抱歉刚刚在这里找到这段代码 - http://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html并且用这段代码解释了互斥锁,但它让我有点不知所措。我了解互斥锁的功能,并且它在关键部分保护共享变量。虽然这里的细节让我感到困惑!据我了解,我们正在使用 pthread_create 创建一个新线程,它正在运行 functionC 进程,该进程递增一个计数器。计数器是 protected 变量,并且由于两个函数同时运行,如果计数器不受互斥量保护,它会返回错误的值。
这是正确的/接近的吗?非常感谢:)。
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
void *functionC();
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
int counter = 0;
main()
{
int rc1, rc2;
pthread_t thread1, thread2;
/* Create independent threads each of which will execute functionC */
if( (rc1=pthread_create( &thread1, NULL, &functionC, NULL)) )
{
printf("Thread creation failed: %d\n", rc1);
}
if( (rc2=pthread_create( &thread2, NULL, &functionC, NULL)) )
{
printf("Thread creation failed: %d\n", rc2);
}
/* Wait till threads are complete before main continues. Unless we */
/* wait we run the risk of executing an exit which will terminate */
/* the process and all threads before the threads have completed. */
pthread_join( thread1, NULL);
pthread_join( thread2, NULL);
exit(0);
}
void *functionC()
{
pthread_mutex_lock( &mutex1 );
counter++;
printf("Counter value: %d\n",counter);
pthread_mutex_unlock( &mutex1 );
}
最佳答案
如果您没有适当的互斥锁,可能会发生这种情况:
// initialization
counter = 0;
// thread 1 runs:
counter++;
// context switch
// thread 2 runs:
counter++;
// context switch
// thread 1 runs and printf "Counter value: 2"
printf("Counter value: %d\n",counter);
// context switch
// thread 2 runs and printf "Counter value: 2"
printf("Counter value: %d\n",counter);
因此,您最终可能会得到以下输出:
Counter value: 2
Counter value: 2
现在,有了互斥量,您可以确保增量及其打印将自动运行,因此您可以 100% 确定输出将是:
Counter value: 1
Counter value: 2
但绝不会:
Counter value: 2
Counter value: 2
关于c - 一些我无法理解的简单 C 代码 - 互斥锁在这里做什么?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4928838/