Node.js/ v8: How to make my own snapshot to accelerate startup
- by Anand
I have a node.js (v0.6.12) application that starts by evaluating a Javascript file, startup.js. It takes a long time to evaluate startup.js, and I'd like to 'bake it in' to a custom build of Node if possible.
The v8 source directory distributed with Node, node/deps/v8/src, contains a SconScript that can almost be used to do this. On line 302, we have
LIBRARY_FILES = '''
runtime.js
v8natives.js
array.js
string.js
uri.js
math.js
messages.js
apinatives.js
date.js
regexp.js
json.js
liveedit-debugger.js
mirror-debugger.js
debug-debugger.js
'''.split()
Those javascript files are present in the same directory. Something in the build process apparently evaluates them, takes a snapshot of state, and saves it as a byte string in node/out/Release/obj/release/snapshot.cc (on Mac OS).
Some customization of the startup snapshot is possible by altering the SconScript. For example, I can change the definition of the builtin Date.toString by altering date.js. I can even add new global variables by adding startup.js to the list of library files, with contents global.test = 1.
However, I can't put just any javascript code in startup.js. If it contains Date.toString = 1;, an error results even though the code is valid at the node repl:
Build failed: -> task failed (err #2):
{task: libv8.a SConstruct -> libv8.a}
make: *** [program] Error 1
And it obviously can't make use of code that depends on libraries Node adds to v8. global.underscore = require('underscore'); causes the same error.
I'd ideally like a tool, customSnapshot, where customSnapshot startup.js evaluates startup.js with node and then dumps a snapshot to a file, snapshot.cc, which I can put into the node source directory. I can then build node and tell it not to rebuild the snapshot.
