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bors bcb05a0ab2 Auto merge of #55043 - oliver-giersch:unchecked_thread_spawning, r=alexcrichton Unchecked thread spawning # Summary Add an unsafe interface for spawning lifetime-unrestricted threads for library authors to build less-contrived, less-hacky safe abstractions on. # Motivation So a few years back scoped threads were entirely removed from the Rust stdlib, the reason being that it was possible to leak the scoped thread's join guards without resorting to unsafe code, which meant the concept was not completely safe, either. Only a maximally-restrictive safe API for thread spawning was kept in the stdlib, that requires `'static` lifetime bounds on both the thread closure and its return type. A number of 3rd party libraries sprung up to offer their implementations for safe scoped threads implementations. These work by essentially hiding the join guards from the user, thus forcing them to join at the end of an (internal) function scope. However, since these libraries have to use the maximally restrictive thread spawning API, they have to resort to some very contrived manipulations and subversions of Rust's type system to basically achieve what this commit does with some minimal restructuring of the current code and exposing a new unsafe function signature for spawning threads without lifetime restrictions. Obviously this is unsafe, but its main use would be to allow library authors to write safe abstractions with and around it. To further illustrate my point, here's a quick summary of the hoops that, for instance `crossbeam`, has to jump through to spawn a lifetime unrestricted thread, all of which would not be necessary if an unsafe API existed as part of the stdlib: 1. Allocate an `Arc<Option<T>>` on the heap where the result with type `T: 'a` will go (in practice requires `Mutex` or `UnsafeCell` as well). 2. Wrap the desired thread closure with lifetime bound `'a` into another closure (also `..: 'a`) that returns `()`, executes the inner closure and writes its result into the pre-allocated `Option<T>`. 3. Box the wrapping closure, cast it to a trait object (`FnBox`) and (unsafely) transmute its lifetime bound from `'a` to `'static`. So while this new `spawn_unchecked` function is certainly not very relevant for general use, since scoped threads are so common I think it makes sense to expose an interface for libraries implementing these to build on. The changes implemented are also very minimal: The current `spawn` function (which internally contains unsafe code) is moved into an unsafe `spawn_unchecked` function, which the safe function then wraps around. # Issues - ~~so far, no documentation for the new function (yet)~~ - the name of the function might be controversial, as `*_unchecked` more commonly indicates that some sort of runtime check is omitted (`unrestricted` may be more fitting) - if accepted, it might make sense to add a freestanding `thread::spawn_unchecked` function similar to the current `thread::spawn` for convenience.		2018-10-28 21:34:12 +00:00
src	Auto merge of #55043 - oliver-giersch:unchecked_thread_spawning, r=alexcrichton	2018-10-28 21:34:12 +00:00
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RELEASES.md	Rollup merge of #55325 - rust-lang:steveklabnik-patch-1, r=frewsxcv	2018-10-26 23:06:38 +08:00
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README.md

The Rust Programming Language

This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.

Quick Start

Read "Installation" from The Book.

Building from Source

Building on *nix

Make sure you have installed the dependencies:
- g++ 4.7 or later or clang++ 3.x or later
- python 2.7 (but not 3.x)
- GNU make 3.81 or later
- cmake 3.4.3 or later
- curl
- git

Clone the source with git:

$ git clone https://github.com/rust-lang/rust.git
$ cd rust

Build and install:
```
$ git submodule update --init --recursive --progress
$ ./x.py build && sudo ./x.py install
```
Note: Install locations can be adjusted by copying the config file from ./config.toml.example to ./config.toml, and adjusting the prefix option under [install]. Various other options, such as enabling debug information, are also supported, and are documented in the config file.

When complete, sudo ./x.py install will place several programs into /usr/local/bin: rustc, the Rust compiler, and rustdoc, the API-documentation tool. This install does not include Cargo, Rust's package manager, which you may also want to build.

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.bat or mingw64_shell.bat from 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 run msys2_shell.cmd -mingw32 or msys2_shell.cmd -mingw64 from 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' and 'cmake'
# 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-python2 \
            mingw-w64-x86_64-cmake \
            mingw-w64-x86_64-gcc

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 2013 (or later) so rustc can use its linker. Make sure to check the “C++ tools” option.

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 the build system doesn't understand then 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 14.0\VC\bin\amd64\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-gnu
- x86_64-pc-windows-gnu
The MSVC ABI
- i686-pc-windows-msvc
- x86_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 Building 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, Server 2008 R2)	✓	✓
Linux (2.6.18 or later)	✓	✓
OSX (10.7 Lion or later)	✓	✓

You may find that other platforms work, but these are our officially supported build environments that are most likely to work.

Rust currently needs between 600MiB and 1.5GiB of RAM to build, depending on platform. If it hits swap, it will take a very long time to build.

There is more advice about hacking on Rust in CONTRIBUTING.md.

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

To contribute to Rust, please see CONTRIBUTING.

Rust has an IRC culture and most real-time collaboration happens in a variety of channels on Mozilla's IRC network, irc.mozilla.org. The most popular channel is #rust, a venue for general discussion about Rust. And a good place to ask for help would be #rust-beginners.

The rustc guide might be a good place to start if you want to find out how various parts of the compiler work.

Also, you may find the rustdocs for the compiler itself useful.

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.

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