WebAssembly in Action With examples using C++ and Emscripten (Gerard Gallant)（Z-Library）

【One-Line Pitch】 A hands-on guide to compiling C and C++ into WebAssembly with Emscripten, so you can run near-native-speed code in the browser and wire it cleanly into JavaScript. Best for web or systems developers who already know some C/C++, JavaScript, and HTML and want a practical path from "hello module" to threading and dynamic linking. 【Book Arc】 - **Opening (~0%–10%)**: Frames the "why" — what WebAssembly is, the asm.js lineage, and the problems it solves (performance, startup time, non-JavaScript languages, code reuse). Establishes the mental model before any tooling. - **Early (~10%–30%)**: Moves into module internals — known vs. custom sections, the binary/text formats, and the WebAssembly JavaScript API (fetch, instantiateStreaming). Then builds a first module from C source through Emscripten to a working HTML page. - **Early–Middle (~30%–45%)**: The code-reuse core: adapting an existing C/C++ codebase with `__EMSCRIPTEN__`, `extern "C"`, and `EMSCRIPTEN_KEEPALIVE`, then calling module functions from JavaScript via `ccall`. - **Middle (~45%–60%)**: Memory and string marshalling — the four basic types, `_malloc`/`_free`, `UTF8ToString`, and replacing `strcpy`-style patterns with host callbacks like `UpdateHostAboutError`. - **Late (~60%–85%)**: Scaling up — dynamic linking of multiple modules at runtime, debugging with the WebAssembly Text Format, and performance work with web workers and pthreads. - **Ending (~85%–100%)**: Consolidation through worked examples, exercises, and appendices; excerpts do not cover the closing chapters in detail. 【Key Takeaways】 - **WebAssembly is a compiler target, not a language you hand-write** (Opening): its binary format is compact, single-pass validatable, and parallel-compilable, which is where the speed and startup advantages come from. - **Static typing enables compile-from-the-start performance** (Opening): unlike JIT'd JavaScript that must be monitored first, Wasm is compiled to machine code immediately, and streaming compilation lets modules initialize as they download. - **Module sections are the architectural backbone** (Early): known sections appear once in fixed order, custom sections can appear anywhere and repeat — understanding this pays off when reading text format or debugging. - **Emscripten is the practical bridge from C/C++ to the browser** (Early–Middle): it generates the JavaScript "plumbing" that downloads, compiles, and instantiates your module so you can focus on your own code. - **Reusing existing C/C++ is a first-class workflow** (Middle): `__EMSCRIPTEN__`, `extern "C"`, and `EMSCRIPTEN_KEEPALIVE` let one codebase serve desktop and web without a rewrite. - **Only four primitive types cross the boundary** (Middle): integers and floats pass directly, but strings and complex data require manual memory management via `_malloc`, `_free`, and `UTF8ToString`. - **Host callbacks beat buffer-passing for error handling** (Middle): replacing `strcpy`-into-a-buffer with a call like `UpdateHostAboutError` simplifies the C side and avoids lifetime headaches. - **Threading and multi-module linking are the advanced frontier** (Late): web workers, pthreads, and runtime dynamic linking are where real performance gains and real complexity live. 【Reading Tips】 - **Deep-read the module-sections and memory chapters** (Early and Middle): these are the conceptual load-bearing walls; skimming them makes later debugging and marshalling feel like magic. - **Skim the introductory "what is WebAssembly" material** if you already know the landscape — it's orientation, not technique. - **Type along with the Emscripten build steps**: the toolchain flags and file layout are easy to misread but obvious once you've run them. - **Treat the exercises and appendices as checkpoints**, especially around `ccall`, exports, and name mangling — they surface the mistakes you'd otherwise hit in production. - **Watch the Windows-style path convention** noted in the text; *nix readers should mentally swap separators. 【Coverage Limits】 This guide is built from stratified excerpts covering roughly the first half of the book in detail; the threading, dynamic-linking, and debugging chapters are represented mainly by the table of contents and blurb, so their specifics are not deeply summarized here.