问题
编辑:正如评论中指出的那样,我对pthread_cond_wait
犯了一个错误,导致它永远不会退出线程。
我正在C中进行多线程分配,在该环境中,我需要使用多线程使用剪切排序对4x4数组进行排序,但是我做不到,因为每当使用pthread_join
时,应用程序就永远不会结束,也永远不会加入。在我控制C将其结束之前,该应用程序一直停留在原处。我弄乱了我的pthread_cond_wait
,这意味着某些线程将永远不会继续。
我猜我在问应该如何使用pthread_wait_cond
,因为当我在if / else语句的两边都具有pthread_wait_cond
时,它什么都不输出,只会卡住。
另外,这现在是主要问题的一部分,但是我已经看到很多人在for循环中启动pthread,但是当我尝试传递给函数的I变量似乎是随机设置的时,有时在获取每个线程时都是正确的它自己的编号,但是有时线程会使用相同的编号创建。我是否需要使用某种互斥体来确保pthread_create
原子发生,我该怎么做?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sched.h>
#include <fcntl.h>
#include <pthread.h>
#define N 4
void intSwap(int *a, int *b);
void *shearSort(void *rowCol);
pthread_cond_t sort0 = PTHREAD_COND_INITIALIZER;
pthread_cond_t sort1 = PTHREAD_COND_INITIALIZER;
pthread_cond_t sort2 = PTHREAD_COND_INITIALIZER;
pthread_cond_t sort3 = PTHREAD_COND_INITIALIZER;
pthread_cond_t writeArray = PTHREAD_COND_INITIALIZER;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
int array[N][N];
pthread_t thread[N];
void *shearSort(void *rowCol) {
int x = 0, y = 0;
printf("rowCol = %d", ((int)*(int*)rowCol));
pthread_mutex_lock(&lock);
if (((int)*(int*)rowCol)%2 == 0) {
for(x = 0; x < N-1; x++) {
for (y = 0; y < N-x-1; y++) {
//pthread_cond_wait(&writeArray, &lock);
if (array[((int)*(int*)rowCol)][y] > array[((int)*(int*)rowCol)][y+1]) {
printf("rowCol = %d, i = %d, j = %d Swapping %d & %d\n", ((int)*(int*)rowCol), x, y, array[((int)*(int*)rowCol)][y], array[((int)*(int*)rowCol)][y+1]);
intSwap(&array[((int)*(int*)rowCol)][y], &array[((int)*(int*)rowCol)][y+1]);
}
//pthread_cond_signal(&writeArray);
}
}
}
else {
for(x = 0; x < N-1; x++) {
for (y = 0; y < N-x-1; y++) {
//pthread_cond_wait(&writeArray, &lock);
if (array[((int)*(int*)rowCol)][y] < array[((int)*(int*)rowCol)][y+1]) {
printf("rowCol = %d, i = %d, j = %d Swapping %d & %d\n", ((int)*(int*)rowCol), x, y, array[((int)*(int*)rowCol)][y], array[((int)*(int*)rowCol)][y+1]);
intSwap(&array[((int)*(int*)rowCol)][y], &array[((int)*(int*)rowCol)][y+1]);
}
//pthread_cond_signal(&writeArray);
}
}
}
pthread_mutex_unlock(&lock);
if(((int)*(int*)rowCol) == 1) {
//pthread_join(thread[0], NULL);
}
if(((int)*(int*)rowCol) == 2) {
//pthread_join(thread[0], NULL);
//pthread_join(thread[1], NULL);
}
if(((int)*(int*)rowCol) == 3) {
//pthread_join(thread[0], NULL);
//pthread_join(thread[1], NULL);
//pthread_join(thread[2], NULL);
}
pthread_exit(NULL);
}
void intSwap(int *a, int *b) {
int temp = *a;
*a = *b;
*b = temp;
}
int main () {
FILE *input;
int i = 0, j = 0;
input = fopen("input.txt" , "r");
if (input != NULL) {
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
fscanf(input, "%d, ", &array[i][j]);
printf("%d, ", array[i][j]);
}
printf("\n");
}
printf("\n");
}
else {
perror( "There's a problem with the input.txt file, it doesn't seem to be there.");
exit( EXIT_FAILURE );
}
// for (i = 0; i < N; i++) {
// pthread_create(&thread[i], NULL, shearSort, (void *)&i);
// }
// for (i = 0; i < N; i++) {
// pthread_join(thread[i], NULL);
// }
int num0 = 0, num1 = 1, num2 = 2, num3 = 3;
pthread_create(&thread[0], NULL, shearSort, (void *)&num0);
pthread_create(&thread[1], NULL, shearSort, (void *)&num1);
pthread_create(&thread[2], NULL, shearSort, (void *)&num2);
pthread_create(&thread[3], NULL, shearSort, (void *)&num3);
pthread_join(thread[num0], NULL);
pthread_join(thread[1], NULL);
pthread_join(thread[2], NULL);
pthread_join(thread[3], NULL);
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
printf("%d, ", array[i][j]);
}
printf("\n");
}
return 0
}
当我在上面的代码中没有在
pthread_cond_wait
上添加注释的情况下运行以上代码时,我从命令行获取了此输出,然后它停止了。5, 3, 9, 10,
2, -3, 11, 8,
20, 17, 19, 30,
24, 21, -2, 16,
rowCol = 0rowCol = 0, i = 0, j = 0 Swapping 5 & 3
rowCol = 1rowCol = 2rowCol = 2, i = 0, j = 0 Swapping 20 & 17
rowCol = 2, i = 0, j = 1 Swapping 20 & 19
^C
现在,当我按原样运行代码时,将得到以下输出:
5, 3, 9, 10,
2, -3, 11, 8,
20, 17, 19, 30,
24, 21, -2, 16,
rowCol = 0rowCol = 0, i = 0, j = 0 Swapping 5 & 3
rowCol = 1rowCol = 1, i = 0, j = 1 Swapping -3 & 11
rowCol = 1, i = 0, j = 2 Swapping -3 & 8
rowCol = 1, i = 1, j = 0 Swapping 2 & 11
rowCol = 1, i = 1, j = 1 Swapping 2 & 8
rowCol = 2rowCol = 2, i = 0, j = 0 Swapping 20 & 17
rowCol = 2, i = 0, j = 1 Swapping 20 & 19
rowCol = 3rowCol = 3, i = 0, j = 2 Swapping -2 & 16
3, 5, 9, 10,
11, 8, 2, -3,
17, 19, 20, 30,
24, 21, 16, -2,
最佳答案
在调用pthread_cond_wait之前,请确保其他线程将其唤醒,因此在调用pthread_cond_wait之前,需要判断是否还有其他线程在使用array
,需要等待是否使用了array
,否则直接进行操作。
请参见下面实现的功能acquireWriteArray
和releaseWriteArray
在pthread_create中,您可以直接传递值,而不传递地址:
pthread_create(&thread[i], NULL, shearSort, (void *)(long)i);
修改后的代码:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sched.h>
#include <fcntl.h>
#include <pthread.h>
#define N 4
void intSwap(int *a, int *b);
void *shearSort(void *rowCol);
pthread_cond_t writeArray = PTHREAD_COND_INITIALIZER;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
int array[N][N];
pthread_t thread[N];
volatile int writeBusy = 0;
void acquireWriteArray()
{
pthread_mutex_lock(&lock);
while (writeBusy) {
pthread_cond_wait(&writeArray, &lock);
}
writeBusy = 1;
}
void releaseWriteArray()
{
writeBusy = 0;
pthread_cond_signal(&writeArray);
pthread_mutex_unlock(&lock);
}
void *shearSort(void *rowCol)
{
int x = 0, y = 0;
int idx = (long)rowCol;
printf("rowCol = %d.\n", idx);
if (idx % 2 == 0) {
for(x = 0; x < N - 1; x++) {
for (y = 0; y < N - x - 1; y++) {
acquireWriteArray();
if (array[idx][y] > array[idx][y + 1]) {
printf("rowCol = %d, i = %d, j = %d Swapping %d & %d\n",
idx, x, y, array[idx][y], array[idx][y + 1]);
intSwap(&array[idx][y], &array[idx][y + 1]);
}
releaseWriteArray();
}
}
} else {
for(x = 0; x < N - 1; x++) {
for (y = 0; y < N - x - 1; y++) {
acquireWriteArray();
if (array[idx][y] < array[idx][y + 1]) {
printf("rowCol = %d, i = %d, j = %d Swapping %d & %d\n",
idx, x, y, array[idx][y], array[idx][y + 1]);
intSwap(&array[idx][y], &array[idx][y + 1]);
}
releaseWriteArray();
}
}
}
return (void *)NULL;
}
void intSwap(int *a, int *b)
{
int temp = *a;
*a = *b;
*b = temp;
}
int main ()
{
FILE *input;
int i = 0, j = 0;
input = fopen("input.txt" , "r");
if (input != NULL) {
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
fscanf(input, "%d, ", &array[i][j]);
printf("%d, ", array[i][j]);
}
printf("\n");
}
printf("\n");
} else {
perror( "There's a problem with the input.txt file, it doesn't seem to be there.");
exit( EXIT_FAILURE );
}
for (i = 0; i < N; i++) {
pthread_create(&thread[i], NULL, shearSort, (void *)(long)i);
}
for (i = 0; i < N; i++) {
pthread_join(thread[i], NULL);
}
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
printf("%d, ", array[i][j]);
}
printf("\n");
}
return 0;
}
关于c - C中的Pthread_cond_wait,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/55210514/