Soften language for notify on unshared memories
#191
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Since #144, we've specified that `memory.atomic.notify` is allowed to be executed on unshared memories, but always returns 0 since it is impossible for there to be anything waiting on an unshared memory since all variations of the wait instructions in Wasm and JS trap or throw exceptions on unshared memories. However, I realized recently that there is no technical reason why [`Atomics.waitAsync`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/waitAsync) shouldn't be able to wait on an unshared memory. Because `Atomics.waitAsync` returns a promise rather than blocking, it can in principle be used to synchronize between multiple asynchronous tasks in flight concurrently in the same JS context, and now that [JSPI](https://github.com/WebAssembly/js-promise-integration/blob/main/proposals/js-promise-integration/Overview.md) is becoming more real, this actually might be a useful thing to do. In particular `Atomics.waitAsync` could be used to build suspending versions of mutexes and condition variables to synchronize between threads running as different asynchronous tasks within a single JS context. Actually realizing this vision of asynchronous threading with JSPI on top of `Atomics.waitAsync` requires changes on the JS side to allow `Atomics.waitAsync` and `Atomics.notify` to be used on unshared ArrayBuffers, but in the meantime we can prepare for that change on the Wasm side by softening the language stating that `memory.atomic.notify` unconditionally returns 0 for unshared memories.
conrad-watt
approved these changes
Sep 13, 2022
|
(I'd also be interested in @syg's take on how likely this is on the JS side) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Since #144, we've specified that
memory.atomic.notifyis allowed to be executed on unshared memories, but always returns 0 since it is impossible for there to be anything waiting on an unshared memory since all variations of the wait instructions in Wasm and JS trap or throw exceptions on unshared memories. However, I realized recently that there is no technical reason whyAtomics.waitAsyncshouldn't be able to wait on an unshared memory. BecauseAtomics.waitAsyncreturns a promise rather than blocking, it can in principle be used to synchronize between multiple asynchronous tasks in flight concurrently in the same JS context, and now that JSPI is becoming more real, this actually might be a useful thing to do. In particularAtomics.waitAsynccould be used to build suspending versions of mutexes and condition variables to synchronize between threads running as different asynchronous tasks within a single JS context.Actually realizing this vision of asynchronous threading with JSPI on top of
Atomics.waitAsyncrequires changes on the JS side to allowAtomics.waitAsyncandAtomics.notifyto be used on unshared ArrayBuffers, but in the meantime we can prepare for that change on the Wasm side by softening the language stating thatmemory.atomic.notifyunconditionally returns 0 for unshared memories.cc @syg