src: let embedders supply a builtin code cache without a snapshot - #65352
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #65352 +/- ##
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- Coverage 90.06% 90.05% -0.01%
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Files 754 754
Lines 255742 255803 +61
Branches 48314 48332 +18
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+ Hits 230341 230373 +32
- Misses 16534 16556 +22
- Partials 8867 8874 +7
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Environments created from the built-in snapshot get the builtins' code cache from that snapshot. An embedder that bootstraps an Environment from scratch (its own isolate and context, no EmbedderSnapshotData) has no way to provide one: every builtin the bootstrap touches is compiled from source in every such process, and each of them then serializes a fresh cache (SaveCodeCache) that only a later worker thread would ever consume. Add node::EmbedderBuiltinCodeCache for that case. Its entries pair a builtin id with a v8::ScriptCompiler::CachedData; Generate(context) compiles every builtin in a context of the right kind of isolate and returns them for a build step to embed, and SetBuiltinCodeCache(isolate_data, cache) attaches them to an IsolateData, next to where a snapshot's code cache lives, so that every Environment created from it afterwards starts with them. The setter runs CachedData::CompatibilityCheck() against the isolate first and returns the result, leaving the IsolateData untouched for a cache made with another V8 version, flag set or read-only snapshot. Entries from a snapshot still merge with it (RefreshCodeCache() now merges instead of assuming a single call). CreateEnvironment() plus LoadEnvironment() of an empty script goes from about 38 ms to 13 ms with a cache attached. ProcessInitializationFlags::kNoHarvestBuiltinCodeCache stops serializing caches for builtins compiled without one, for embedders that supply their own or never create workers. The default is unchanged because worker threads copy the harvested cache. A cctest generates a cache, attaches it, checks that a new Environment's bootstrap compiles from it and that a corrupted cache is refused; embedtest gains --no-harvest-builtin-code-cache for a test that a worker does or does not find a harvested cache depending on the flag. Signed-off-by: Shelley Vohr <shelley.vohr@gmail.com>
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An embedder that creates its Environments without Node's snapshot (its own isolate, no
EmbedderSnapshotData) compiles every builtin the bootstrap touches from source in each such process, and then serializes a fresh code cache for each of them that only a later worker thread ever reads. This adds a way to attach a cache built ahead of time to anIsolateData, plus a flag to skip the runtime serialization;nodeitself is unchanged.CreateEnvironment()+LoadEnvironment(env, "0"), fresh context, linux x64, n=6EmbedderBuiltinCodeCacheattached to theIsolateDatanode::EmbedderBuiltinCodeCacheholds entries pairing a builtin id with av8::ScriptCompiler::CachedData.EmbedderBuiltinCodeCache::Generate(context)compiles every builtin in a context made withnode::NewContext()and returns them for a build step to embed;node::SetBuiltinCodeCache(isolate_data, cache)attaches them next to where a snapshot's code cache lives, so every Environment created from thatIsolateDataafterwards starts with them (they share the buffers; the cache object can be freed after the call). The setter runsCachedData::CompatibilityCheck()against the isolate and returns the result, leaving theIsolateDatauntouched for a cache made with another V8 version, flag set or read-only snapshot. A snapshot's entries still merge with it, soRefreshCodeCache()merges withinsert_or_assigninstead of asserting a single call.ProcessInitializationFlags::kNoHarvestBuiltinCodeCachestopsLookupAndCompile()from serializing a cache for builtins compiled without one. The default stays as it is because worker threads start from that harvested cache.The per-context scripts
NewContext()runs (internal/per_context/*) are outside an Environment and keep compiling from source.Tests: a cctest generates a cache, attaches it, checks that a new Environment compiles
internal/bootstrap/nodeand everything outsideinternal/per_context/*from it, and that a corrupted cache is refused and anullptrclears it; a cctest for theRefreshCodeCachemerge;embedtestgains--no-harvest-builtin-code-cachefor an embedding test that a worker started with and without the flag does and doesn't find a harvested cache. embedding, cctest and the default suite pass.Disclosure: the code, tests, measurements and this description were written by Claude Code, directed and reviewed by @codebytere.