tools/code_cache/README.md

# Node.js code cache builder

This is the V8 code cache builder of Node.js. It pre-compiles all the
JavaScript native modules of Node.js and serializes the code cache (including
the bytecodes) that will be embeded into the Node.js executable. When a Node.js
JavaScript native module is `require`d at runtime, Node.js can deserialize from
the code cache instead of parsing the source code and generating the bytecode
for it before execution, which should reduce the load time of these JavaScript
native modules.

## How it's built and used

The code cache builder is built with the `mkcodecache` target in `node.gyp`
when `node_use_node_code_cache` is set to true, which is currently done by
default.

In the default build of the Node.js executable, to embed the V8 code cache of
the native modules into the Node.js executable, `libnode` is first built with
these unresolved symbols:

- `node::native_module::has_code_cache`
- `node::native_module::NativeModuleEnv::InitializeCodeCache`

Then the `mkcodecache` executable is built with C++ files in this directory,
as well as `src/node_code_cache_stub.cc` which defines the unresolved symbols.

`mkcodecache` is run to generate a C++ file
`<(SHARED_INTERMEDIATE_DIR)/node_code_cache.cc` that is similar to
`src/node_code_cache_stub.cc` in structure, but contains the code cache data
written as static char array literals. Then `libnode` is built with
`node_code_cache.cc` to produce the final Node.js executable with the code
cache data embedded.

For debugging, Node.js can be built without code cache if
`--without-node-code-cache` is passed to `configure`. Note that even if the
code cache is not pre-compiled and embedded into the Node.js executable, the
internal infrastructure is still used to share code cache between the main
thread and worker threads (if there is any).