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rt: EnterGuard should not be Send (#5766)

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Removes `Send` from `EnterGuard` (returned by `Handle::enter()`. The
guard type changes a thread-local variable on drop. If the guard is
moved to a different thread, it would modify the wrong thread-local.

This is a **breaking change** but it fixes a bug and prevents incorrect
user behavior. If user code breaks because of this, it is because they
(most likely) have a bug in their code.
This commit is contained in:
Carl Lerche 2023-06-05 14:09:43 -07:00 committed by GitHub
parent 15712018da
commit e75ca93d30
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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 11 additions and 1 deletions
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4
tokio/src/runtime/context.rs
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@ -159,6 +159,9 @@ cfg_rt! {
pub(crate) struct SetCurrentGuard {
old_handle: Option<scheduler::Handle>,
old_seed: RngSeed,
// Should not be `Send` since it must be *dropped* on the same thread as
// created, but there is no issue with sync access.
_p: PhantomData<crate::util::markers::SyncNotSend>,
}
/// Guard tracking that a caller has entered a runtime context.
@ -308,6 +311,7 @@ cfg_rt! {
SetCurrentGuard {
old_handle,
old_seed,
_p: PhantomData,
}
}
}

4
tokio/src/util/markers.rs Normal file
View File

@ -0,0 +1,4 @@
/// Marker for types that are `Sync` but not `Send`
pub(crate) struct SyncNotSend(*mut ());
unsafe impl Sync for SyncNotSend {}

2
tokio/src/util/mod.rs
View File

@ -79,3 +79,5 @@ pub(crate) mod error;
#[cfg(feature = "io-util")]
pub(crate) mod memchr;
pub(crate) mod markers;

2
tokio/tests/async_send_sync.rs
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@ -532,7 +532,7 @@ async_assert_fn!(tokio::task::unconstrained(BoxFutureSend<()>): Send & !Sync & U
async_assert_fn!(tokio::task::unconstrained(BoxFutureSync<()>): Send & Sync & Unpin);
assert_value!(tokio::runtime::Builder: Send & Sync & Unpin);
assert_value!(tokio::runtime::EnterGuard<'_>: Send & Sync & Unpin);
assert_value!(tokio::runtime::EnterGuard<'_>: !Send & Sync & Unpin);
assert_value!(tokio::runtime::Handle: Send & Sync & Unpin);
assert_value!(tokio::runtime::Runtime: Send & Sync & Unpin);