CppCon2018
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vinniefalco
Use of std::queue instead of std::vector for outgoing messages
More natural for this task and more efficient when removing the first element.
I got a question for you, how much memory does std::queue allocate when you insert the first element?
According to https://en.cppreference.com/w/cpp/container/deque: "deques typically have large minimal memory cost; a deque holding just one element has to allocate its full internal array (e.g. 8 times the object size on 64-bit libstdc++; 16 times the object size or 4096 bytes, whichever is larger, on 64-bit libc++)". But is it a problem here? According to another study (https://www.codeproject.com/Articles/5425/An-In-Depth-Study-of-the-STL-Deque-Container) std::deque still shows better performance on push_back()'s and pop_front()'s than std::vector.
@pdimov what do you think about this? queue looks correct on paper but vector has its own simplistic charm...
deque/queue is probably better.
#include <vector>
#include <deque>
#include <chrono>
#include <memory>
#include <iostream>
template<class T> void pop_front( std::deque<T> & v )
{
v.pop_front();
}
template<class T> void pop_front( std::vector<T> & v )
{
v.erase( v.begin() );
}
template<class V> void test( V&& v, int N, int M )
{
for( int i = 0; i < M; ++i )
{
v.push_back( std::make_shared<int>() );
}
auto tp1 = std::chrono::high_resolution_clock::now();
for( int i = 0; i < N; ++i )
{
auto w = v.front();
pop_front( v );
v.push_back( w );
}
auto tp2 = std::chrono::high_resolution_clock::now();
std::cout << std::chrono::duration_cast<std::chrono::milliseconds>( tp2 - tp1 ).count() << " ms\n";
}
int main()
{
int const N = 1000000;
int const M = 10;
std::cout << "vector: "; test( std::vector<std::shared_ptr<int>>(), N, M );
std::cout << " deque: "; test( std::deque<std::shared_ptr<int>>(), N, M );
}
N=1000000, M=1:
vector: 31 ms
deque: 33 ms
N=1000000, M=10:
vector: 52 ms
deque: 34 ms
N=1000000, M=100:
vector: 282 ms
deque: 34 ms
N=1000000, M=1000:
vector: 2516 ms
deque: 33 ms
N=1000000, M=10000:
vector: 25852 ms
deque: 37 ms