Tracking this as a single bit is actually largely uninteresting
to the runtime. To handle priority escalation properly, we really
need to track this at a finer grain of detail: recording that the
task is running on a specific thread, enqueued on a specific actor,
or so on. But starting by tracking a single bit is important for
two reasons:
- First, it's more realistic about the performance overheads of
tasks: we're going to be doing this tracking eventually, and
the cost of that tracking will be dominated by the atomic
access, so doing that access now sets the baseline about right.
- Second, it ensures that we've actually got runtime involvement
in all the right places to do this tracking.
A propos of the latter: there was no runtime involvement with
awaiting a continuation, which is a point at which the task
potentially transitions from running to suspended. We must do
the tracking as part of this transition, rather than recognizing
in the run-loops that a task is still active and treating it as
having suspended, because the latter point potentially races with
the resumption of the task. To do this, I've had to introduce
a runtime function, swift_continuation_await, to do this awaiting
rather than inlining the atomic operation on the continuation.
As part of doing this work, I've also fixed a bug where we failed
to load-acquire in swift_task_escalate before walking the task
status records to invoke escalation actions.
I've also fixed several places where the handling of task statuses
may have accidentally allowed the task to revert to uncancelled.
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
I added Builtin.buildMainActorExecutor before, but because I never
implemented it correctly in IRGen, it's not okay to use it on old
versions, so I had to introduce a new feature only for it.
The shim dispatch queue class in the Concurrency runtime is rather
awful, but I couldn't think of a reasonable alternative without
just entirely hard-coding the witness table in the runtime.
It's not ABI, at least.
Changes the task, taskGroup, asyncLet wait funtion call ABIs.
To reduce code size pass the context parameters and resumption function
as arguments to the wait function.
This means that the suspend point does not need to store parent context
and resumption to the suspend point's context.
```
void swift_task_future_wait_throwing(
OpaqueValue * result,
SWIFT_ASYNC_CONTEXT AsyncContext *callerContext,
AsyncTask *task,
ThrowingTaskFutureWaitContinuationFunction *resume,
AsyncContext *callContext);
```
The runtime passes the caller context to the resume entry point saving
the load of the parent context in the resumption function.
This patch adds a `Metadata *` field to `GroupImpl`. The await entry
pointer no longer pass the metadata pointer and there is a path through
the runtime where the task future is no longer available.
`pthread_self` is not portable to all platforms. Introduce a
`_swift_get_current_thread_id` to abstract over accessing the current
thread ID. On Windows, the thread ID and thread handle are two separate
entities, unlike POSIX threads which treats them the same.
This commit changes JobFlags storage to be 32bits, but leaves the runtime
API expressed in terms of size_t. This allows us to pack an Id in the
32bits we freed up.
The offset of this Id in the AsyncTask is an ABI constant. This way
introspection tools can extract the currently running task identifier
without any need for special APIs.
- Introduce an UnownedSerialExecutor type into the concurrency library.
- Create a SerialExecutor protocol which allows an executor type to
change how it executes jobs.
- Add an unownedExecutor requirement to the Actor protocol.
- Change the ABI for ExecutorRef so that it stores a SerialExecutor
witness table pointer in the implementation field. This effectively
makes ExecutorRef an `unowned(unsafe) SerialExecutor`, except that
default actors are represented without a witness table pointer (just
a bit-pattern).
- Synthesize the unownedExecutor method for default actors (i.e. actors
that don't provide an unownedExecutor property).
- Make synthesized unownedExecutor properties `final`, and give them
a semantics attribute specifying that they're for default actors.
- Split `Builtin.buildSerialExecutorRef` into a few more precise
builtins. We're not using the main-actor one yet, though.
Pitch thread:
https://forums.swift.org/t/support-custom-executors-in-swift-concurrency/44425
Also, do this for the initial slab for the task's allocator itself.
This avoids memory allocations for async-lets.
In case the async-task's memory demand does not exceed the initial slab size, it is now completely malloc-free.
The refcount bits of an async-let task are initialized to "immortal" so that ARC operations don't have an effect on the task.
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.
Previously, if this happened, we simply left the actor in a running
state, causing any further jobs submitted to it to never be executed.
I can only speculate why this wasn't showing up in testing.
Also, change swift_job_run so that it prevents switching if the executor
passed in is not generic. This is an entrypoint for arbitrary executors
and generally should not allow unexpected switching (if someday custom
executors participate in that scheme). This infrastructure will also
be useful for implementing the `async let` semantics of running
synchronously until the task reaches a suspension point.
Finally, improve the #if'ed logging code throughout the task/actor runtime.
Fill out the metadata for Job to have a Dispatch-compatible vtable. When available, use the dispatch_enqueue_onto_queue_4Swift to enqueue Jobs directly onto queues. Otherwise, keep using dispatch_async_f as we have been.
rdar://75227953
Throwing functions pass the error result in `swiftself` to the resume
partial function.
Therefore, `() async -> ()` to `() async throws -> ()` is not ABI compatible.
TODO: go through remaining failing IRGen async tests and replace the
illegal convert_functions.
Most of the async runtime functions have been changed to not
expect the task and executor to be passed in. When knowing the
task and executor is necessary, there are runtime functions
available to recover them.
The biggest change I had to make to a runtime function signature
was to swift_task_switch, which has been altered to expect to be
passed the context and resumption function instead of requiring
the caller to park the task. This has the pleasant consequence
of allowing the implementation to very quickly turn around when
it recognizes that the current executor is satisfactory. It does
mean that on arm64e we have to sign the continuation function
pointer as an argument and then potentially resign it when
assigning into the task's resume slot.
rdar://70546948
First, just call an async -> T function instead of forcing the caller
to piece together which case we're in and perform its own copy. This
ensures that the task is actually kept alive properly.
Second, now that we no longer implicitly depend on the waiting tasks
being run synchronously, go ahead and schedule them to run on the
global executor.
This solves some problems which were blocking the work on TLS-ifying
the task/executor state.
Previously, the error stored in the async context was of type SwiftError
*. In order to enable the context to be callee released, make it
indirect and change its type to SwiftError **.
rdar://71378532
move comments to the wired up continuations
remove duplicated continuations; leep the wired up ones
before moving to C++ for queue impl
trying to next wait via channel_poll
submitting works; need to impl next()
Currently, the only thing in the system that donates a thread
to run it is swift_runAndBlockThread, but we'll probably need
others. Nothing in the concurrency runtime should block via a
semaphore in this configuration.
As an outrageous hack, work around the layering problems with
using libdispatch from the concurrency library on non-Darwin
systems by making those systems use the cooperative global
executor. This is only acceptable as a temporary solution
for landing this change and setting things onto the right
long-term design.
