Shared programming using library routines, Computer Networking

Shared Programming Using Library Routines

The most well-liked of them is the use of combo function called fork() and join(). Fork() function is used to make a new child process. By calling join() function parent process waits the terminations of the child process to obtain the desired result.

Example 11: Consider the following set of statements

Process A                                 Process B

:                                                      :

fork B ;                                                      :

:                                                                :

join B;                                                      end B;

In the above set of statements process A makes a child process B by the statement fork B. Then A and B continue their computations independently up to  A reaches the join statement, At this stage, if B is already ended, then A continues implementing the next statement otherwise it waits for B to finish.

 In the shared memory model, a common trouble is to synchronize the processes. It may be possible that more than one process is trying to concurrently modify the similar variable. To solve this problem many synchronization mechanism like test_and_set, monitors and semaphores have been used. We shall not go into the details of these mechanisms. Quite, we shall represent them by a pair of two processes called lock and unlock. Whenever a process P locks a common variable, then only P can use that variable. Other simultaneous processes have to wait for the common variable until P calls the unlock on that variable. Let us see the effect of locking on the output of a program when we do not use lock and when we use lock.

Example 12

Let us write a pseudocode to find sum of the two functions f(A) + f(B). In the first algorithm we shall not use locking.

Process A                               Process B

sum = 0                                           :

:                                                  :

fork B                                    sum = sum+ f(B)

:                                                   :

sum = sum + f(A)                         end B

:

join B

:

end A

If process A implements the statement sum = sum + f (A) and writes the results into main memory followed by the computation of sum by process B, then we get the right result. But consider the case when B implements the statement sum = sum + f (B) before process A could write result into the main memory. Then the sum contains only f(B) which is not right. To avoid such inconsistencies, we use locking.

Process A                               Process B

sum = 0                                           :

:                                                  :

:                                                  lock sum

fork B                                    sum = sum + f(B)

:                                                   unlock sum

 lock sum                                        :

sum = sum + f(A)                         end B

unlock sum

:

join B

:

end A

In this case whenever a process gets the sum variable, it locks it so that no other process can access that variable which makes sure the consistency in results.

Posted Date: 3/4/2013 5:16:53 AM | Location : United States







Related Discussions:- Shared programming using library routines, Assignment Help, Ask Question on Shared programming using library routines, Get Answer, Expert's Help, Shared programming using library routines Discussions

Write discussion on Shared programming using library routines
Your posts are moderated
Related Questions
State about the Bus Topology Comments 1 - Requires less cabling than a star network 2 - If there is a central cable problem entire netwo. rk goes down 3 - Less e

Difference between synchronous tdm and statistical tdm

A generic algorithm is mostly analyzed on the basis of the following parameters: the time complexity (implementation time) and the space complexity (amount of space necessary). Usu



What is anonymous FTP and why would you use it Anonymous FTP enables users to join to a host without using a valid login and password. Generally, anonymous FTP uses a login kno

Network Devices a.Hub b.Repeater c.Bridge d.Gateway e.Switch f.Router Connecting devices can  classified  into networking and internetworking  devices when

i have been given a question:- any 50 numbers are given and to find out the 1)frequency of odd and even numbers 2)frequency of positive and negative numbers

Recognize the command to disable CDP on an interface Ans) Router(config-if)# no cdp enable

As discussed in the earlier section each computer linked to the Internet has a unique address. Let's assume your IP address is 1.2.3.4 & you wish to send a message to the computer