📅  最后修改于: 2023-12-03 15:39:24.311000             🧑  作者: Mango
银行家算法是用于避免死锁的资源分配算法。具有CERA的Excel表格示例中的实现了银行家算法。
银行家算法通过记录系统中每个资源的数量,以及进程已经占用和需要的数量,来决定是否能够分配资源,以避免死锁的发生。
算法包括以下步骤:
以下代码是带有CERA的Excel表格示例中,实现银行家算法的关键代码片段:
'服务器资源数量
Dim available(3) As Integer
available(1) = 10
available(2) = 5
available(3) = 7
'每个进程已经占有和需要的资源数量
Dim allocation(3,3) As Integer
allocation(1,1) = 0
allocation(1,2) = 1
allocation(1,3) = 0
allocation(2,1) = 2
allocation(2,2) = 0
allocation(2,3) = 0
allocation(3,1) = 3
allocation(3,2) = 0
allocation(3,3) = 2
Dim need(3,3) As Integer
need(1,1) = 7
need(1,2) = 4
need(1,3) = 3
need(2,1) = 3
need(2,2) = 2
need(2,3) = 2
need(3,1) = 9
need(3,2) = 0
need(3,3) = 2
'检查进程是否能够完成分配
Function isSafe() As Boolean
Dim work(3) As Integer
Dim finish(3) As Boolean
Dim i As Integer
Dim j As Integer
For j = 1 To 3
work(j) = available(j)
Next j
For i = 1 To 3
finish(i) = False
Next i
i = 1
While i <= 3
If finish(i) = False And need(i,1) <= work(1) And need(i,2) <= work(2) And need(i,3) <= work(3) Then
work(1) = work(1) + allocation(i,1)
work(2) = work(2) + allocation(i,2)
work(3) = work(3) + allocation(i,3)
finish(i) = True
i = 0
End If
i = i + 1
Wend
For i = 1 To 3
If finish(i) = False Then
isSafe = False
Exit Function
End If
Next i
isSafe = True
End Function
以上示例代码是通过VBScript实现的,可以在Excel中创建宏来调用该函数。
例如,在Excel表格中,创建名为 "isSafe" 的宏,将以下代码复制到宏函数中:
Function isSafe() As Boolean
'......
End Function
然后,在Excel表格的某个单元格中输入以下公式:
=isSafe()
该公式的返回值为 True 或 False,分别表示系统是否安全或不安全。