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We can obtain the banker's alg

[问答题]

We can obtain the banker's algorithm for a single resource type from the general banker's algorithm simply by reducing the dimensionality of the various arrays by 1. Show through an example that the multiple-resource-type banker's scheme cannot be implemented by individual application of the single-resource-type scheme to each resource type.
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Consider a system with resources A, B, and C and processes P0, P1, P2, P3, and P4 with the following values of Allocation:

Allocation

	A	B	C
P0	0	1	0
P1	3	0	2
P2	3	0	2
P3	2	1	1
P4	0	0	2

And the following value of Need:
Need

	A	B	C
P0	7	4	3
P1	0	2	0
P2	6	0	0
P3	0	1	1
P4	4	3	1

If the value of Available is (2 3 0), we can see that a request from process P0 for (0 2 0) cannot be satisfied as this lowers Available to (2 1 0) and no process could safely finish.
However, if we were to treat the three resources as three single-resource types of the banker's algorithm, we get the following:
For resource A (which we have 2 available),

	Allocated	Need
P0	3	2
P1	0	2
P2	0	0
P3	1	1
P4	0	3

Processes could safely finish in the order of P1,P3,P4,P2, P0.
For resource B (which we now have 1 available as 2 were assumed assigned to process P0),

	Allocated	Need
P0	3	2
p1	0	2
p2	0	0
p3	1	1
p4	0	3

Processes could safely finish in the order of P2, P3, P1, P0, P4.
And finally, for For resource C (which we have O available),

	Allocated Need	Need
P0	0	3
P1	2	0
P2	2	0
P3	1	1
P4	2	1

Processes could safely finish in the order of P1, , P0, P3, P4.
As we can see, if we use the banker's algorithm for multiple resource types, the request for resources (0 2 0) from process PO is denied as it
leaves the system in an unsafe state. However, if we consider the banker 's algorithm for the three separate resources where we use a single resource type, the request is granted. Therefore, if we have multiple resource types, we must use the banker's algorithm for multiple resource types

发表于 2018-03-23 22:06:52 回复(0)