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Small documentation update from `node::NodeMainInstance::GetEmbeddedSnapshotData` to `node::SnapshotBuilder::GetEmbeddedSnapshotData`. PR-URL: https://github.com/nodejs/node/pull/53544 Reviewed-By: Luigi Pinca <luigipinca@gmail.com> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com> Reviewed-By: Chengzhong Wu <legendecas@gmail.com> |
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| node_mksnapshot.cc | ||
| README.md | ||
Node.js startup snapshot builder
This is the V8 startup snapshot builder of Node.js. Not to be confused with V8's own snapshot builder, which builds a snapshot containing JavaScript builtins, this builds a snapshot containing Node.js builtins that can be deserialized on top of V8's own startup snapshot. When Node.js is launched, instead of executing code to bootstrap, it can deserialize the context from an embedded snapshot, which readily contains the result of the bootstrap, so that Node.js can start up faster.
Currently only the main context of the main Node.js instance supports snapshot deserialization, and the snapshot does not yet cover the entire bootstrap process. Work is being done to expand the support.
How it's built and used
The snapshot builder is built with the node_mksnapshot target in node.gyp
when node_use_node_snapshot is set to true, which is currently done by
default.
In the default build of the Node.js executable, to embed a V8 startup snapshot
into the Node.js executable, libnode is first built with these unresolved
symbols:
node::SnapshotBuilder::GetEmbeddedSnapshotData
Then the node_mksnapshot executable is built with C++ files in this
directory, as well as src/node_snapshot_stub.cc which defines the unresolved
symbols.
node_mksnapshot is run to generate a C++ file
<(SHARED_INTERMEDIATE_DIR)/node_snapshot.cc that is similar to
src/node_snapshot_stub.cc in structure, but contains the snapshot data
written as static char array literals. Then libnode is built with
node_snapshot.cc to produce the final Node.js executable with the snapshot
data embedded.
For debugging, Node.js can be built without Node.js's own snapshot if
--without-node-snapshot is passed to configure. A Node.js executable
with Node.js snapshot embedded can also be launched without deserializing
from it if the command line argument --no-node-snapshot is passed.