Advanced Operating Systems - Inter-Process Communication PDF

M1IL - Advanced Operating Systems 3rd chapter Inter-Process Communication Presented by: Abdelaziz Kella  ❏ Inter process communication (IPC) is a mechanism which allows processes to communicate with each Interaction other and synchr...

M1IL - Advanced Operating Systems 3rd chapter Inter-Process Communication Presented by: Abdelaziz Kella  ❏ Inter process communication (IPC) is a mechanism which allows processes to communicate with each Interaction other and synchronize their actions. Processes within Among a system may be: Independent process Co-operating process Processes A process is independent if A process is co-operating it cannot affect or be if it can affect or be affected by the other affected by the other processes executing in the processes executing in the system system. Any process that does not Any process that share share data with any other data with any other process is IP process is CP ❏ Reasons for cooperating processes: ❏ Information sharing ❏ Computation speedup ❏ Modularity ❏ Convenience  ❏ In a multi-process application these are the various degrees of interaction: Interaction 1. Competing processes: Processes Among themselves do not share anything. But OS has to share the system resources among Processes these processes “competing” for system resources such as disk, file or printer. Co-operating processes : Results of one or more processes may be needed for another process. 2. Co-operation by sharing : Example: Sharing of an IO buffer. Concept of critical section (e.g Critical section & Mutual exclusion) 3. Co-operation by communication : Example: typically no data sharing, but co-ordination thru’ synchronization becomes essential in certain applications. Types of IPC Mechanisms IPC mechanisms can be categorized into: ❏ Shared Memory: - Processes access a common memory space for communication ❏ Semaphores: - Used for controlling access to shared resources and synchronization ❏ Message Passing: - Processes communicate by sending and receiving messages  Unicast vs MultiCast ❏ In distributed computing, two or more processes engage in IPC using a protocol agreed upon by the processes. ❏ A process may be a sender at some points during a protocol, a receiver at other points. ❏ When communication is from one process to a single other process, the IPC is said to be a unicast, e.g., Socket communication. ❏ When communication is from one process to a group of processes, the IPC is said to be a multicast, e.g., Publish/Subscribe Message model, a topic that we will explore in a later chapter.  Types of IPC communication ❏ The IPC operations may provide the synchronization necessary using blocking. A blocking operation issued by a process will block further processing of the process until the operation is fulfilled. ❏ Alternatively, IPC operations may be asynchronous or nonblocking. An asynchronous operation issued by a process will not block further processing of the process. Instead, the process is free to proceed with its processing, and may optionally be notified by the system when the operation is fulfilled. Types of IPC communication Message Passing: Concepts and Examples Fundamentals Practical Examples Synchronous Communication: Sender waits for Client-Server Models: Web applications using the receiver to acknowledge receipt message passing for requests and responses Asynchronous Communication: Sender continues Microservices: Services communicate via without waiting for acknowledgment messages in distributed systems IPC in Networking Context of Networking: - IPC concepts extend to processes communicating over a network ❏ Remote Procedure Calls RPC / Java RMI Remote Method Invocation): Allows a program to execute a procedure on another address space ❏ Sockets ❏ HTTP requests/responses and Its variants  Remote Procedure Calls ❏ These are interprocess communication techniques that are used for client/server based applications. A remote procedure call is also known as a subroutine call or a function call. ❏ A client has a request that the RPC translates and sends to the server. This request may be a procedure or a function call to a remote server. When the server receives the request, it sends the required response back to the client.  Sockets ❏ Sockets facilitate communication between two processes on the same machine or different machines. ❏ They are used in a client/server framework and consist of the IP address and port number. Many application protocols use sockets for data connection and data transfer between a client and a server.  Sockets ❏ Sockets need to be bound to a port number and an internet address in order to send and receive messages. ❏ Each socket has a transport protocol TCP or UDP. ❏ Interprocess communication consists of transmitting a message between a socket in one process and a socket in another process.  TCP Stream communication ❏ The API to the TCP protocol provides the abstraction of a stream of bytes to be written to or read from. ❏ Characteristics of the stream abstraction: ❏ Message sizes ❏ Lost messages ❏ Flow control ❏ Message destinations ❏ Many services that run over TCP connections, with reserved port number are: ❏ HTTP Hypertext Transfer Protocol) ❏ FTP File Transfer Protocol) ❏ Telnet ❏ SMTP Simple Mail Transfer Protocol) Java implementation of TCP Streams ❏ The Java interface to TCP streams is provided in the classes: ❏ ServerSocket ❏ It is used by a server to create a socket at server port to listen for connect requests from clients. ❏ Socket ❏ It is used by a pair of processes with a connection. ❏ The client uses a constructor to create a socket and connect it to the remote host and port of a server. ❏ It provides methods for accessing input and output streams associated with a socket. Java implementation of TCP Streams  UDP Datagram communication ❏ UDP datagram properties ❏ No guarantee of order preservation ❏ Message loss and duplications are possible ❏ Necessary steps ❏ Creating a socket ❏ Binding a socket to a port and local Internet address ❏ A client binds to any free local port ❏ A server binds to a server port ❏ Blocking ❏ Send: non-blocking ❏ upon arrival, message is placed in a queue for the socket that is bound to the destination port. ❏ Receive: blocking ❏ Pre-emption by timeout possible ❏ If process wishes to continue while waiting for packet, use separate thread UDP Datagram communication flow Java implementation of UDP Datagrams ❏ The Java API provides datagram communication by two classes: 1. DatagramPacket ❏ It provides a constructor to make an array of bytes comprising: Message content Length of message Internet address Local port number ❏ It provides another similar constructor for receiving a message. ❏ Java implementation of UDP Datagrams ❏ The Java API provides datagram communication by two classes: 2. DatagramSocket ❏ This class supports sockets for sending and receiving UDP datagram. ❏ It provides a constructor with port number as argument. ❏ No-argument constructor is used to choose a free local port. ❏ DatagramSocket methods are: ✓ send and receive ✓ setSoTimeout ✓ connect Relationship between DatagramPacket & DatagramSocket