Adding upstream version 115.7.0esr.upstream/115.7.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 485 insertions, 0 deletions

diff --git a/third_party/rust/tokio/src/runtime/task/harness.rs b/third_party/rust/tokio/src/runtime/task/harness.rs
new file mode 100644
index 0000000000..261dccea41
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/harness.rs
@@ -0,0 +1,485 @@
+use crate::future::Future;
+use crate::runtime::task::core::{Cell, Core, CoreStage, Header, Trailer};
+use crate::runtime::task::state::Snapshot;
+use crate::runtime::task::waker::waker_ref;
+use crate::runtime::task::{JoinError, Notified, Schedule, Task};
+
+use std::mem;
+use std::mem::ManuallyDrop;
+use std::panic;
+use std::ptr::NonNull;
+use std::task::{Context, Poll, Waker};
+
+/// Typed raw task handle.
+pub(super) struct Harness<T: Future, S: 'static> {
+    cell: NonNull<Cell<T, S>>,
+}
+
+impl<T, S> Harness<T, S>
+where
+    T: Future,
+    S: 'static,
+{
+    pub(super) unsafe fn from_raw(ptr: NonNull<Header>) -> Harness<T, S> {
+        Harness {
+            cell: ptr.cast::<Cell<T, S>>(),
+        }
+    }
+
+    fn header_ptr(&self) -> NonNull<Header> {
+        self.cell.cast()
+    }
+
+    fn header(&self) -> &Header {
+        unsafe { &self.cell.as_ref().header }
+    }
+
+    fn trailer(&self) -> &Trailer {
+        unsafe { &self.cell.as_ref().trailer }
+    }
+
+    fn core(&self) -> &Core<T, S> {
+        unsafe { &self.cell.as_ref().core }
+    }
+}
+
+impl<T, S> Harness<T, S>
+where
+    T: Future,
+    S: Schedule,
+{
+    /// Polls the inner future. A ref-count is consumed.
+    ///
+    /// All necessary state checks and transitions are performed.
+    /// Panics raised while polling the future are handled.
+    pub(super) fn poll(self) {
+        // We pass our ref-count to `poll_inner`.
+        match self.poll_inner() {
+            PollFuture::Notified => {
+                // The `poll_inner` call has given us two ref-counts back.
+                // We give one of them to a new task and call `yield_now`.
+                self.core()
+                    .scheduler
+                    .yield_now(Notified(self.get_new_task()));
+
+                // The remaining ref-count is now dropped. We kept the extra
+                // ref-count until now to ensure that even if the `yield_now`
+                // call drops the provided task, the task isn't deallocated
+                // before after `yield_now` returns.
+                self.drop_reference();
+            }
+            PollFuture::Complete => {
+                self.complete();
+            }
+            PollFuture::Dealloc => {
+                self.dealloc();
+            }
+            PollFuture::Done => (),
+        }
+    }
+
+    /// Polls the task and cancel it if necessary. This takes ownership of a
+    /// ref-count.
+    ///
+    /// If the return value is Notified, the caller is given ownership of two
+    /// ref-counts.
+    ///
+    /// If the return value is Complete, the caller is given ownership of a
+    /// single ref-count, which should be passed on to `complete`.
+    ///
+    /// If the return value is Dealloc, then this call consumed the last
+    /// ref-count and the caller should call `dealloc`.
+    ///
+    /// Otherwise the ref-count is consumed and the caller should not access
+    /// `self` again.
+    fn poll_inner(&self) -> PollFuture {
+        use super::state::{TransitionToIdle, TransitionToRunning};
+
+        match self.header().state.transition_to_running() {
+            TransitionToRunning::Success => {
+                let header_ptr = self.header_ptr();
+                let waker_ref = waker_ref::<T, S>(&header_ptr);
+                let cx = Context::from_waker(&*waker_ref);
+                let res = poll_future(&self.core().stage, cx);
+
+                if res == Poll::Ready(()) {
+                    // The future completed. Move on to complete the task.
+                    return PollFuture::Complete;
+                }
+
+                match self.header().state.transition_to_idle() {
+                    TransitionToIdle::Ok => PollFuture::Done,
+                    TransitionToIdle::OkNotified => PollFuture::Notified,
+                    TransitionToIdle::OkDealloc => PollFuture::Dealloc,
+                    TransitionToIdle::Cancelled => {
+                        // The transition to idle failed because the task was
+                        // cancelled during the poll.
+
+                        cancel_task(&self.core().stage);
+                        PollFuture::Complete
+                    }
+                }
+            }
+            TransitionToRunning::Cancelled => {
+                cancel_task(&self.core().stage);
+                PollFuture::Complete
+            }
+            TransitionToRunning::Failed => PollFuture::Done,
+            TransitionToRunning::Dealloc => PollFuture::Dealloc,
+        }
+    }
+
+    /// Forcibly shuts down the task.
+    ///
+    /// Attempt to transition to `Running` in order to forcibly shutdown the
+    /// task. If the task is currently running or in a state of completion, then
+    /// there is nothing further to do. When the task completes running, it will
+    /// notice the `CANCELLED` bit and finalize the task.
+    pub(super) fn shutdown(self) {
+        if !self.header().state.transition_to_shutdown() {
+            // The task is concurrently running. No further work needed.
+            self.drop_reference();
+            return;
+        }
+
+        // By transitioning the lifecycle to `Running`, we have permission to
+        // drop the future.
+        cancel_task(&self.core().stage);
+        self.complete();
+    }
+
+    pub(super) fn dealloc(self) {
+        // Release the join waker, if there is one.
+        self.trailer().waker.with_mut(drop);
+
+        // Check causality
+        self.core().stage.with_mut(drop);
+
+        unsafe {
+            drop(Box::from_raw(self.cell.as_ptr()));
+        }
+    }
+
+    // ===== join handle =====
+
+    /// Read the task output into `dst`.
+    pub(super) fn try_read_output(self, dst: &mut Poll<super::Result<T::Output>>, waker: &Waker) {
+        if can_read_output(self.header(), self.trailer(), waker) {
+            *dst = Poll::Ready(self.core().stage.take_output());
+        }
+    }
+
+    /// Try to set the waker notified when the task is complete. Returns true if
+    /// the task has already completed. If this call returns false, then the
+    /// waker will not be notified.
+    pub(super) fn try_set_join_waker(self, waker: &Waker) -> bool {
+        can_read_output(self.header(), self.trailer(), waker)
+    }
+
+    pub(super) fn drop_join_handle_slow(self) {
+        // Try to unset `JOIN_INTEREST`. This must be done as a first step in
+        // case the task concurrently completed.
+        if self.header().state.unset_join_interested().is_err() {
+            // It is our responsibility to drop the output. This is critical as
+            // the task output may not be `Send` and as such must remain with
+            // the scheduler or `JoinHandle`. i.e. if the output remains in the
+            // task structure until the task is deallocated, it may be dropped
+            // by a Waker on any arbitrary thread.
+            //
+            // Panics are delivered to the user via the `JoinHandle`. Given that
+            // they are dropping the `JoinHandle`, we assume they are not
+            // interested in the panic and swallow it.
+            let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+                self.core().stage.drop_future_or_output();
+            }));
+        }
+
+        // Drop the `JoinHandle` reference, possibly deallocating the task
+        self.drop_reference();
+    }
+
+    /// Remotely aborts the task.
+    ///
+    /// The caller should hold a ref-count, but we do not consume it.
+    ///
+    /// This is similar to `shutdown` except that it asks the runtime to perform
+    /// the shutdown. This is necessary to avoid the shutdown happening in the
+    /// wrong thread for non-Send tasks.
+    pub(super) fn remote_abort(self) {
+        if self.header().state.transition_to_notified_and_cancel() {
+            // The transition has created a new ref-count, which we turn into
+            // a Notified and pass to the task.
+            //
+            // Since the caller holds a ref-count, the task cannot be destroyed
+            // before the call to `schedule` returns even if the call drops the
+            // `Notified` internally.
+            self.core()
+                .scheduler
+                .schedule(Notified(self.get_new_task()));
+        }
+    }
+
+    // ===== waker behavior =====
+
+    /// This call consumes a ref-count and notifies the task. This will create a
+    /// new Notified and submit it if necessary.
+    ///
+    /// The caller does not need to hold a ref-count besides the one that was
+    /// passed to this call.
+    pub(super) fn wake_by_val(self) {
+        use super::state::TransitionToNotifiedByVal;
+
+        match self.header().state.transition_to_notified_by_val() {
+            TransitionToNotifiedByVal::Submit => {
+                // The caller has given us a ref-count, and the transition has
+                // created a new ref-count, so we now hold two. We turn the new
+                // ref-count Notified and pass it to the call to `schedule`.
+                //
+                // The old ref-count is retained for now to ensure that the task
+                // is not dropped during the call to `schedule` if the call
+                // drops the task it was given.
+                self.core()
+                    .scheduler
+                    .schedule(Notified(self.get_new_task()));
+
+                // Now that we have completed the call to schedule, we can
+                // release our ref-count.
+                self.drop_reference();
+            }
+            TransitionToNotifiedByVal::Dealloc => {
+                self.dealloc();
+            }
+            TransitionToNotifiedByVal::DoNothing => {}
+        }
+    }
+
+    /// This call notifies the task. It will not consume any ref-counts, but the
+    /// caller should hold a ref-count.  This will create a new Notified and
+    /// submit it if necessary.
+    pub(super) fn wake_by_ref(&self) {
+        use super::state::TransitionToNotifiedByRef;
+
+        match self.header().state.transition_to_notified_by_ref() {
+            TransitionToNotifiedByRef::Submit => {
+                // The transition above incremented the ref-count for a new task
+                // and the caller also holds a ref-count. The caller's ref-count
+                // ensures that the task is not destroyed even if the new task
+                // is dropped before `schedule` returns.
+                self.core()
+                    .scheduler
+                    .schedule(Notified(self.get_new_task()));
+            }
+            TransitionToNotifiedByRef::DoNothing => {}
+        }
+    }
+
+    pub(super) fn drop_reference(self) {
+        if self.header().state.ref_dec() {
+            self.dealloc();
+        }
+    }
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) fn id(&self) -> Option<&tracing::Id> {
+        self.header().id.as_ref()
+    }
+
+    // ====== internal ======
+
+    /// Completes the task. This method assumes that the state is RUNNING.
+    fn complete(self) {
+        // The future has completed and its output has been written to the task
+        // stage. We transition from running to complete.
+
+        let snapshot = self.header().state.transition_to_complete();
+
+        // We catch panics here in case dropping the future or waking the
+        // JoinHandle panics.
+        let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+            if !snapshot.is_join_interested() {
+                // The `JoinHandle` is not interested in the output of
+                // this task. It is our responsibility to drop the
+                // output.
+                self.core().stage.drop_future_or_output();
+            } else if snapshot.has_join_waker() {
+                // Notify the join handle. The previous transition obtains the
+                // lock on the waker cell.
+                self.trailer().wake_join();
+            }
+        }));
+
+        // The task has completed execution and will no longer be scheduled.
+        let num_release = self.release();
+
+        if self.header().state.transition_to_terminal(num_release) {
+            self.dealloc();
+        }
+    }
+
+    /// Releases the task from the scheduler. Returns the number of ref-counts
+    /// that should be decremented.
+    fn release(&self) -> usize {
+        // We don't actually increment the ref-count here, but the new task is
+        // never destroyed, so that's ok.
+        let me = ManuallyDrop::new(self.get_new_task());
+
+        if let Some(task) = self.core().scheduler.release(&me) {
+            mem::forget(task);
+            2
+        } else {
+            1
+        }
+    }
+
+    /// Creates a new task that holds its own ref-count.
+    ///
+    /// # Safety
+    ///
+    /// Any use of `self` after this call must ensure that a ref-count to the
+    /// task holds the task alive until after the use of `self`. Passing the
+    /// returned Task to any method on `self` is unsound if dropping the Task
+    /// could drop `self` before the call on `self` returned.
+    fn get_new_task(&self) -> Task<S> {
+        // safety: The header is at the beginning of the cell, so this cast is
+        // safe.
+        unsafe { Task::from_raw(self.cell.cast()) }
+    }
+}
+
+fn can_read_output(header: &Header, trailer: &Trailer, waker: &Waker) -> bool {
+    // Load a snapshot of the current task state
+    let snapshot = header.state.load();
+
+    debug_assert!(snapshot.is_join_interested());
+
+    if !snapshot.is_complete() {
+        // The waker must be stored in the task struct.
+        let res = if snapshot.has_join_waker() {
+            // There already is a waker stored in the struct. If it matches
+            // the provided waker, then there is no further work to do.
+            // Otherwise, the waker must be swapped.
+            let will_wake = unsafe {
+                // Safety: when `JOIN_INTEREST` is set, only `JOIN_HANDLE`
+                // may mutate the `waker` field.
+                trailer.will_wake(waker)
+            };
+
+            if will_wake {
+                // The task is not complete **and** the waker is up to date,
+                // there is nothing further that needs to be done.
+                return false;
+            }
+
+            // Unset the `JOIN_WAKER` to gain mutable access to the `waker`
+            // field then update the field with the new join worker.
+            //
+            // This requires two atomic operations, unsetting the bit and
+            // then resetting it. If the task transitions to complete
+            // concurrently to either one of those operations, then setting
+            // the join waker fails and we proceed to reading the task
+            // output.
+            header
+                .state
+                .unset_waker()
+                .and_then(|snapshot| set_join_waker(header, trailer, waker.clone(), snapshot))
+        } else {
+            set_join_waker(header, trailer, waker.clone(), snapshot)
+        };
+
+        match res {
+            Ok(_) => return false,
+            Err(snapshot) => {
+                assert!(snapshot.is_complete());
+            }
+        }
+    }
+    true
+}
+
+fn set_join_waker(
+    header: &Header,
+    trailer: &Trailer,
+    waker: Waker,
+    snapshot: Snapshot,
+) -> Result<Snapshot, Snapshot> {
+    assert!(snapshot.is_join_interested());
+    assert!(!snapshot.has_join_waker());
+
+    // Safety: Only the `JoinHandle` may set the `waker` field. When
+    // `JOIN_INTEREST` is **not** set, nothing else will touch the field.
+    unsafe {
+        trailer.set_waker(Some(waker));
+    }
+
+    // Update the `JoinWaker` state accordingly
+    let res = header.state.set_join_waker();
+
+    // If the state could not be updated, then clear the join waker
+    if res.is_err() {
+        unsafe {
+            trailer.set_waker(None);
+        }
+    }
+
+    res
+}
+
+enum PollFuture {
+    Complete,
+    Notified,
+    Done,
+    Dealloc,
+}
+
+/// Cancels the task and store the appropriate error in the stage field.
+fn cancel_task<T: Future>(stage: &CoreStage<T>) {
+    // Drop the future from a panic guard.
+    let res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        stage.drop_future_or_output();
+    }));
+
+    match res {
+        Ok(()) => {
+            stage.store_output(Err(JoinError::cancelled()));
+        }
+        Err(panic) => {
+            stage.store_output(Err(JoinError::panic(panic)));
+        }
+    }
+}
+
+/// Polls the future. If the future completes, the output is written to the
+/// stage field.
+fn poll_future<T: Future>(core: &CoreStage<T>, cx: Context<'_>) -> Poll<()> {
+    // Poll the future.
+    let output = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        struct Guard<'a, T: Future> {
+            core: &'a CoreStage<T>,
+        }
+        impl<'a, T: Future> Drop for Guard<'a, T> {
+            fn drop(&mut self) {
+                // If the future panics on poll, we drop it inside the panic
+                // guard.
+                self.core.drop_future_or_output();
+            }
+        }
+        let guard = Guard { core };
+        let res = guard.core.poll(cx);
+        mem::forget(guard);
+        res
+    }));
+
+    // Prepare output for being placed in the core stage.
+    let output = match output {
+        Ok(Poll::Pending) => return Poll::Pending,
+        Ok(Poll::Ready(output)) => Ok(output),
+        Err(panic) => Err(JoinError::panic(panic)),
+    };
+
+    // Catch and ignore panics if the future panics on drop.
+    let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        core.store_output(output);
+    }));
+
+    Poll::Ready(())
+}