[英]Killing Threads with pthreads - C
我有一個C pthread程序,在main中創建N個線程來更新全局變量。 Main還在所有這些更新線程上調用pthread_join以等待它們完成。 我還有2個觀察者線程使用pthread條件變量來檢查全局變量是高於還是低於某些數字,如果是,它會殺死所有更新線程和其他觀察者線程。 但是,我在這最后一部分遇到了麻煩..殺死其他線程。 我的程序完成它應該做的但卻永遠不會完成...它只是卡住了。 在每個觀察者線程結束時調用exit(0)可以正常工作,但我覺得這個解決方案太懶了,我真的想學習如何從一個單獨的線程中殺死其他線程並返回main。
這是我的代碼:
#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);
}
不鼓勵pthread_cancel
,而是正確的方法是替換while(1){
by while(!killed[index]){
。 然后,殺死你設置的線程killed[index]
。 如果你有C11編譯器,請使用http://en.cppreference.com/w/c/atomic/atomic_flag ,否則你可能需要一個pthread_mutex
來保護被killed
數組。
示例: https : //gustedt.wordpress.com/2012/01/22/simple-c11-atomics-atomic_flag/
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