bc74dd711f
Avoid SeqCst or static mut in mach_timebase_info and QueryPerformanceFrequency caches This patch went through a couple iterations but the end result is replacing a pattern where an `AtomicUsize` (updated with many SeqCst ops) guards a `static mut` with a single `AtomicU64` that is known to use 0 as a value indicating that it is not initialized. The code in both places exists to cache values used in the conversion of Instants to Durations on macOS, iOS, and Windows. I have no numbers to prove that this improves performance (It seems a little futile to benchmark something like this), but it's much simpler, safer, and in practice we'd expect it to be faster everywhere where Relaxed operations on AtomicU64 are cheaper than SeqCst operations on AtomicUsize, which is a lot of places. Anyway, it also removes a bunch of unsafe code and greatly simplifies the logic, so IMO that alone would be worth it unless it was a regression. If you want to take a look at the assembly output though, see https://godbolt.org/z/rbr6vn for x86_64, https://godbolt.org/z/cqcbqv for aarch64 (Note that this just the output of the mac side, but i'd expect the windows part to be the same and don't feel like doing another godbolt for it). There are several versions of this function in the godbolt: - `info_new`: version in the current patch - `info_less_new`: version in initial PR - `info_original`: version currently in the tree - `info_orig_but_better_orderings`: a version that just tries to change the original code's orderings from SeqCst to the (probably) minimal orderings required for soundness/correctness. The biggest concern I have here is if we can use AtomicU64, or if there are targets that dont have it that this code supports. AFAICT: no. (If that changes in the future, it's easy enough to do something different for them) r? `@Amanieu` because he caught a couple issues last time I tried to do a patch reducing orderings 😅 --- <details> <summary>I rewrote this whole message so the original is inside here</summary> I happened to notice the code we use for caching the result of mach_timebase_info uses SeqCst exclusively. However, thinking a little more, it's actually pretty easy to avoid the static mut by packing the timebase info into an AtomicU64. This entirely avoids needing to do the compare_exchange. The AtomicU64 can be read/written using Relaxed ops, which on current macos/ios platforms (x86_64/aarch64) have no overhead compared to direct loads/stores. This simplifies the code and makes it a lot safer too. I have no numbers to prove that this improves performance (It seems a little futile to benchmark something like this), although it should do that on both targets it applies to. That said, it also removes a bunch of unsafe code and simplifies the logic (arguably at least — there are only two states now, initialized or not), so I think it's a net win even without concrete numbers. If you want to take a look at the assembly output though, see below. It has the new version, the original, and a version of the original with lower Orderings (which is still worse than the version in this PR) - godbolt.org/z/obfqf9 x86_64-apple-darwin - godbolt.org/z/Wz5cWc aarch64-unknown-linux-gnu (godbolt can't do aarch64-apple-ios but that doesn't matter here) A different (and more efficient) option than this would be to just use the AtomicU64 and use the knowledge that after initialization the denominator should be nonzero... That felt like it's relying on too many things I'm not confident in, so I didn't want to do that. </details> |
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| .github | ||
| compiler | ||
| library | ||
| src | ||
| .gitattributes | ||
| .gitignore | ||
| .gitmodules | ||
| .mailmap | ||
| Cargo.lock | ||
| Cargo.toml | ||
| CODE_OF_CONDUCT.md | ||
| config.toml.example | ||
| configure | ||
| CONTRIBUTING.md | ||
| COPYRIGHT | ||
| LICENSE-APACHE | ||
| LICENSE-MIT | ||
| README.md | ||
| RELEASES.md | ||
| rustfmt.toml | ||
| triagebot.toml | ||
| x.py | ||
This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.
Note: this README is for users rather than contributors. If you wish to contribute to the compiler, you should read the Getting Started of the rustc-dev-guide instead of this section.
Quick Start
Read "Installation" from The Book.
Installing from Source
The Rust build system uses a Python script called x.py to build the compiler,
which manages the bootstrapping process. More information about it can be found
by running ./x.py --help or reading the rustc dev guide.
Building on a Unix-like system
-
Make sure you have installed the dependencies:
g++5.1 or later orclang++3.5 or laterpython3 or 2.7- GNU
make3.81 or later cmake3.4.3 or laterninjacurlgitsslwhich comes inlibssl-devoropenssl-develpkg-configif you are compiling on Linux and targeting Linux
-
Clone the source with
git:git clone https://github.com/rust-lang/rust.git cd rust
-
Configure the build settings:
The Rust build system uses a file named
config.tomlin the root of the source tree to determine various configuration settings for the build. Copy the defaultconfig.toml.exampletoconfig.tomlto get started.cp config.toml.example config.tomlIf you plan to use
x.py installto create an installation, it is recommended that you set theprefixvalue in the[install]section to a directory.Create install directory if you are not installing in default directory
-
Build and install:
./x.py build && ./x.py installWhen complete,
./x.py installwill place several programs into$PREFIX/bin:rustc, the Rust compiler, andrustdoc, the API-documentation tool. This install does not include Cargo, Rust's package manager. To build and install Cargo, you may run./x.py install cargoor set thebuild.extendedkey inconfig.tomltotrueto build and install all tools.
Building on Windows
There are two prominent ABIs in use on Windows: the native (MSVC) ABI used by Visual Studio, and the GNU ABI used by the GCC toolchain. Which version of Rust you need depends largely on what C/C++ libraries you want to interoperate with: for interop with software produced by Visual Studio use the MSVC build of Rust; for interop with GNU software built using the MinGW/MSYS2 toolchain use the GNU build.
MinGW
MSYS2 can be used to easily build Rust on Windows:
-
Grab the latest MSYS2 installer and go through the installer.
-
Run
mingw32_shell.batormingw64_shell.batfrom wherever you installed MSYS2 (i.e.C:\msys64), depending on whether you want 32-bit or 64-bit Rust. (As of the latest version of MSYS2 you have to runmsys2_shell.cmd -mingw32ormsys2_shell.cmd -mingw64from the command line instead) -
From this terminal, install the required tools:
# Update package mirrors (may be needed if you have a fresh install of MSYS2) pacman -Sy pacman-mirrors # Install build tools needed for Rust. If you're building a 32-bit compiler, # then replace "x86_64" below with "i686". If you've already got git, python, # or CMake installed and in PATH you can remove them from this list. Note # that it is important that you do **not** use the 'python2', 'cmake' and 'ninja' # packages from the 'msys2' subsystem. The build has historically been known # to fail with these packages. pacman -S git \ make \ diffutils \ tar \ mingw-w64-x86_64-python \ mingw-w64-x86_64-cmake \ mingw-w64-x86_64-gcc \ mingw-w64-x86_64-ninja -
Navigate to Rust's source code (or clone it), then build it:
./x.py build && ./x.py install
MSVC
MSVC builds of Rust additionally require an installation of Visual Studio 2017
(or later) so rustc can use its linker. The simplest way is to get the
Visual Studio, check the “C++ build tools” and “Windows 10 SDK” workload.
(If you're installing cmake yourself, be careful that “C++ CMake tools for Windows” doesn't get included under “Individual components”.)
With these dependencies installed, you can build the compiler in a cmd.exe
shell with:
python x.py build
Currently, building Rust only works with some known versions of Visual Studio. If you have a more recent version installed and the build system doesn't understand, you may need to force rustbuild to use an older version. This can be done by manually calling the appropriate vcvars file before running the bootstrap.
CALL "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvars64.bat"
python x.py build
Specifying an ABI
Each specific ABI can also be used from either environment (for example, using the GNU ABI in PowerShell) by using an explicit build triple. The available Windows build triples are:
- GNU ABI (using GCC)
i686-pc-windows-gnux86_64-pc-windows-gnu
- The MSVC ABI
i686-pc-windows-msvcx86_64-pc-windows-msvc
The build triple can be specified by either specifying --build=<triple> when
invoking x.py commands, or by copying the config.toml file (as described
in Installing From Source), and modifying the
build option under the [build] section.
Configure and Make
While it's not the recommended build system, this project also provides a
configure script and makefile (the latter of which just invokes x.py).
./configure
make && sudo make install
When using the configure script, the generated config.mk file may override the
config.toml file. To go back to the config.toml file, delete the generated
config.mk file.
Building Documentation
If you’d like to build the documentation, it’s almost the same:
./x.py doc
The generated documentation will appear under doc in the build directory for
the ABI used. I.e., if the ABI was x86_64-pc-windows-msvc, the directory will be
build\x86_64-pc-windows-msvc\doc.
Notes
Since the Rust compiler is written in Rust, it must be built by a precompiled "snapshot" version of itself (made in an earlier stage of development). As such, source builds require a connection to the Internet, to fetch snapshots, and an OS that can execute the available snapshot binaries.
Snapshot binaries are currently built and tested on several platforms:
| Platform / Architecture | x86 | x86_64 |
|---|---|---|
| Windows (7, 8, 10, ...) | ✓ | ✓ |
| Linux (kernel 2.6.32, glibc 2.11 or later) | ✓ | ✓ |
| macOS (10.7 Lion or later) | (*) | ✓ |
(*): Apple dropped support for running 32-bit binaries starting from macOS 10.15 and iOS 11. Due to this decision from Apple, the targets are no longer useful to our users. Please read our blog post for more info.
You may find that other platforms work, but these are our officially supported build environments that are most likely to work.
Getting Help
The Rust community congregates in a few places:
- Stack Overflow - Direct questions about using the language.
- users.rust-lang.org - General discussion and broader questions.
- /r/rust - News and general discussion.
Contributing
If you are interested in contributing to the Rust project, please take a look at the Getting Started guide in the rustc-dev-guide.
License
Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.
See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.
Trademark
The Rust programming language is an open source, community project governed by a core team. It is also sponsored by the Mozilla Foundation (“Mozilla”), which owns and protects the Rust and Cargo trademarks and logos (the “Rust Trademarks”).
If you want to use these names or brands, please read the media guide.
Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.