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Make JsonEncode() a bit faster #10400

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Make JsonEncode() a bit faster #10400

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e510c03
String: provide operator+ for String&&, not only const String&
Al2Klimov Apr 1, 2025
d01fc22
JsonEncoder#GetResult(): std::move(), not copy, data
Al2Klimov Apr 2, 2025
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6 changes: 3 additions & 3 deletions lib/base/json.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,7 @@ class JsonEncoder
String GetResult();

private:
std::vector<char> m_Result;
std::string m_Result;
String m_CurrentKey;
std::stack<std::bitset<2>> m_CurrentSubtree;

Expand Down Expand Up @@ -450,14 +450,14 @@ template<bool prettyPrint>
inline
String JsonEncoder<prettyPrint>::GetResult()
{
return String(m_Result.begin(), m_Result.end());
return std::move(m_Result);
}

template<bool prettyPrint>
inline
void JsonEncoder<prettyPrint>::AppendChar(char c)
{
m_Result.emplace_back(c);
m_Result.push_back(c);
}

template<bool prettyPrint>
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10 changes: 10 additions & 0 deletions lib/base/string.cpp
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Expand Up @@ -333,11 +333,21 @@ String icinga::operator+(const String& lhs, const char *rhs)
return lhs.GetData() + rhs;
}

String icinga::operator+(String&& lhs, const char *rhs)
{
return std::move(lhs.GetData()) + rhs;
}

String icinga::operator+(const char *lhs, const String& rhs)
{
return lhs + rhs.GetData();
}

String icinga::operator+(const char *lhs, String&& rhs)
{
return lhs + std::move(rhs.GetData());
}
Comment on lines +336 to +349
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How did you get here? Like how did you get to the conclusion that this will be a useful optimization?

(Also, I really wonder if there's actually an implementation of std::string that allows prepending without reallocation (unless you prepend the empty string), but well, a corresponding overload of operator+ is provided for std::string.)

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How did you get here? Like how did you get to the conclusion that this will be a useful optimization?

Checkout 27e1850 and Cmd+LClick the + sign in

icinga2/lib/base/json.cpp

Line 199 in 27e1850

return stateMachine.GetResult() + "\n";

CLion will open String icinga::operator+(const String&,const char*) which copies the string.

(Also, I really wonder if there's actually an implementation of std::string that allows prepending without reallocation

As long as there's enough free capacity, there's no reason to reallocate.

a corresponding overload of operator+ is provided for std::string.)

Exactly.


bool icinga::operator==(const String& lhs, const String& rhs)
{
return lhs.GetData() == rhs.GetData();
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2 changes: 2 additions & 0 deletions lib/base/string.hpp
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Expand Up @@ -144,7 +144,9 @@ std::istream& operator>>(std::istream& stream, String& str);

String operator+(const String& lhs, const String& rhs);
String operator+(const String& lhs, const char *rhs);
String operator+(String&& lhs, const char *rhs);
String operator+(const char *lhs, const String& rhs);
String operator+(const char *lhs, String&& rhs);

bool operator==(const String& lhs, const String& rhs);
bool operator==(const String& lhs, const char *rhs);
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