Chapter 18: Problem 5

Describe the wait-die and wound-wait protocols for deadlock prevention.

Short Answer

Expert verified

Wait-Die and Wound-Wait are two deadlock prevention protocols. In Wait-Die, an older transaction forces a younger one to wait if the older one is waiting for a resource the younger one holds. In Wound-Wait, an older transaction forces a younger one to roll back if the younger one is holding a resource that the older one needs.

Step by step solution

Define Deadlock

Start off by defining what a deadlock is. A deadlock is a state in which each member of a group is waiting for some resource that is held by another member of the group.

Explain the Wait-Die Algorithm

Then, explain the Wait-Die algorithm. In this scheme, if a transaction request cannot be granted because the desired item is held in an exclusive mode by another transaction, the timestamps of two transactions are compared. If the requesting transaction is younger than the one holding the lock, it is forced to wait. However, if the requesting transaction is older, it preempts the younger one, forcing it to roll back.

Explain the Working of Wait-Die Algorithm

Further explain the working of the wait-die scheme with an example. If a transaction Ti issues a write(Q) operation and if Q is held by a younger transaction Tj, then transaction Ti is allowed to wait. If Q is held by Tj which is older than Ti, then Ti is rolled back (dies). The older transaction can inflict a wound on the younger one, causing it to be rolled back.

Explain the Wound-Wait Algorithm

Next, explain the wound-wait algorithm. It is a deadlock prevention scheme which is based on the timestamp ordering protocol. Here, a transaction may be wound up if it is waiting for a resource that is held by some other younger transaction.

Explain the Working of Wound-Wait Algorithm

Finally, explain the working of Wound-Wait Algorithm with an example. If transaction Ti needs a data item currently held by Tj, then Ti forces Tj to roll back if Ti is older than Tj. However, if Ti is younger, then Ti waits. In other words, a younger transaction is wounded (rolled back) by an older one if it causes the old one to wait.

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Describe the wait-die and wound-wait protocols for deadlock prevention.

Short Answer

Step by step solution

Define Deadlock

Explain the Wait-Die Algorithm

Explain the Working of Wait-Die Algorithm

Explain the Wound-Wait Algorithm

Explain the Working of Wound-Wait Algorithm

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