比方说,有是在C两个线程(并行线程)++程序:Pthread冻结标准输出?
- 的
main thread
- 的
child thread
什么程序做很简单:
- 绑定两个线程到两个不同的核心。
- 将两个线程的优先级设置为非常高的值(
child thread
为-99,main thread
为-98)。 child thread
正在执行一些使用100%CPU的繁重任务。- 在创建
child thread
之后,main thread
正在尝试调用printf()。
问题是,一旦创建了子线程,它将冻结stdout,并且控制台上不再有任何东西被打印出来。但是,程序退出时,所有消息突然显示在控制台中。下面是一个.cpp文件证明这样的效果:
main.cpp中:
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/mman.h>
bool EXIT = false;
void signal_handler(int signal){
EXIT = true;
}
void *child_thread(void *x_args){
printf("Setting child thread CPU affinity (Core #1)...\n");
cpu_set_t cpuset;
CPU_ZERO(&cpuset);
CPU_SET(1, &cpuset);
if (pthread_setaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuset)){
perror("Cannot set child thread CPU affinity");
printf("Exit\n");
exit(1);
}
printf("Locking memory of child thread...\n");
mlockall(MCL_CURRENT | MCL_FUTURE);
printf("Setting child thread priority (-99)...\n");
struct sched_param sched_param;
sched_param.sched_priority = sched_get_priority_max(SCHED_FIFO)-1;
if (sched_setscheduler(0, SCHED_FIFO, &sched_param)){
perror("Cannot set child thread priority");
printf("Exit\n");
exit(1);
}
printf("Entering while loop inside child thread...\n");
while(!EXIT){}
return NULL;
}
int main(){
signal(SIGINT, signal_handler);
pthread_t thread;
printf("Setting main thread CPU affinity (Core #0)...\n");
cpu_set_t cpuset;
CPU_ZERO(&cpuset);
CPU_SET(0, &cpuset);
if (pthread_setaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuset)){
perror("Cannot set main thread CPU affinity");
printf("Exit.\n");
exit(1);
}
printf("Locking memory of main thread...\n");
mlockall(MCL_CURRENT | MCL_FUTURE);
printf("Setting main thread priority (-98)...\n");
struct sched_param sched_param;
sched_param.sched_priority = sched_get_priority_max(SCHED_FIFO)-2;
if (sched_setscheduler(0, SCHED_FIFO, &sched_param)){
perror("Cannot set main thread priority");
printf("Exit.\n");
exit(1);
}
printf("Creating child thread...\n");
if (pthread_create(&thread, NULL, child_thread, NULL)){
perror("Cannot create child thread");
printf("Exit.\n");
exit(1);
}
printf("Entering while loop in main thread...\n");
while(!EXIT){
sleep(1);
printf("I can't see this until I press Ctrl+C!\n");
}
pthread_join(thread, NULL);
printf("Exit.\n");
return 0;
}
你可以编译:
sudo ./main
:
g++ main.cpp -pthread -o main
然后运行它
然后,在输出以下内容后,您应该看到stdout会冻结:
Setting main thread CPU affinity (Core #0)...
Locking memory of main thread...
Setting main thread priority (-98)...
Creating child thread...
Entering while loop in main thread...
Setting child thread CPU affinity (Core #1)...
即使在一个小时后,您将不会再看到输出。但是当Ctrl+C
被按下。你会看到所有的消息传出来:
I can't see this until I press Ctrl+C!
I can't see this until I press Ctrl+C!
I can't see this until I press Ctrl+C!
I can't see this until I press Ctrl+C!
I can't see this until I press Ctrl+C!
I can't see this until I press Ctrl+C!
I can't see this until I press Ctrl+C!
I can't see this until I press Ctrl+C!
的main thread
实际上是在后台运行,因为如果你注释掉while循环(睡眠和printf)内的两条线,你可以看到,它也使用100%的CPU。但是ht
我在这里错过了什么?
可悲的是我不能重现这个问题。 – johnchen902
@ johnchen902也许这是操作系统相关的?我正在使用Ubuntu14.04-LTS。如果未设置线程优先级,则问题不会显示。例如,如果我没有'sudo'运行它,一切正常。 – hhy
问题解决了。在Tav的答案下看到我的评论。 – hhy