Lecture 6 - Process - Part 2 PDF

Chapter 3: Processes Operating System Concepts – 10 th Edition Silberschatz, Galvin and Gagne ©2018  Outline ▪ Process Concept ▪ Process Scheduling ▪ Operations on Processes ▪ Interprocess Communication...

Chapter 3: Processes Operating System Concepts – 10 th Edition Silberschatz, Galvin and Gagne ©2018  Outline ▪ Process Concept ▪ Process Scheduling ▪ Operations on Processes ▪ Interprocess Communication ▪ IPC in Shared-Memory Systems ▪ IPC in Message-Passing Systems ▪ Examples of IPC Systems ▪ Communication in Client-Server Systems Operating System Concepts – 10 th Edition 3.2 Silberschatz, Galvin and Gagne ©2018  Objectives ▪ Identify the separate components of a process and illustrate how they are represented and scheduled in an operating system. ▪ Describe how processes are created and terminated in an operating system, including developing programs using the appropriate system calls that perform these operations. ▪ Describe and contrast interprocess communication using shared memory and message passing. ▪ Design programs that uses pipes and POSIX shared memory to perform interprocess communication. ▪ Describe client-server communication using sockets and remote procedure calls. ▪ Design kernel modules that interact with the Linux operating system. Operating System Concepts – 10 th Edition 3.3 Silberschatz, Galvin and Gagne ©2018  Interprocess Communication ▪ Processes within a system may be independent or cooperating ▪ Cooperating process can affect or be affected by other processes, including sharing data ▪ Reasons for cooperating processes: Information sharing Computation speedup Modularity Convenience ▪ Cooperating processes need interprocess communication (IPC) ▪ Two models of IPC Shared memory Message passing Operating System Concepts – 10 th Edition 3.4 Silberschatz, Galvin and Gagne ©2018  Communications Models (a) Shared memory. (b) Message passing. Operating System Concepts – 10 th Edition 3.5 Silberschatz, Galvin and Gagne ©2018  Producer-Consumer Problem ▪ Paradigm for cooperating processes: producer process produces information that is consumed by a consumer process ▪ Two variations: unbounded-buffer places no practical limit on the size of the buffer:  Producer never waits  Consumer waits if there is no buffer to consume bounded-buffer assumes that there is a fixed buffer size  Producer must wait if all buffers are full  Consumer waits if there is no buffer to consume Operating System Concepts – 10 th Edition 3.6 Silberschatz, Galvin and Gagne ©2018  IPC – Shared Memory ▪ An area of memory shared among the processes that wish to communicate ▪ The communication is under the control of the users processes not the operating system. ▪ Major issues is to provide mechanism that will allow the user processes to synchronize their actions when they access shared memory. ▪ Synchronization is discussed in great details in Chapters 6 & 7. Operating System Concepts – 10 th Edition 3.7 Silberschatz, Galvin and Gagne ©2018  Bounded-Buffer – Shared-Memory Solution ▪ Shared data #define BUFFER_SIZE 10 typedef struct {... } item; item buffer[BUFFER_SIZE]; int in = 0; int out = 0; ▪ Solution is correct, but can only use BUFFER_SIZE-1 elements Operating System Concepts – 10 th Edition 3.8 Silberschatz, Galvin and Gagne ©2018  Producer Process – Shared Memory item next_produced; while (true) { while (((in + 1) % BUFFER_SIZE) == out) ; buffer[in] = next_produced; in = (in + 1) % BUFFER_SIZE; } Operating System Concepts – 10 th Edition 3.9 Silberschatz, Galvin and Gagne ©2018  Consumer Process – Shared Memory item next_consumed; while (true) { while (in == out) ; next_consumed = buffer[out]; out = (out + 1) % BUFFER_SIZE; } Operating System Concepts – 10 th Edition 3.10 Silberschatz, Galvin and Gagne ©2018  What about Filling all the Buffers? ▪ Suppose that we wanted to provide a solution to the consumer- producer problem that fills all the buffers. ▪ We can do so by having an integer counter that keeps track of the number of full buffers. ▪ Initially, counter is set to 0. ▪ The integer counter is incremented by the producer after it produces a new buffer. ▪ The integer counter is and is decremented by the consumer after it consumes a buffer. Operating System Concepts – 10 th Edition 3.11 Silberschatz, Galvin and Gagne ©2018  Producer while (true) { while (counter == BUFFER_SIZE) ; buffer[in] = next_produced; in = (in + 1) % BUFFER_SIZE; counter++; } Operating System Concepts – 10 th Edition 3.12 Silberschatz, Galvin and Gagne ©2018  Consumer while (true) { while (counter == 0) ; next_consumed = buffer[out]; out = (out + 1) % BUFFER_SIZE; counter--; } Operating System Concepts – 10 th Edition 3.13 Silberschatz, Galvin and Gagne ©2018  Race Condition ▪ counter++ could be implemented as register1 = counter register1 = register1 + 1 counter = register1 ▪ counter-- could be implemented as register2 = counter register2 = register2 - 1 counter = register2 ▪ Consider this execution interleaving with “count = 5” initially: S0: producer execute register1 = counter {register1 = 5} S1: producer execute register1 = register1 + 1 {register1 = 6} S2: consumer execute register2 = counter {register2 = 5} S3: consumer execute register2 = register2 – 1 {register2 = 4} S4: producer execute counter = register1 {counter = 6 } S5: consumer execute counter = register2 {counter = 4} Operating System Concepts – 10 th Edition 3.14 Silberschatz, Galvin and Gagne ©2018  Race Condition (Cont.) ▪ Question – why was there no race condition in the first solution (where at most N – 1) buffers can be filled? ▪ More in Chapter 6. Operating System Concepts – 10 th Edition 3.15 Silberschatz, Galvin and Gagne ©2018  IPC – Message Passing ▪ Processes communicate with each other without resorting to shared variables ▪ IPC facility provides two operations: send(message) receive(message) ▪ The message size is either fixed or variable Operating System Concepts – 10 th Edition 3.16 Silberschatz, Galvin and Gagne ©2018  Message Passing (Cont.) ▪ If processes P and Q wish to communicate, they need to: Establish a communication link between them Exchange messages via send/receive ▪ Implementation issues: How are links established? Can a link be associated with more than two processes? How many links can there be between every pair of communicating processes? What is the capacity of a link? Is the size of a message that the link can accommodate fixed or variable? Is a link unidirectional or bi-directional? Operating System Concepts – 10 th Edition 3.17 Silberschatz, Galvin and Gagne ©2018  Implementation of Communication Link ▪ Physical: Shared memory Hardware bus Network ▪ Logical: Direct or indirect Synchronous or asynchronous Automatic or explicit buffering Operating System Concepts – 10 th Edition 3.18 Silberschatz, Galvin and Gagne ©2018  Direct Communication ▪ Processes must name each other explicitly: send (P, message) – send a message to process P receive(Q, message) – receive a message from process Q ▪ Properties of communication link Links are established automatically A link is associated with exactly one pair of communicating processes Between each pair there exists exactly one link The link may be unidirectional, but is usually bi-directional Operating System Concepts – 10 th Edition 3.19 Silberschatz, Galvin and Gagne ©2018  Indirect Communication ▪ Messages are directed and received from mailboxes (also referred to as ports) Each mailbox has a unique id Processes can communicate only if they share a mailbox ▪ Properties of communication link Link established only if processes share a common mailbox A link may be associated with many processes Each pair of processes may share several communication links Link may be unidirectional or bi-directional Operating System Concepts – 10 th Edition 3.20 Silberschatz, Galvin and Gagne ©2018  Indirect Communication (Cont.) ▪ Operations Create a new mailbox (port) Send and receive messages through mailbox Delete a mailbox ▪ Primitives are defined as: send(A, message) – send a message to mailbox A receive(A, message) – receive a message from mailbox A Operating System Concepts – 10 th Edition 3.21 Silberschatz, Galvin and Gagne ©2018  Indirect Communication (Cont.) ▪ Mailbox sharing P1, P2, and P3 share mailbox A P1, sends; P2 and P3 receive Who gets the message? ▪ Solutions Allow a link to be associated with at most two processes Allow only one process at a time to execute a receive operation Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was. Operating System Concepts – 10 th Edition 3.22 Silberschatz, Galvin and Gagne ©2018  Synchronization Message passing may be either blocking or non-blocking ▪ Blocking is considered synchronous Blocking send -- the sender is blocked until the message is received Blocking receive -- the receiver is blocked until a message is available ▪ Non-blocking is considered asynchronous Non-blocking send -- the sender sends the message and continue Non-blocking receive -- the receiver receives:  A valid message, or  Null message ▪ Different combinations possible If both send and receive are blocking, we have a rendezvous Operating System Concepts – 10 th Edition 3.23 Silberschatz, Galvin and Gagne ©2018  Producer-Consumer: Message Passing ▪ Producer message next_produced; while (true) { send(next_produced); } ▪ Consumer message next_consumed; while (true) { receive(next_consumed) } Operating System Concepts – 10 th Edition 3.24 Silberschatz, Galvin and Gagne ©2018  Buffering ▪ Queue of messages attached to the link. ▪ Implemented in one of three ways 1. Zero capacity – no messages are queued on a link. Sender must wait for receiver (rendezvous) 2. Bounded capacity – finite length of n messages Sender must wait if link full 3. Unbounded capacity – infinite length Sender never waits Operating System Concepts – 10 th Edition 3.25 Silberschatz, Galvin and Gagne ©2018  Examples of IPC Systems – Windows ▪ Message-passing centric via advanced local procedure call (LPC) facility Only works between processes on the same system Uses ports (like mailboxes) to establish and maintain communication channels Communication works as follows:  The client opens a handle to the subsystem’s connection port object.  The client sends a connection request.  The server creates two private communication ports and returns the handle to one of them to the client.  The client and server use the corresponding port handle to send messages or callbacks and to listen for replies. Operating System Concepts – 10 th Edition 3.26 Silberschatz, Galvin and Gagne ©2018  Local Procedure Calls in Windows Operating System Concepts – 10 th Edition 3.27 Silberschatz, Galvin and Gagne ©2018  Pipes ▪ Acts as a conduit allowing two processes to communicate ▪ Issues: Is communication unidirectional or bidirectional? In the case of two-way communication, is it half or full-duplex? Must there exist a relationship (i.e., parent-child) between the communicating processes? Can the pipes be used over a network? ▪ Ordinary pipes – cannot be accessed from outside the process that created it. Typically, a parent process creates a pipe and uses it to communicate with a child process that it created. ▪ Named pipes – can be accessed without a parent-child relationship. Operating System Concepts – 10 th Edition 3.28 Silberschatz, Galvin and Gagne ©2018  Ordinary Pipes ▪ Ordinary Pipes allow communication in standard producer-consumer style ▪ Producer writes to one end (the write-end of the pipe) ▪ Consumer reads from the other end (the read-end of the pipe) ▪ Ordinary pipes are therefore unidirectional ▪ Require parent-child relationship between communicating processes ▪ Windows calls these anonymous pipes Operating System Concepts – 10 th Edition 3.29 Silberschatz, Galvin and Gagne ©2018  Named Pipes ▪ Named Pipes are more powerful than ordinary pipes ▪ Communication is bidirectional ▪ No parent-child relationship is necessary between the communicating processes ▪ Several processes can use the named pipe for communication ▪ Provided on both UNIX and Windows systems Operating System Concepts – 10 th Edition 3.30 Silberschatz, Galvin and Gagne ©2018  Communications in Client-Server Systems ▪ Sockets ▪ Remote Procedure Calls Operating System Concepts – 10 th Edition 3.31 Silberschatz, Galvin and Gagne ©2018  Sockets ▪ A socket is defined as an endpoint for communication ▪ Concatenation of IP address and port – a number included at start of message packet to differentiate network services on a host ▪ The socket 161.25.19.8:1625 refers to port 1625 on host 161.25.19.8 ▪ Communication consists between a pair of sockets ▪ All ports below 1024 are well known, used for standard services ▪ Special IP address 127.0.0.1 (loopback) to refer to system on which process is running Operating System Concepts – 10 th Edition 3.32 Silberschatz, Galvin and Gagne ©2018  Socket Communication Operating System Concepts – 10 th Edition 3.33 Silberschatz, Galvin and Gagne ©2018  Sockets in Java ▪ Three types of sockets Connection-oriented (TCP) Connectionless (UDP) MulticastSocket class– data can be sent to multiple recipients ▪ Consider this “Date” server in Java: Operating System Concepts – 10 th Edition 3.34 Silberschatz, Galvin and Gagne ©2018  Sockets in Java The equivalent Date client Operating System Concepts – 10 th Edition 3.35 Silberschatz, Galvin and Gagne ©2018  Remote Procedure Calls ▪ Remote procedure call (RPC) abstracts procedure calls between processes on networked systems Again uses ports for service differentiation ▪ Stubs – client-side proxy for the actual procedure on the server ▪ The client-side stub locates the server and marshalls the parameters ▪ The server-side stub receives this message, unpacks the marshalled parameters, and performs the procedure on the server ▪ On Windows, stub code compile from specification written in Microsoft Interface Definition Language (MIDL) Operating System Concepts – 10 th Edition 3.36 Silberschatz, Galvin and Gagne ©2018  Remote Procedure Calls (Cont.) ▪ Data representation handled via External Data Representation (XDL) format to account for different architectures Big-endian and little-endian ▪ Remote communication has more failure scenarios than local Messages can be delivered exactly once rather than at most once ▪ OS typically provides a rendezvous (or matchmaker) service to connect client and server Operating System Concepts – 10 th Edition 3.37 Silberschatz, Galvin and Gagne ©2018  Execution of RPC Operating System Concepts – 10 th Edition 3.38 Silberschatz, Galvin and Gagne ©2018  End of Chapter 3 Operating System Concepts – 10 th Edition Silberschatz, Galvin and Gagne ©2018