Question

我不断听说在 Windows 中创建新进程非常昂贵。但我找不到确切的数字。是否有周期的极点数? 2GHz 的双核心处理器上有多少毫秒?

我在Python写了一个测试程序,每个过程测量5米, 但我不知道其中有多少是Python的额外间接费用。我猜不多。

Answer 1

互换问题!

如前所述,管理费高居不下。好奇的是,如果很快地写出一个小基准来获得一些拇指,那么线条和过程的创建需要多长时间,以及这些时间之间的关系。

#include <windows.h>
#include <stdio.h>
#include <conio.h>

#define MIN   0
#define AVG   1
#define MAX   2

DWORD WINAPI thread(LPVOID lpvData)
{
    return (0);
}

int main()
{
    BOOL result;
    int iteration;
    int i;
    STARTUPINFO si;
    PROCESS_INFORMATION pi;
    DWORD tStart;
    DWORD tEllapsed;
    double tCall;
    int spawnCount;
    HANDLE hThread;
    DWORD threadId;
    double ratio;
    double statCreateProcess[3];
    double statCreateThread[3];


    for (iteration = 0; iteration < 16; iteration++)
    {
        /*
        **  Measure creation time of process
        */
        tEllapsed = 0;
        spawnCount = 0;
        for (i = 0; i < 100; i++)
        {
            ZeroMemory(&si, sizeof(si));
            si.cb = sizeof(si);
            ZeroMemory(&pi, sizeof(pi));

            tStart = GetTickCount();
            result = CreateProcess(NULL,
                                   "cmd.exe",
                                   NULL,
                                   NULL,
                                   FALSE,
                                   NORMAL_PRIORITY_CLASS,
                                   NULL,
                                   NULL,
                                   &si,
                                   &pi);

            if (result != FALSE)
            {
                tEllapsed += GetTickCount() - tStart;
                spawnCount++;

                // clean up...
                TerminateProcess(pi.hProcess, 0);
                CloseHandle(pi.hThread);
                CloseHandle(pi.hProcess);
            }
        }
        tCall = tEllapsed / (double)spawnCount;
        printf("average creation time of process: %0.3fms
", tCall);

        // track statistics...
        if (iteration > 0)
        {
            if (statCreateProcess[MIN] > tCall)
                statCreateProcess[MIN] = tCall;
            statCreateProcess[AVG] += tCall;
            if (statCreateProcess[MAX] < tCall)
                statCreateProcess[MAX] = tCall;
        }
        else
        {
            statCreateProcess[MIN] = tCall;
            statCreateProcess[AVG] = tCall;
            statCreateProcess[MAX] = tCall;
        }


        /* measure creation time of thread */
        spawnCount = 0;
        tStart = GetTickCount();
        for (i = 0; i < 5000; i++)
        {           
            hThread = CreateThread(NULL,
                                   0,
                                   thread,
                                   NULL,
                                   0,
                                   &threadId);
            if (hThread != NULL)
            {
                spawnCount++;

                // clean up...
                CloseHandle(hThread);
            }
        }
        tEllapsed = GetTickCount() - tStart;
        tCall = tEllapsed / (double)spawnCount;
        printf("average creation time of thread: %0.3fms
", tCall);

        // track statistics...
        if (iteration > 0)
        {
            if (statCreateThread[MIN] > tCall)
                statCreateThread[MIN] = tCall;
            statCreateThread[AVG] += tCall;
            if (statCreateThread[MAX] < tCall)
                statCreateThread[MAX] = tCall;
        }
        else
        {
            statCreateThread[MIN] = tCall;
            statCreateThread[AVG] = tCall;
            statCreateThread[MAX] = tCall;
        }
    } /* for (iteration = ...) */

    statCreateProcess[AVG] /= iteration;
    statCreateThread[AVG] /= iteration;

    printf("

--- CreateProcess(..) ---
");
    printf("minimum execution time ...: %0.3fms
", statCreateProcess[MIN]);
    printf("average execution time ...: %0.3fms
", statCreateProcess[AVG]);
    printf("maximum execution time ...: %0.3fms
", statCreateProcess[MAX]);
    printf("
--- CreateThread(..) ---
");
    printf("minimum execution time ...: %0.3fms
", statCreateThread[MIN]);
    printf("average execution time ...: %0.3fms
", statCreateThread[AVG]);
    printf("maximum execution time ...: %0.3fms
", statCreateThread[MAX]);

    ratio = statCreateProcess[AVG] / statCreateThread[AVG];
    printf("

ratio: %0.3f

", ratio);

    getch();
    return (0);
}

我在我的电脑(i5 3.2GHz; Windows 7)上做了几次运行,

--- CreateProcess(..) ---
minimum execution time ...: 11.860ms
average execution time ...: 12.756ms
maximum execution time ...: 14.980ms

--- CreateThread(..) ---
minimum execution time ...: 0.034ms
average execution time ...: 0.037ms
maximum execution time ...: 0.044ms


ratio: 342.565

正如预期的那样,CreateProcess(.)的变异性更大,因为涉及的系统电话更多,而被另一线条中断的可能性更大。记住创建线条的时间甚至更短, 因为时间测量包括整个控制环( 否则 GetTickCount(.) ) 。

在运行 Windows XP(运行于上述同一台机器)的虚拟PC上进行的另一项测试产生了以下数值:

--- CreateProcess(..) ---
minimum execution time ...: 22.630ms
average execution time ...: 24.666ms
maximum execution time ...: 27.340ms

--- CreateThread(..) ---
minimum execution time ...: 0.076ms
average execution time ...: 0.086ms
maximum execution time ...: 0.100ms


ratio: 287.982

CreateProcess (.) 和 CreateTread (.) 的平均执行时间比相当接近。

查看其他机器和Windows版本的值将会是互换的。如果在不同的机器和Windows版本中,大约300的比值大致相同,我并不感到惊讶。

所以,让我们来总结: 创建进程(.) 比 Windows 上的 CreateTreadTread (.) 慢得多。但实际上, 我非常震惊它有多慢...

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