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src: avoid copying SEA snapshot data #65841

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colinhacks wants to merge 1 commit into from
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src: avoid copying SEA snapshot data #65841

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7 changes: 6 additions & 1 deletion src/env.h
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Original file line number Diff line number Diff line change
Expand Up @@ -583,6 +583,7 @@ struct SnapshotData {
// The result of v8::SnapshotCreator::CreateBlob() during the snapshot
// building process.
v8::StartupData v8_snapshot_blob_data{nullptr, 0};
DataOwnership v8_snapshot_blob_data_ownership = DataOwnership::kOwned;

IsolateDataSerializeInfo isolate_data_info;
// TODO(joyeecheung): there should be a vector of env_info once we snapshot
Expand All @@ -602,7 +603,11 @@ struct SnapshotData {
bool Check() const;
static bool FromFile(SnapshotData* out, FILE* in);
static bool FromBlob(SnapshotData* out, const std::vector<char>& in);
static bool FromBlob(SnapshotData* out, std::string_view in);
// If the V8 data is not owned, `in` must outlive `out`.
static bool FromBlob(SnapshotData* out,
std::string_view in,
DataOwnership v8_snapshot_blob_data_ownership =
DataOwnership::kOwned);
static const SnapshotData* FromEmbedderWrapper(
const EmbedderSnapshotData* data);
EmbedderSnapshotData::Pointer AsEmbedderWrapper() const;
Expand Down
6 changes: 5 additions & 1 deletion src/node.cc
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Expand Up @@ -1522,7 +1522,11 @@ bool LoadSnapshotData(const SnapshotData** snapshot_data_ptr) {
std::unique_ptr<SnapshotData> read_data =
std::make_unique<SnapshotData>();
std::string_view snapshot = sea.main_code_or_snapshot;
if (SnapshotData::FromBlob(read_data.get(), snapshot)) {
// The SEA resource remains mapped for the process lifetime, so V8 can
// consume the startup data directly from the executable image.
if (SnapshotData::FromBlob(read_data.get(),
snapshot,
SnapshotData::DataOwnership::kNotOwned)) {
*snapshot_data_ptr = read_data.release();
return true;
} else {
Expand Down
45 changes: 32 additions & 13 deletions src/node_snapshotable.cc
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Expand Up @@ -158,6 +158,27 @@ class SnapshotDeserializer : public BlobDeserializer<SnapshotDeserializer> {
template <typename T>
requires(!std::is_arithmetic_v<T> && !std::same_as<T, std::string>)
T Read();

v8::StartupData ReadV8StartupData(
SnapshotData::DataOwnership ownership) {
Debug("Read<v8::StartupData>()\n");

int raw_size = ReadArithmetic<int>();
Debug("size=%d\n", raw_size);

CHECK_GT(raw_size, 0); // There should be no startup data of size 0.
if (ownership == SnapshotData::DataOwnership::kOwned) {
// The data pointer of v8::StartupData would be deleted so it must be
// new'ed.
std::unique_ptr<char> buf = std::unique_ptr<char>(new char[raw_size]);
ReadArithmetic<char>(buf.get(), raw_size);
return v8::StartupData{buf.release(), raw_size};
}

const char* data = sink.data() + read_total;
read_total += raw_size;
return v8::StartupData{data, raw_size};
}
};

class SnapshotSerializer : public BlobSerializer<SnapshotSerializer> {
Expand All @@ -181,17 +202,7 @@ class SnapshotSerializer : public BlobSerializer<SnapshotSerializer> {
// [ |raw_size| bytes ] contents
template <>
v8::StartupData SnapshotDeserializer::Read() {
Debug("Read<v8::StartupData>()\n");

int raw_size = ReadArithmetic<int>();
Debug("size=%d\n", raw_size);

CHECK_GT(raw_size, 0); // There should be no startup data of size 0.
// The data pointer of v8::StartupData would be deleted so it must be new'ed.
std::unique_ptr<char> buf = std::unique_ptr<char>(new char[raw_size]);
ReadArithmetic<char>(buf.get(), raw_size);

return v8::StartupData{buf.release(), raw_size};
return ReadV8StartupData(SnapshotData::DataOwnership::kOwned);
}

template <>
Expand Down Expand Up @@ -640,7 +651,9 @@ bool SnapshotData::FromBlob(SnapshotData* out, const std::vector<char>& in) {
return FromBlob(out, std::string_view(in.data(), in.size()));
}

bool SnapshotData::FromBlob(SnapshotData* out, std::string_view in) {
bool SnapshotData::FromBlob(SnapshotData* out,
std::string_view in,
DataOwnership v8_snapshot_blob_data_ownership) {
SnapshotDeserializer r(in);
r.Debug("SnapshotData::FromBlob()\n");

Expand All @@ -656,7 +669,9 @@ bool SnapshotData::FromBlob(SnapshotData* out, std::string_view in) {
return false;
}

out->v8_snapshot_blob_data = r.Read<v8::StartupData>();
out->v8_snapshot_blob_data =
r.ReadV8StartupData(v8_snapshot_blob_data_ownership);
out->v8_snapshot_blob_data_ownership = v8_snapshot_blob_data_ownership;
r.Debug("Read isolate_data_info\n");
out->isolate_data_info = r.Read<IsolateDataSerializeInfo>();
out->env_info = r.Read<EnvSerializeInfo>();
Expand Down Expand Up @@ -701,6 +716,7 @@ bool SnapshotData::Check() const {

SnapshotData::~SnapshotData() {
if (data_ownership == DataOwnership::kOwned &&
v8_snapshot_blob_data_ownership == DataOwnership::kOwned &&
v8_snapshot_blob_data.data != nullptr) {
delete[] v8_snapshot_blob_data.data;
}
Expand Down Expand Up @@ -822,6 +838,9 @@ namespace node {
// -- v8_snapshot_blob_data begins --
{ v8_snapshot_blob_data, v8_snapshot_blob_size },
// -- v8_snapshot_blob_data ends --
// -- v8_snapshot_blob_data_ownership begins --
SnapshotData::DataOwnership::kNotOwned,
// -- v8_snapshot_blob_data_ownership ends --
// -- isolate_data_info begins --
)" << data->isolate_data_info
<< R"(
Expand Down
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