如何獲得正確的pthread執行順序
[英]How to get the correct order of execution of pthreads
問題描述
我正在使用pthreads做直方圖，並且經過長時間的努力..最后它說：
Segmentation Fault (Core Dumped)
不幸的是我有這條線
p=(struct1 *)malloc(sizeof(struct1));
從命令行將值獲取到結構變量后。.因此，這已清除。.感謝@DNT告訴我。
現在，當我嘗試執行以下程序時。.有時顯示輸出，有時輸出到which_bin函數並顯示以下內容
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
我的問題是，為什么同一編在運行時顯示不同的輸出。我對它到底在尋找什么感到困惑。
#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 */
我添加了幾行，以查看是否所有線程都在訪問其功能。
output 1:
Hi
th1 from Gen_data
th3 from Gen_func
Data = 0.000000 doesn't belong to a bin!
Quitting
在輸出1中，我可以看到未執行th2並且程序結束顯示錯誤。
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
在輸出2中，所有線程均被執行，輸出也被執行。
我感到困惑的是，為什么線程th2沒有被執行，以及如何確保所有線程都以正確的順序運行。
我想知道程序在邏輯上是否錯誤？ 如果在這種情況下在邏輯上是錯誤的，為什么有時會顯示直方圖輸出..謝謝！
1 個解決方案
解決方案1
0 已采納 2014-04-24 21:16:33
不能保證線程執行的順序。 在現代的多核處理器上，線程甚至可以並發執行。 不能保證Gen_bins線程在func線程之前完成。 由於您的線程訪問和操作相同的數據結構，結果如您所知是不可預測的。
盡管我認為此應用程序不需要線程，但請進行以下更改以確保線程按列出的順序執行。 更改：
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);
至：
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);
這樣可以確保每個線程在下一個線程啟動之前執行並完成。 同樣，由於線程不是並發執行的，因此該程序不需要線程化，只會增加復雜性。
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