nodejs-mozilla/tools/code_cache

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 required 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).