Re: std::string reference counting performance

[Liviu Nicoara]

On 10/21/12 21:44, Liviu Nicoara wrote:
On 10/21/12 21:11, Liviu Nicoara wrote:
Hi all,
I ran the attached test case, s.cpp, and timed it:

Gosh darn it, attached the wrong files. Here are the right ones.

Made the same mistake twice. My apologies for the clutter. Here are the 
right ones.

Liviu

* Deep-copy

$ for f in 16 8 4 2 1; do time ./s $f 50000000; done
16, 50000000    0m9.438s        2m15.615s       0m10.799s
 8, 50000000    0m6.973s        0m55.579s       0m0.006s
 4, 50000000    0m6.942s        0m27.505s       0m0.001s
 2, 50000000    0m6.888s        0m13.753s       0m0.002s
 1, 50000000    0m6.800s        0m6.799s        0m0.001s

* Ref-counted

$ for f in 16 8 4 2 1; do time ./s $f 50000000; done
16, 50000000    2m19.098s       2m36.278s       30m38.488s
 8, 50000000    1m47.757s       2m7.278s        10m18.418s
 4, 50000000    4m27.425s       5m56.620s       10m13.892s
 2, 50000000    0m17.667s       0m22.560s       0m10.695s
 1, 50000000    0m2.923s        0m2.921s        0m0.001s

#include <iostream>
#include <locale>

#include <cstdio>
#include <cstdlib>
#include <cstring>

#include <pthread.h>
#include <unistd.h>

#define MAX_THREADS 128

static long nloops = 10000000, nthreads = 16;
static bool volatile pwait = true;

////////////////////////////////////////////////////////////////////////

extern "C" {

static void* 
f (void* pv)
{
    std::string const& s = *reinterpret_cast< std::string* > (pv);

    volatile unsigned long n = 0;

    while (pwait) ;

    for (int i = 0; i < nloops; ++i) {
#if !defined (NO_DEEP_COPY)
        const std::string tmp (s.c_str (), s.size ());
#else
        const std::string tmp = s;
#endif // NO_DEEP_COPY

        n += strlen (tmp.c_str ());
    }

    return (void*)n;
}

} // extern "C"

int
main (int argc, char** argv)
{
    switch (argc) {
    case 3:
        nloops = atol (argv [2]);
    case 2:
        nthreads = atol (argv [1]);
        break;
    }

    pthread_t tid [MAX_THREADS] = { 0 };

    if (nthreads > MAX_THREADS)
        nthreads = MAX_THREADS;

    printf ("%ld, %ld\n", nthreads, nloops);

    pthread_setconcurrency (nthreads);

    std::string s ("Hello, world.");
    
    for (int i = 0; i < nthreads; ++i) {
        if (pthread_create (tid + i, 0, f, &s))
            exit (-1);
    }

    usleep (50);
    pwait = false;

    for (int i = 0; i < nthreads; ++i) {
        if (tid [i])
            pthread_join (tid [i], 0);
    }

    return 0;
}