Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Berkeley Software Distribution wikipedia , lookup
Plan 9 from Bell Labs wikipedia , lookup
Mobile operating system wikipedia , lookup
Spring (operating system) wikipedia , lookup
Copland (operating system) wikipedia , lookup
Unix security wikipedia , lookup
Burroughs MCP wikipedia , lookup
Security-focused operating system wikipedia , lookup
Chapter 5: Processes Process Concept Chapter 5: Processes & Threads Process Scheduling Operations on Processes Interprocess Communication Communication in Client-Server Systems Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition, Operating System Concepts – 8th Edition Objectives 5.2 Silberschatz, Galvin and Gagne ©2009 Process Concept An operating system executes a variety of programs: To introduce the notion of a process -- a program in execution which forms the basis of all computation execution, To describe the various features of processes, including scheduling, creation and termination, and communication To describe communication in client-server systems z Batch system – jobs z 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 A process includes: z Operating System Concepts – 8th Edition 5.3 Silberschatz, Galvin and Gagne ©2009 z program counter stack z data section Operating System Concepts – 8th Edition 5.4 Silberschatz, Galvin and Gagne ©2009 Process State Diagram of Process State As a process executes, it changes state z new: The process is being created z running: Instructions are being executed z waiting: The process is waiting for some event to occur z ready: The process is waiting to be assigned to a processor z terminated: The process has finished execution Operating System Concepts – 8th Edition 5.5 Silberschatz, Galvin and Gagne ©2009 Process Control Block (PCB) Operating System Concepts – 8th Edition 5.6 Silberschatz, Galvin and Gagne ©2009 Process Control Block (PCB) Information associated with each process Process state Program counter CPU registers CPU scheduling information Memory-management information Accounting information I/O status information Operating System Concepts – 8th Edition 5.7 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.8 Silberschatz, Galvin and Gagne ©2009 CPU Switch From Process to Process Process Scheduling Queues 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 – 8th Edition 5.9 Silberschatz, Galvin and Gagne ©2009 Ready Queue And Various I/O Device Queues Operating System Concepts – 8th Edition 5.11 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.10 Silberschatz, Galvin and Gagne ©2009 Representation of Process Scheduling Operating System Concepts – 8th Edition 5.12 Silberschatz, Galvin and Gagne ©2009 Schedulers Addition of Medium Term Scheduling Long Long-term term scheduler (or job scheduler) – selects which processes should be brought into the ready queue Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU 5.13 Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition Schedulers (Cont) Silberschatz, Galvin and Gagne ©2009 Context Switch Short-term scheduler is invoked very frequently (milliseconds) ⇒ (must be fast) Long-term scheduler is invoked very infrequently (seconds, minutes) ⇒ (may be slow) 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 The long-term scheduler controls the degree of multiprogramming z I/O bound process – spends more time doing I/O than I/O-bound computations, many short CPU bursts z CPU-bound process – spends more time doing computations; f few very long CPU C bursts 5.15 Context-switch time is overhead; the system does no useful work while switching Processes can be described as either: Operating System Concepts – 8th Edition 5.14 Silberschatz, Galvin and Gagne ©2009 Time dependent on hardware support Operating System Concepts – 8th Edition 5.16 Silberschatz, Galvin and Gagne ©2009 Process Creation Process Creation (Cont) Parent process create children processes, which, in turn create other processes forming a tree of processes processes, Generally, process identified and managed via a process identifier (pid) Resource sharing Address space z Child d duplicate li t off parentt z Child has a program loaded into it UNIX examples z Parent and children share all resources z fork system call creates new process z Children share subset of parent’s resources z z Parent and child share no resources exec system call used after a fork to replace the process’ memory space with a new program Execution z Parent and children execute concurrently z Parent waits until children terminate Operating System Concepts – 8th Edition 5.17 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition Process Creation 5.18 Silberschatz, Galvin and Gagne ©2009 Process Termination Process executes last statement and asks the operating system to delete it (exit) z Output data from child to parent (via wait) z Process’ resources are deallocated by operating system Parent may terminate execution of children processes (abort) z Child has exceeded allocated resources z Task assigned to child is no longer required z If parent is exiting Some operating system do not allow child to continue if its parent terminates – Operating System Concepts – 8th Edition 5.19 Silberschatz, Galvin and Gagne ©2009 All children terminated - cascading termination Operating System Concepts – 8th Edition 5.20 Silberschatz, Galvin and Gagne ©2009 Interprocess Communication Communications Models Processes within a system may be independent or cooperating Cooperating C ti process can affect ff t or be b affected ff t d by b other th processes, including sharing data Reasons for cooperating processes: z Information sharing z Computation speedup z Modularity z Convenience Cooperating processes need interprocess communication (IPC) Two models of IPC z Shared memory y z Message passing Operating System Concepts – 8th Edition 5.21 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 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 z Information sharing z Computation speed speed-up up z Modularity z Convenience Operating System Concepts – 8th Edition 5.23 Silberschatz, Galvin and Gagne ©2009 5.22 Silberschatz, Galvin and Gagne ©2009 Producer-Consumer Problem Paradigm g for cooperating p gp processes, p producer p process produces information that is consumed by a consumer process z unbounded-buffer unbounded buffer places no practical limit on the size of the buffer z bounded-buffer assumes that there is a fixed buffer size Operating System Concepts – 8th Edition 5.24 Silberschatz, Galvin and Gagne ©2009 Bounded-Buffer – Producer Bounded-Buffer – Shared-Memory Solution Shared data while (true) { /* Produce an item */ #define BUFFER_SIZE 10 typedef struct { while (((in = (in + 1) % BUFFER SIZE count) == out) ... ; /* do nothing -- no free buffers */ } item;; buffer[in] = item; in = (in + 1) % BUFFER SIZE; item buffer[BUFFER_SIZE]; [ _ ] } int in = 0; int out = 0; Solution is correct, but can only use BUFFER_SIZE-1 elements 5.25 Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009 Bounded Buffer – Consumer Operating System Concepts – 8th Edition 5.26 Silberschatz, Galvin and Gagne ©2009 Interprocess Communication – Message Passing Mechanism for processes to communicate and to synchronize their actions while (true) { Message system – processes communicate with each other without resorting to shared variables while (in == out) IPC facility provides two operations: ; // do nothing -- nothing to consume z send(message) – message size fixed or variable receive(message) If P and Q wish to communicate, they need to: z establish a communication link between them z exchange messages via send/receive Implementation of communication link z physical (e.g., shared memory, hardware bus) z logical (e.g., logical properties) z // remove an item from the buffer item = buffer[out]; out = (out + 1) % BUFFER SIZE; return item; } Operating System Concepts – 8th Edition 5.27 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.28 Silberschatz, Galvin and Gagne ©2009 Implementation Questions How are links established? Direct Communication Processes must name each other explicitly: Can C a lilink kb be associated i t d with ith more th than ttwo processes? ? z send d (P, (P message)) – send d a message tto process P How many links can there be between every pair of communicating z receive(Q, message) – receive a message from process Q processes? Properties of communication link What is the capacity of a link? z Links are established automatically Is the size of a message that the link can accommodate fixed or variable? z A link is associated with exactly one pair of communicating processes Is a link unidirectional or bi-directional? z Between each pair there exists exactly one link z The link may be unidirectional, but is usually bi-directional Operating System Concepts – 8th Edition 5.29 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition Indirect Communication Messages are directed and received from mailboxes (also referred to as ports) 5.30 Indirect Communication Operations z create a new mailbox z Each mailbox has a unique id z send and receive messages through mailbox z Processes can communicate only y if theyy share a mailbox z destroy a mailbox Properties of communication link Silberschatz, Galvin and Gagne ©2009 Primitives are defined as: z Link established only if processes share a common mailbox send(A, message) – send a message to mailbox A z A link may be associated with many processes receive(A, message) – receive a message from mailbox A z Each pair of processes may share several communication links z Link may be unidirectional or bi bi-directional directional Operating System Concepts – 8th Edition 5.31 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.32 Silberschatz, Galvin and Gagne ©2009 Indirect Communication Mailbox sharing z P1, P2, and d P3 share h mailbox ilb A z P1, sends; P2 and P3 receive z Who gets the message? Synchronization Message passing may be either blocking or non-blocking Bl ki is Blocking i considered id d synchronous h Solutions z Allow a link to be associated with at most two processes z Allow only one process at a time to execute a receive operation z Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was was. Operating System Concepts – 8th Edition 5.33 Silberschatz, Galvin and Gagne ©2009 Buffering z Blocking send has the sender block until the message is received z Blocking receive has the receiver block until a message is available Non blocking is considered asynchronous Non-blocking z Non-blocking send has the sender send the message and continue z Non-blocking receive has the receiver receive a valid message or null Operating System Concepts – 8th Edition 5.34 Silberschatz, Galvin and Gagne ©2009 Communications in Client-Server Systems Queue of messages attached to the link; implemented in one of three ways Sockets Remote R t P Procedure d Calls C ll 1. Zero capacity – 0 messages Sender must wait for receiver (rendezvous) Remote Method Invocation (Java) 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 – 8th Edition 5.35 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.36 Silberschatz, Galvin and Gagne ©2009 Sockets Socket Communication A socket is defined as an endpoint for communication Concatenation C t ti off IP address dd and d portt The socket 161.25.19.8:1625 refers to port 1625 on host 161.25.19.8 Communication consists between a pair of sockets Operating System Concepts – 8th Edition 5.37 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition Remote Procedure Calls 5.38 Silberschatz, Galvin and Gagne ©2009 Execution of RPC Remote procedure call (RPC) abstracts procedure calls between processes on networked systems 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 peforms the procedure on the server Operating System Concepts – 8th Edition 5.39 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.40 Silberschatz, Galvin and Gagne ©2009 Remote Method Invocation Marshalling Parameters Remote Method Invocation (RMI) is a Java mechanism similar to RPCs RMI allows ll a JJava program on one machine hi tto iinvoke k a method th d on a remote object Operating System Concepts – 8th Edition 5.41 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.42 Silberschatz, Galvin and Gagne ©2009 Content Overview Multithreading M ltith di M Models d l Thread Libraries Threads Operating System Concepts – 8th Edition, Threading Issues Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.44 Silberschatz, Galvin and Gagne ©2009 Objectives Single and Multithreaded Processes To introduce the notion of a thread — a fundamental unit of CPU utilization that forms the basis of multithreaded computer systems To examine issues related to multithreaded programming Operating System Concepts – 8th Edition 5.45 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition Benefits Silberschatz, Galvin and Gagne ©2009 Multicore Programming Responsiveness Multicore systems putting pressure on programmers, challenges include Resource Sharing Economy Scalability Operating System Concepts – 8th Edition 5.46 5.47 Silberschatz, Galvin and Gagne ©2009 z Di idi activities Dividing ti iti z Balance z Data splitting z Data dependency z Testing and debugging Operating System Concepts – 8th Edition 5.48 Silberschatz, Galvin and Gagne ©2009 Multithreaded Server Architecture Operating System Concepts – 8th Edition 5.49 Silberschatz, Galvin and Gagne ©2009 Concurrent Execution on a Single-core System 5.50 Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009 User Threads Parallel Execution on a Multicore System Thread management done by user-level threads library Three primary thread libraries: Operating System Concepts – 8th Edition 5.51 Silberschatz, Galvin and Gagne ©2009 z POSIX Pthreads z Win32 threads z Java threads Operating System Concepts – 8th Edition 5.52 Silberschatz, Galvin and Gagne ©2009 Kernel Threads Multithreading Models Supported by the Kernel Many-to-One Examples One-to-One z Windows XP/2000 z Solaris z Linux z Tru64 UNIX z Mac OS X Many-to-Many 5.53 Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009 Many-to-One Operating System Concepts – 8th Edition 5.54 Silberschatz, Galvin and Gagne ©2009 Many-to-One Model Many user-level threads mapped to single kernel thread Examples: E l z Solaris Green Threads z GNU Portable Threads Operating System Concepts – 8th Edition 5.55 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.56 Silberschatz, Galvin and Gagne ©2009 One-to-One One-to-one Model Each user-level thread maps to kernel thread Examples E l z Windows NT/XP/2000 z Linux z Solaris 9 and later Operating System Concepts – 8th Edition 5.57 Silberschatz, Galvin and Gagne ©2009 Many-to-Many Model Operating System Concepts – 8th Edition 5.58 Silberschatz, Galvin and Gagne ©2009 Many-to-Many Model Allows All many user llevell th threads d tto b be mapped d tto many kkernell threads Allows the operating system to create a sufficient number of kernel threads Solaris prior to version 9 Windows NT/2000 with the ThreadFiber package Operating System Concepts – 8th Edition 5.59 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.60 Silberschatz, Galvin and Gagne ©2009 Two-level Model Two-level Model Similar to M:M, except that it allows a user thread to be bound to kernel thread Examples z IRIX z HP-UX z Tru64 UNIX z Solaris 8 and earlier Operating System Concepts – 8th Edition 5.61 Silberschatz, Galvin and Gagne ©2009 Thread Cancellation Terminating g a thread before it has finished Two general approaches: z Asynchronous cancellation terminates the target th d immediately thread i di t l z Deferred cancellation allows the target thread to periodically check if it should be cancelled Operating System Concepts – 8th Edition 5.63 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8th Edition 5.62 Silberschatz, Galvin and Gagne ©2009