线程具有相同的id [英] threads have the same id
问题描述
我学习线程。我已阅读,线程终止后,它跳出函数(即作为参数传递给pthread_create的功能)。
所以我创建循环线程,它们被执行,之后他们被终止。
(抱歉有些长code)
I learn threads. I have read that thread terminates after it is out of a function (that is passed as parameter to pthread_create function). So I create threads in the loop, they are executed and afterwards they are terminated. (sorry for some long code)
但是,当我调用一个函数pthread_create的,新主题得到相同的ID。为什么?
But when I call a function pthread_create, new threads get the same ids. Why?
struct data {
FILE *f;
};
void *read_line_of_file(void *gdata) {
pthread_mutex_lock(&g_count_mutex); // only one thread can work with file,
//doing so we block other threads from accessing it
data *ldata = (data *) gdata;
char line[80];
int ret_val =fscanf(ldata->f,"%s",line);
pthread_mutex_unlock(&g_count_mutex); // allow other threads to access it
if (ret_val != EOF)
printf("%s %lu\n ", line, pthread_self());
// some time consuming operations, while they are being executed by one thread,
// other threads are not influenced by it (if there are executed on different cores)
volatile int a=8;
for (int i=0;i <10000;i++ )
for (int i=0;i <10000;i++ ) {
a=a/7+i;
}
if (ret_val == EOF) // here thread ends
pthread_exit((void *)1);
pthread_exit((void *)0);
}
int main() {
int kNumber_of_threads=3, val=0;
pthread_t threads[kNumber_of_threads];
int ret_val_from_thread=0;
data mydata;
mydata.f = fopen("data.txt","r");
if ( mydata.f == NULL) {
printf("file is not found\n");
return 0;
}
for( ; val != 1 ;) {
// THIS IS THAT PLACE, IDs are the same (according to the number of processes),
// I expected them to be changing..
for(int i=0; i<kNumber_of_threads; i++) {
pthread_create(&threads[i],NULL,read_line_of_file, &mydata);
}
for(int i=0; i<kNumber_of_threads; i++) {
pthread_join(threads[i], (void **) &ret_val_from_thread);
if (ret_val_from_thread != 0)
val = ret_val_from_thread;
}
printf(" next %d\n",val);
}
printf("work is finished\n");
fclose(mydata.f);
return 0;
}
作为结果,我看到线程该ID没有被更改:
as result, I see that id of threads are not being changed:
我不知道,真的是创造了新的主题?
I wonder, are new threads really created?
在此先感谢!
推荐答案
主题的ID只保证是当前正在运行的线程之间的不同。如果你摧毁一个线程,并创建一个新的,它很可能是一个previously使用线程ID创建的。
Thread IDs are only guaranteed to be different among currently running threads. If you destroy a thread and create a new one, it may well be created with a previously used thread ID.
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