This patch introduces `--build-snapshot` and `--snapshot-blob` options
for creating and using user land snapshots.
For the initial iteration, user land CJS modules and ESM are not yet
supported in the snapshot, so only one single file can be snapshotted
(users can bundle their applications into a single script with their
bundler of choice to build a snapshot though).
A subset of builtins should already work, and support for more builtins
are being added. This PR includes tests checking that the TypeScript
compiler and the marked markdown renderer (and the builtins they use)
can be snapshotted and deserialized.
To generate a snapshot using `snapshot.js` as entry point and write the
snapshot blob to `snapshot.blob`:
```
$ echo "globalThis.foo = 'I am from the snapshot'" > snapshot.js
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js
```
To restore application state from `snapshot.blob`, with `index.js` as
the entry point script for the deserialized application:
```
$ echo "console.log(globalThis.foo)" > index.js
$ node --snapshot-blob snapshot.blob index.js
I am from the snapshot
```
Users can also use the `v8.startupSnapshot` API to specify an entry
point at snapshot building time, thus avoiding the need of an additional
entry script at deserialization time:
```
$ echo "require('v8').startupSnapshot.setDeserializeMainFunction(() => console.log('I am from the snapshot'))" > snapshot.js
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js
$ node --snapshot-blob snapshot.blob
I am from the snapshot
```
Note that this patch only adds functionality to the `node` executable
for building run-time user-land snapshots, the generated snapshot is
stored into a separate file on disk. Building a single binary with both
Node.js and an embedded snapshot has already been possible with the
`--node-snapshot-main` option to the `configure` script if the user
compiles Node.js from source. It would be a different task to enable the
`node` executable to produce a single binary that contains both Node.js
and an embedded snapshot without building Node.js from source, which
should be layered on top of the SEA (Single Executable Apps) initiative.
Known limitations/bugs that are being fixed in the upstream:
- V8 hits a DCHECK when deserializing certain mutated globals, e.g.
`Error.stackTraceLimit` (it should work fine in the release build,
however): https://chromium-review.googlesource.com/c/v8/v8/+/3319481
- Layout of V8's read-only heap can be inconsistent after
deserialization, resulting in memory corruption:
https://bugs.chromium.org/p/v8/issues/detail?id=12921
PR-URL: https://github.com/nodejs/node/pull/38905
Refs: https://github.com/nodejs/node/issues/35711
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Documentation style guide
This style guide helps us create organized and easy-to-read documentation. It provides guidelines for organization, spelling, formatting, and more.
These are guidelines rather than strict rules. Content is more important than formatting. You do not need to learn the entire style guide before contributing to documentation. Someone can always edit your material later to conform with this guide.
- Documentation is in markdown files with names formatted as
lowercase-with-dashes.md.- Use an underscore in the filename only if the underscore is part of the
topic name (e.g.,
child_process). - Some files, such as top-level markdown files, are exceptions.
- Use an underscore in the filename only if the underscore is part of the
topic name (e.g.,
- Documents should be word-wrapped at 80 characters.
.editorconfigdescribes the preferred formatting.- A plugin is available for some editors to apply these rules.
- Check changes to documentation with
make test-doc -jorvcbuild test-doc. - Use US spelling.
- Use serial commas.
- Avoid first-person pronouns (I, we).
- Exception: we recommend foo is preferable to foo is recommended.
- Use gender-neutral pronouns and gender-neutral plural nouns.
- OK: they, their, them, folks, people, developers
- NOT OK: his, hers, him, her, guys, dudes
- When combining wrapping elements (parentheses and quotes), place terminal
punctuation:
- Inside the wrapping element if the wrapping element contains a complete clause.
- Outside of the wrapping element if the wrapping element contains only a fragment of a clause.
- Documents must start with a level-one heading.
- Prefer affixing links (
[a link][]) to inlining links ([a link](http://example.com)). - When documenting APIs, update the YAML comment associated with the API as appropriate. This is especially true when introducing or deprecating an API.
- When documenting APIs, every function should have a usage example or link to an example that uses the function.
- For code blocks:
-
Use language-aware fences. (
```js) -
For the info string, use one of the following.
Meaning Info string Bash bashC cC++ cppCoffeeScript coffeeDiff diffHTTP httpJavaScript jsJSON jsonMarkdown markdownPlaintext textPowershell powershellR rShell Session consoleIf one of your language-aware fences needs an info string that is not already on this list, you may use
textuntil the grammar gets added toremark-preset-lint-node. -
Code need not be complete. Treat code blocks as an illustration or aid to your point, not as complete running programs. If a complete running program is necessary, include it as an asset in
assets/code-examplesand link to it.
-
- When using underscores, asterisks, and backticks, please use
backslash-escaping:
\_,\*, and\`. - Constructors should use PascalCase.
- Instances should use camelCase.
- Denote methods with parentheses:
socket.end()instead ofsocket.end. - Function arguments or object properties should use the following format:
* `name` {type|type2} Optional description. **Default:** `value`.
- For example:
*byteOffset{integer} Index of first byte to expose. Default:0.
- The
typeshould refer to a Node.js type or a JavaScript type.
- Function returns should use the following format:
* Returns: {type|type2} Optional description.- E.g.
* Returns: {AsyncHook} A reference toasyncHook.
- Use official styling for capitalization in products and projects.
- OK: JavaScript, Google's V8
- NOT OK: Javascript, Google's v8
- Use Node.js and not Node, NodeJS, or similar variants.
- When referring to the executable,
nodeis acceptable.
- When referring to the executable,
- Be direct.
- When referring to a version of Node.js in prose, use Node.js and the version
number. Do not prefix the version number with v in prose. This is to avoid
confusion about whether v8 refers to Node.js 8.x or the V8 JavaScript
engine.
- OK: Node.js 14.x, Node.js 14.3.1
- NOT OK: Node.js v14
- Use sentence-style capitalization for headings.
See also API documentation structure overview in doctools README.
For topics not covered here, refer to the Microsoft Writing Style Guide.