a2e98e9f0e
Fix a segfault in CVDisplayLink
We see 1-2 crashes a day on macOS on the `CVDisplayLink` thread.
```
Segmentation fault: 11 on thread 9325960 (CVDisplayLink)
CoreVideo CVHWTime::reset()
CoreVideo CVXTime::reset()
CoreVideo CVDisplayLink::runIOThread()
libsystem_pthread.dylib _pthread_start
libsystem_pthread.dylib thread_start
```
With the help of the Zed AI, I dove into the crash report, which looks
like this:
```
Crashed Thread: 49 CVDisplayLink
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x00000000000001f6
Exception Codes: 0x0000000000000001, 0x00000000000001f6
Thread 49 Crashed:: CVDisplayLink
0 CoreVideo 0x18c1ed994 CVHWTime::reset() + 64
1 CoreVideo 0x18c1ee474 CVXTime::reset() + 52
2 CoreVideo 0x18c1ee198 CVDisplayLink::runIOThread() + 176
3 libsystem_pthread.dylib 0x18285ac0c _pthread_start + 136
4 libsystem_pthread.dylib 0x182855b80 thread_start + 8
Thread 49 crashed with ARM Thread State (64-bit):
x0: 0x0000000000000000 x1: 0x000000018c206e08 x2: 0x0000002c00001513 x3: 0x0001d4630002a433
x4: 0x00000e2100000000 x5: 0x0001d46300000000 x6: 0x000000000000002c x7: 0x0000000000000000
x8: 0x000000000000002e x9: 0x000000004d555458 x10: 0x0000000000000000 x11: 0x0000000000000000
x12: 0x0000000000000000 x13: 0x0000000000000000 x14: 0x0000000000000000 x15: 0x0000000000000000
x16: 0x0000000182856a9c x17: 0x00000001f19bc540 x18: 0x0000000000000000 x19: 0x0000600003c56ed8
x20: 0x000000000002a433 x21: 0x0000000000000000 x22: 0x0000000000000000 x23: 0x0000000000000000
x24: 0x0000000000000000 x25: 0x0000000000000000 x26: 0x0000000000000000 x27: 0x0000000000000000
x28: 0x0000000000000000 fp: 0x000000016b02ade0 lr: 0x000000018c1ed984
sp: 0x000000016b02adc0 pc: 0x000000018c1ed994 cpsr: 0x80001000
far: 0x00000000000001f6 esr: 0x92000006 (Data Abort) byte read Translation fault
Binary Images:
0x1828c9000 - 0x182e07fff com.apple.CoreFoundation (6.9) <df489a59-b4f6-32b8-9bb4-9b832960aa52> /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation
```
Using lldb to disassemble `CVHWTime::reset()` (and the AI to interpret
it), the crash is caused by dereferencing the pointer at the start of
the CVHWTime struct + 0x1c8. In this case the pointer has (the clearly
nonsense) value 0x2e (and 0x2e + 0x1c8 = 0x1f6, the failing address).
As to how this could happen...
Looking at the implementation of `CVDisplayLinkRelease`, it calls
straight into `CFRelease` on the main thread; and so it is not safe to
call `CVDisplayLinkRelease` concurrently with other threads that access
the CVDisplayLink. While we already stopped the display link, it turns
out that `CVDisplayLinkStop` just sets a flag on the struct to instruct
the io-thread to exit "soon", and returns immediately. That means we
don't know when the other thread will actually exit, and so we can't
safely call `CVDisplayLinkRelease`.
So, for now, we just leak these objects. They should be created
relatively infrequently (when the app is foregrounded/backgrounded), so
I don't think this is a huge problem.
Release Notes:
- Fix a rare crash on macOS when putting the app in the background.
|
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|---|---|---|
| .. | ||
| docs | ||
| examples | ||
| resources/windows | ||
| src | ||
| tests | ||
| build.rs | ||
| Cargo.toml | ||
| LICENSE-APACHE | ||
| README.md | ||
Welcome to GPUI!
GPUI is a hybrid immediate and retained mode, GPU accelerated, UI framework for Rust, designed to support a wide variety of applications.
Getting Started
GPUI is still in active development as we work on the Zed code editor and isn't yet on crates.io. You'll also need to use the latest version of stable Rust and be on macOS or Linux. Add the following to your Cargo.toml:
gpui = { git = "https://github.com/zed-industries/zed" }
Everything in GPUI starts with an Application. You can create one with Application::new(), and kick off your application by passing a callback to Application::run(). Inside this callback, you can create a new window with App::open_window(), and register your first root view. See gpui.rs for a complete example.
Dependencies
GPUI has various system dependencies that it needs in order to work.
macOS
On macOS, GPUI uses Metal for rendering. In order to use Metal, you need to do the following:
- Install Xcode from the macOS App Store, or from the Apple Developer website. Note this requires a developer account.
Ensure you launch XCode after installing, and install the macOS components, which is the default option.
-
Install Xcode command line tools
xcode-select --install -
Ensure that the Xcode command line tools are using your newly installed copy of Xcode:
sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
The Big Picture
GPUI offers three different registers depending on your needs:
-
State management and communication with
Entity's. Whenever you need to store application state that communicates between different parts of your application, you'll want to use GPUI's entities. Entities are owned by GPUI and are only accessible through an owned smart pointer similar to anRc. See theapp::contextmodule for more information. -
High level, declarative UI with views. All UI in GPUI starts with a view. A view is simply an
Entitythat can be rendered, by implementing theRendertrait. At the start of each frame, GPUI will call this render method on the root view of a given window. Views build a tree ofelements, lay them out and style them with a tailwind-style API, and then give them to GPUI to turn into pixels. See thedivelement for an all purpose swiss-army knife of rendering. -
Low level, imperative UI with Elements. Elements are the building blocks of UI in GPUI, and they provide a nice wrapper around an imperative API that provides as much flexibility and control as you need. Elements have total control over how they and their child elements are rendered and can be used for making efficient views into large lists, implement custom layouting for a code editor, and anything else you can think of. See the
elementmodule for more information.
Each of these registers has one or more corresponding contexts that can be accessed from all GPUI services. This context is your main interface to GPUI, and is used extensively throughout the framework.
Other Resources
In addition to the systems above, GPUI provides a range of smaller services that are useful for building complex applications:
-
Actions are user-defined structs that are used for converting keystrokes into logical operations in your UI. Use this for implementing keyboard shortcuts, such as cmd-q. See the
actionmodule for more information. -
Platform services, such as
quit the apporopen a URLare available as methods on theapp::App. -
An async executor that is integrated with the platform's event loop. See the
executormodule for more information., -
The
[gpui::test]macro provides a convenient way to write tests for your GPUI applications. Tests also have their own kind of context, aTestAppContextwhich provides ways of simulating common platform input. Seeapp::test_contextandtestmodules for more details.
Currently, the best way to learn about these APIs is to read the Zed source code, ask us about it at a fireside hack, or drop a question in the Zed Discord. We're working on improving the documentation, creating more examples, and will be publishing more guides to GPUI on our blog.