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以下代码用于测试我系统上 libjpeg-turbo 的性能

unsigned char *source; 
unsigned int _jpegSize = 0; 
unsigned long long GetTime( void )
{
    struct timeval tv;
    struct timezone tz;

    gettimeofday(&tv, &tz);

    return tv.tv_sec * 1000000ULL + tv.tv_usec;
}
int main(int argc,char**argv)
{
    if(argc < 3)
        return 0;
    char *fileName = argv[1];
    int fileSize = atoi(argv[2]);

    source = (unsigned char*)malloc(fileSize);
    ReadFile(argv[1],fileSize); //Reads the file and copy the data to source buffer

for(int i=0; i<500; i++)
{

    unsigned char* _compressedImage = source;   
    int jpegSubsamp, width, height;
    tjhandle _jpegDecompressor = tjInitDecompress();
    tjDecompressHeader2(_jpegDecompressor, _compressedImage, fileSize, &width, &height, &jpegSubsamp);
    unsigned char dstBuffer[width*height*3]; //!< will contain the decompressed image

    unsigned long long t1 = GetTime();

    tjDecompress2(_jpegDecompressor, _compressedImage, fileSize, dstBuffer, width, 0/*pitch*/, height, TJPF_RGB, TJFLAG_FASTDCT);

    unsigned long long t2 = GetTime();
    printf("TimeTaken: %llu microseconds for %f ms\n", t2-t1,(float)((t2-t1)/(1000))); 

    tjDestroy(_jpegDecompressor);    
    usleep(50000);   
}

它在 for 循环中重复解码 jpeg 图像。在我的系统上， tjDecompress2需要大约5-7 毫秒来解码 1024x768 图像。问题是，如果我 在循环末尾添加一个usleep(50000)命令，则tjDecompress2的执行时间会增加到25-28ms。这种行为的原因是什么以及如何解决。基本上我想以 20 FPS 从 ma USB 相机读取 MJPEG 图像并使用 libjpeg-turbo 对其进行解码，因此添加usleep(5000)的目的是模拟两个连续帧到达之间的时间

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