feat: implement basic async IO with timers (#6505)

This PR implements a basic async framework as well as asynchronously
running timers using libuv.

---------

Co-authored-by: Sofia Rodrigues <[email protected]>
Co-authored-by: Markus Himmel <[email protected]>
Co-authored-by: Markus Himmel <[email protected]>

src/Std/Internal.lean

@@ -4,7 +4,9 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Henrik Böving
 -/
 prelude
+import Std.Internal.Async
 import Std.Internal.Parsec
+import Std.Internal.UV
 
 /-!
 This directory is used for components of the standard library that are either considered

src/Std/Internal/Async.lean

@@ -0,0 +1,8 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Henrik Böving
+-/
+prelude
+import Std.Internal.Async.Basic
+import Std.Internal.Async.Timer

src/Std/Internal/Async/Basic.lean

@@ -0,0 +1,115 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Henrik Böving
+-/
+prelude
+import Init.Core
+import Init.System.IO
+import Init.System.Promise
+
+namespace Std
+namespace Internal
+namespace IO
+namespace Async
+
+/--
+A `Task` that may resolve to a value or an `IO.Error`.
+-/
+def AsyncTask (α : Type u) : Type u := Task (Except IO.Error α)
+
+namespace AsyncTask
+
+/--
+Construct an `AsyncTask` that is already resolved with value `x`.
+-/
+@[inline]
+protected def pure (x : α) : AsyncTask α := Task.pure <| .ok x
+
+instance : Pure AsyncTask where
+  pure := AsyncTask.pure
+
+/--
+Create a new `AsyncTask` that will run after `x` has finished.
+If `x`:
+- errors, return an `AsyncTask` that resolves to the error.
+- succeeds, run `f` on the result of `x` and return the `AsyncTask` produced by `f`.
+-/
+@[inline]
+protected def bind (x : AsyncTask α) (f : α → AsyncTask β) : AsyncTask β :=
+  Task.bind x fun r =>
+    match r with
+    | .ok a => f a
+    | .error e => Task.pure <| .error e
+
+/--
+Create a new `AsyncTask` that will run after `x` has finished.
+If `x`:
+- errors, return an `AsyncTask` that reolves to the error.
+- succeeds, return an `AsyncTask` that resolves to `f x`.
+-/
+@[inline]
+def map (f : α → β) (x : AsyncTask α) : AsyncTask β :=
+  Task.map (x := x) fun r =>
+    match r with
+    | .ok a => .ok (f a)
+    | .error e => .error e
+
+/--
+Similar to `bind`, however `f` has access to the `IO` monad. If `f` throws an error, the returned
+`AsyncTask` resolves to that error.
+-/
+@[inline]
+def bindIO (x : AsyncTask α) (f : α → IO (AsyncTask β)) : BaseIO (AsyncTask β) :=
+  IO.bindTask x fun r =>
+    match r with
+    | .ok a => f a
+    | .error e => .error e
+
+/--
+Similar to `bind`, however `f` has access to the `IO` monad. If `f` throws an error, the returned
+`AsyncTask` resolves to that error.
+-/
+@[inline]
+def mapIO (f : α → IO β) (x : AsyncTask α) : BaseIO (AsyncTask β) :=
+  IO.mapTask (t := x) fun r =>
+    match r with
+    | .ok a => f a
+    | .error e => .error e
+
+/--
+Block until the `AsyncTask` in `x` finishes.
+-/
+def block (x : AsyncTask α) : IO α := do
+  let res := x.get
+  match res with
+  | .ok a => return a
+  | .error e => .error e
+
+/--
+Create an `AsyncTask` that resolves to the value of `x`.
+-/
+@[inline]
+def ofPromise (x : IO.Promise (Except IO.Error α)) : AsyncTask α :=
+  x.result
+
+/--
+Create an `AsyncTask` that resolves to the value of `x`.
+-/
+@[inline]
+def ofPurePromise (x : IO.Promise α) : AsyncTask α :=
+  x.result.map pure
+
+/--
+Obtain the `IO.TaskState` of `x`.
+-/
+@[inline]
+def getState (x : AsyncTask α) : BaseIO IO.TaskState :=
+  IO.getTaskState x
+
+end AsyncTask
+
+end Async
+end IO
+end Internal
+end Std

src/Std/Internal/Async/Timer.lean

@@ -0,0 +1,139 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Henrik Böving
+-/
+prelude
+import Std.Time
+import Std.Internal.UV
+import Std.Internal.Async.Basic
+
+
+namespace Std
+namespace Internal
+namespace IO
+namespace Async
+
+/--
+`Sleep` can be used to sleep for some duration once.
+The underlying timer has millisecond resolution.
+-/
+structure Sleep where
+  private ofNative ::
+    native : Internal.UV.Timer
+
+namespace Sleep
+
+/--
+Set up a `Sleep` that waits for `duration` milliseconds.
+This function only initializes but does not yet start the timer.
+-/
+@[inline]
+def mk (duration : Std.Time.Millisecond.Offset) : IO Sleep := do
+  let native ← Internal.UV.Timer.mk duration.toInt.toNat.toUInt64 false
+  return ofNative native
+
+/--
+If:
+- `s` is not yet running start it and return an `AsyncTask` that will resolve once the previously
+   configured `duration` has run out.
+- `s` is already or not anymore running return the same `AsyncTask` as the first call to `wait`.
+-/
+@[inline]
+def wait (s : Sleep) : IO (AsyncTask Unit) := do
+  let promise ← s.native.next
+  return .ofPurePromise promise
+
+/--
+If:
+- `s` is still running the timer restarts counting from now and finishes after `duration`
+  milliseconds.
+- `s` is not yet or not anymore running this is a no-op.
+-/
+@[inline]
+def reset (s : Sleep) : IO Unit :=
+  s.native.reset
+
+/--
+If:
+- `s` is still running this stops `s` without resolving any remaining `AsyncTask`s that were created
+  through `wait`. Note that if another `AsyncTask` is binding on any of these it is going hang
+  forever without further intervention.
+- `s` is not yet or not anymore running this is a no-op.
+-/
+@[inline]
+def stop (s : Sleep) : IO Unit :=
+  s.native.stop
+
+end Sleep
+
+/--
+Return an `AsyncTask` that resolves after `duration`.
+-/
+def sleep (duration : Std.Time.Millisecond.Offset) : IO (AsyncTask Unit) := do
+  let sleeper ← Sleep.mk duration
+  sleeper.wait
+
+/--
+`Interval` can be used to repeatedly wait for some duration like a clock.
+The underlying timer has millisecond resolution.
+-/
+structure Interval where
+  private ofNative ::
+    native : Internal.UV.Timer
+
+
+namespace Interval
+
+/--
+Setup up an `Interval` that waits for `duration` milliseconds.
+This function only initializes but does not yet start the timer.
+-/
+@[inline]
+def mk (duration : Std.Time.Millisecond.Offset) (_ : 0 < duration := by decide) : IO Interval := do
+  let native ← Internal.UV.Timer.mk duration.toInt.toNat.toUInt64 true
+  return ofNative native
+
+/--
+If:
+- `i` is not yet running start it and return an `AsyncTask` that resolves right away as the 0th
+  multiple of `duration` has elapsed.
+- `i` is already running and:
+  - the tick from the last call of `i` has not yet finished return the same `AsyncTask` as the last
+    call
+  - the tick frrom the last call of `i` has finished return a new `AsyncTask` that waits for the
+    closest next tick from the time of calling this function.
+- `i` is not running aymore this is a no-op.
+-/
+@[inline]
+def tick (i : Interval) : IO (AsyncTask Unit) := do
+  let promise ← i.native.next
+  return .ofPurePromise promise
+
+/--
+If:
+- `Interval.tick` was called on `i` before the timer restarts counting from now and the next tick
+   happens in `duration`.
+- `i` is not yet or not anymore running this is a no-op.
+-/
+@[inline]
+def reset (i : Interval) : IO Unit :=
+  i.native.reset
+
+/--
+If:
+- `i` is still running this stops `i` without resolving any remaing `AsyncTask` that were created
+  through `tick`. Note that if another `AsyncTask` is binding on any of these it is going hang
+  forever without further intervention.
+- `i` is not yet or not anymore running this is a no-op.
+-/
+@[inline]
+def stop (i : Interval) : IO Unit :=
+  i.native.stop
+
+end Interval
+
+end Async
+end IO
+end Internal
+end Std

src/Std/Internal/UV.lean

@@ -0,0 +1,119 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sofia Rodrigues
+-/
+prelude
+import Init.System.IO
+import Init.System.Promise
+
+namespace Std
+namespace Internal
+namespace UV
+
+namespace Loop
+
+/--
+Options for configuring the event loop behavior.
+-/
+structure Loop.Options where
+  /--
+  Accumulate the amount of idle time the event loop spends in the event provider.
+  -/
+  accumulateIdleTime : Bool := False
+
+  /--
+  Block a SIGPROF signal when polling for new events. It's commonly used for unnecessary wakeups
+  when using a sampling profiler.
+  -/
+  blockSigProfSignal : Bool := False
+
+/--
+Configures the event loop with the specified options.
+-/
+@[extern "lean_uv_event_loop_configure"]
+opaque configure (options : Loop.Options) : BaseIO Unit
+
+/--
+Checks if the event loop is still active and processing events.
+-/
+@[extern "lean_uv_event_loop_alive"]
+opaque alive : BaseIO Bool
+
+end Loop
+
+private opaque TimerImpl : NonemptyType.{0}
+
+/--
+`Timer`s are used to generate `IO.Promise`s that resolve after some time.
+
+A `Timer` can be in one of 3 states:
+- Right after construction it's initial.
+- While it is ticking it's running.
+- If it has stopped for some reason it's finished.
+
+This together with whether it was set up as `repeating` with `Timer.new` determines the behavior
+of all functions on `Timer`s.
+-/
+def Timer : Type := TimerImpl.type
+
+instance : Nonempty Timer := TimerImpl.property
+
+namespace Timer
+
+/--
+This creates a `Timer` in the initial state and doesn't run it yet.
+- If `repeating` is `false` this constructs a timer that resolves once after `durationMs`
+  milliseconds, counting from when it's run.
+- If `repeating` is `true` this constructs a timer that resolves after multiples of `durationMs`
+  milliseconds, counting from when it's run. Note that this includes the 0th multiple right after
+  starting the timer. Furthermore a repeating timer will only be freed after `Timer.stop` is called.
+-/
+@[extern "lean_uv_timer_mk"]
+opaque mk (timeout : UInt64) (repeating : Bool) : IO Timer
+
+/--
+This function has different behavior depending on the state and configuration of the `Timer`:
+- if `repeating` is `false` and:
+  - it is initial, run it and return a new `IO.Promise` that is set to resolve once `durationMs`
+    milliseconds have elapsed. After this `IO.Promise` is resolved the `Timer` is finished.
+  - it is running or finished, return the same `IO.Promise` that the first call to `next` returned.
+- if `repeating` is `true` and:
+  - it is initial, run it and return a new `IO.Promise` that resolves right away
+    (as it is the 0th multiple of `durationMs`).
+  - it is running, check whether the last returned `IO.Promise` is already resolved:
+     - If it is, return a new `IO.Promise` that resolves upon finishing the next cycle
+     - If it is not, return the last `IO.Promise`
+     This ensures that the returned `IO.Promise` resolves at the next repetition of the timer.
+  - if it is finished, return the last `IO.Promise` created by `next`. Notably this could be one
+    that never resolves if the timer was stopped before fulfilling the last one.
+-/
+@[extern "lean_uv_timer_next"]
+opaque next (timer : @& Timer) : IO (IO.Promise Unit)
+
+/--
+This function has different behavior depending on the state and configuration of the `Timer`:
+- If it is initial or finished this is a no-op.
+- If it is running and `repeating` is `false` this will delay the resolution of the timer until
+  `durationMs` milliseconds after the call of this function.
+- Delay the resolution of the next tick of the timer until `durationMs` milliseconds after the
+  call of this function, then continue normal ticking behavior from there.
+-/
+@[extern "lean_uv_timer_reset"]
+opaque reset (timer : @& Timer) : IO Unit
+
+/--
+This function has different behavior depending on the state of the `Timer`:
+- If it is initial or finished this is a no-op.
+- If it is running the execution of the timer is stopped and it is put into the finished state.
+  Note that if the last `IO.Promise` generated by `next` is unresolved and being waited
+  on this creates a memory leak and the waiting task is not going to be awoken anymore.
+-/
+@[extern "lean_uv_timer_stop"]
+opaque stop (timer : @& Timer) : IO Unit
+
+end Timer
+
+end UV
+end Internal
+end Std