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
答案可能取决于目标操作系统。例如,我所熟悉的至少一个RTOS实现允许对单个OS互斥量进行多个连续的“get”操作,只要它们都来自同一个线程上下文中。在允许另一个线程获得互斥量之前,多个get必须被相等数量的put替换。这与二进制信号量不同,对于二进制信号量,无论线程上下文如何,一次只允许一个get。
这种互斥锁背后的思想是,通过一次只允许一个上下文修改数据来保护对象。即使线程获得了互斥量,然后调用进一步修改对象的函数(并在自己的操作周围获得/放置保护互斥量),这些操作仍然应该是安全的,因为它们都发生在单个线程下。
{
mutexGet(); // Other threads can no longer get the mutex.
// Make changes to the protected object.
// ...
objectModify(); // Also gets/puts the mutex. Only allowed from this thread context.
// Make more changes to the protected object.
// ...
mutexPut(); // Finally allows other threads to get the mutex.
}
当然,在使用此特性时,必须确保单个线程中的所有访问都是安全的!
我不确定这种方法有多普遍,或者它是否适用于我所熟悉的系统之外。有关这种互斥锁的示例,请参阅ThreadX RTOS。
其他回答
互斥锁:假设我们有临界区线程T1想要访问它,然后按照以下步骤进行。 T1:
锁 使用临界区 解锁
二进制信号量:它基于信号等待和信号工作。 等待将“s”的值减少1,通常“s”的值初始化为值“1”, 信号(s)使“s”值加1。如果“s”值为1表示没有人在使用临界区,当“s”值为0时表示临界区正在使用。 假设线程T2正在使用临界区,那么它遵循以下步骤。 T2:
Wait (s)//最初的s值是1,调用Wait后,它的值减少了1,即0 利用临界区 信号(s) //现在s值增加,变成1
Main difference between Mutex and Binary semaphore is in Mutext if thread lock the critical section then it has to unlock critical section no other thread can unlock it, but in case of Binary semaphore if one thread locks critical section using wait(s) function then value of s become "0" and no one can access it until value of "s" become 1 but suppose some other thread calls signal(s) then value of "s" become 1 and it allows other function to use critical section. hence in Binary semaphore thread doesn't have ownership.
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。
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。
互斥锁只能由获得它的线程释放。 二进制信号量可以由任何线程(或进程)发出信号。
因此,信号量更适合于一些同步问题,如生产者-消费者。
在Windows上,二进制信号量更像事件对象而不是互斥对象。
在窗口,差异如下所示。 MUTEX:成功执行等待的进程必须执行一个信号,反之亦然。二进制信号量:不同的进程可以在一个信号量上执行等待或信号操作。
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