我正在使用pthreads做直方图并经过长时间的努力...最后它说：
Segmentation Fault (Core Dumped)
不幸的是我有这条线
p=(struct1 *)malloc(sizeof(struct1));
从命令行获取结构变量的值后..所以这被清除了..感谢@DNT让我知道..
现在当我尝试执行以下程序时..它有时会显示输出，有时它会转到which_bin函数并输出以下内容
output type 1(which is not the correct output):
Data = 0.000000 doesn't belong to a bin!
Quitting
output type 2(almost the correct output of histo with time taken by threads):
10.000-28.000:
28.000-46.000:
46.000-64.000:
64.000-82.000:
82.000-100.000: XXXXXXXXXX
The code to be timed took 0.000415 seconds
我的问题是为什么当跑步显示不同的输出时同样的编程...我很困惑它正是在寻找...
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include "timer.h"
void Usage(char prog_name[]);
void Gen_data(void *p);
void Gen_bins(void *p);
int Which_bin(void *p);
void Print_histo(void *p);
void func(void *p);
struct test
{
int bin_count, i, bin;
float min_meas, max_meas;
float* bin_maxes;
int* bin_counts;
int data_count;
float* data;
};
typedef struct test struct1;
int main(int argc, char* argv[])
{
double start, finish, elapsed;
GET_TIME(start);
struct1 *p;
pthread_t th1, th2, th3;
p=(struct1 *)malloc(sizeof(struct1));
if (argc != 5)
Usage(argv[0]);
p->bin_count = strtol(argv[1], NULL, 10);
p->min_meas = strtof(argv[2], NULL);
p->max_meas = strtof(argv[3], NULL);
p->data_count = strtol(argv[4], NULL, 10);
p->bin_maxes = malloc(p->bin_count*sizeof(float));
p->bin_counts = malloc(p->bin_count*sizeof(int));
p->data = malloc(p->data_count*sizeof(float));
pthread_create(&th1,NULL,(void*) Gen_data,(void*) p);
pthread_create(&th2,NULL,(void*) Gen_bins,(void*) p);
pthread_create(&th3,NULL,(void*) func,(void*) p);
printf("Hi\n");
pthread_join(th1,NULL);
pthread_join(th2,NULL);
pthread_join(th3,NULL);
Print_histo(p);
free(p->data);
free(p->bin_maxes);
free(p->bin_counts);
GET_TIME(finish);
elapsed = finish - start;
printf("The code to be timed took %f seconds\n", elapsed);
return 0;
} /* main */
void func(void *p)
{
int i;
struct1 *args;
args=(struct1*)p;
for (i = 0; i < args->data_count; i++)
{
args->bin = Which_bin(args);
args->bin_counts[args->bin]++;
}
# ifdef DEBUG
printf("bin_counts = ");
for (i = 0; i < args->bin_count; i++)
printf("%d ", args->bin_counts[i]);
printf("\n");
# endif
}
/*---------------------------------------------------------------------
* Function: Usage
* Purpose: Print a message showing how to run program and quit
* In arg: prog_name: the name of the program from the command line
*/
void Usage(char prog_name[] /* in */)
{
fprintf(stderr, "usage: %s ", prog_name);
fprintf(stderr, "<bin_count> <min_meas> <max_meas> <data_count>\n");
exit(0);
} /* Usage */
void Gen_data(void *p)
{
struct1 *args;
args=(struct1*)p;
int i;
srandom(0);
for (i = 0; i < args->data_count; i++)
args->data[i] = args->min_meas + (args->max_meas - args->min_meas)*random()/((double) RAND_MAX);
#ifdef DEBUG
printf("data = ");
for (i = 0; i < args->data_count; i++)
printf("%4.3f ", args->data[i]);
printf("\n");
#endif
} /* Gen_data */
void Gen_bins(void* p)
{
struct1 *args;
args=(struct1*)p;
float bin_width;
int i;
bin_width = (args->max_meas - args->min_meas)/args->bin_count;
for (i = 0; i < args->bin_count; i++)
{
args->bin_maxes[i] = args->min_meas + (i+1)*bin_width;
args->bin_counts[i] = 0;
}
# ifdef DEBUG
printf("bin_maxes = ");
for (i = 0; i < args->bin_count; i++)
printf("%4.3f ", args->bin_maxes[i]);
printf("\n");
# endif
}
int Which_bin(void* p)
{
struct1 *args;
args=(struct1*)p;
int bottom = 0, top = args->bin_count-1;
int mid;
float bin_max, bin_min;
while (bottom <= top)
{
mid = (bottom + top)/2;
bin_max = args->bin_maxes[mid];
bin_min = (mid == 0) ? args->min_meas: args->bin_maxes[mid-1];
if (*(args->data) >= bin_max)
bottom = mid+1;
else if (*(args->data) < bin_min)
top = mid-1;
else
return mid;
}
fprintf(stderr, "Data = %f doesn't belong to a bin!\n", args->data);
fprintf(stderr, "Quitting\n");
exit(-1);
}
void Print_histo(void *p)
{
struct1 *args;
args=(struct1*)p;
int i, j;
float bin_max, bin_min;
for (i = 0; i < args->bin_count; i++)
{
bin_max = args->bin_maxes[i];
bin_min = (i == 0) ? args->min_meas: args->bin_maxes[i-1];
printf("%.3f-%.3f:\t", bin_min, bin_max);
for (j = 0; j < args->bin_counts[i]; j++)
printf("X");
printf("\n");
}
}
/* Print_histo */ #include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include "timer.h"
void Usage(char prog_name[]);
void Gen_data(void *p);
void Gen_bins(void *p);
int Which_bin(void *p);
void Print_histo(void *p);
void func(void *p);
pthread_mutex_t lock;
struct test
{
int bin_count, i, bin;
float min_meas, max_meas;
float* bin_maxes;
int* bin_counts;
int data_count;
float* data;
};
typedef struct test struct1;
int main(int argc, char* argv[])
{
if (pthread_mutex_init(&lock, NULL) != 0)
{
printf("\n mutex init failed\n");
return 1;
}
double start, finish, elapsed;
GET_TIME(start);
struct1 *p;
pthread_t th1, th2, th3;
p=(struct1 *)malloc(sizeof(struct1));
if (argc != 5)
Usage(argv[0]);
p->bin_count = strtol(argv[1], NULL, 10);
p->min_meas = strtof(argv[2], NULL);
p->max_meas = strtof(argv[3], NULL);
p->data_count = strtol(argv[4], NULL, 10);
p->bin_maxes = malloc(p->bin_count*sizeof(float));
p->bin_counts = malloc(p->bin_count*sizeof(int));
p->data = malloc(p->data_count*sizeof(float));
pthread_create(&th1,NULL,(void*) Gen_data,(void*) p);
pthread_create(&th2,NULL,(void*) Gen_bins,(void*) p);
pthread_create(&th3,NULL,(void*) func,(void*) p);
printf("Hi\n");
pthread_join(th1,NULL);
pthread_join(th2,NULL);
pthread_join(th3,NULL);
Print_histo(p);
free(p->data);
free(p->bin_maxes);
free(p->bin_counts);
GET_TIME(finish);
elapsed = finish - start;
printf("The code to be timed took %f seconds\n", elapsed);
return 0;
} /* main */
void func(void *p)
{
pthread_mutex_lock(&lock);
printf("th3 from Gen_func\n");
int i;
struct1 *args;
args=(struct1*)p;
for (i = 0; i < args->data_count; i++)
{
args->bin = Which_bin(args);
args->bin_counts[args->bin]++;
}
# ifdef DEBUG
printf("bin_counts = ");
for (i = 0; i < args->bin_count; i++)
printf("%d ", args->bin_counts[i]);
printf("\n");
# endif
pthread_mutex_unlock(&lock);
}
/*---------------------------------------------------------------------
* Function: Usage
* Purpose: Print a message showing how to run program and quit
* In arg: prog_name: the name of the program from the command line
*/
void Usage(char prog_name[] /* in */)
{
fprintf(stderr, "usage: %s ", prog_name);
fprintf(stderr, "<bin_count> <min_meas> <max_meas> <data_count>\n");
exit(0);
} /* Usage */
void Gen_data(void *p)
{
pthread_mutex_lock(&lock);
printf("th1 from Gen_data\n");
struct1 *args;
args=(struct1*)p;
int i;
srandom(0);
for (i = 0; i < args->data_count; i++)
args->data[i] = args->min_meas + (args->max_meas - args->min_meas)*random()/((double) RAND_MAX);
#ifdef DEBUG
printf("data = ");
for (i = 0; i < args->data_count; i++)
printf("%4.3f ", args->data[i]);
printf("\n");
#endif
pthread_mutex_unlock(&lock);
} /* Gen_data */
void Gen_bins(void* p)
{
pthread_mutex_lock(&lock);
printf("th2 from Gen_bins\n");
struct1 *args;
args=(struct1*)p;
float bin_width;
int i;
bin_width = (args->max_meas - args->min_meas)/args->bin_count;
for (i = 0; i < args->bin_count; i++)
{
args->bin_maxes[i] = args->min_meas + (i+1)*bin_width;
args->bin_counts[i] = 0;
}
# ifdef DEBUG
printf("bin_maxes = ");
for (i = 0; i < args->bin_count; i++)
printf("%4.3f ", args->bin_maxes[i]);
printf("\n");
# endif
pthread_mutex_unlock(&lock);
}
int Which_bin(void* p)
{
struct1 *args;
args=(struct1*)p;
int bottom = 0, top = args->bin_count-1;
int mid;
float bin_max, bin_min;
while (bottom <= top)
{
mid = (bottom + top)/2;
bin_max = args->bin_maxes[mid];
bin_min = (mid == 0) ? args->min_meas: args->bin_maxes[mid-1];
if (*(args->data) >= bin_max)
bottom = mid+1;
else if (*(args->data) < bin_min)
top = mid-1;
else
return mid;
}
fprintf(stderr, "Data = %f doesn't belong to a bin!\n", args->data);
fprintf(stderr, "Quitting\n");
exit(-1);
}
void Print_histo(void *p)
{
struct1 *args;
args=(struct1*)p;
int i, j;
float bin_max, bin_min;
for (i = 0; i < args->bin_count; i++)
{
bin_max = args->bin_maxes[i];
bin_min = (i == 0) ? args->min_meas: args->bin_maxes[i-1];
printf("%.3f-%.3f:\t", bin_min, bin_max);
for (j = 0; j < args->bin_counts[i]; j++)
printf("X");
printf("\n");
}
}
/* Print_histo */
我添加了行以查看所有线程是否正在访问其功能..我观察到了这一点..
output 1:
Hi
th1 from Gen_data
th3 from Gen_func
Data = 0.000000 doesn't belong to a bin!
Quitting
在输出1中，我可以看到th2没有执行，程序结束显示错误..
output 2:
th1 from Gen_data
Hi
th2 from Gen_bins
th3 from Gen_func
10.000-28.000:
28.000-46.000:
46.000-64.000:
64.000-82.000:
82.000-100.000: XXXXXXXXXX
The code to be timed took 0.000348 seconds
在输出2中，所有线程都被执行，输出也是如此..
我很困惑，为什么线程th2没有被执行，我如何确保所有线程以正确的顺序运行..
我想知道该程序是否在逻辑错误？如果在逻辑上这是错误的，为什么它有时会显示直方图输出..谢谢！
答案 0 :(得分：0)
无法保证线程执行顺序。在现代的多核处理器上，线程甚至可以同时执行。无法保证Gen_bins线程在func线程之前完成。由于您的线程访问和操作相同的数据结构，因此您注意到结果是不可预测的。
虽然我认为此应用程序不需要线程，但请进行以下更改以确保线程按列出的顺序执行。变化：
pthread_create(&th1,NULL,(void*) Gen_data,(void*) p);
pthread_create(&th2,NULL,(void*) Gen_bins,(void*) p);
pthread_create(&th3,NULL,(void*) func,(void*) p);
pthread_join(th1,NULL);
pthread_join(th2,NULL);
pthread_join(th3,NULL);
为：
pthread_create(&th1,NULL,(void*) Gen_data,(void*) p);
pthread_join(th1,NULL);
pthread_create(&th2,NULL,(void*) Gen_bins,(void*) p);
pthread_join(th2,NULL);
pthread_create(&th3,NULL,(void*) func,(void*) p);
pthread_join(th3,NULL);
这确保每个线程在下一次启动之前执行并完成。同样，由于线程不是并发执行的，因此该程序不需要线程化，只会增加复杂性。