Std :: string memory management

Question

I have a problem managing memory using std :: string.

I have an application - a multi-threaded server with separate threads (I need to join them, they will perform the task and exit), and I found that after a while the memory usage becomes quite high. I started experimenting where the problem is, and I created a test program that demonstrates the problem.

#include <iostream>

#include <string>
#include <pthread.h>

pthread_t           thread[100];

using namespace std;

class tst {
    public:
        tst() {
            //cout << "~ Create" << endl;
        }
        ~tst() {
            //cout << "~ Delete" << endl;
        }
        void calc() {
            string TTT;
            for (int ii=0; ii<100000; ii++) {
                TTT+="abcdenbsdmnbfsmdnfbmsndbfmsndb ";
            }
        }
};

void *testThread (void *arg) {
    int cnt=*(int *) arg;
    cout << cnt << " ";
    tst *TEST=new tst;
    TEST->calc();
    delete TEST;
    pthread_exit((void *)0);
}

int main (int argc, char * const argv[]) {

cout << "---------------------------------------------------" << endl;
sleep(5);

    for (int oo=0; oo<100; oo++) {
        pthread_create(&thread[oo], NULL, testThread, &oo);
        pthread_detach(thread[oo]);
    }
    cout << endl;
    cout << "---------------------------------------------------" << endl;

    sleep(5);

    for (int oo=0; oo<100; oo++) {
        pthread_create(&thread[oo], NULL, testThread, &oo);
        pthread_detach(thread[oo]);
    }
    cout << endl;
    cout << "---------------------------------------------------" << endl;

    sleep(5);
    exit(0);
}

after the first “---”, the memory usage is 364 KB, after the second - 19 MB, after the third - 33.5 MB. There is another strange thing: each run shows a different memory usage, but basically the last memory usage is about 50% more than after the second “---”.

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Answer 1

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Answer 2

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string TTT;

// We know how big the string will get, so pre-alloc memory for it to avoid the 
// inefficiencies of the default allocation strategy as the string grows.

TTT.reserve(3100001);

for (int ii=0; ii<100000; ii++) {
    TTT+="abcdenbsdmnbfsmdnfbmsndbfmsndb ";
}

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Answer 3

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Answer 4

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Answer 5

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void *testThread (void *arg) {
    if (1) {
        int cnt=*(int *) arg;
        cout << cnt << " ";
        tst *TEST=new tst;
        TEST->calc();
        delete TEST;
    }
    pthread_exit((void *)0);
}

... ,