functions.
These were introduced in an early draft implementation of async let, but
never used by a released compiler. They are not used as symbols by any
app binaries. There's no reason to keep carrying them.
While I'm at it, dramatically improve the documentation of the remaining
async let API functions.
The `_SwiftConcurrencyShims` module was imported `@_implementationOnly` which
was causing warnings to be emitted during the stdlib build. The module
currently serves no purpose; the only declaration it contains is a defunct
`_SwiftContext` struct which is not referenced by anything. The module needs to
continue to exist for source compatibility, though, since it is part of the
toolchain and imported publicly from other modules.
The concurrency runtime now deploys back to macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, which corresponds to the 5.1 release of the stdlib.
Adjust macro usages accordingly.
Change the code generation patterns for `async let` bindings to use an ABI based on the following
functions:
- `swift_asyncLet_begin`, which starts an `async let` child task, but which additionally
now associates the `async let` with a caller-owned buffer to receive the result of the task.
This is intended to allow the task to emplace its result in caller-owned memory, allowing the
child task to be deallocated after completion without invalidating the result buffer.
- `swift_asyncLet_get[_throwing]`, which replaces `swift_asyncLet_wait[_throwing]`. Instead of
returning a copy of the value, this entry point concerns itself with populating the local buffer.
If the buffer hasn't been populated, then it awaits completion of the task and emplaces the
result in the buffer; otherwise, it simply returns. The caller can then read the result out of
its owned memory. These entry points are intended to be used before every read from the
`async let` binding, after which point the local buffer is guaranteed to contain an initialized
value.
- `swift_asyncLet_finish`, which replaces `swift_asyncLet_end`. Unlike `_end`, this variant
is async and will suspend the parent task after cancelling the child to ensure it finishes
before cleaning up. The local buffer will also be deinitialized if necessary. This is intended
to be used on exit from an `async let` scope, to handle cleaning up the local buffer if necessary
as well as cancelling, awaiting, and deallocating the child task.
- `swift_asyncLet_consume[_throwing]`, which combines `get` and `finish`. This will await completion
of the task, leaving the result value in the result buffer (or propagating the error, if it
throws), while destroying and deallocating the child task. This is intended as an optimization
for reading `async let` variables that are read exactly once by their parent task.
To avoid an epoch break with existing swiftinterfaces and ABI clients, the old builtins and entry
points are kept intact for now, but SILGen now only generates code using the new interface.
This new interface fixes several issues with the old async let codegen, including use-after-free
crashes if the `async let` was never awaited, and the inability to read from an `async let` variable
more than once.
rdar://77855176
introduce new options parameter to all task spawning
[Concurrency] ABI for asynclet start to accept options
[Concurrency] fix unittest usages of changed task creation ABI
[Concurrency] introduce constants for parameter indexes in ownership
[Concurrency] fix test/SILOptimizer/closure_lifetime_fixup_concurrency.swift
The closure does not escape the startAsyncLet - endAsyncLet scope. Even though it's (potentially) running on a different thread.
The substantial change in the runtime is to not call swift_release on the closure context if it's a non-escaping closure.
