[UGC NET Computer science]
Resources are allocated
to the process on non-shareable basis is
[Paper II June 2012]
(A) mutual exclusion
(B) hold and wait
(C) no pre-emption
(D) circular wait
Answer is A and Conceptually explanation of the above question is given below.
What is Deadlock?
The processes may block
each other. Nobody can use the resource. Deadlock can only occur if the
processes need more than one resource at the same time.
When Deadlock may
arise?
Deadlock may arise if the following four conditions hold simultaneously:
1. Mutual
exclusion. : - Non-sharable
resources are used. Only one process can use the resource at any given instant
of time.
2. Hold
and wait. : - A process holds at
least one resource and requests another resource that is held by another
process.
3. No
preemption. : - Resources
that a process holds, can only be voluntarily released by the process itself. The
operating system must not de-allocate resources once they have been allocated;
they must be released by the holding process voluntarily.
4. Circular
wait. : - A circular chain of
processes exist, in which each process holds a resource requested by the next
process in the chain. Process such that P1 is waiting for a resource held by process P2, process P2 is waiting for a resource held by process P3 and
so on until process Pn is waiting for a resource held by process P1. This is a circular wait.
What is Mutual Exclusion?
Mutual exclusion (often abbreviated to mutex). It is the one of the situation which can cause
for deadlock when non sharable devices or resources are accessed by more than
one task or processes. Non sharable means only one person or process can access
that device or resource.
When
more than one process wants the same resource, then Race condition may occur. Race
Condition means more than one processes or task are trying to
access the same resource.
Mutual
Exclusion make sure at most one process may enter a critical section.
What is a critical section?
It is the program section accessing shared
resource(s), only one process can be in this section at a time.
Data errors or inconsistencies may occur when
shared resources or devices are access and modified at the same time by more
than one resource.
Sections of a program that might cause these
problems are called critical section.
A critical
section will terminate in fixed given time and a process, thread or task will
have to wait for a fixed time to enter.
When failure to control the access to a critical
section is called a race condition because success or failure depends on the ability of
one process to exit the critical section before another process enters the
critical section.
What is
Concurrent programming?
Concurrent
programming is a form of computing in which several computations are
executing during overlapping time periods concurrently instead
of sequentially.
