win32 mutithread-busyloop

把代码放进VS2008跑，因为用了多线程C runtime lib，所以并不会像书中说的那么stupid：

/* * BusyWait.c * * Sample code for Multithreading Applications in Win32 * This is from Chapter 3, Listing 3-1 * * Demonstrate the effect on performance * of using a busy loop. First call the * worker routine with just a function call * to get a baseline performance reading, * then create a second thread and a * busy loop. * * Build command: cl /MD busywait.c */#define WIN32_LEAN_AND_MEAN#include <stdio.h>#include <stdlib.h>#include <windows.h>#include <time.h>#include "MtVerify.h"DWORD WINAPI ThreadFunc(LPVOID);int main(){    HANDLE hThrd;    DWORD exitCode = 0;    DWORD threadId;    DWORD begin;    DWORD elapsed;    puts("Timing normal function call...");    begin = GetTickCount();    ThreadFunc(0);    elapsed = GetTickCount()-begin;    printf("Function call took: %d.%.03d seconds\n\n",                elapsed/1000, elapsed%1000);        puts("Timing thread + busy loop...");    begin = GetTickCount();    MTVERIFY( hThrd = CreateThread(NULL,        0,        ThreadFunc,        (LPVOID)1,        0,        &threadId )    );    /* This busy loop chews up lots of CPU time */    for (;;)    {        GetExitCodeThread(hThrd, &exitCode);        if ( exitCode != STILL_ACTIVE )            break;    }    elapsed = GetTickCount()-begin;    printf("Thread + busy loop took: %d.%.03d seconds\n",                elapsed/1000, elapsed%1000);    MTVERIFY( CloseHandle(hThrd) );    return EXIT_SUCCESS;}/* * Cute little busy work routine that computes the value * of PI using probability.  Highly dependent on having * a good random number generator (rand is iffy) */DWORD WINAPI ThreadFunc(LPVOID n){    int i;    int inside = 0;    double val;    UNREFERENCED_PARAMETER(n);    /* Seed the random-number generator */    srand( (unsigned)time( NULL ) );    for (i=0; i<1000000; i++)    {        double x = (double)(rand())/RAND_MAX;        double y = (double)(rand())/RAND_MAX;        if ( (x*x + y*y) <= 1.0 )            inside++;    }    val = (double)inside / i;    printf("PI = %.4g\n", val*4);    return 0;}