假设我在一个进程中有三个线程th1，th2和th3，并且有三个寄存器（数组）a，b和c。 th1和th2仅写入三个寄存器之一，th3仅从这些寄存器读取数据。 th1，th2和th3将按条件变量的连续顺序b / c工作。两个条件变量cv1和cv2分别用于（th1，th2）和（th2，th3）之间的信号传递。工作程序如下：
首先th1将一些东西写到'a'数组中，然后发信号（使用cv1）等待它的th2。
从th1接收信号后，th2开始写入同一阵列'a'，然后信号（使用cv2）th3读取'a'。
th3在从th2接收信号时开始读取“ a”（相同的阵列）。
以上3个步骤以相同的方式重复“ b”和“ c”。
我的C代码如下：
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <pthread.h>
void* th1();
void* th2();
void* th3();
int a[40], b[40], c[40], rn;
pthread_mutex_t mutex1, mutex2, mutex3;
pthread_cond_t cv1, cv2;
int main()
{
pthread_t t[3];
pthread_mutex_init(&mutex1, NULL);
pthread_mutex_init(&mutex2, NULL);
pthread_mutex_init(&mutex3, NULL);
pthread_cond_init(&cv1, NULL);
pthread_cond_init(&cv2, NULL);
pthread_create(&t[0], NULL, th1, NULL);
pthread_create(&t[1], NULL, th2, NULL);
pthread_create(&t[2], NULL, th3, NULL);
pthread_join(t[0], NULL);
pthread_join(t[1], NULL);
pthread_join(t[2], NULL);
pthread_mutex_destroy(&mutex1);
pthread_mutex_destroy(&mutex2);
pthread_mutex_destroy(&mutex3);
pthread_cond_destroy(&cv1);
pthread_cond_destroy(&cv2);
return 0;
}
void* th1()
{
pthread_mutex_lock(&mutex1);
for(int i=0; i<20; i++)
{
a[i]=i;
}
pthread_cond_signal(&cv1);
puts("a signal sent...");
pthread_mutex_unlock(&mutex1);
pthread_mutex_lock(&mutex2);
for(int i=0; i<20; i++)
{
b[i]=i;
}
pthread_cond_signal(&cv1);
puts("b signal sent...");
pthread_mutex_unlock(&mutex2);
pthread_mutex_lock(&mutex3);
for(int i=0; i<20; i++)
{
c[i]=i;
}
pthread_cond_signal(&cv1);
puts("c signal sent...");
pthread_mutex_unlock(&mutex3);
pthread_exit(NULL);
}
void* th2()
{
pthread_mutex_lock(&mutex1);
pthread_cond_wait(&cv1, &mutex1);
puts("signal recv form th1 for writing 'a'...\n");
for(int i=0; i<=20; i++)
{
a[i+20]=i+20;
}
pthread_cond_signal(&cv2);
pthread_mutex_unlock(&mutex1);
pthread_mutex_lock(&mutex2);
pthread_cond_wait(&cv1, &mutex2);
puts("signal recv from th1 for writing 'b'...\n");
for(int i=0; i<=20; i++)
{
b[i+20]=i+20;
}
pthread_cond_signal(&cv2);
pthread_mutex_unlock(&mutex2);
pthread_mutex_lock(&mutex3);
pthread_cond_wait(&cv1, &mutex3);
puts("signal recv from th1 for writing 'c'...\n");
for(int i=0; i<=20; i++)
{
c[i+20]=i+20;
}
pthread_cond_signal(&cv2);
pthread_mutex_unlock(&mutex3);
pthread_exit(NULL);
}
void* th3()
{
pthread_mutex_lock(&mutex1);
pthread_cond_wait(&cv2, &mutex1);
puts(" signal recv from th2 for reading 'a'...\n");
for(int i=0; i<=40; i++)
{
printf("%d :",a[i]);
}
printf("\n\n");
pthread_mutex_unlock(&mutex1);
pthread_mutex_lock(&mutex2);
pthread_cond_wait(&cv2, &mutex2);
puts(" signal recv from th2 for reading 'b'...\n");
for(int i=0; i<=40; i++)
{
printf("%d :",b[i]);
}
printf("\n\n");
pthread_mutex_unlock(&mutex2);
pthread_mutex_lock(&mutex3);
pthread_cond_wait(&cv2, &mutex3);
puts(" signal recv from th2 for reading 'c'...\n");
for(int i=0; i<=40; i++)
{
printf("%d :",c[i]);
}
printf("\n\n");
pthread_mutex_unlock(&mutex3);
pthread_exit(NULL);
}
仅显示后的输出块：
mohtashim-ul-haq@mohtashim-pc:~/Documents/rough$ gcc tread.c -o tread -lpthread
mohtashim-ul-haq@mohtashim-pc:~/Documents/rough$ ./tread
a signal sent...
b signal sent...
c signal sent...
我的预期输出是这样的：
a signal sent
signal recv form th1 for writing 'a'...
signal recv from th2 for reading 'a'...
1 2 3 4 ..... 40
b signal sent
signal recv form th1 for writing 'b'...
signal recv from th2 for reading 'b'...
1 2 3 4 ..... 40
c signal sent
signal recv form th1 for writing 'c'...
signal recv from th2 for reading 'c'...
1 2 3 4 ..... 40
我想，我不明白条件变量如何与互斥体一起工作。任何帮助吗？
最佳答案
您需要集成事件“信号”，会说您需要存储是否发出了信号（通知状态改变）。
对于第一个事件（“ a”读取），对代码的调整可能如下所示：
int a_read = 0; /* to store the event "a had been read" actually happened */
void* th1(void * pvunused)
{
pthread_mutex_lock(&mutex1);
for(int i=0; i<20; i++)
{
a[i]=i;
}
a_read = 1;
pthread_cond_signal(&cv1);
...
void* th2(void * pvunused)
{
pthread_mutex_lock(&mutex1);
while (0 == a_read) /* Theoretical an "if" would do here,
using "while" lets you stay on the safe side, in case
a "spurious wake-up" (https://en.wikipedia.org/wiki/Spurious_wakeup)
occurred. */
{
pthread_cond_wait(&cv1, &mutex1);
}
...
关于c - 使用条件变量进行线程间通信？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/44772001/