4. Lecture - 4 (1).ppt

Chapter 3: Processes Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013  Chapter 3: Processes Process Concept Process Scheduling Operations on Processes Interprocess Communicati...

Chapter 3: Processes Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013  Chapter 3: Processes Process Concept Process Scheduling Operations on Processes Interprocess Communication Examples of IPC Systems Communication in Client-Server Systems Operating System Concepts – 9th Edition 3.2 Silberschatz, Galvin and Gagne ©2013  Objectives To introduce the notion of a process -- a program in execution, which forms the basis of all computation To describe the various features of processes, including scheduling, creation and termination, and communication To explore interprocess communication using shared memory and message passing To describe communication in client-server systems Operating System Concepts – 9th Edition 3.3 Silberschatz, Galvin and Gagne ©2013  Process Concept An operating system executes a variety of programs:  Batch system – jobs  Time-shared systems – user programs or tasks Textbook uses the terms job and process almost interchangeably Process – a program in execution; process execution must progress in sequential fashion Multiple parts  The program code, also called text section  Current activity including program counter, processor registers  Stack containing temporary data  Function parameters, return addresses, local variables  Data section containing global variables  Heap containing memory dynamically allocated during run time Operating System Concepts – 9th Edition 3.4 Silberschatz, Galvin and Gagne ©2013  Process Concept (Cont.) Program is passive entity stored on disk (executable file), process is active  Program becomes process when executable file loaded into memory  A process is defined as an entity which represents the basic unit of work to be implemented in the system. Execution of program started via GUI mouse clicks, command line entry of its name, etc One program can be several processes  Consider multiple users executing the same program Operating System Concepts – 9th Edition 3.5 Silberschatz, Galvin and Gagne ©2013  Process in Memory Operating System Concepts – 9th Edition 3.6 Silberschatz, Galvin and Gagne ©2013  Process State As a process executes, it changes state  new: The process is being created  running: Instructions are being executed  waiting: The process is waiting for some event to occur  ready: The process is waiting to be assigned to a processor  terminated: The process has finished execution Operating System Concepts – 9th Edition 3.7 Silberschatz, Galvin and Gagne ©2013  Process States New → Ready: The operating system creates a process and prepares the process to be executed, then the operating system moved the process into “Ready Queue“. Ready → Running: When it is time to select a process to run. The operating system selects one of the jobs from the ready queue and moves the process from the ready state to the running state. Running → Terminated: When the execution of a process has completed, then the operating system terminates that process from running state. Running → Ready: When the time slot of the processor expired, then the operating system shifted the running process to the ready state. Running → Waiting: A process is put into the waiting state. If the process needs an event to occur or an I/O device. The operating system doesn’t provide the I/O device then the process moved to the waiting state by the operating state. Waiting → Ready: A process in the blocked state is moved to the ready state when the event for which it has been waiting occurs. Operating System Concepts – 9th Edition 3.8 Silberschatz, Galvin and Gagne ©2013  Diagram of Process State Operating System Concepts – 9th Edition 3.9 Silberschatz, Galvin and Gagne ©2013  Diagram of Process State Main Memory Secondary Memory Operating System Concepts – 9th Edition 3.10 Silberschatz, Galvin and Gagne ©2013  Process Control Block (PCB) Information associated with each process (also called task control block) Process state – running, waiting, etc Program counter – location of instruction to next execute CPU registers – contents of all process- centric registers CPU scheduling information- priorities, scheduling queue pointers Memory-management information – memory allocated to the process Accounting information – CPU used, clock time elapsed since start, time limits I/O status information – I/O devices allocated to process, list of open files Operating System Concepts – 9th Edition 3.11 Silberschatz, Galvin and Gagne ©2013  CPU Switch From Process to Process Operating System Concepts – 9th Edition 3.12 Silberschatz, Galvin and Gagne ©2013  Process Scheduling Maximize CPU use, quickly switch processes onto CPU for time sharing The process scheduling is the activity of the process manager that handles the removal of the running process from the CPU and the selection of another process on the basis of a particular strategy. Process scheduling is an essential part of a Multiprogramming operating systems. Such operating systems allow more than one process to be loaded into the executable memory at a time and the loaded process shares the CPU using time multiplexing. Operating System Concepts – 9th Edition 3.13 Silberschatz, Galvin and Gagne ©2013  Process Scheduling Process scheduler selects among available processes for next execution on CPU Maintains scheduling queues of processes  Job queue – set of all processes in the system  Ready queue – set of all processes residing in main memory, ready and waiting to execute  Device queues – set of processes waiting for an I/O device  Processes migrate among the various queues Operating System Concepts – 9th Edition 3.14 Silberschatz, Galvin and Gagne ©2013  Ready Queue And Various I/O Device Queues Operating System Concepts – 9th Edition 3.15 Silberschatz, Galvin and Gagne ©2013  Representation of Process Scheduling Queueing diagram represents queues, resources, flows Operating System Concepts – 9th Edition 3.16 Silberschatz, Galvin and Gagne ©2013  Schedulers Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU  Sometimes the only scheduler in a system  Short-term scheduler is invoked frequently (milliseconds)  (must be fast) Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue  Long-term scheduler is invoked infrequently (seconds, minutes)  (may be slow)  The long-term scheduler controls the degree of multiprogramming (The number of processes that the system supports in memory) The more is the degree of multiprogramming the better is the CPU utilization. Processes can be described as either:  I/O-bound process – spends more time doing I/O than computations, many short CPU bursts  CPU-bound process – spends more time doing computations; few very long CPU bursts Long-term scheduler strives for good process mix Operating System Concepts – 9th Edition 3.17 Silberschatz, Galvin and Gagne ©2013  Addition of Medium-Term Scheduling Medium-term scheduler can be added if degree of multiple programming needs to decrease  Remove process from memory, store on disk, bring back in from disk to continue execution: swapping Operating System Concepts – 9th Edition 3.19 Silberschatz, Galvin and Gagne ©2013  S. Long-Term Scheduler Short-Term Scheduler Medium-Term Scheduler N. 1 It is a job scheduler It is a CPU scheduler It is a process swapping scheduler. 2 Speed is lesser than short Speed is fastest among Speed is in between both term scheduler other two short- and long-term scheduler. 3 It controls the degree of It provides lesser control It reduces the degree of multiprogramming over degree of multiprogramming. multiprogramming 4 It selects processes from It selects those processes It can re-introduce the pool and loads them into which are ready to execute process into memory and memory for execution execution can be continued. Operating System Concepts – 9th Edition 3.20 Silberschatz, Galvin and Gagne ©2013  Context Switch When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process via a context switch Context of a process represented in the PCB Context-switch time is overhead; the system does no useful work while switching  The more complex the OS and the PCB  the longer the context switch Time dependent on hardware support  Some hardware provides multiple sets of registers per CPU  multiple contexts loaded at once Operating System Concepts – 9th Edition 3.21 Silberschatz, Galvin and Gagne ©2013  Multiprogramming Multiprogramming – We have many processes ready to run. There are two types of multiprogramming:  Pre-emption – Process is forcefully removed from CPU. Pre-emption is also called as time sharing or multitasking.  Non-pre-emption – Processes are not removed until they complete the execution. Degree of multiprogramming – The number of processes that can reside in the ready state at maximum decides the degree of multiprogramming, e.g., if the degree of programming = 100, this means 100 processes can reside in the ready state at maximum. Operating System Concepts – 9th Edition 3.22 Silberschatz, Galvin and Gagne ©2013  Operations on Processes System must provide mechanisms for:  process creation,  process termination,  and so on as detailed next Operating System Concepts – 9th Edition 3.23 Silberschatz, Galvin and Gagne ©2013  Process Creation Parent process create children processes, which, in turn create other processes, forming a tree of processes Generally, process identified and managed via a process identifier (pid) Resource sharing options  Parent and children share all resources  Children share subset of parent’s resources  Parent and child share no resources Execution options  Parent and children execute concurrently  Parent waits until children terminate Operating System Concepts – 9th Edition 3.24 Silberschatz, Galvin and Gagne ©2013  A Tree of Processes in Linux Operating System Concepts – 9th Edition 3.25 Silberschatz, Galvin and Gagne ©2013  Process Creation (Cont.) Address space  Child duplicate of parent  Child has a program loaded into it UNIX examples  fork() system call creates new process  exec() system call used after a fork() to replace the process’ memory space with a new program Operating System Concepts – 9th Edition 3.26 Silberschatz, Galvin and Gagne ©2013  Process Termination Returns status data from child to parent (via wait()) Process’ resources are deallocated by operating system Parent may terminate the execution of children processes using the abort() system call. Some reasons for doing so:  Child has exceeded allocated resources  Task assigned to child is no longer required  The parent is exiting and the operating systems does not allow a child to continue if its parent terminates Operating System Concepts – 9th Edition 3.27 Silberschatz, Galvin and Gagne ©2013  Process Termination Process termination occurs when the process is terminated. The exit() system call is used by most operating systems for process termination. Some of the causes of process termination are as follows −  A process may be terminated after its execution is naturally completed. This process leaves the processor and releases all its resources.  A child process may be terminated if its parent process requests for its termination.  A process can be terminated if it tries to use a resource that it is not allowed to. For example - A process can be terminated for trying to write into a read only file.  If an I/O failure occurs for a process, it can be terminated. For example - If a process requires the printer and it is not working, then the process will be terminated.  In most cases, if a parent process is terminated then its child processes are also terminated. This is done because the child process cannot exist without the parent process.  If a process requires more memory than is currently available in the system, then it is terminated because of memory shortage. Operating System Concepts – 9th Edition 3.28 Silberschatz, Galvin and Gagne ©2013  Process Termination Some operating systems do not allow child to exists if its parent has terminated. If a process terminates, then all its children must also be terminated.  cascading termination. All children, grandchildren, etc. are terminated.  The termination is initiated by the operating system. The parent process may wait for termination of a child process by using the wait()system call. The call returns status information and the pid of the terminated process pid = wait(&status); If no parent waiting (did not invoke wait()) process is a zombie If parent terminated without invoking wait , process is an orphan Operating System Concepts – 9th Edition 3.29 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.30 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.31 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.32 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.33 Silberschatz, Galvin and Gagne ©2013  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 inter-process communication (IPC) Two models of IPC  Shared memory  Message passing Operating System Concepts – 9th Edition 3.34 Silberschatz, Galvin and Gagne ©2013  Communications Models (a) Message passing. (b) shared memory. Operating System Concepts – 9th Edition 3.35 Silberschatz, Galvin and Gagne ©2013  Shared memory vs Message passing Message passing is useful for exchanging smaller amounts of data, because no conflicts need to be avoided. Message passing is also easier to implement than is shared memory for inter-process communication. Shared memory is faster than message passing because message passing systems are typically implemented using system calls and thus require the more time consuming task of kernel intervention. In contrast, in shared memory systems, system calls are required only to establish shared memory regions. Once shared memory is established, a;; accesses are treated as routine memory accesses and no assistance from kernel is required. Operating System Concepts – 9th Edition 3.36 Silberschatz, Galvin and Gagne ©2013  Cooperating Processes Independent process cannot affect or be affected by the execution of another process Cooperating process can affect or be affected by the execution of another process Advantages of process cooperation  Information sharing  Computation speed-up  Modularity  Convenience Operating System Concepts – 9th Edition 3.37 Silberschatz, Galvin and Gagne ©2013  Producer-Consumer Problem Paradigm for cooperating processes, producer process produces information that is consumed by a consumer process Is a multi-process synchronization problem Also known as the bounded-buffer problem Two processes share a common buffer  Producer : One of them is producer puts information in the buffer  Consumer : One of them is consumer takes information out of the buffer The problem is to make sure that the producer won't try to add data into the buffer if it's full and that the consumer won't try to remove data from an empty buffer. unbounded-buffer places no practical limit on the size of the buffer bounded-buffer assumes that there is a fixed buffer size Operating System Concepts – 9th Edition 3.38 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.39 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.40 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.41 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.42 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.43 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.44 Silberschatz, Galvin and Gagne ©2013  What's the problem here? The following are the problems that might occur in the Producer- Consumer:  The producer should produce data only when the buffer is not full. If the buffer is full, then the producer shouldn't be allowed to put any data into the buffer.  The consumer should consume data only when the buffer is not empty. If the buffer is empty, then the consumer shouldn't be allowed to take any data from the buffer.  The producer and consumer should not access the buffer at the same time. Operating System Concepts – 9th Edition 3.45 Silberschatz, Galvin and Gagne ©2013  Interprocess Communication – 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 Chapter 5. Operating System Concepts – 9th Edition 3.46 Silberschatz, Galvin and Gagne ©2013  Interprocess Communication – Message Passing Mechanism for processes to communicate and to synchronize their actions Message system – 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 – 9th Edition 3.47 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.48 Silberschatz, Galvin and Gagne ©2013  Message Passing (Cont.) Implementation of communication link  Physical:  Shared memory  Hardware bus  Network  Logical:  Direct or indirect  Synchronous or asynchronous  Automatic or explicit buffering Operating System Concepts – 9th Edition 3.49 Silberschatz, Galvin and Gagne ©2013  Direct Communication Symmetric and asymmetric Symmetric: In the Direct Communication, each process that wants to communicate must explicitly name the recipient or sender of the communication. In this scheme, the send and receive primitives are defined as follows : 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 – 9th Edition 3.50 Silberschatz, Galvin and Gagne ©2013  Direct Communication In asymmetry only the sender names the recipient; the recipient is not required to name the sender. In this scheme, the send and receive primitives are defined as follows: Send(P, message): Send a message to process P. receive(id, message):Receive a message from any process; the variable id is set to the name of the process with which communication has taken place. Disadvantage of symmetric and asymmetric schemes  The disadvantage in both symmetric and asymmetric schemes is the limited modularity of the resulting process definitions. Changing the name of a process may necessitate examining all other process definitions. Operating System Concepts – 9th Edition 3.51 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.52 Silberschatz, Galvin and Gagne ©2013  Indirect Communication Operations  create a new mailbox (port)  send and receive messages through mailbox  destroy 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 – 9th Edition 3.53 Silberschatz, Galvin and Gagne ©2013  Indirect Communication 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 – 9th Edition 3.54 Silberschatz, Galvin and Gagne ©2013  Indirect Communication A mailbox may be owned either by a process or by the operating system. If the mailbox is owned by a process (that is, the mail box is part of the address space of the process), then we distinguish between the owner (which can only receive messages through this mailbox) and the user (which can only send messages to the mailbox). Since each mailbox has a unique owner, there can be no confusion about which process should receive a message sent to this mailbox. When a process that owns a mailbox terminates, the mailbox disappears. Any process that subsequently sends a message to this mailbox must be notified that the mail box no longer exists. Operating System Concepts – 9th Edition 3.55 Silberschatz, Galvin and Gagne ©2013  Indirect Communication In contrast, a mailbox that is owned by the operating system has an existence of its own. It is independent and is not attached to any particular process. The operating system then must provide a mechanism that allows a process to do the following:  Create a new mailbox.  Send and receive messages through the mailbox.  Delete a mailbox. The process that creates a new mailbox is that mailbox’s owner by default. Initially, the owner is the only process that can receive messages through this mailbox. However, the ownership and receiving privilege may be passed to other processes through appropriate system calls. Of course, this provision could result in multiple receivers for each mailbox. Operating System Concepts – 9th Edition 3.56 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.57 Silberschatz, Galvin and Gagne ©2013  Synchronization (Cont.) Producer-consumer becomes trivial message next_produced; while (true) { send(next_produced); } message next_consumed; while (true) { receive(next_consumed); } Operating System Concepts – 9th Edition 3.58 Silberschatz, Galvin and Gagne ©2013  Buffering Queue of messages attached to the link. implemented in one of three ways Zero capacity: The queue has maximum length 0; thus, the link cannot have any messages waiting in it. In this case, the sender must block until the recipient receives the message. The zero-capacity case is sometimes referred to as a message system with no buffering; Bounded capacity: The queue has finite length n thus, at most n messages can reside in it. If the queue is not full when a new message is sent, the latter is placed in the queue (either the message is copied or a pointer to the message is kept), and the sender can continue execution without waiting. The link has a finite capacity, however. If the link is full, the sender must block until space is available in the queue. It is also known as automatic buffering. Unbounded capacity: The queue has potentially infinite length; thus, any number of messages can wait in it. The sender never blocks. It is also known as automatic buffering. Operating System Concepts – 9th Edition 3.59 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.60 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.61 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 3.62 Silberschatz, Galvin and Gagne ©2013  Examples of IPC Systems - Mach Mach communication is message based  Even system calls are messages  Each task gets two mailboxes at creation- Kernel and Notify  Only three system calls needed for message transfer msg_send(), msg_receive(), msg_rpc()  Mailboxes needed for communication, created via port_allocate()  Send and receive are flexible, for example four options if mailbox full:  Wait indefinitely  Wait at most n milliseconds  Return immediately  Temporarily cache a message Operating System Concepts – 9th Edition 3.63 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.64 Silberschatz, Galvin and Gagne ©2013  Local Procedure Calls in Windows Operating System Concepts – 9th Edition 3.65 Silberschatz, Galvin and Gagne ©2013  Examples of IPC Systems - POSIX POSIX Shared Memory  Process first creates shared memory segment shm_fd = shm_open(name, O CREAT | O RDWR, 0666);  Also used to open an existing segment to share it  Set the size of the object ftruncate(shm fd, 4096);  Now the process could write to the shared memory sprintf(shared memory, "Writing to shared memory"); Operating System Concepts – 9th Edition 3.66 Silberschatz, Galvin and Gagne ©2013  IPC POSIX Producer Operating System Concepts – 9th Edition 3.67 Silberschatz, Galvin and Gagne ©2013  IPC POSIX Consumer Operating System Concepts – 9th Edition 3.68 Silberschatz, Galvin and Gagne ©2013  Communications in Client-Server Systems Sockets Remote Procedure Calls Pipes Remote Method Invocation (Java) Operating System Concepts – 9th Edition 3.69 Silberschatz, Galvin and Gagne ©2013  Multitasking in Mobile Systems Some mobile systems (e.g., early version of iOS) allow only one process to run, others suspended Due to screen real estate, user interface limits iOS provides for a  Single foreground process- controlled via user interface  Multiple background processes– in memory, running, but not on the display, and with limits  Limits include single, short task, receiving notification of events, specific long-running tasks like audio playback Android runs foreground and background, with fewer limits  Background process uses a service to perform tasks  Service can keep running even if background process is suspended  Service has no user interface, small memory use Operating System Concepts – 9th Edition 3.70 Silberschatz, Galvin and Gagne ©2013  Multiprocess Architecture – Chrome Browser Many web browsers ran as single process (some still do)  If one web site causes trouble, entire browser can hang or crash Google Chrome Browser is multiprocess with 3 different types of processes:  Browser process manages user interface, disk and network I/O  Renderer process renders web pages, deals with HTML, Javascript. A new renderer created for each website opened  Runs in sandbox restricting disk and network I/O, minimizing effect of security exploits  Plug-in process for each type of plug-in Operating System Concepts – 9th Edition 3.71 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.72 Silberschatz, Galvin and Gagne ©2013  Socket Communication Operating System Concepts – 9th Edition 3.73 Silberschatz, Galvin and Gagne ©2013  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: Operating System Concepts – 9th Edition 3.74 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.75 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.76 Silberschatz, Galvin and Gagne ©2013  Execution of RPC Operating System Concepts – 9th Edition 3.77 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.78 Silberschatz, Galvin and Gagne ©2013  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 See Unix and Windows code samples in textbook Operating System Concepts – 9th Edition 3.79 Silberschatz, Galvin and Gagne ©2013  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 – 9th Edition 3.80 Silberschatz, Galvin and Gagne ©2013  #include int pipe(int pipefd); // pipe() function creates a unidirectional pipe for IPC. On success it return two file descriptors pipefd and pipefd. // pipefd is the reading end of the pipe. So, the process which will receive the data should use this file descriptor. // pipefd is the writing end of the pipe. So, the process that wants to send the data should use this file descriptor. #include #include #include #include int main() { int fd,n; char buffer; pid_t p; pipe(fd); //creates a unidirectional pipe with two end fd and fd p=fork(); if(p>0) //parent { printf("Parent Passing value to child\n"); write(fd,"hello\n",6); //fd is the write end of the pipe wait(); } else // child { printf("Child printing received value\n"); n=read(fd,buffer,100); //fd is the read end of the pipe write(1,buffer,n); } } Operating System Concepts – 9th Edition 3.81 Silberschatz, Galvin and Gagne ©2013  End of Chapter 3 Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013