我有一个C pthread 程序,在主线程中创建了N个更新全局变量的线程。主线程还调用pthread_join等待这些更新线程完成。我还有2个监视线程,它们使用pthread条件变量来检查全局变量是否超过或低于某些数字,如果是,就会终止所有更新线程和另一个监视线程。然而,我在最后一部分遇到了麻烦...杀死其他线程。我的程序做了它应该做的事情,但从未完成...它只是卡住了。在每个观察线程结束时调用exit(0)可以解决问题,但我觉得这太懒了,我真的想学习如何从单独的线程中杀死其他线程并返回到主函数。
以下是我的代码:
#include <pthread.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
void *update(void *i);
void *watchIncrease();
void *watchDecrease();
//init globals
double marketValue;
int numThreads;
double *stocks;
double ceiling;
double floor_;
int flag;
pthread_t *threads;
pthread_t watchIncreaseThread;
pthread_t watchDecreaseThread;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t threshold_ceiling;
pthread_cond_t threshold_floor_;
int main(int argc, char **argv){
numThreads = atoi(argv[1]);
int level = atoi(argv[2]);
marketValue = 100 * numThreads;
//initialize personal stocks for threads
stocks = (double *) malloc(sizeof(double) * numThreads);
int i;
for(i = 0; i < numThreads; i++) stocks[i] = 100;
//initialize floor/ceiling
double percent = (double) level / 100;
double cap = marketValue * percent;
ceiling = marketValue + cap;
floor_ = marketValue - cap;
//seed rand()
srand(time(NULL));
//create threads
pthread_cond_init(&threshold_ceiling,NULL);
pthread_cond_init(&threshold_floor_,NULL);
int rc = pthread_create(&watchIncreaseThread,NULL,watchIncrease,NULL);
assert(rc == 0);
rc = pthread_create(&watchDecreaseThread,NULL,watchDecrease,NULL);
assert(rc == 0);
threads = (pthread_t *)malloc(sizeof(pthread_t) * numThreads);
assert(threads != NULL);
for(i = 0; i < numThreads; i++){
int rc = pthread_create(&threads[i],NULL,update,(void *)i);
assert(rc == 0);
}
int j;
for(j = 0; j < numThreads; j++){
pthread_join(threads[j],NULL);
}
return 0;
}
void *update(void *i){
int index = (int)i;
double max = 2;
double val;
while(1){
int rc = pthread_mutex_lock (&lock);
assert(rc == 0);
val = max * ((double)rand()/(double)RAND_MAX - 0.5);
stocks[index] += val;
marketValue += val;
pthread_cond_signal (&threshold_ceiling);
pthread_cond_signal (&threshold_floor_);
pthread_mutex_unlock(&lock);
}
}
void *watchIncrease(){
int rc = pthread_mutex_lock(&lock);
assert(rc == 0);
while(marketValue < ceiling){
pthread_cond_wait(&threshold_ceiling, &lock);
}
printf("Market Up to %.2f\n",marketValue);
int i;
double sum = 0;
for(i = 0; i < numThreads; i++){
sum += stocks[i];
}
printf("Total Market Price of %d stocks: %.2f\n",numThreads,sum);
for(i = 0; i < numThreads; i++){
rc = pthread_cancel(threads[i]);
assert(rc == 0);
}
pthread_cancel(watchDecreaseThread);
pthread_mutex_unlock(&lock);
pthread_exit(NULL);
//exit(0);
}
void *watchDecrease(){
int rc = pthread_mutex_lock(&lock);
assert(rc == 0);
while(marketValue > floor_){
pthread_cond_wait(&threshold_floor_, &lock);
}
printf("Market Down to %.2f\n",marketValue);
int i;
double sum = 0;
for(i = 0; i < numThreads; i++){
sum += stocks[i];
}
printf("Total Market Price of %d stocks: %.2f\n",numThreads,sum);
for(i = 0; i < numThreads; i++){
rc = pthread_cancel(threads[i]);
assert(rc == 0);
}
pthread_cancel(watchIncreaseThread);
pthread_mutex_unlock(&lock);
pthread_exit(NULL);
//exit(0);
}
update()
中的while
循环中没有指定作为pthread_cancel()
取消点的函数。您可以决定启用异步取消,但更明智的解决方案是在pthread_mutex_unlock()
之后添加pthread_testcancel()
。 - EOFpthread_mutex_lock()
、pthread_mutex_unlock()
和pthread_cond_signal()
都不是异步取消安全 ( https://www.gnu.org/software/libc/manual/html_node/POSIX-Safety-Concepts.html )。如前所述,在while
循环的开头或结尾(互斥锁未被锁定的位置)执行pthread_testcancel()
是更好的选择。 - sonicwave