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A modern runtime for JavaScript and TypeScript.
https://deno.com/
dd8cbf5e29
Fixes #22995. Fixes #23000. There were a handful of bugs here causing the hang (each with a corresponding minimized test): - We were canceling recv futures when `receiveMessageOnPort` was called, but this caused the "receive loop" in the message port to exit. This was due to the fact that `CancelHandle`s are never reset (i.e., once you `cancel` a `CancelHandle`, it remains cancelled). That meant that after `receieveMessageOnPort` was called, the subsequent calls to `op_message_port_recv_message` would throw `Interrupted` exceptions, and we would exit the loop. The cancellation, however, isn't actually necessary. `op_message_port_recv_message` only borrows the underlying port for long enough to poll the receiver, so the borrow there could never overlap with `op_message_port_recv_message_sync`. - Calling `MessagePort.unref()` caused the "receive loop" in the message port to exit. This was because we were setting `messageEventListenerCount` to 0 on unref. Not only does that break the counter when multiple `MessagePort`s are present in the same thread, but we also exited the "receive loop" whenever the listener count was 0. I assume this was to prevent the recv promise from keeping the event loop open. Instead of this, I chose to just unref the recv promise as needed to control the event loop. - The last bug causing the hang (which was a doozy to debug) ended up being an unfortunate interaction between how we implement our messageport "receive loop" and a pattern found in `npm:piscina` (which angular uses). The gist of it is that piscina uses an atomic wait loop along with `receiveMessageOnPort` in its worker threads, and as the worker is getting started, the following incredibly convoluted series of events occurs: 1. Parent sends a MessagePort `p` to worker 2. Parent sends a message `m` to the port `p` 3. Parent notifies the worker with `Atomics.notify` that a new message is available 4. Worker receives message, adds "message" listener to port `p` 5. Adding the listener triggers `MessagePort.start()` on `p` 6. Receive loop in MessagePort.start receives the message `m`, but then hits an await point and yields (before dispatching the "message" event) 7. Worker continues execution, starts the atomic wait loop, and immediately receives the existing notification from the parent that a message is available 8. Worker attempts to receive the new message `m` with `receiveMessageOnPort`, but this returns `undefined` because the receive loop already took the message in 6 9. Atomic wait loop continues to next iteration, waiting for the next message with `Atomic.wait` 10. `Atomic.wait` blocks the worker thread, which prevents the receive loop from continuing and dispatching the "message" event for the received message 11. The parent waits for the worker to respond to the first message, and waits 12. The thread can't make any more progress, and the whole process hangs The fix I've chosen here (which I don't particularly love, but it works) is to just delay the `MessagePort.start` call until the end of the event loop turn, so that the atomic wait loop receives the message first. This prevents the hang. --- Those were the main issues causing the hang. There ended up being a few other small bugs as well, namely `exit` being emitted multiple times, and not patching up the message port when it's received by `receiveMessageOnPort`. |
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Deno
Deno
(/ˈdiːnoʊ/, pronounced
dee-no) is a JavaScript, TypeScript, and WebAssembly runtime with secure
defaults and a great developer experience. It's built on V8,
Rust, and Tokio.
Learn more about the Deno runtime in the documentation.
Installation
Install the Deno runtime on your system using one of the commands below. Note that there are a number of ways to install Deno - a comprehensive list of installation options can be found here.
Shell (Mac, Linux):
curl -fsSL https://deno.land/install.sh | sh
PowerShell (Windows):
irm https://deno.land/install.ps1 | iex
Homebrew (Mac):
brew install deno
Chocolatey (Windows):
choco install deno
Build and install from source
Complete instructions for building Deno from source can be found in the manual here.
Your first Deno program
Deno can be used for many different applications, but is most commonly used to
build web servers. Create a file called server.ts and include the following
TypeScript code:
Deno.serve((_req: Request) => {
return new Response("Hello, world!");
});
Run your server with the following command:
deno run --allow-net server.ts
This should start a local web server on http://localhost:8000.
Learn more about writing and running Deno programs in the docs.
Additional resources
- Deno Docs: official guides and reference docs for the Deno runtime, Deno Deploy, and beyond.
- Deno Standard Library: officially supported common utilities for Deno programs.
- deno.land/x: registry for third-party Deno modules.
- Developer Blog: Product updates, tutorials, and more from the Deno team.
Contributing
We appreciate your help! To contribute, please read our contributing instructions.