【发布时间】：2015-09-04 12:43:21
【问题描述】：
在这里完成一项任务。让代码工作并计算饼图，但我收到以下错误的随机值除外：
./piesync 10 3 在 3 个线程中用 10 个项计算的 pi 是 3.14183961892940200045 * `./piesync' 中的错误：free()：下一个大小无效（快速）：0x0000000001ca3010 *
./piesync 100 5 * `./piesync' 中的错误：双重释放或损坏（输出）：0x0000000000ee5040 *
我知道这可能与数组或互斥锁有关，但不知道是什么。
代码：
//Pini Vaknine
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
//global variables
int N, T;
double gpie = 3.0;
pthread_mutex_t mutex;
//pie function
void* pie_runner(void* arg)
{
long j = (long)arg;
long lower = (N/T)*(j-1)+1;
long upper = ((N/T)*(j));
double myPartialSum = 0;
//printf("lower=%lu upper=%lu\n",lower , upper);
for(long i = lower; i <= upper; i++)
{
if(i % 2 == 0){
myPartialSum -= 4.0/((2*i)*(2*i+1)*(2*i+2));
//printf("vsum %lu = %f\n", j, vsum[j]);
}
else{
myPartialSum += 4.0/((2*i)*(2*i+1)*(2*i+2));
//printf("vsum %lu = %f\n", j, vsum[j]);
}
}
pthread_mutex_lock (&mutex);
gpie = gpie + myPartialSum;
pthread_mutex_unlock (&mutex);
pthread_exit(0);
//return NULL;
}
int main(int argc, char **argv)
{
if(argc != 3) {
printf("Error: Must send it 2 parameters, you sent %d\n", argc-1);
exit(1);
}
N = atoi(argv[1]);
T = atoi(argv[2]);
if(N <= T) {
printf("Error: Number of terms must be greater then number of threads.\n");
exit(1);
}
//launch threads
pthread_attr_t attr;
pthread_t *tids = (pthread_t *) calloc(T, sizeof(pthread_t));
if(tids == NULL) {
fprintf(stderr, "Memory allocation problem\n");
exit(1);
}
pthread_mutex_init(&mutex, NULL);
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
for(long i = 1; i<=T; i++)
{
int r = pthread_create(&tids[i], &attr, pie_runner, (void*)i);
if(r<0) {
printf("ERROR: pthread_create() returned %d\n", r);
exit(2);
}
}
//wait for threads...
for(int k = 1; k<=T; k++)
{
pthread_join(tids[k], NULL);
}
printf("pi computed with %d terms in %d threads is %.20f\n", N, T, gpie);
pthread_mutex_destroy(&mutex);
pthread_attr_destroy(&attr);
free(tids);
return 0;
}
【问题讨论】：
-
C 使用零索引循环和数组/指针。