二进制信号量或互斥量
在计算信号量时，没有提供相互排斥，因为有一组同时需要在临界区执行的进程。
然而，二进制信号严格提供互斥。 在这里，临界区域不能有超过1个槽位，而临界区域最多只能有1个槽位。 信号量只能有两个值，0或1。
下面，我们来看看二进制信号量的编程实现。
StructBsemaphore
{
enum Value(0,1); //value is enumerated data type which can only have two values 0 or 1.
Queue type L;
}
/* L contains all PCBs corresponding to process
Blocked while processing down operation unsuccessfully.
*/
Down (Bsemaphore S)
{
if (s.value == 1) // if a slot is available in the
//critical section then let the process enter in the queue.
{
S.value = 0; // initialize the value to 0 so that no other process can read it as 1.
}
else
{
put the process (PCB) in S.L; //if no slot is available
//then let the process wait in the blocked queue.
sleep();
}
}
Up (Bsemaphore S)
{
if (S.L is empty) //an empty blocked processes list implies that no process
//has ever tried to get enter in the critical section.
{
S.Value =1;
}
else
{
Select a process from S.L;
Wakeup(); // if it is not empty then wake the first process of the blocked queue.
}
}
