Question

there are fundamental models of interprocess communication: shared memory and message passing.Compare between these two models in terms of: using system calls , implementation of distributed operating system, performance of execution , synchronization issue between processes. Justify the answer in each case

Answer 1

Comparison between shared memory and message passing interprocess communication model:
Shared memory interprocess communication model:

In terms of system calls, they are required only to establish shared-memory regions and when established, all accesses to the shared memory are considered routine or regular memory accesses without any assistance from the kernel and hence, shared memory is faster.

In terms of implementation of a distributed operating system, it is not ideal for a distributed operating system as in distributed operating system the computers do not share their main memory as each one of them is an isolated computer system. Hence, interprocess communication mechanism through shared memory such as semaphores, cannot be used. Hence, the message passing interprocess communication model is used.

In terms of performance of execution, when multiple processes are executing simultaneously, they share some resources or use information from other processes. One process during its execution creates information about certain calculations or computations, or resources used and stores it as a record in the shared memory. The second process uses the same reading the shared and stored information in the record in shared memory for its execution purpose. There is a possibility of overlapping of multiple processes either writing or reading the same information in the shared memory. It can run processes which would, in turn, execute programs concurrently. The throughput is high. It can be used for real-time processing.

In terms of synchronization issue between processes, the shared memory model uses the shared memory to be simultaneously accessed by multiple processes to read and write so processes communicate with one another. All POSIX systems and Windows operating systems use shared memory. It is difficult to be implemented than in Message Passing model. The memory communication is convenient and is faster to the maximum on the same machine as connection setup does not take much time and it is happening at memory speeds. It has synchronization and memory protection problems though. Basically, memory is shared amongst processes to exchange information writing and read from it. Processes overwrite to the same location simultaneously.

Message passing interprocess communication model:

In terms of system calls, it is implemented using system calls and hence it is a more time-consuming task of kernel intervention.

In terms of implementation of distributed operating system, it is useful in a distributed environment where the communicating processes reside and run on different network connected systems such as a networked cluster of nodes where nodes are networked together, each with multiple cores using their own its own local memory and the communication happens between the nodes and cores through messages in the queues.

In terms of performance of execution, there is a possibility of blocking from writing or reading the information stored in the message queue due to either the received process has not at all received any message from the queue making it full for any further message to be written or the reading process does not have anything to be read as the writing process has not written anything yet, respectively in the message queue. This problem blocks the execution time in waiting for both, the writing and the reading processes. It cannot run processes, which, in turn, would not execute programs concurrently. The throughput is low. It is not ideal for real-time processing.

In terms of synchronization issue between processes, it lets multiple processes to read and write data to a message queue without being connected to one another. Sending and receiving processes are involved in this model. These written messages are stored on the queue for the corresponding recipient processes to read them. Hence, message queues are useful for interprocess communication used by Windows XP, Mac, and most operating systems. Message queue for the synchronization of interprocess communication is tolerant of higher communication latencies. It is easier to be implemented than in synchronization of interprocess communication in a shared memory model. The communication is slower on the same machine as connection setup takes time. Basically, messages are exchanged amongst processes.