二进制信号量和互斥量之间有区别吗?或者它们本质上是相同的?


当前回答

互斥量和二进制信号量是相同的用法,但实际上,它们是不同的。

对于互斥锁,只有锁定了它的线程才能解锁它。如果有其他线程来锁定它,它将等待。

对于信号电话来说,情况就不是这样了。信号量没有与特定的线程ID绑定。

其他回答

正如这里许多人提到的,互斥锁用于保护关键代码段(又名临界段)。你将在同一个线程中获得互斥锁(lock),进入临界区,释放互斥锁(unlock)。

在使用信号量时,您可以让一个线程(例如线程a)等待一个信号量,直到另一个线程(例如线程B)完成任何任务,然后为线程a设置信号量以停止等待,并继续其任务。

虽然二进制信号量可以用作互斥量,但互斥量是一个更具体的用例,因为只有锁定了互斥量的进程才应该解锁它。这种所有权限制使我们有可能对以下情况提供保护:

意外释放 递归死锁 任务死亡死锁

这些限制并不总是存在,因为它们降低了速度。在代码开发期间,您可以暂时启用这些检查。

例如,你可以在互斥锁中启用错误检查属性。错误检查互斥量返回EDEADLK,如果你试图锁定同一个互斥量两次,如果你解锁了一个不是你的互斥量,返回EPERM。

pthread_mutex_t mutex;
pthread_mutexattr_t attr;
pthread_mutexattr_init (&attr);
pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_ERRORCHECK_NP);
pthread_mutex_init (&mutex, &attr);

一旦初始化,我们可以将这些检查放在我们的代码中,就像这样:

if(pthread_mutex_unlock(&mutex)==EPERM)
 printf("Unlock failed:Mutex not owned by this thread\n");

最好的解决方案

唯一的区别是

1.互斥锁-> lock和unlock属于锁定互斥锁的线程。

2.信号量->没有所有权,即;如果一个线程调用semwait(s),任何其他线程都可以调用sempost(s)来移除锁。

它们的同步语义非常不同:

互斥对象允许对给定资源的序列化访问,即多个线程等待一个锁,一次一个,正如前面所说,线程拥有锁,直到锁完成:只有这个特定的线程可以解锁它。 二进制信号量是一个值为0和1的计数器:任务阻塞在它上,直到任何任务执行sem_post。信号量宣布资源可用,并提供等待机制,直到发出可用信号。

因此,可以将互斥锁视为在任务之间传递的令牌,将信号量视为交通红灯(它向某人发出信号,表示可以继续进行)。

I think most of the answers here were confusing especially those saying that mutex can be released only by the process that holds it but semaphore can be signaled by ay process. The above line is kind of vague in terms of semaphore. To understand we should know that there are two kinds of semaphore one is called counting semaphore and the other is called a binary semaphore. In counting semaphore handles access to n number of resources where n can be defined before the use. Each semaphore has a count variable, which keeps the count of the number of resources in use, initially, it is set to n. Each process that wishes to uses a resource performs a wait() operation on the semaphore (thereby decrementing the count). When a process releases a resource, it performs a release() operation (incrementing the count). When the count becomes 0, all the resources are being used. After that, the process waits until the count becomes more than 0. Now here is the catch only the process that holds the resource can increase the count no other process can increase the count only the processes holding a resource can increase the count and the process waiting for the semaphore again checks and when it sees the resource available it decreases the count again. So in terms of binary semaphore, only the process holding the semaphore can increase the count, and count remains zero until it stops using the semaphore and increases the count and other process gets the chance to access the semaphore.

二进制信号量和互斥量之间的主要区别在于,信号量是一种信号机制,而互斥量是一种锁定机制,但二进制信号量的功能似乎与互斥量类似,这造成了混乱,但两者是适用于不同类型工作的不同概念。