# Linux获取时间以及定时长休眠总结(Centos 8 stream)

我不是女神ヾ 2022-09-12 07:50 23阅读 0赞

自用：  
需要精确时间不要使用clock()函数而要使用gettimeofday()函数;  
使用nanosleep()函数控制休眠时间测试得到如下结果：  
clock()函数精度在1ms(vmware中2ms)且不稳定，有时上浮有时下浮；  
gettimeofday()函数精度一般在100us(vmware中1ms)以内，稳定上浮；

例外：**当命令休眠时间正好在1ms时**，clock()可以做到10us以内的精度，但不稳定，周期性会出现1ms的上浮误差(不适用于vmware)

测试过程中发现clock和gettimeofday误差会同时爆增，说明nanosleep的睡眠时间不绝对稳定，需要作相关处理。

#include <iostream>
    #include <ctime>
    #include <sys/time.h>
    #include "registers_input.h"
    
    U32* time_counting;
    
    using namespace std;
    
    struct timespec req;
    
    void VehicleEnvMain(void)
    { 
        clock_t start;
        clock_t end;
        *time_counting = 0;
        req.tv_sec = 0;
        req.tv_nsec = 2000 * 1000;
        struct timeval tvBegin;
        struct timeval tvNow;
        unsigned int nTimeTest = 0;
        gettimeofday(&tvBegin, NULL);
        long o = tvBegin.tv_sec * 1000000 + tvBegin.tv_usec;
        //while(1)
        for (int i = 0; i < 500; i++)
        { 
            //if((clock()-start) > 0) /*clock()返回的值为0.001ms*/
            { 
                (*time_counting)++;
                start = clock();
                gettimeofday(&tvBegin, NULL);
                int u = nanosleep(&req, NULL);
                end = clock();
                gettimeofday(&tvNow, NULL);
                nTimeTest = (tvNow.tv_sec - tvBegin.tv_sec) * 1000000 + tvNow.tv_usec - tvBegin.tv_usec;
                cout << (end - start) << " state "<< u << " " << (tvNow.tv_sec * 1000000 + tvNow.tv_usec -o)  << " " << nTimeTest << "\n";
            }
            //if((clock()-o)>=1000)
            //{ 
            // break;
            //}
            
        }
        cout << (*time_counting) << "\n";
        /* cout << "CPU time used: " << 1000.0 * (end - start) / CLOCKS_PER_SEC << " ms\n"; cout << start << "\n"; cout << end; cout << "\n"; */
    }

设定休眠2000us时的结果：

1969 state 0 12528 2085
    1953 state 0 14612 2079
    1973 state 0 16676 2058
    2220 state 0 18791 2104
    1929 state 0 20858 2056
    1957 state 0 22945 2080
    1935 state 0 25034 2082
    1936 state 0 27119 2080
    2381 state 0 29203 2079
    1971 state 0 31289 2081
    1966 state 0 33353 2057
    1999 state 0 35448 2085
    1947 state 0 37539 2081
    1956 state 0 39628 2083
    1970 state 0 41720 2086
    2196 state 0 43789 2063
    1934 state 0 45850 2056
    1928 state 0 47912 2056

设定休眠1000us时的结果：

1003 state 0 57948 1057
    1034 state 0 59042 1087
    2002 state 0 60086 1034
    1003 state 0 61152 1057
    1000 state 0 62218 1056
    1002 state 0 63281 1055
    1025 state 0 64365 1077
    1002 state 0 65446 1074
    1001 state 0 66530 1079
    1002 state 0 67620 1084
    1002 state 0 68700 1075
    1002 state 0 69783 1079
    1000 state 0 70861 1074
    1002 state 0 71941 1074
    1001 state 0 73003 1056
    2000 state 0 74090 1081
    1001 state 0 75113 1017
    1004 state 0 76177 1057
    1033 state 0 77273 1086
    1000 state 0 78340 1057
    1001 state 0 79426 1077
    1002 state 0 80508 1074
    1001 state 0 81570 1056
    1001 state 0 82630 1055
    1001 state 0 83716 1080