[Concurrency] Provide a Swift interface for custom main and global executors. #79789

al45tair · 2025-03-05T10:26:34Z

Reorganise the Concurrency code so that it's possible to completely implement executors (both main and global) in Swift.

Provide API to choose the desired executors for your application.

Also make Task.Sleep wait using the current executor, not the global executor, and expose APIs on Clock to allow for conversion between time bases.

rdar://141348916

al45tair · 2025-03-05T10:27:51Z

@swift-ci Please smoke test

al45tair · 2025-03-05T10:28:49Z

(This is not yet complete; there's a problem I need to resolve relating to setting the main executor.)

ktoso

Just a few minor comments so far; overall this is looking great :)

include/swift/Runtime/Concurrency.h

stdlib/public/Concurrency/CFExecutor.swift

stdlib/public/Concurrency/CMakeLists.txt

stdlib/public/Concurrency/ContinuousClock.swift

stdlib/public/Concurrency/DispatchExecutor.swift

stdlib/public/Concurrency/GlobalConcurrentExecutor.swift

al45tair · 2025-03-07T20:13:26Z

@swift-ci Please test

al45tair · 2025-03-10T19:04:46Z

@swift-ci Please test

al45tair · 2025-03-11T14:56:17Z

@swift-ci Please test

al45tair · 2025-03-11T17:06:08Z

@swift-ci Please test

al45tair · 2025-03-12T16:28:58Z

@swift-ci Please test

Reorganise the Concurrency code so that it's possible to completely implement executors (both main and global) in Swift. Provide API to choose the desired executors for your application. Also make `Task.Sleep` wait using the current executor, not the global executor, and expose APIs on `Clock` to allow for conversion between time bases. rdar://141348916

Added an `-executor-factory` argument to the compiler to let you safely specify the executors you wish to use (by naming a type that returns them). Also added some tests of the new functionality. rdar://141348916

Remove the hacky support for mapping clocks to a Dispatch clock ID, in favour of clocks publishing traits and having the Dispatch executor select the clock on the basis of those traits.

Fix a couple of potential ABI breaks. Also add the new functions and types to the baseline lists. rdar://141348916

The rename appears to have had some kind of potentially ABI breaking consequence. rdar://141348916

Remove a printf() I'd added for debugging. rdar://141348916

Embedded Swift doesn't have MainActor, so remove it. rdar://141348916

We can't use blocks, because Swift doesn't support them on Linux or Windows. Instead, use a C function pointer, and box up the handler. rdar://141348916

Rename `DispatchTaskExecutor` to `DispatchGlobalTaskExecutor` as we may want to use the former for an executor that runs things on an arbitrary Dispatch queue. Rename `DispatchExecutor` to `DispatchExecutorProtocol`; again, we might want the name for something else. Add `@Sendable` attribute to `registerEvent`. Fix missing `extern "C" SWIFT_CC(swift)` on `_swift_exit` (merge error). Remove stray whitespace from `CMakeLists.txt` rdar://141348916

Also fix a missing availability annotation. rdar://141348916

This needed an update to make things build on Linux and Windows. rdar://141348916

Remove `supportsScheduling` in favour of a type-based approach. Update the storage for `ClockTraits` to `UInt32`. Adjust ordering of executors for `currentExecutor`. rdar://141348916

EventableExecutor is being removed, for now, but hopefully will return in some form in the future. The `asSchedulable` implementation needs to change for reasons of ABI stability. rdar://141348916

al45tair · 2025-03-14T16:40:52Z

SE proposal is here: swiftlang/swift-evolution#2654

al45tair · 2025-03-14T16:48:10Z

WASI concurrency tests failed, which is not a great surprise, as I've only just discovered that those were a thing.

Also tweak the sleep implementations to let the hooks run if there isn't a `SchedulableExecutor` (for hooked mode). rdar://141348916

al45tair · 2025-03-17T13:10:56Z

@swift-ci Please test

Fix up availability after the non-Darwin changes. Also update the ABI baseline. Fix a Win32 typo. rdar://141348916

al45tair · 2025-03-17T16:25:42Z

@swift-ci Please test

We need to annotate the `timestamp()` function for watchOS (apparently not for macOS for some reason). rdar://141348916

Fix a typo that caused us to not include the correct code for platforms that use "singlethreaded" concurrency. Also use `var` not `let` for the computed property in `PlatformExecutorFactory`. rdar://141348916

We need to explicitly require `libdispatch` here, otherwise the Windows build will fail. rdar://141348916

al45tair · 2025-03-18T10:44:53Z

@swift-ci Please test

CooperativeExecutor needs to store its timestamp out-of-line for 32-bit architectures (like WASI). rdar://141348916

al45tair · 2025-03-18T15:48:08Z

@swift-ci Please test

`CooperativeExecutor` should fall back to heap allocations if the task allocator isn't available when it's enqueuing delayed jobs. Also, remove the reference to `DispatchGlobalExecutor` from the custom executor test. rdar://141348916

al45tair · 2025-03-18T18:01:56Z

@swift-ci Please test

Fix a couple of `unsafe` warnings. Also update `withUnsafeExecutorPrivateData` to use typed throws instead of `rethrow`. rdar://141348916

al45tair · 2025-03-18T18:38:40Z

@swift-ci Please test

al45tair · 2025-03-18T18:53:40Z

@swift-ci Please test Linux platform

al45tair · 2025-03-19T09:28:19Z

OK. Everything is now passing except for the minimalstdlib configuration.

When in task-to-thread model concurrency mode, there is no `MainActor` and we cannot use `ExecutorJob`, so disable various things. rdar://141348916

al45tair · 2025-03-19T11:24:18Z

@swift-ci Please test

al45tair · 2025-03-19T15:47:37Z

@swift-ci Please test Windows platform

al45tair

Spotted a couple of mistakes in comments.

stdlib/public/Concurrency/Executor.swift

stdlib/public/Concurrency/ExecutorImpl.swift

test/Concurrency/Runtime/clocks.swift

ktoso

LGTM! Just small things here and there, feel free to merge and let's follow up on what makes sense to address 👍

ktoso · 2025-03-20T12:51:04Z

include/swift/AST/FeatureAvailability.def

@@ -80,6 +80,7 @@ FEATURE(IsolatedDeinit,                                 (6, 1))

 FEATURE(ValueGenericType,                               (6, 2))
 FEATURE(InitRawStructMetadata2,                         (6, 2))
+FEATURE(CustomExecutors,                                (6, 2))


Maybe this is CustomGlobalExecutors? Custom executor sounds like the actor ones hm...

Btw, i noticed TaskExecutor is FUTURE...? That's not right is it? 🤔

ktoso · 2025-03-20T12:52:07Z

include/swift/AST/DiagnosticsSIL.def

+ERROR(cannot_find_executor_factory_type, none,
+      "the specified executor factory '%0' could not be found", (StringRef))
+ERROR(executor_factory_must_conform, none,
+      "the executor factory '%0' does not conform to 'ExecutorFactory'", (Type))


Nitpick, your call: Maybe better to get the type name passed in?

ktoso · 2025-03-20T13:25:58Z

lib/SILGen/SILGen.cpp

@@ -507,6 +511,46 @@ FuncDecl *SILGenModule::getExit() {
  return exitFunction;
 }

+Type SILGenModule::getExecutorFactory() {


Is this maybe getConfiguredExecutorFactory?

ktoso · 2025-03-20T13:28:45Z

lib/SILGen/SILGen.cpp

+ProtocolDecl *SILGenModule::getExecutorFactoryProtocol() {
+  auto &ctx = getASTContext();
+
+  return ctx.getProtocol(KnownProtocolKind::ExecutorFactory);


Do we need this func? There should be ctx.getExecutorFactoryDecl() generated since you added it to KnownProtocols.def

ktoso · 2025-03-20T13:31:26Z

stdlib/public/Concurrency/Actor.cpp

+      return SerialExecutorRef::generic();
+    return executor;
+  }
+  return swift_getMainExecutor();


is this really right? if yes, can you add a comment?

Say we're just on some random thread, there's no executor tracking, we're not on the main executor though -- this seems a bit off?

ktoso · 2025-03-21T05:44:55Z

stdlib/public/Concurrency/ExecutorBridge.cpp

+      0, "Incorrect actor executor assumption; expected '%.*s' executor.\n",
+      (int)typeName.length, typeName.data);
+  }
+}


looks good, thanks for moving these over to ExecutorBridge now

ktoso · 2025-03-21T05:47:50Z

stdlib/public/Concurrency/PartialAsyncTask.swift

+  ///
+  /// N.B. Because this allocator is stack disciplined, explicitly
+  /// deallocating memory will also deallocate all memory allocated
+  /// after the block being deallocated.


I think I had this question before already: that's now how we behave today, if you deallocate "in wrong order" we crash; are we really changing that? That was good for detecting we messed up somehow, while deallocating other things like this may hide bugs in stack discipline...?

ktoso · 2025-03-21T05:48:42Z

stdlib/public/Concurrency/PlatformExecutorLinux.swift

+    = DispatchGlobalTaskExecutor()
+}
+
+#endif // os(Linux)


I really like how those Platform...swift look now 👍

ktoso · 2025-03-21T05:49:13Z

stdlib/public/Concurrency/Task.cpp

+  //if (auto identity = reinterpret_cast<HeapObject *>(jobQueue)) {
+  //  return SerialExecutorRef::forOrdinary(
+  //      identity, _swift_task_getDispatchQueueSerialExecutorWitnessTable());
+  //}


ktoso · 2025-03-21T05:51:07Z

test/Concurrency/Runtime/custom_main_executor.swift

@@ -0,0 +1,92 @@
+// RUN: %target-run-simple-swift(-Xfrontend -disable-availability-checking -g %import-libdispatch -parse-as-library -executor-factory SimpleExecutorFactory) | %FileCheck %s


Do we need a test specifying the executor factory in another module?

al45tair · 2025-03-21T09:05:39Z

LGTM! Just small things here and there, feel free to merge and let's follow up on what makes sense to address 👍

Sounds good. Will merge and then make a new PR to address the various things noted on this one.

…tors" This reverts commit 8443b5f, reversing changes made to 4c75d7b.

al45tair requested review from ktoso and rjmccall as code owners March 5, 2025 10:26

al45tair marked this pull request as draft March 5, 2025 10:29

al45tair force-pushed the custom-executors branch from 5ac5fad to aeae636 Compare March 6, 2025 13:18

ktoso reviewed Mar 6, 2025

View reviewed changes

al45tair force-pushed the custom-executors branch from d861a9f to 8ef09ef Compare March 10, 2025 12:14

al45tair force-pushed the custom-executors branch from b4f96b8 to ff1575a Compare March 11, 2025 14:55

al45tair requested a review from ktoso March 11, 2025 17:16

al45tair force-pushed the custom-executors branch 2 times, most recently from ca24acd to 47efda5 Compare March 12, 2025 13:24

al45tair added 13 commits March 13, 2025 13:34

[Concurrency] More work on the custom executor implementation.

55afa47

Added an `-executor-factory` argument to the compiler to let you safely specify the executors you wish to use (by naming a type that returns them). Also added some tests of the new functionality. rdar://141348916

[Concurrency] Add clock traits.

d89ea19

Remove the hacky support for mapping clocks to a Dispatch clock ID, in favour of clocks publishing traits and having the Dispatch executor select the clock on the basis of those traits.

[Concurrency] Fix potential ABI breakages.

5ae6de2

Fix a couple of potential ABI breaks. Also add the new functions and types to the baseline lists. rdar://141348916

[Concurrency] Rename ExecutorJob back to PartialAsyncTask.

2298651

The rename appears to have had some kind of potentially ABI breaking consequence. rdar://141348916

[Concurrency] Remove spurious printf().

3a7fc7c

Remove a printf() I'd added for debugging. rdar://141348916

[Concurrency][Embedded] Remove MainActor/MainExecutor everywhere.

ef0e09d

Embedded Swift doesn't have MainActor, so remove it. rdar://141348916

[Concurrency] Don't use blocks.

d14b937

We can't use blocks, because Swift doesn't support them on Linux or Windows. Instead, use a C function pointer, and box up the handler. rdar://141348916

[Concurrency] Mark expressions as unsafe.

fc67cc3

Also fix a missing availability annotation. rdar://141348916

[Concurrency] Update header file.

23d0ca7

This needed an update to make things build on Linux and Windows. rdar://141348916

[Concurrency] Update following pitch comments.

444bbd5

Remove `supportsScheduling` in favour of a type-based approach. Update the storage for `ClockTraits` to `UInt32`. Adjust ordering of executors for `currentExecutor`. rdar://141348916

[Concurrency] Remove EventableExecutor, alter asSchedulable.

00e7ef2

EventableExecutor is being removed, for now, but hopefully will return in some form in the future. The `asSchedulable` implementation needs to change for reasons of ABI stability. rdar://141348916

al45tair requested review from xedin and DougGregor as code owners March 14, 2025 16:13

[Concurrency] Add CooperativeExecutor, use it.

f0defd8

Also tweak the sleep implementations to let the hooks run if there isn't a `SchedulableExecutor` (for hooked mode). rdar://141348916

[Concurrency] Fix availability.

ed08858

Fix up availability after the non-Darwin changes. Also update the ABI baseline. Fix a Win32 typo. rdar://141348916

al45tair added 3 commits March 17, 2025 18:48

[Concurrency] Another missing availability annotation.

ad5b76a

We need to annotate the `timestamp()` function for watchOS (apparently not for macOS for some reason). rdar://141348916

[Concurrency] Fix a typo and use var not let.

167449f

Fix a typo that caused us to not include the correct code for platforms that use "singlethreaded" concurrency. Also use `var` not `let` for the computed property in `PlatformExecutorFactory`. rdar://141348916

[Concurrency][Tests] Require libdispatch in the sleep test.

4576d53

We need to explicitly require `libdispatch` here, otherwise the Windows build will fail. rdar://141348916

[Concurrency][32-bit] Store timestamp out-of-line on 32-bit.

60fb31c

CooperativeExecutor needs to store its timestamp out-of-line for 32-bit architectures (like WASI). rdar://141348916

[Concurrency] Fix some warnings, use typed throws.

0da95eb

Fix a couple of `unsafe` warnings. Also update `withUnsafeExecutorPrivateData` to use typed throws instead of `rethrow`. rdar://141348916

[Concurrency] Disable various things for task-to-thread model.

c20aa66

When in task-to-thread model concurrency mode, there is no `MainActor` and we cannot use `ExecutorJob`, so disable various things. rdar://141348916

al45tair commented Mar 20, 2025

View reviewed changes

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stdlib/public/Concurrency/ExecutorImpl.swift Show resolved Hide resolved

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ktoso reviewed Mar 21, 2025

View reviewed changes

al45tair merged commit 8443b5f into swiftlang:main Mar 21, 2025
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al45tair mentioned this pull request Mar 21, 2025

Revert "[Concurrency] Provide a Swift interface for custom main and global executors." #80194

Closed

al45tair added a commit to al45tair/swift that referenced this pull request Mar 21, 2025

Revert "Merge pull request swiftlang#79789 from al45tair/custom-execu…

25f7d07

…tors" This reverts commit 8443b5f, reversing changes made to 4c75d7b.

glessard mentioned this pull request Mar 22, 2025

Revert "[Concurrency] Provide a Swift interface for custom main and global executors." #80224

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al45tair commented Mar 21, 2025

		@@ -0,0 +1,92 @@
		// RUN: %target-run-simple-swift(-Xfrontend -disable-availability-checking -g %import-libdispatch -parse-as-library -executor-factory SimpleExecutorFactory) \| %FileCheck %s

[Concurrency] Provide a Swift interface for custom main and global executors. #79789

[Concurrency] Provide a Swift interface for custom main and global executors. #79789

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al45tair commented Mar 21, 2025