {
+        OnceCell {
+            state: AtomicU8::new(COMPLETE),
+            value: UnsafeCell::new(Some(value)),
+        }
+    }
+
+    /// Safety: synchronizes with store to value via Release/Acquire.
+    #[inline]
+    pub(crate) fn is_initialized(&self) -> bool {
+        self.state.load(Ordering::Acquire) == COMPLETE
+    }
+
+    /// Safety: synchronizes with store to value via `is_initialized` or mutex
+    /// lock/unlock, writes value only once because of the mutex.
+    #[cold]
+    pub(crate) fn initialize<F, E>(&self, f: F) -> Result<(), E>
+    where
+        F: FnOnce() -> Result<T, E>,
+    {
+        let mut f = Some(f);
+        let mut res: Result<(), E> = Ok(());
+        let slot: *mut Option<T> = self.value.get();
+        initialize_inner(&self.state, &mut || {
+            // We are calling user-supplied function and need to be careful.
+            // - if it returns Err, we unlock mutex and return without touching anything
+            // - if it panics, we unlock mutex and propagate panic without touching anything
+            // - if it calls `set` or `get_or_try_init` re-entrantly, we get a deadlock on
+            //   mutex, which is important for safety. We *could* detect this and panic,
+            //   but that is more complicated
+            // - finally, if it returns Ok, we store the value and store the flag with
+            //   `Release`, which synchronizes with `Acquire`s.
+            let f = unsafe { super::take_unchecked(&mut f) };
+            match f() {
+                Ok(value) => unsafe {
+                    // Safe b/c we have a unique access and no panic may happen
+                    // until the cell is marked as initialized.
+                    debug_assert!((*slot).is_none());
+                    *slot = Some(value);
+                    true
+                },
+                Err(err) => {
+                    res = Err(err);
+                    false
+                }
+            }
+        });
+        res
+    }
+
+    /// Get the reference to the underlying value, without checking if the cell
+    /// is initialized.
+    ///
+    /// # Safety
+    ///
+    /// Caller must ensure that the cell is in initialized state, and that
+    /// the contents are acquired by (synchronized to) this thread.
+    pub(crate) unsafe fn get_unchecked(&self) -> &T {
+        debug_assert!(self.is_initialized());
+        let slot: &Option<T> = &*self.value.get();
+        match slot {
+            Some(value) => value,
+            // This unsafe does improve performance, see `examples/bench`.
+            None => {
+                debug_assert!(false);
+                hint::unreachable_unchecked()
+            }
+        }
+    }
+
+    /// Gets the mutable reference to the underlying value.
+    /// Returns `None` if the cell is empty.
+    pub(crate) fn get_mut(&mut self) -> Option<&mut T> {
+        // Safe b/c we have an exclusive access
+        let slot: &mut Option<T> = unsafe { &mut *self.value.get() };
+        slot.as_mut()
+    }
+}
+
+struct Guard<'a> {
+    state: &'a AtomicU8,
+    new_state: u8,
+}
+
+impl<'a> Drop for Guard<'a> {
+    fn drop(&mut self) {
+        self.state.store(self.new_state, Ordering::Release);
+        unsafe {
+            let key = self.state as *const AtomicU8 as usize;
+            parking_lot_core::unpark_all(key, parking_lot_core::DEFAULT_UNPARK_TOKEN);
+        }
+    }
+}
+
+// Note: this is intentionally monomorphic
+#[inline(never)]
+fn initialize_inner(state: &AtomicU8, init: &mut dyn FnMut() -> bool) {
+    loop {
+        let exchange =
+            state.compare_exchange_weak(INCOMPLETE, RUNNING, Ordering::Acquire, Ordering::Acquire);
+        match exchange {
+            Ok(_) => {
+                let mut guard = Guard {
+                    state,
+                    new_state: INCOMPLETE,
+                };
+                if init() {
+                    guard.new_state = COMPLETE;
+                }
+                return;
+            }
+            Err(COMPLETE) => return,
+            Err(RUNNING) => unsafe {
+                let key = state as *const AtomicU8 as usize;
+                parking_lot_core::park(
+                    key,
+                    || state.load(Ordering::Relaxed) == RUNNING,
+                    || (),
+                    |_, _| (),
+                    parking_lot_core::DEFAULT_PARK_TOKEN,
+                    None,
+                );
+            },
+            Err(INCOMPLETE) => (),
+            Err(_) => debug_assert!(false),
+        }
+    }
+}
+
+#[test]
+fn test_size() {
+    use std::mem::size_of;
+
+    assert_eq!(
+        size_of::<OnceCell<bool>>(),
+        1 * size_of::<bool>() + size_of::<u8>()
+    );
+}