CS 385: HW3–Due 31 Oct
Jon A. Solworth
October 26, 2003
1. In 2phase commit, if the deadlock occurs the transaction must abort. This abort is
part of the atomic operation and is performed by waiting a fixed amount of time for a
lock (say 1 second) and if it is not obtained, all locks are released all locations updated
by the transaction are restored, and the program branches back to the start of the
transaction.
Implement both get read lock and get write lock code implementing abort.
2. Can the following rules lead to deadlock? If so, give an example or if not explain why
not.
(a) Each process runs at a different (fixed) priority. If a higher priority process would
block on a resource held by a lower priority process, it kills the low priority process.
(b) Resources are numbered by integers. All odd numbered resources are requested
before any even even ones.
(c) Resources are requested in any order, but it is possible to time-share the resource
by 1) saving the state associated with one processes use of the resource and 2)
restoring the state associated with another process.
(d) Resources are numbered 0 through 5. A process requests either resource 0 or 5,
then 3 or 4, and then may request 1 and then may request 2.
(e) If all the resources requested are available they are allocaated otherwise the re-
questing process releases all the resources it holds.
3. Consider a systen with 3 resources A,B, and Cwith respective quantities NA,NB,
NC. Write a set of resource allocation/release routines (with error checking) for each
of Dijkstra’s 4 conditions which avoids deadlock by denying that condition (that is,
you should have 4 sets of routines).
4. In the following wait-for graph, is the system in deadlock?
1
