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Add LocalTaskObj to core::task #51814

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merged 4 commits into from
Jun 26, 2018
Merged

Add LocalTaskObj to core::task #51814

merged 4 commits into from
Jun 26, 2018

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MajorBreakfast
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@MajorBreakfast MajorBreakfast commented Jun 26, 2018 •
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  • Splits libcore/task.rs into submodules
  • Adds LocalTaskObj and SpawnLocalObjError (-> Commit for this)

Note: To make reviewing easy, both actions have their own commit

r? @cramertj

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 26, 2018
@MajorBreakfast MajorBreakfast mentioned this pull request Jun 26, 2018
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cramertj
cramertj reviewed Jun 26, 2018
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src/libcore/task/mod.rs Outdated
pub use self::poll::Poll;

mod spawn_error;
pub use self::spawn_error::{SpawnErrorKind, SpawnObjError};
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IMO the errors don't deserve their own file-- I'd move them in with the executor (since that's what uses them).

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Done

cramertj
cramertj reviewed Jun 26, 2018
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src/libcore/task/spawn_error.rs Outdated
fn from(error: SpawnObjError) -> SpawnLocalObjError {
unsafe {
// Safety: Both structs have the same memory layout
mem::transmute::<SpawnObjError, SpawnLocalObjError>(error)
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No need to transmute here-- just move the fields over.

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Will it have the same performance?

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Yup.

cramertj
cramertj reviewed Jun 26, 2018
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src/libcore/task/spawn_error.rs Outdated
/// To make this operation safe one has to ensure that the `UnsafeTask`
/// instance from which the `LocalTaskObj` stored inside was created
/// actually implements `Send`.
pub unsafe fn as_spawn_obj_error(self) -> SpawnObjError {
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@cramertj cramertj Jun 26, 2018 •
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What is this for? This seems like a pretty big footgun.

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https://github.com/rust-lang-nursery/futures-rs/pull/1046/files#diff-9c6376c5ce46d9e39358812a3269ab6bR259

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@cramertj cramertj Jun 26, 2018 •
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You don't need anything unsafe to implement that. You can implement spawn_obj by inlining the body of spawn_local_obj and using into only if upgrade succeeds.

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You mean copy paste?

cramertj
cramertj reviewed Jun 26, 2018
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src/libcore/task/task.rs Outdated
@@ -30,7 +30,7 @@ unsafe impl Send for TaskObj {}
impl TaskObj {
/// Create a `TaskObj` from a custom trait object representation.
#[inline]
pub fn new<T: UnsafeTask>(t: T) -> TaskObj {
pub fn new<T: UnsafeTask + Send>(t: T) -> TaskObj {
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@cramertj cramertj Jun 26, 2018 •
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Rather than repeating all the logic between TaskObj and LocalTaskObj, I'd make TaskObj into a single-field wrapper around LocalTaskObj that just adds Send-ability at the cost of requiring Send to construct (in new).

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The current way was inspired by the way it is done for LocalWaker & Waker. You're right. A single field struct is nicer

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Waker and LocalWaker are a bit different because they actually call different functions, but it's possible they could be combined further as well.

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Ok good point. Anyhow I think the current waker code is good. At closer inspection it really shows that a lot of considerations went into it.

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MajorBreakfast commented Jun 26, 2018 •
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I removed the conversions for SpawnErrorObj. If I you want me to set the fields instead of transmute, then there is no reason to put the conversions in libcore because this can be done anywhere because the fields are public.

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cramertj commented Jun 26, 2018 •
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@MajorBreakfast The fields of TaskObj and LocalTaskObj aren't public, so if you want an unsafe conversion from LocalTaskObj -> TaskObj, it will need to be in core: https://github.com/rust-lang/rust/pull/51814/files#diff-c756fc15162cb40ebeb296a1699a84b5R24

Edit: oh, you meant for the errors. I see you kept https://github.com/rust-lang/rust/pull/51814/files#diff-c756fc15162cb40ebeb296a1699a84b5R44

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r=me with travis passing. Thanks!

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@bors r+

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bors commented Jun 26, 2018

📌 Commit b39ea1d has been approved by cramertj

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 26, 2018
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bors commented Jun 26, 2018

⌛ Testing commit b39ea1d with merge 84804c3...

bors added a commit that referenced this pull request Jun 26, 2018
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Auto merge of #51814 - MajorBreakfast:local-task-obj, r=cramertj
84804c3 
Add `LocalTaskObj` to `core::task`

- Splits `libcore/task.rs` into submodules
- Adds `LocalTaskObj` and `SpawnLocalObjError` (-> [Commit for this](433e6b3))

Note: To make reviewing easy, both actions have their own commit

r? @cramertj
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bors commented Jun 26, 2018

☀️ Test successful - status-appveyor, status-travis
Approved by: cramertj
Pushing 84804c3 to master...

@bors bors merged commit b39ea1d into rust-lang:master Jun 26, 2018
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