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os: performance improvement in vector allocation
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We were using the result vector with an object which is not a primitive
data type, and going with the constructor allocation pattern it creates
a size of that vector and also initializes the spaces with the data type
as well which is in our case is `Local<Value>`. It leads to waste of
some CPU cycles and instead we just wanted to have some reserved space
in our vector.

We can use `reserve` method on vector to reserve some space for the
vector but doesn't initialize the value since we are anyways doing it in
the following loop.

PR-URL: #36748
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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yashLadha authored and ruyadorno committed Jan 25, 2021
1 parent 8d49ce9 commit 89a7941
Showing 1 changed file with 21 additions and 19 deletions.
40 changes: 21 additions & 19 deletions src/node_os.cc
Original file line number Diff line number Diff line change
Expand Up @@ -112,16 +112,17 @@ static void GetCPUInfo(const FunctionCallbackInfo<Value>& args) {
// assemble them into objects in JS than to call Object::Set() repeatedly
// The array is in the format
// [model, speed, (5 entries of cpu_times), model2, speed2, ...]
std::vector<Local<Value>> result(count * 7);
for (int i = 0, j = 0; i < count; i++) {
std::vector<Local<Value>> result;
result.reserve(count * 7);
for (int i = 0; i < count; i++) {
uv_cpu_info_t* ci = cpu_infos + i;
result[j++] = OneByteString(isolate, ci->model);
result[j++] = Number::New(isolate, ci->speed);
result[j++] = Number::New(isolate, ci->cpu_times.user);
result[j++] = Number::New(isolate, ci->cpu_times.nice);
result[j++] = Number::New(isolate, ci->cpu_times.sys);
result[j++] = Number::New(isolate, ci->cpu_times.idle);
result[j++] = Number::New(isolate, ci->cpu_times.irq);
result.emplace_back(OneByteString(isolate, ci->model));
result.emplace_back(Number::New(isolate, ci->speed));
result.emplace_back(Number::New(isolate, ci->cpu_times.user));
result.emplace_back(Number::New(isolate, ci->cpu_times.nice));
result.emplace_back(Number::New(isolate, ci->cpu_times.sys));
result.emplace_back(Number::New(isolate, ci->cpu_times.idle));
result.emplace_back(Number::New(isolate, ci->cpu_times.irq));
}

uv_free_cpu_info(cpu_infos, count);
Expand Down Expand Up @@ -182,7 +183,8 @@ static void GetInterfaceAddresses(const FunctionCallbackInfo<Value>& args) {
}

Local<Value> no_scope_id = Integer::New(isolate, -1);
std::vector<Local<Value>> result(count * 7);
std::vector<Local<Value>> result;
result.reserve(count * 7);
for (i = 0; i < count; i++) {
const char* const raw_name = interfaces[i].name;

Expand Down Expand Up @@ -216,18 +218,18 @@ static void GetInterfaceAddresses(const FunctionCallbackInfo<Value>& args) {
family = env->unknown_string();
}

result[i * 7] = name;
result[i * 7 + 1] = OneByteString(isolate, ip);
result[i * 7 + 2] = OneByteString(isolate, netmask);
result[i * 7 + 3] = family;
result[i * 7 + 4] = FIXED_ONE_BYTE_STRING(isolate, mac);
result[i * 7 + 5] =
interfaces[i].is_internal ? True(isolate) : False(isolate);
result.emplace_back(name);
result.emplace_back(OneByteString(isolate, ip));
result.emplace_back(OneByteString(isolate, netmask));
result.emplace_back(family);
result.emplace_back(FIXED_ONE_BYTE_STRING(isolate, mac));
result.emplace_back(
interfaces[i].is_internal ? True(isolate) : False(isolate));
if (interfaces[i].address.address4.sin_family == AF_INET6) {
uint32_t scopeid = interfaces[i].address.address6.sin6_scope_id;
result[i * 7 + 6] = Integer::NewFromUnsigned(isolate, scopeid);
result.emplace_back(Integer::NewFromUnsigned(isolate, scopeid));
} else {
result[i * 7 + 6] = no_scope_id;
result.emplace_back(no_scope_id);
}
}

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