7e02af8798
This adds transparent compression for non-active/non-viewport scrollback pages, reducing physical memory for compressed pages by anywhere from 70% to 90%. Compression is obviously highly dependent on the shape of the data, but these are the numbers I got for normal scrollback. Due to compression being available, I bumped the default scrollback limit from 10MB to 50MB. On average, a full scrollback still uses less memory than the prior limit due to the compression ratios. ## Demo Here is a demo video showing me filling my scrollback and using the inspector so you can see the live compression/decompression activity and results: https://github.com/user-attachments/assets/7b9d0383-42f7-47bf-8b3f-853e3f89549c ## Resident vs. Virtual Memory This PR works by lowering _resident/physicalmemory, but doesn't touch _virtual_ memory. Practically what this means is that users need to make sure they're looking at resident memory to see the change. We use OS primitives like `MADV_DONTNEED` on Linux or `MADV_FREE_REUSABLE` on Darwin to discard our physical memory, but retain our virtual memory allocations. This is awesome because it means our decompression is infallible: the OS has already given us the memory, but it just remaps it at that point. This is baked into the core implementation, so compression only works on systems that support an OS primitive to retain virtual mappings while discarding physical. Today, that is macOS and 64-bit Linux. Other operating systems have support we just haven't coded it up yet. ## Implementation A major refactor had to happen to PageList to represent nodes as either resident or compressed. Pins typically accessed node content directly so we had to add a bunch of helpers to read metadata without decompression (but some access requires it). Compression is relatively slow and its important we don't impact IO performance. So we support incremental compression passes and they only run when the terminal is idle (250ms timer on the render thread that resets on any activity). Benchmarks show zero regression in IO throughput on this change. In order to maintain the no-libc invariant for libghostty-vt, we use a hand-written (an AI assisted optimization) LZ4 compression implementation. The performance and compression ratio is _okay_. Its a good first step for this. I think in the future I want to look at other implementations we can bring in based on build configuration. ## Performance Measured with a saved 7.3 MB corpus made by repeating `gh --help` output into a 120x80 terminal with a 50 MB scrollback limit on my machine: | compression measurement | result | |-------------------------|--------| | pages compressed | 121 | | raw page backing | 49.56 MB | | encoded storage | 3.03 MB (6.11% of raw) | | estimated physical memory savings | 46.53 MB (93.89%) | | full compression | 30.3 ms total, 12.2 ms over the 18.1 ms no-op baseline (~101 µs/page) | | incremental drain | 29.7 ms total, 11.6 ms over baseline (~96 µs/page) | | compress and restore | 33.5 ms total, 3.2 ms over full compression (~26 µs/page to restore) | The workload above is especially repetitive, so its 6.11% encoded ratio is better than the 10% to 30% expected for text-heavy terminal history in general. Steady-state throughput is unchanged within noise (`terminal-stream` benchmarks and manual `cat` timings). ## libghostty-vt The same caller-driven compression controls are exposed to Zig and C. Note that compression _is not automatic_ for libghostty users. Callers must determine their own definition of "idle" and when to compress and call our incremental callback APIs to perform the compression. Decompression is automatic and as-needed (and will trigger recompression-required flags so callers are aware). ## LLM Notes This work was done in concert with Codex. I reviewed and rewrote/reshaped pretty much every change extensively, particularly PageList/Terminal. This PR message is written by hand, commit messages are LLM written but reviewed.
Ghostty
Fast, native, feature-rich terminal emulator pushing modern features.
A native GUI or embeddable library via libghostty.
About
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Download
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Documentation
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Contributing
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Developing
About
Ghostty is a terminal emulator that differentiates itself by being fast, feature-rich, and native. While there are many excellent terminal emulators available, they all force you to choose between speed, features, or native UIs. Ghostty provides all three.
libghostty is a cross-platform, zero-dependency C and Zig library
for building terminal emulators or utilizing terminal functionality
(such as style parsing). Anyone can use libghostty to build a terminal
emulator or embed a terminal into their own applications. See
Ghostling for a minimal complete project
example or the examples directory
for smaller examples of using libghostty in C and Zig.
For more details, see About Ghostty.
Download
See the download page on the Ghostty website.
Documentation
See the documentation on the Ghostty website.
Contributing and Developing
If you have any ideas, issues, etc. regarding Ghostty, or would like to contribute to Ghostty through pull requests, please check out our "Contributing to Ghostty" document. Those who would like to get involved with Ghostty's development as well should also read the "Developing Ghostty" document for more technical details.
Roadmap and Status
Ghostty is stable and in use by millions of people and machines daily.
The high-level ambitious plan for the project, in order:
| # | Step | Status |
|---|---|---|
| 1 | Standards-compliant terminal emulation | ✅ |
| 2 | Competitive performance | ✅ |
| 3 | Rich windowing features -- multi-window, tabbing, panes | ✅ |
| 4 | Native Platform Experiences | ✅ |
| 5 | Cross-platform libghostty for Embeddable Terminals |
✅ |
| 6 | Ghostty-only Terminal Control Sequences | ❌ |
Additional details for each step in the big roadmap below:
Standards-Compliant Terminal Emulation
Ghostty implements all of the regularly used control sequences and can run every mainstream terminal program without issue. For legacy sequences, we've done a comprehensive xterm audit comparing Ghostty's behavior to xterm and building a set of conformance test cases.
In addition to legacy sequences (what you'd call real "terminal" emulation), Ghostty also supports more modern sequences than almost any other terminal emulator. These features include things like the Kitty graphics protocol, Kitty image protocol, clipboard sequences, synchronized rendering, light/dark mode notifications, and many, many more.
We believe Ghostty is one of the most compliant and feature-rich terminal emulators available.
Terminal behavior is partially a de jure standard (i.e. ECMA-48) but mostly a de facto standard as defined by popular terminal emulators worldwide. Ghostty takes the approach that our behavior is defined by (1) standards, if available, (2) xterm, if the feature exists, (3) other popular terminals, in that order. This defines what the Ghostty project views as a "standard."
Competitive Performance
Ghostty is generally in the same performance category as the other highest performing terminal emulators.
"The same performance category" means that Ghostty is much faster than traditional or "slow" terminals and is within an unnoticeable margin of the well-known "fast" terminals. For example, Ghostty and Alacritty are usually within a few percentage points of each other on various benchmarks, but are both something like 100x faster than Terminal.app and iTerm. However, Ghostty is much more feature rich than Alacritty and has a much more native app experience.
This performance is achieved through high-level architectural decisions and low-level optimizations. At a high-level, Ghostty has a multi-threaded architecture with a dedicated read thread, write thread, and render thread per terminal. Our renderer uses OpenGL on Linux and Metal on macOS. Our read thread has a heavily optimized terminal parser that leverages CPU-specific SIMD instructions. Etc.
Rich Windowing Features
The Mac and Linux (build with GTK) apps support multi-window, tabbing, and splits with additional features such as tab renaming, coloring, etc. These features allow for a higher degree of organization and customization than single-window terminals.
Native Platform Experiences
Ghostty is a cross-platform terminal emulator but we don't aim for a least-common-denominator experience. There is a large, shared core written in Zig but we do a lot of platform-native things:
- The macOS app is a true SwiftUI-based application with all the things you would expect such as real windowing, menu bars, a settings GUI, etc.
- macOS uses a true Metal renderer with CoreText for font discovery.
- macOS supports AppleScript, Apple Shortcuts (AppIntents), etc.
- The Linux app is built with GTK.
- The Linux app integrates deeply with systemd if available for things like always-on, new windows in a single instance, cgroup isolation, etc.
Our goal with Ghostty is for users of whatever platform they run Ghostty on to think that Ghostty was built for their platform first and maybe even exclusively. We want Ghostty to feel like a native app on every platform, for the best definition of "native" on each platform.
Cross-platform libghostty for Embeddable Terminals
In addition to being a standalone terminal emulator, Ghostty is a
C-compatible library for embedding a fast, feature-rich terminal emulator
in any 3rd party project. This library is called libghostty.
Due to the scope of this project, we're breaking libghostty down into
separate libraries, starting with libghostty-vt. The goal of
this project is to focus on parsing terminal sequences and maintaining
terminal state. This is covered in more detail in this
blog post.
libghostty-vt is already available and usable today for Zig and C and
is compatible for macOS, Linux, Windows, and WebAssembly. The functionality
is extremely stable (since its been proven in Ghostty GUI for a long time),
but the API signatures are still in flux.
libghostty is already heavily in use. See examples
for small examples of using libghostty in C and Zig or the
Ghostling project for a
complete example. See awesome-libghostty
for a list of projects and resources related to libghostty.
We haven't tagged libghostty with a version yet and we're still working on a better docs experience, but our Doxygen website is a good resource for the C API.
Ghostty-only Terminal Control Sequences
We want and believe that terminal applications can and should be able to do so much more. We've worked hard to support a wide variety of modern sequences created by other terminal emulators towards this end, but we also want to fill the gaps by creating our own sequences.
We've been hesitant to do this up until now because we don't want to create more fragmentation in the terminal ecosystem by creating sequences that only work in Ghostty. But, we do want to balance that with the desire to push the terminal forward with stagnant standards and the slow pace of change in the terminal ecosystem.
We haven't done any of this yet.
Crash Reports
Ghostty has a built-in crash reporter that will generate and save crash
reports to disk. The crash reports are saved to the $XDG_STATE_HOME/ghostty/crash
directory. If $XDG_STATE_HOME is not set, the default is ~/.local/state.
Crash reports are not automatically sent anywhere off your machine.
Crash reports are only generated the next time Ghostty is started after a crash. If Ghostty crashes and you want to generate a crash report, you must restart Ghostty at least once. You should see a message in the log that a crash report was generated.
Note
Use the
ghostty +crash-reportCLI command to get a list of available crash reports. A future version of Ghostty will make the contents of the crash reports more easily viewable through the CLI and GUI.
Crash reports end in the .ghosttycrash extension. The crash reports are in
Sentry envelope format. You can
upload these to your own Sentry account to view their contents, but the format
is also publicly documented so any other available tools can also be used.
The ghostty +crash-report CLI command can be used to list any crash reports.
A future version of Ghostty will show you the contents of the crash report
directly in the terminal.
To send the crash report to the Ghostty project, you can use the following CLI command using the Sentry CLI:
SENTRY_DSN=https://e914ee84fd895c4fe324afa3e53dac76@o4507352570920960.ingest.us.sentry.io/4507850923638784 sentry-cli send-envelope --raw <path to ghostty crash>
Warning
The crash report can contain sensitive information. The report doesn't purposely contain sensitive information, but it does contain the full stack memory of each thread at the time of the crash. This information is used to rebuild the stack trace but can also contain sensitive data depending on when the crash occurred.