标签：use 性能 ostringstream malloc 测试 printf include oss op

ostringstream 性能测试

分析与建议

性能分析

1. ostringstream 格式转换的性能并不差，至少从测试上看与 snprintf 差距不是数量级上的

2. 每次创建一个 ostringstream 对象都会触发一次全局 locale 对象的引用计数递增（参考1，参考2），多线程场景下有 false sharing 的性能损耗，而且很明显

3. 不要重复的创建与销毁 ostringstream 对象，避免 false sharing

4. ostringstream 会在堆上创建内存，系统会优化 malloc/free，所以不必太过关注这个问题

测试结果

下面代码在我机器（4 cores，g++ -O2）上运行的结果如下，false sharing 的影响可以从线程增加但 use_oss 函数耗时未降上看出来

Thread num from 1 to 9

1: use_printf/585, use_printf_op/582, use_printf_malloc/682, use_printf_malloc_op/582, use_oss_op/658, use_oss/3115,
2: use_printf/294, use_printf_op/291, use_printf_malloc/341, use_printf_malloc_op/292, use_oss_op/329, use_oss/3752,
3: use_printf/195, use_printf_op/194, use_printf_malloc/228, use_printf_malloc_op/194, use_oss_op/219, use_oss/3616,
4: use_printf/147, use_printf_op/147, use_printf_malloc/172, use_printf_malloc_op/147, use_oss_op/166, use_oss/3636,
5: use_printf/119, use_printf_op/118, use_printf_malloc/138, use_printf_malloc_op/118, use_oss_op/135, use_oss/3721,
6: use_printf/105, use_printf_op/100, use_printf_malloc/119, use_printf_malloc_op/102, use_oss_op/113, use_oss/3791,
7: use_printf/118, use_printf_op/134, use_printf_malloc/134, use_printf_malloc_op/115, use_oss_op/126, use_oss/3778,
8: use_printf/112, use_printf_op/116, use_printf_malloc/122, use_printf_malloc_op/114, use_oss_op/137, use_oss/3791,
9: use_printf/104, use_printf_op/102, use_printf_malloc/123, use_printf_malloc_op/101, use_oss_op/124, use_oss/3792,

测试代码

#include <map>
#include <future>
#include <iostream>
#include <numeric>
#include <sstream>
#include <string.h>
#include <thread>
#include <vector>

int use_oss(int cnt)
{
    int cnt_tmp = 0;
    while (cnt--) {
        std::ostringstream oss;
        oss.str("");
        oss.clear();
        oss << "hi" << 999;
        cnt_tmp += oss.str().size();
    }

    return cnt_tmp;
}

int use_oss_op(int cnt)
{
    int cnt_tmp = 0;
    std::ostringstream oss;
    while (cnt--) {
        oss.str("");
        oss.clear();
        oss << "hi" << 999 << std::flush;
        cnt_tmp += oss.str().size();
    }

    return cnt_tmp;
}

int use_printf(int cnt)
{
    int cnt_tmp = 0;
    while (cnt--) {
        char buf[64];
        snprintf(buf, sizeof(buf), "hi%d", 999);
        cnt_tmp += strlen(buf);
    }

    return cnt_tmp;
}

int use_printf_op(int cnt)
{
    int cnt_tmp = 0;
    char buf[64];
    while (cnt--) {
        snprintf(buf, sizeof(buf), "hi%d", 999);
        cnt_tmp += strlen(buf);
    }

    return cnt_tmp;
}

int use_printf_malloc(int cnt)
{
    int cnt_tmp = 0;
    while (cnt--) {
        char* buf = (char*)malloc(64);
        snprintf(buf, sizeof(buf), "hi%d", 999);
        cnt_tmp += strlen(buf);
        free(buf);
    }

    return cnt_tmp;
}

int use_printf_malloc_op(int cnt)
{
    int cnt_tmp = 0;
    char* buf = (char*)malloc(64);
    while (cnt--) {
        snprintf(buf, sizeof(buf), "hi%d", 999);
        cnt_tmp += strlen(buf);
    }

    free(buf);
    return cnt_tmp;
}

// 1*2*3*4*5*6*7*8*9 = 362880
const int TOTAL_USE_CNT  = 1 * 2 * 3 * 4 * 5 * 6 * 7 * 8 * 9 * 30;
const int MAX_THREAD_NUM = 9;

int main()
{
    std::map<decltype(use_oss)*, std::string> funs;
    
    funs[use_oss]    = "use_oss";
    funs[use_oss_op] = "use_oss_op";

    funs[use_printf]           = "use_printf";
    funs[use_printf_op]        = "use_printf_op";
    funs[use_printf_malloc]    = "use_printf_malloc";
    funs[use_printf_malloc_op] = "use_printf_malloc_op";

    std::cout << "Thread num from 1 to " << MAX_THREAD_NUM << std::endl << std::endl;
    for (int t = 1; t <= MAX_THREAD_NUM; t++) {
        int USE_CNT_PER_THREAD = TOTAL_USE_CNT / t;

        std::cout << t <<": ";
        size_t acc = 0;
        for (auto p : funs) {

            auto f = p.first;
            std::vector<std::future<int>> future_vec;
            future_vec.reserve(11);
            auto ms_begin = std::chrono::steady_clock::now();
            for (int i = 0; i < t; i++) {
                future_vec.push_back(std::async(std::launch::async,
                    [USE_CNT_PER_THREAD,f]() -> int { return f(USE_CNT_PER_THREAD); }));
            }

            for (auto& f : future_vec) {
                f.wait();
                acc += f.get();
            }
            auto ms_end = std::chrono::steady_clock::now();
            auto mc_s = std::chrono::duration_cast<std::chrono::milliseconds>(ms_end - ms_begin);
            std::cout << funs[f] << "/" << mc_s.count() << ", ";
        }
        std::cout << std::endl;
    }
}

标签：use,性能,ostringstream,malloc,测试,printf,include,oss,op
来源： https://www.cnblogs.com/jiahu-Blog/p/13259343.html

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