## Shared programming using library routines, Computer Networking

Assignment Help:

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.

#### What is network architecture, What is Network Architecture? When two o...

What is Network Architecture? When two or more computer are linked with one another for the purpose of communicating data electronically, besides physical connection of comput

#### Default cdp broadcast update rate for cisco routers, What is the default CD...

What is the default CDP broadcast update rate for Cisco routers? Ans) Cisco Discovery Protocol is a proprietary protocol to permit you to access configuration information on oth

#### Describe network infrastructure design, Question : a) Explain why perv...

Question : a) Explain why pervasive computing can be termed as a "technology that disappears". b) List and briefly explain four main components of a MOTE used in Wireless

#### Wireless transmission, what are the main problems of signal propagation?why...

what are the main problems of signal propagation?why do radio waves not always follow a straight line?why is reflection both useful and harmful?

#### Network, do you do paraphrase

do you do paraphrase

#### Why congestion occurs, Q. Why congestion occurs? Congestion Emerg...

Q. Why congestion occurs? Congestion Emerge if the load on the network is greater than the capacity of the network - Load that is the number of packets sent to the net

#### Internet control message protocol layer, Simulate extremely limited forms o...

Simulate extremely limited forms of IP and ICMP. You will simulate 6 computers, 4 hosts and 2 routers, that are connected in an imaginary network with the topology as shown belo

#### What is domain names, Q. What is Domain Names ? - Full domain name is a...

Q. What is Domain Names ? - Full domain name is a sequence of labels separated by dots (.) - Fully competent domain name (FQDN) contains the full name of a host cis.usouthal

#### Describe the different steps in distributed problem solving, QUESTION (...

QUESTION (a) Four important benefits of Multi-Agent Systems are modularity, efficiency, reliability and flexibility. Briefly explain these benefits (b) Agents work together

#### Layered architecture - computer network, Layered Architecture The best...

Layered Architecture The best  way to  understand  any complex system is to break  it into  pieces  and then analyze what they  do and  how they interact. The most logical app