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  Message Delivery Protocol ·          A protocol is a set of rules and conventions shared by communicating entities . ·          Message passing can be blocking or non blocking . ·          In blocking protocol , a sender process is blocked till the message selivered to the . in this case , sender process has guarantee that the message sent by it ie delivered before it continues its execution . A blocking protocol normally includes: 1.        Blocking send : the sender process is blocked until the message is received by the receiving process or by the mailbox. 2.        Blocking receive : the receiver nlocks until a message is available thus when both sender as well as receiver is blocked ,it is known as rebdevezevous . this combination allows for tight sysnchronization between process. ·          In non blockeing protocol , asender continues the execution after performing a send operation irrespective of whether the message is delivered or not ·          A non blockin

  Direct Communication ·          Direct communication establishes a link between two processes. A communication link is a unidirectional path along which information flows. ·          two processes use single communication link to share information. ·          In this   metod, there cannot be more that one link between two processes                                                     direct communication ·          Send and receive function used in direct communication are given below : ·          Send(process name , message ,(receive(process name , message)             Send(A, message )- send a message to process A             Receive(A, message )-receive a message from process B Indirect communication ·          In indirect communication , no direct communication link exists between two processes. ·          In this , messages are sent to and received from mailbox. ·          A mailbox is a specialized repository where message can be placed by processes and from

      ENTERPROCESS COMMUNICATION AND SYNCHRONIZATION ·          In multi programming environment multiple process co-exit . a single   program may be broken into number of processes. ·          The process are classified into two categories : independent processes and cooperating processes. ·          An independent process is a standalone process that does not share any data with any other process. It cannot affect or be affected by the other processes executing   in the system. In other words, the modification made to an independent process does not affect the functioning of other process. ·          A cooperating processes is a process that shares data with other processes in a system it can affect or be affectedly the other processes executing in the system ·          Cooperating processes can communicate in a shred memory environment . ·          The various reasons for using cooperating processes are: 1.        Information sharing : when several   users want to acce

  Multilevel Feedback queue scheduling (MFQ) ·          Multilevel feedback queue scheduling is an enhancement of multi-levelqueue scheduling. In this scheme, processes can move between the different queue ·          The various processes are separates in different queue on the basis of their CPU Burst Char characteristics ·          If a process consumes a lot of CPU time , it is placed into a lower priority queue. Thus I/O bound and interactive process are placed in the higher priority queue and CPU bound pricesses are in lower priority ·          If a processes waits too long in a lower priority queue it is moved higher priority queue. Such an aging prevents starvation. ·          The top priority queue is given smallest CPU time Quantum ·          If the quantum expires before the process voluntarily relinquishes the CPU, the process is placed at the back of the next lower queue. ·          In many multi-level feedback schemes, the quantum gives too the process as it

  Multi Level Queue Scheduling (MLQ) ·          Multilevel queue scheduling classifies the processes according to their types for example, a multilevel queue scheduling algorithm makes a common. ·          In this scheduling ready queue is divided into various queue that are called sub queues. A subqueue is a distinct operational queue ·          The process are permanently assigned to subqueues, generally based on some property of the process such as memory size,priority or process type ·          Each subqueue has its process sucheduling algorithm. For example interactive process at the foreground may use round robin scheduling while batch jobs at the background may use the FCFS method ·          For example, consider a system with four different queues 1.        System processes 2.        Interactive processes 3.        End-user processes 4.        Interactive processes ·          In this example, each queue has absolute priority absolute over low priority queues