Asynchronous Programming in Rust: Learn asynchronous programming by building working examples of futures, green threads, and runtimes

Cover....1 Title Page....2 Copyright....3 Dedication....4 Contributors....5 Table of Contents....8 Preface....14 Part 1: Asynchronous Programming Fundamentals....22 Chapter 1: Concurrency and Asynchronous Programming: a Detailed Overview....24 Technical requirements....25 An evolutionary journey of multitasking....25 Non-preemptive multitasking....25 Preemptive multitasking....26 Hyper-threading....26 Multicore processors....27 Do you really write synchronous code?....27 Concurrency versus parallelism....28 The mental model I use....29 Let’s draw some parallels to process economics....30 Concurrency and its relation to I/O....32 What about threads provided by the operating system?....33 Choosing the right reference frame....33 Asynchronous versus concurrent....33 The role of the operating system....34 Concurrency from the operating system’s perspective....34 Teaming up with the operating system....35 Communicating with the operating system....35 The CPU and the operating system....36 Down the rabbit hole....37 How does the CPU prevent us from accessing memory we’re not supposed to access?....38 But can’t we just change the page table in the CPU?....39 Interrupts, firmware, and I/O....40 A simplified overview....40 Interrupts....43 Firmware....43 Summary....44 Chapter 2: Concurrency and Asynchronous Programming: a Detailed OverviewHow Programming Languages Model Asynchronous Program Flow....46 Definitions....47 Threads....48 Threads provided by the operating system....50 Creating new threads takes time....50 Each thread has its own stack....50 Context switching....51 Scheduling....51 The advantage of decoupling asynchronous operations from OS threads....52 Example....52 Fibers and green threads....54 Each stack has a fixed space....55 Context switching....56 Scheduling....56 FFI....57 Callback based approaches....58 Coroutines: promises and futures....59 Coroutines and async/await....60 Summary....62 Chapter 3: Understanding OS-Backed Event Queues, System Calls, and Cross-Platform Abstractions....64 Technical requirements....65 Running the Linux examples....66 Why use an OS-backed event queue?....66 Blocking I/O....67 Non-blocking I/O....67 Event queuing via epoll/kqueue and IOCP....68 Readiness-based event queues....68 Completion-based event queues....69 epoll, kqueue, and IOCP....70 Cross-platform event queues....71 System calls, FFI, and cross-platform abstractions....72 The lowest level of abstraction....72 The next level of abstraction....76 The highest level of abstraction....82 Summary....82 Part 2: Event Queues and Green Threads....84 Chapter 4: Create Your Own Event Queue....86 Technical requirements....86 Design and introduction to epoll....87 Is all I/O blocking?....93 The ffi module....94 Bitflags and bitmasks....97 Level-triggered versus edge-triggered events....99 The Poll module....102 The main program....105 Summary....114 Chapter 5: Creating Our Own Fibers....116 Technical requirements....117 How to use the repository alongside the book....117 Background information....118 Instruction sets, hardware architectures, and ABIs....118 The System V ABI for x86-64....120 A quick introduction to Assembly language....123 An example we can build upon....124 Setting up our project....124 An introduction to Rust inline assembly macro....126 Running our example....128 The stack....130 What does the stack look like?....130 Stack sizes....132 Implementing our own fibers....133 Implementing the runtime....136 Guard, skip, and switch functions....142 Finishing thoughts....146 Summary....147 Part 3: Futures and async/await in Rust....148 Chapter 6: Futures in Rust....150 What is a future?....151 Leaf futures....151 Non-leaf futures....151 A mental model of an async runtime....152 What the Rust language and standard library take care of....154 I/O vs CPU-intensive tasks....155 Summary....156 Chapter 7: Coroutines and async/await....158 Technical requirements....158 Introduction to stackless coroutines....159 An example of hand-written coroutines....160 Futures module....162 HTTP module....163 Do all futures have to be lazy?....167 Creating coroutines....168 async/await....175 coroutine/wait....176 corofy—the coroutine preprocessor....176 b-async-await—an example of a coroutine/wait transformation....177 c-async-await—concurrent futures....181 Final thoughts....186 Summary....187 Chapter 8: Runtimes, Wakers, and the Reactor-Executor Pattern....188 Technical requirements....189 Introduction to runtimes and why we need them....190 Reactors and executors....191 Improving our base example....192 Design....194 Changing the current implementation....198 Creating a proper runtime....205 Step 1 – Improving our runtime design by adding a Reactor and a Waker....208 Creating a Waker....209 Changing the Future definition....212 Step 2 – Implementing a proper Executor....213 Step 3 – Implementing a proper Reactor....220 Experimenting with our new runtime....229 An example using concurrency....229 Running multiple futures concurrently and in parallel....230 Summary....232 Chapter 9: Coroutines, Self-Referential Structs, and Pinning....234 Technical requirements....235 Improving our example 1 – variables....235 Setting up the base example....236 Improving our base example....238 Improving our example 2 – references....243 Improving our example 3 – this is… not… good…....248 Discovering self-referential structs....250 What is a move?....252 Pinning in Rust....254 Pinning in theory....255 Definitions....255 Pinning to the heap....256 Pinning to the stack....258 Pin projections and structural pinning....261 Improving our example 4 – pinning to the rescue....262 future.rs....263 http.rs....263 Main.rs....265 executor.rs....267 Summary....269 Chapter 10: Creating Your Own Runtime....272 Technical requirements....272 Setting up our example....274 main.rs....274 future.rs....275 http.rs....275 executor.rs....277 reactor.rs....280 Experimenting with our runtime....282 Challenges with asynchronous Rust....286 Explicit versus implicit reactor instantiation....286 Ergonomics versus efficiency and flexibility....287 Common traits that everyone agrees about....288 Async drop....289 The future of asynchronous Rust....290 Summary....290 Epilogue....293 Index....296 About PACKT....302 Other Books You May Enjoy....303