Kunall Banerjee
9bde578ef5
Some context behind this change: I’ve been meaning to look into this because I kept running into this crash when working on [other](https://github.com/zed-industries/zed/issues/61040) fixes. Everything worked fine in dev builds, right up until you tried to create a new Agent Thread using an ACP adapter. The crash reports in this instance were throwing me off: I was seeing different things each time. So, I had Fable look into this. It did so by binary-searching the minimum thread stack on which a probe replicating Zed’s exact handler chain can dispatch one message. Full methodology, probe source, and raw numbers can be found in [this gist](https://gist.github.com/yeskunall/2ac2b00f51389d9388d607974f6f8a04). The results of the probe are as follows: | SDK | Minimum stack (dev profile) | vs. 512 KiB GCD budget | |---|---|---| | 1.3.0 | 409,600–413,696 B | fit, ~100 KiB headroom | | 2.0.0 | 507,904–512,000 B | entire budget before runtime overhead | The oversized frames are monomorphized into `agent_servers`, not the SDK crate -- a `[profile.dev.package]` opt-level override on `agent-client-protocol` does **not** fix this (see gist), and optimized builds collapse the frames entirely, which is why only dev builds crashed. It found that the real signature is `fault_address == stack_pointer` on a `com.apple.root.default-qos` thread inside the ACP dispatch specialization, which I then had it verify across six local `.ips` reports. It seems in #61570, we pushed the dispatch chain past the GCD budget, explained further below: `AcpConnection::stdio` polled the ACP client connection future via `background_spawn`, which on macOS executes runnables on [GCD’s](https://developer.apple.com/documentation/DISPATCH) global-queue workers. Those threads have kernel-fixed, unconfigurable [512 KiB stacks](https://github.com/apple-oss-distributions/libpthread/blob/42d026df5b07825070f60134b980a1ec2552dfee/kern/kern_internal.h#L154). In unoptimized builds, the SDK’s chained-handler dispatch needs **~0.5 MiB of stack per inbound message** (again, see linked gist), so the first message overflows the guard page and takes the process down. Therefore, this 512 KiB constraint is **macOS-only**. Linux doesn’t use GCD -- GPUI [spawns its own `std::thread` workers](https://github.com/zed-industries/zed/blob/82878540b5410b288a2c92cb9ee5675533e4d807/crates/gpui_linux/src/linux/dispatcher.rs#L39) ([2 MiB Rust default](https://github.com/rust-lang/rust/blob/59807616e1fa2540724bfbac14d7976d7e4a3860/library/std/src/sys/thread/unix.rs#L26)). Windows uses [the OS thread pool](https://github.com/zed-industries/zed/blob/82878540b5410b288a2c92cb9ee5675533e4d807/crates/gpui_windows/src/dispatcher.rs#L68), which [inherits the executable’s stack reserve](https://github.com/MicrosoftDocs/sdk-api/blob/4502fff176b3b56beddb6a63c9f980377b11ba9b/sdk-api-src/content/threadpoolapiset/nf-threadpoolapiset-setthreadpoolstackinformation.md?plain=1#L58) -- [1 MB linker default](https://github.com/MicrosoftDocs/win32/blob/2eb6588c6703d31599285bbb06563c3d41b57590/desktop-src/ProcThread/thread-stack-size.md?plain=1#L17), but Zed already bumps it to 8 MiB in [crates/zed/build.rs:88](https://github.com/zed-industries/zed/blob/82878540b5410b288a2c92cb9ee5675533e4d807/crates/zed/build.rs#L88) (see [TODO comment](https://github.com/zed-industries/zed/blob/82878540b5410b288a2c92cb9ee5675533e4d807/crates/zed/build.rs#L87)). --- Release Notes: - N/A
Zed
Welcome to Zed, a high-performance, multiplayer code editor from the creators of Atom and Tree-sitter.
Installation
On macOS, Linux, and Windows you can download Zed directly or install Zed via your local package manager (macOS/Linux/Windows).
Other platforms are not yet available:
- Web (tracking discussion)
Developing Zed
Contributing
See CONTRIBUTING.md for ways you can contribute to Zed.
Also... we're hiring! Check out our jobs page for open roles.
Licensing
Zed source code is licensed primarily under GPL-3.0-or-later, with Apache-2.0 components where marked.
License information for third party dependencies must be correctly provided for CI to pass.
We use cargo-about to automatically comply with open source licenses. If CI is failing, check the following:
- Is it showing a
no license specifiederror for a crate you've created? If so, addpublish = falseunder[package]in your crate's Cargo.toml. - Is the error
failed to satisfy license requirementsfor a dependency? If so, first determine what license the project has and whether this system is sufficient to comply with this license's requirements. If you're unsure, ask a lawyer. Once you've verified that this system is acceptable add the license's SPDX identifier to theacceptedarray inscript/licenses/zed-licenses.toml. - Is
cargo-aboutunable to find the license for a dependency? If so, add a clarification field at the end ofscript/licenses/zed-licenses.toml, as specified in the cargo-about book.
Sponsorship
Zed is developed by Zed Industries, Inc., a for-profit company.
If you’d like to financially support the project, you can do so via GitHub Sponsors. Sponsorships go directly to Zed Industries and are used as general company revenue. There are no perks or entitlements associated with sponsorship.