我有一个多线程程序,我在所有 pthread_create 之前和所有 pthread_join 之后开始分析时间。
现在我发现这一次,我们称之为X,如下面的“在 xms 中完成”所示, 实际上是用户 + sys时间输出。在我的应用程序中,a.out 的 number 参数控制要生成的线程数。./a.out 1生成 1 个 pthread 和./a.out 2生成 2 个线程,其中每个线程执行相同数量的工作。
我期待 X 是实时而不是用户 + 系统时间。有人可以告诉我为什么不是这样吗?那么这真的意味着我的应用程序确实在并行运行,线程之间没有任何锁定。
[jithin@whatsoeverclever tests]$ time ./a.out 1
Done in 320ms
real 0m0.347s
user 0m0.300s
sys 0m0.046s
[jithin@whatsoeverclever tests]$ time ./a.out 2
Done in 450ms
real 0m0.266s
user 0m0.383s
sys 0m0.087s
[jithin@whatsoeverclever tests]$ time ./a.out 3
Done in 630ms
real 0m0.310s
user 0m0.532s
sys 0m0.105s
代码
int main(int argc, char **argv) {
//Read the words
getWords();
//Set number of words to use
int maxWords = words.size();
if(argc > 1) {
int numWords = atoi(argv[1]);
if(numWords > 0 && numWords < maxWords) maxWords = numWords;
}
//Init model
model = new Model(MODEL_PATH);
pthread_t *threads = new pthread_t[maxWords];
pthread_attr_t attr;
void *status;
// Initialize and set thread joinable
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
int rc;
clock_t startTime = clock();
for(unsigned i=0; i<maxWords; i++) {
//create thread
rc = pthread_create(&threads[i], NULL, processWord, (void *)&words[i] );
if (rc){
cout << "Error:unable to create thread: " << i << "," << rc << endl;
exit(-1);
}
}
// free attribute and wait for the other threads
pthread_attr_destroy(&attr);
for(unsigned i=0; i<maxWords; i++) {
rc = pthread_join(threads[i], &status);
if (rc){
cout << "Error:unable to join thread: " << i << "," << rc << endl;
exit(-1);
}
}
clock_t endTime = clock();
float diff = (((float)endTime - (float)startTime) / 1000000.0F ) * 1000;
cout<<"Done in "<< diff << "ms\n";
delete[] threads;
delete model;
}