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Joyee Cheung
bfb4ca8e94
Instead of passing the snapshot blob, the per-isolate data indices and the EnvSerializeInfo separately, use the aggregate type Snapshot to carry these around, and refactor NodeMainInstance so that it owns the v8::Isolate::CreateParams when it owns its isolate. This also gets rid of the owns_isolate_ and deserialize_mode_ booleans in NodeMainInstance since NodeMainInstance can compute these by just checking if it has pointers to the CreateParams or the SnapshotData. PR-URL: https://github.com/nodejs/node/pull/42360 Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Darshan Sen <raisinten@gmail.com>
42 lines
1.9 KiB
Markdown
42 lines
1.9 KiB
Markdown
# Node.js startup snapshot builder
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This is the V8 startup snapshot builder of Node.js. Not to be confused with
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V8's own snapshot builder, which builds a snapshot containing JavaScript
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builtins, this builds a snapshot containing Node.js builtins that can be
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deserialized on top of V8's own startup snapshot. When Node.js is launched,
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instead of executing code to bootstrap, it can deserialize the context from
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an embedded snapshot, which readily contains the result of the bootstrap, so
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that Node.js can start up faster.
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Currently only the main context of the main Node.js instance supports snapshot
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deserialization, and the snapshot does not yet cover the entire bootstrap
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process. Work is being done to expand the support.
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## How it's built and used
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The snapshot builder is built with the `node_mksnapshot` target in `node.gyp`
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when `node_use_node_snapshot` is set to true, which is currently done by
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default.
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In the default build of the Node.js executable, to embed a V8 startup snapshot
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into the Node.js executable, `libnode` is first built with these unresolved
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symbols:
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- `node::NodeMainInstance::GetEmbeddedSnapshotData`
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Then the `node_mksnapshot` executable is built with C++ files in this
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directory, as well as `src/node_snapshot_stub.cc` which defines the unresolved
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symbols.
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`node_mksnapshot` is run to generate a C++ file
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`<(SHARED_INTERMEDIATE_DIR)/node_snapshot.cc` that is similar to
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`src/node_snapshot_stub.cc` in structure, but contains the snapshot data
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written as static char array literals. Then `libnode` is built with
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`node_snapshot.cc` to produce the final Node.js executable with the snapshot
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data embedded.
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For debugging, Node.js can be built without Node.js's own snapshot if
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`--without-node-snapshot` is passed to `configure`. A Node.js executable
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with Node.js snapshot embedded can also be launched without deserializing
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from it if the command line argument `--no-node-snapshot` is passed.
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