aster.cloud aster.cloud
  • /
  • Platforms
    • Public Cloud
    • On-Premise
    • Hybrid Cloud
    • Data
  • Architecture
    • Design
    • Solutions
    • Enterprise
  • Engineering
    • Automation
    • Software Engineering
    • Project Management
    • DevOps
  • Programming
  • Tools
  • About
aster.cloud aster.cloud
  • /
  • Platforms
    • Public Cloud
    • On-Premise
    • Hybrid Cloud
    • Data
  • Architecture
    • Design
    • Solutions
    • Enterprise
  • Engineering
    • Automation
    • Software Engineering
    • Project Management
    • DevOps
  • Programming
  • Tools
  • About
  • Programming
  • Software

Swift System Is Now Open Source

  • relay
  • September 25, 2020
  • 4 minute read

In June, Apple introduced Swift System, a new library for Apple platforms that provides idiomatic interfaces to system calls and low-level currency types. I’m excited to announce that we’re open-sourcing System and adding Linux support! Our vision is for System to eventually act as the single home for low-level system interfaces for all supported Swift platforms.

 

Goodbye Imported C Interfaces

Most operating systems today support some flavor of system interfaces written in C that have existed for decades. While it is possible to use these APIs directly from Swift, these weakly-typed system interfaces imported from C can be error-prone and unwieldy. For example, the open system call (available on UNIX-like operating systems such as Linux and Apple platforms) imports as a pair of global functions:

<span class="kd">func</span> <span class="nf">open</span><span class="p">(</span><span class="n">_</span> <span class="nv">path</span><span class="p">:</span> <span class="kt">UnsafePointer</span><span class="o"><</span><span class="kt">CChar</span><span class="o">></span><span class="p">,</span> <span class="n">_</span> <span class="nv">oflag</span><span class="p">:</span> <span class="kt">Int32</span><span class="p">)</span> <span class="o">-></span> <span class="kt">Int32</span>
<span class="kd">func</span> <span class="nf">open</span><span class="p">(</span><span class="n">_</span> <span class="nv">path</span><span class="p">:</span> <span class="kt">UnsafePointer</span><span class="o"><</span><span class="kt">CChar</span><span class="o">></span><span class="p">,</span> <span class="n">_</span> <span class="nv">oflag</span><span class="p">:</span> <span class="kt">Int32</span><span class="p">,</span> <span class="n">_</span> <span class="nv">mode</span><span class="p">:</span> <span class="n">mode_t</span><span class="p">)</span> <span class="o">-></span> <span class="kt">Int32</span>

These weakly-typed functions suffer from several shortcomings and fail to utilize the expressivity and type safety of Swift:

  • File descriptors, alongside options, commands, errno, and other values, are imported as ordinary Int32s.
  • The oflag argument is actually a logical OR-ing of exactly one file access mode and any number of flags, but this is not captured in the type of oflag.
  • Callers of open have to remember to check for a negative return value indicating an error, and if so check the value of the global variable errno to know what error occurred. Additionally, some system calls may be canceled if a signal occurred, requiring callers to remember to write a loop around such calls checking for EINTR errors.
  • File paths are unmanaged pointers, and if they are derived from a managed object (e.g. Array<CChar>), then callers must ensure that array is always null-terminated.
Read More  Building Apps For Android Automotive OS

None of these semantic rules are captured in the API’s signature, preventing the programming language from guiding the user towards correct usage of the API.

 

Hello Idiomatic Swift Interfaces

The System module brings various language features to bear to improve expressivity and eliminate these opportunities for error. For example, System defines the open system call as a static function with defaulted arguments in the FileDescriptor namespace:

<span class="kd">extension</span> <span class="kt">FileDescriptor</span> <span class="p">{</span>
  <span class="c1">/// Opens or creates a file for reading or writing.</span>
  <span class="c1">///</span>
  <span class="c1">/// - Parameters:</span>
  <span class="c1">///  - path: The location of the file to open.</span>
  <span class="c1">///  - mode: The read and write access to use.</span>
  <span class="c1">///  - options: The behavior for opening the file.</span>
  <span class="c1">///  - permissions: The file permissions to use for created files.</span>
  <span class="c1">///  - retryOnInterrupt: Whether to retry the open operation</span>
  <span class="c1">///    if it throws `Errno.interrupted`.</span>
  <span class="c1">///    The default is `true`.</span>
  <span class="c1">///    Pass `false` to try only once and throw an error upon interruption.</span>
  <span class="c1">/// - Returns: A file descriptor for the open file</span>
  <span class="c1">///</span>
  <span class="c1">/// The corresponding C function is `open`.</span>
  <span class="kd">public</span> <span class="kd">static</span> <span class="kd">func</span> <span class="nf">open</span><span class="p">(</span>
    <span class="n">_</span> <span class="nv">path</span><span class="p">:</span> <span class="kt">FilePath</span><span class="p">,</span>
    <span class="n">_</span> <span class="nv">mode</span><span class="p">:</span> <span class="kt">FileDescriptor</span><span class="o">.</span><span class="kt">AccessMode</span><span class="p">,</span>
     <span class="nv">options</span><span class="p">:</span> <span class="kt">FileDescriptor</span><span class="o">.</span><span class="kt">OpenOptions</span> <span class="o">=</span> <span class="kt">FileDescriptor</span><span class="o">.</span><span class="kt">OpenOptions</span><span class="p">(),</span>
     <span class="nv">permissions</span><span class="p">:</span> <span class="kt">FilePermissions</span><span class="p">?</span> <span class="o">=</span> <span class="kc">nil</span><span class="p">,</span>
     <span class="nv">retryOnInterrupt</span><span class="p">:</span> <span class="kt">Bool</span> <span class="o">=</span> <span class="kc">true</span>
  <span class="p">)</span> <span class="k">throws</span> <span class="o">-></span> <span class="kt">FileDescriptor</span>
<span class="p">}</span>

When one compares this version of open to the original version from C, several significant differences stand out:

  • System pervasively uses raw representable structs and option sets. These strong types help catch mistakes at compile time and are trivial to convert to and from the weaker C types.
  • Errors are thrown using the standard language mechanism and cannot be missed. Further, all system calls interruptible by a signal take a defaulted-true retryOnInterrupt argument, causing them to retry on failure. When combined, these two changes dramatically simplify error and signal handling.
  • FilePath is a managed, null-terminated bag-of-bytes that conforms to ExpressibleByStringLiteral — far safer to work with than a UnsafePointer<CChar>.

The result is code that reads and behaves like idiomatic Swift. For example, this code creates a file path from a string literal and uses it to open and append to a log file:

<span class="k">let</span> <span class="nv">message</span><span class="p">:</span> <span class="kt">String</span> <span class="o">=</span> <span class="s">"Hello, world!"</span> <span class="o">+</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span>
<span class="k">let</span> <span class="nv">path</span><span class="p">:</span> <span class="kt">FilePath</span> <span class="o">=</span> <span class="s">"/tmp/log"</span>
<span class="k">let</span> <span class="nv">fd</span> <span class="o">=</span> <span class="k">try</span> <span class="kt">FileDescriptor</span><span class="o">.</span><span class="nf">open</span><span class="p">(</span>
  <span class="n">path</span><span class="p">,</span> <span class="o">.</span><span class="n">writeOnly</span><span class="p">,</span> <span class="nv">options</span><span class="p">:</span> <span class="p">[</span><span class="o">.</span><span class="n">append</span><span class="p">,</span> <span class="o">.</span><span class="n">create</span><span class="p">],</span> <span class="nv">permissions</span><span class="p">:</span> <span class="o">.</span><span class="n">ownerReadWrite</span><span class="p">)</span>
<span class="k">try</span> <span class="n">fd</span><span class="o">.</span><span class="n">closeAfter</span> <span class="p">{</span>
  <span class="n">_</span> <span class="o">=</span> <span class="k">try</span> <span class="n">fd</span><span class="o">.</span><span class="nf">writeAll</span><span class="p">(</span><span class="n">message</span><span class="o">.</span><span class="n">utf8</span><span class="p">)</span>
<span class="p">}</span>

 

Read More  Top 10 Countries With The Best Programmers In The World

A Multi-platform Library

System is a multi-platform library, not a cross-platform one. It provides a separate set of APIs and behaviors on every supported platform, closely reflecting the underlying OS interfaces. A single import will pull in the native platform interfaces specific for the targeted OS.

Our immediate goal is to simplify building cross-platform libraries and applications such as SwiftNIO and the Swift Package Manager. System does not eliminate the need for #if os() conditionals to implement cross-platform abstractions, but it does make it safer and more expressive to fill out the platform-specific parts.

 

What’s Next?

System is only in its infancy—it currently includes a small number of system calls, currency types, and convenience functionality. As part of the effort to increase the API coverage, we’ll be working to adopt System in the Swift Package Manager. This will include enhancements to FilePath and adding support for the recently announced Swift on Windows.

There’s a ton of exciting work left to do. System (especially the forthcoming Windows support!) is a fantastic opportunity to get involved in the Swift project and help it grow into a strong, vibrant, cross-platform ecosystem.

 

Get Involved

Your experience, feedback, and contributions are greatly encouraged!

  • Get started by trying out the System package on GitHub,
  • Discuss the library and get help in the Swift System forum,
  • Open an issue with problems you find or ideas you have for improvements,
  • And as always, pull requests are welcome!

 

Questions?

Please feel free to ask questions about this post in the associated thread on the Swift forums.

Read More  How I Recognize And Prevent Burnout In Open Source

 

Michael Ilseman is an engineer on the Swift Standard Library team at Apple.
relay

Related Topics
  • GitHub
  • Open Source
  • Swift
  • Swift System
  • SwiftNIO
You May Also Like
View Post
  • Computing
  • Software
  • Tools

Docker’s Bad Week

  • March 27, 2023
View Post
  • Software
  • Software Engineering
  • Tools

How To Use Bash

  • March 17, 2023
View Post
  • Software
  • Technology

Own Your Cloud With NextcloudPi On The Raspberry Pi

  • March 16, 2023
View Post
  • Software
  • Software Engineering

Python 3.12.0 Alpha 6 Released

  • March 15, 2023
mobile-laptop-developer-christina-wocintechchat-com-UTw3j_aoIKM-unsplash
View Post
  • Data
  • Software
  • Solutions

Build Customer Trust Through Secure Front End App Development & Cyber Security

  • March 14, 2023
View Post
  • Automation
  • Programming

Learn Expect By Writing And Automating A Simple Game

  • March 14, 2023
View Post
  • Software
  • Tech
  • Technology

A New Smartphone Operating System That Puts Privacy First

  • March 10, 2023
View Post
  • Software

Open Source Software Leader The Eclipse Foundation Previews Its Showcase At Embedded World 2023

  • March 8, 2023

Stay Connected!
LATEST
  • 1
    Kubernetes K8s.gcr.io Redirect: What You Need To Know As An Anthos Or GKE User
    • March 30, 2023
  • 2
    Oracle Helidon Taps Virtual Threads For ‘Pure Performance’
    • March 29, 2023
  • 3
    2022 State Of DevOps Report Data Deep Dive: Good Team Culture
    • March 29, 2023
  • 4
    Google Data Cloud & AI Summit : In Less Than 12 Hours From Now
    • March 29, 2023
  • 5
    A 5-Minute Tour Of The Fediverse
    • March 28, 2023
  • 6
    Bringing Observability To Cloud Security
    • March 28, 2023
  • 7
    How AI Can Improve Digital Security
    • March 27, 2023
  • 8
    Docker’s Bad Week
    • March 27, 2023
  • 9
    My First Pull Request At Age 14
    • March 24, 2023
  • 10
    AWS Chatbot Now Integrated Into Microsoft Teams
    • March 24, 2023
about
Hello World!

We are aster.cloud. We’re created by programmers for programmers.

Our site aims to provide guides, programming tips, reviews, and interesting materials for tech people and those who want to learn in general.

We would like to hear from you.

If you have any feedback, enquiries, or sponsorship request, kindly reach out to us at:

[email protected]
Most Popular
  • 1
    Introducing GPT-4 In Azure OpenAI Service
    • March 21, 2023
  • 2
    IBM And Fundación Ikerbasque Partner To Launch Groundbreaking Quantum Computational Center
    • March 24, 2023
  • 3
    Cleveland Clinic And IBM Unveil First Quantum Computer Dedicated To Healthcare Research
    • March 20, 2023
  • 4
    Verify POST Endpoint Availability With Uptime Checks
    • March 24, 2023
  • 5
    Oracle Cloud Infrastructure to Increase the Reliability, Efficiency, and Simplicity of Large-Scale Kubernetes Environments at Reduced Costs
    • March 20, 2023
  • /
  • Platforms
  • Architecture
  • Engineering
  • Programming
  • Tools
  • About

Input your search keywords and press Enter.