Re: Memory leak with dynamic array

[bearophile]

Few dynamic array benchmarks that can show you more differences between C++ and 
D2.

Timings dmd, N=5_000_000, NLOOPS=15, T=double, seconds:
  C++ v1: 0.67
  C++ v1: 0.72  
  D v1:   6.47 (uses >1 GB RAM)
  D v2:   0.76
  D v3:   5.25

dmd v2.043, dmd -O -release -inline
g++ 4.4.1, -O3 -Wall -s

-----------------

// D v.1
import std.c.stdio: printf;

void main() {
    alias double T;
    enum int N = 5_000_000;
    enum int NLOOPS = 15;

    T[] arr;
    arr.length = N;

    foreach (i; 0 .. NLOOPS) {
        arr.length = 0;

        foreach (j; 0 .. N)
            arr ~= j;

        printf("At iteration %d, arr has %u elements.\n", i, arr.length);
    }
}

-----------------

// D v.2
import std.c.stdio: printf;

void main() {
    alias double T;
    enum int N = 5_000_000;
    enum int NLOOPS = 15;

    auto arr = new T[N];

    foreach (i; 0 .. NLOOPS) {
        uint arr_len = 0;

        foreach (j; 0 .. N) {
            arr[arr_len] = j;
            arr_len++;
        }

        printf("At iteration %d, arr has %u elements.\n", i, arr_len);
    }
}

-----------------

// D v.3
import std.c.stdio: printf;

void main() {
    alias double T;
    enum int N = 5_000_000;
    enum int NLOOPS = 15;

    T[] arr;
    arr.reserve(N);

    foreach (i; 0 .. NLOOPS) {
        arr.length = 0;
        arr.assumeSafeAppend;

        foreach (j; 0 .. N)
            arr ~= j;

        printf("At iteration %d, arr has %u elements.\n", i, arr.length);
    }
}

-----------------

// C++ v.1
#include "stdio.h"
#include <vector>

int main() {
    typedef double T;
    const int N = 5000000;
    const int NLOOPS = 15;

    std::vector<T> arr;
    arr.reserve(N);

    for (int i = 0; i < NLOOPS; i++) {
        arr.clear();

        for (int j = 0; j < N; j++)
            arr.push_back(j);

        printf("At iteration %d, arr has %u elements.\n", i, arr.size());
    }
}

-----------------

// C++ v.2
#include "stdio.h"
#include <vector>

int main() {
    typedef double T;
    const int N = 5000000;
    const int NLOOPS = 15;

    std::vector<T> arr(N);

    for (int i = 0; i < NLOOPS; i++) {
        size_t arr_len = 0;

        for (int j = 0; j < N; j++) {
            arr[arr_len] = j;
            arr_len++;
        }

        printf("At iteration %d, arr has %u elements.\n", i, arr_len);
    }
}

-----------------

Bye,
bearophile