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Issue 29398655:
Issue 5062 - [emscripten] Allow generation of custom bindings code (Closed)
Base URL: https://hg.adblockplus.org/adblockpluscore
Patch Set: Improved binding generation
Created April 4, 2017, 3:40 p.m.
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|---|---|
| 1 Adblock Plus core | 1 Adblock Plus core |
| 2 ================= | 2 ================= |
| 3 | 3 |
| 4 This repository contains the generic Adblock Plus code that's shared between | 4 This repository contains the generic Adblock Plus code that's shared between |
| 5 platforms. This repository is not designed to be used directly, but instead to | 5 platforms. This repository is not designed to be used directly, but instead to |
| 6 serve as a dependency for `adblockplus`, `adblockpluschrome` and | 6 serve as a dependency for `adblockplus`, `adblockpluschrome` and |
| 7 `libadblockplus`. | 7 `libadblockplus`. |
| 8 | 8 |
| 9 Compiling C++ code | 9 Compiling C++ code |
| 10 ------------------ | 10 ------------------ |
| 11 | 11 |
| 12 ### Purpose | 12 ### Purpose |
| 13 | 13 |
| 14 In order to improve performance and memory usage, some of the code (located | 14 In order to improve performance and memory usage, some of the code (located |
| 15 inside the `compiled` directory) is written in C++ and compiled to JavaScript | 15 inside the `compiled` directory) is written in C++ and compiled to JavaScript |
| 16 via Empscripten. | 16 via Empscripten. |
| 17 | 17 |
| 18 ### Requirements | 18 ### Requirements |
| 19 | 19 |
| 20 * [Emscripten 1.37.3](https://github.com/kripken/emscripten) | 20 * [Emscripten 1.37.3](https://github.com/kripken/emscripten) |
| 21 * [Python 2.7](https://www.python.org) | 21 * [Python 2.7](https://www.python.org) |
| 22 * [Node.js 6 or higher](https://nodejs.org/en/) | |
| 23 | 22 |
| 24 ### Running Emscripten | 23 ### Running Emscripten |
| 25 | 24 |
| 26 *Note*: The `compile` script will likely be replaced by a more elaborate | 25 After installing and configuring Emscripten you can run the following command: |
| 27 solution later. | |
| 28 | |
| 29 Before you start make sure to edit the `compile` script and make sure that | |
| 30 `EMSCRIPTEN_PATH` constant at the top of it points to your Emscripten install. | |
| 31 After that run the following command: | |
| 32 | 26 |
| 33 python compile | 27 python compile |
| 34 | 28 |
| 35 This will produce a `lib/compiled.js` exporting the classes defined in C++ code. | 29 This will produce a `lib/compiled.js` exporting the classes defined in C++ code. |
| 36 | 30 |
| 37 ### Technical details | 31 ### Technical details |
| 38 | 32 |
| 39 Compilation is currently a two-step process. In the first step, | 33 Compilation is currently a two-step process. In the bindings generation step, |
| 40 `compiled/bindings.cpp` (definitions of classes to be exported) is compiled into | 34 the source files are compiled into `compiled/bindings.cpp.js` with the |
| 41 `compiled/bindings.cpp.js` with `PRINT_BINDINGS` symbol defined. This | 35 `PRINT_BINDINGS` symbol defined. This application is then executed via Node.js |
| 42 application is then executed via Node.js and will print JavaScript wrappers for | 36 and will print JavaScript wrappers for the C++ classes to |
| 43 the C++ classes to `compiled/bindings.js`. | 37 `compiled/bindings.js` according to definitions within the `EMSCRIPTEN_BINDINGS` |
| 38 macro in `compiled/bindings.cpp`. | |
| 44 | 39 |
| 45 In the next step all the C++ files in `compiled` directory are compiled, | 40 In the actual compilation step the source files are compiled into |
| 46 including `compiled/bindings.cpp` - without `PRINT_BINDINGS` symbol the | 41 `lib/compiled.js` without the `PRINT_BINDINGS` symbol, so that the |
| 47 `EMSCRIPTEN_BINDINGS` macro in this file will ignore its contents but rather | 42 `EMSCRIPTEN_BINDINGS` macro ignores its contents and merely emits some generic |
| 48 emit some functions necessary for the JavaScript bindings to work. The | 43 functions necessary for the JavaScript bindings to work. The previously |
| 49 `compiled/bindings.js` file is added to the end of Emscripten output. | 44 generated `compiled/bindings.js` file is added to the end of Emscripten output. |
| 50 | 45 |
| 51 The binding generation approach is heavily inspired by | 46 The binding generation approach is heavily inspired by |
| 52 [embind](http://kripken.github.io/emscripten-site/docs/porting/connecting_cpp_an d_javascript/embind.html). | 47 [embind](http://kripken.github.io/emscripten-site/docs/porting/connecting_cpp_an d_javascript/embind.html). |
| 53 However, embind doesn't use a separate build step to produce the bindings, the | 48 However, embind doesn't use a separate build step to produce the bindings, the |
| 54 bindings are rather generated dynamically at run time. As a side-effect, it | 49 bindings are rather generated dynamically at run time. As a side-effect, it |
| 55 increases the build size considerably and also imposes a significant performance | 50 increases the build size considerably and also imposes a significant performance |
| 56 penalty. Also, generating JavaScript code dynamically is discouraged for browser | 51 penalty. Also, generating JavaScript code dynamically is discouraged for browser |
| 57 extensions. | 52 extensions. |
| 58 | 53 |
| 59 *Note*: The tricky part when generating JavaScript bindings is determining the | 54 *Note*: The tricky part when generating JavaScript bindings is determining the |
| 60 mangled names of C++ methods. In order to do that, `compiled/bindings.cpp.js` | 55 mangled names of C++ methods. In order to do that, `compiled/bindings.cpp.js` |
| 61 will call these methods with invalid parameters and make them crash. The | 56 will call these methods with invalid parameters and make them crash. The |
| 62 resulting `abort()` call is then caught by JavaScript code that reads out the | 57 resulting `abort()` call is then caught by JavaScript code that reads out the |
| 63 method name from the stack. With this approach relying on some Emscripten | 58 method name from the stack. With this approach relying on some Emscripten |
| 64 internals, we have to require a specific Emscripten version. | 59 internals, we have to require a specific Emscripten version. |
| 65 | 60 |
| 66 Running the unit tests | 61 Running the unit tests |
| 67 ---------------------- | 62 ---------------------- |
| 68 | 63 |
| 69 You first need to run `npm install` in the repository directory in order to | 64 You first need to run `npm install` in the repository directory in order to |
| 70 install the required dependencies. After that you can run `npm test` which will | 65 install the required dependencies. After that you can run `npm test` which will |
| 71 execute all tests in the `test` directory of the repository. You can also | 66 execute all tests in the `test` directory of the repository. You can also |
| 72 specify specific test files on the command line, e.g. | 67 specify specific test files on the command line, e.g. |
| 73 `npm test test/synchronizer.js`. | 68 `npm test test/synchronizer.js`. |
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