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

Chapter 3: Processes Operating System Concepts – 10th Edition Silberschatz, Galvin and Gagne ©2018  Chapter 3: Processes 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 – 10th 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 – 10th Edition 3.3 Silberschatz, Galvin and Gagne ©2018  Process Concept An operating system executes a variety of programs that run as a process. 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 – 10th Edition 3.4 Silberschatz, Galvin and Gagne ©2018  Process Concept (Cont.) Program is passive entity stored on disk (executable file); process is active  Program becomes process when executable file loaded into memory 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 – 10th Edition 3.5 Silberschatz, Galvin and Gagne ©2018  Process in Memory Operating System Concepts – 10th Edition 3.6 Silberschatz, Galvin and Gagne ©2018  Memory Layout of a C Program Operating System Concepts – 10th Edition 3.7 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.8 Silberschatz, Galvin and Gagne ©2018  Diagram of Process State Operating System Concepts – 10th Edition 3.9 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.10 Silberschatz, Galvin and Gagne ©2018  Threads So far, process has a single thread of execution Consider having multiple program counters per process  Multiple locations can execute at once  Multiple threads of control -> threads Must then have storage for thread details, multiple program counters in PCB Explore in detail in Chapter 4 Operating System Concepts – 10th Edition 3.11 Silberschatz, Galvin and Gagne ©2018  Process Representation in Linux Represented by the C structure task_struct pid t_pid; long state; unsigned int time_slice struct task_struct *parent; struct list_head children; struct files_struct *files; struct mm_struct *mm; Operating System Concepts – 10th Edition 3.12 Silberschatz, Galvin and Gagne ©2018  Process Scheduling Maximize CPU use, quickly switch processes onto CPU core Process scheduler selects among available processes for next execution on CPU core Maintains scheduling queues of processes  Ready queue – set of all processes residing in main memory, ready and waiting to execute  Wait queues – set of processes waiting for an event (i.e. I/O)  Processes migrate among the various queues Operating System Concepts – 10th Edition 3.13 Silberschatz, Galvin and Gagne ©2018  Ready and Wait Queues Operating System Concepts – 10th Edition 3.14 Silberschatz, Galvin and Gagne ©2018  Representation of Process Scheduling Operating System Concepts – 10th Edition 3.15 Silberschatz, Galvin and Gagne ©2018  CPU Switch From Process to Process A context switch occurs when the CPU switches from one process to another. Operating System Concepts – 10th Edition 3.16 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.17 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.18 Silberschatz, Galvin and Gagne ©2018  Operations on Processes System must provide mechanisms for:  process creation  process termination Operating System Concepts – 10th Edition 3.19 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.20 Silberschatz, Galvin and Gagne ©2018  A Tree of Processes in Linux Operating System Concepts – 10th Edition 3.21 Silberschatz, Galvin and Gagne ©2018  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  Parent process calls wait() for the child to terminate Operating System Concepts – 10th Edition 3.22 Silberschatz, Galvin and Gagne ©2018  C Program Forking Separate Process Operating System Concepts – 10th Edition 3.23 Silberschatz, Galvin and Gagne ©2018  Creating a Separate Process via Windows API Operating System Concepts – 10th Edition 3.24 Silberschatz, Galvin and Gagne ©2018  Process Termination Process executes last statement and then asks the operating system to delete it using the exit() system call.  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 – 10th Edition 3.25 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.26 Silberschatz, Galvin and Gagne ©2018  Android Process Importance Hierarchy Mobile operating systems often have to terminate processes to reclaim system resources such as memory. From most to least important: o Foreground process o Visible process o Service process o Background process o Empty process Android will begin terminating processes that are least important. Operating System Concepts – 10th Edition 3.27 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.28 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 – 10th Edition 3.29 Silberschatz, Galvin and Gagne ©2018  Communications Models (a) Shared memory. (b) Message passing. Operating System Concepts – 10th Edition 3.30 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.31 Silberschatz, Galvin and Gagne ©2018  Producer-Consumer Problem Paradigm for cooperating processes, producer process produces information that is consumed by a consumer process  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 – 10th Edition 3.32 Silberschatz, Galvin and Gagne ©2018  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 Chapters 6 & 7. Operating System Concepts – 10th Edition 3.33 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 – 10th Edition 3.34 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 – 10th Edition 3.35 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 – 10th Edition 3.36 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.37 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 – 10th Edition 3.38 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.39 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 – 10th Edition 3.40 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 – 10th Edition 3.41 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.42 Silberschatz, Galvin and Gagne ©2018  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 – 10th Edition 3.43 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 – 10th Edition 3.44 Silberschatz, Galvin and Gagne ©2018  Producer – Shared Memory message next_produced; while (true) { send(next_produced); } Operating System Concepts – 10th Edition 3.45 Silberschatz, Galvin and Gagne ©2018  Consumer– Shared Memory message next_consumed; while (true) { receive(next_consumed) } Operating System Concepts – 10th Edition 3.46 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 – 10th Edition 3.47 Silberschatz, Galvin and Gagne ©2018  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  Set the size of the object ftruncate(shm_fd, 4096);  Use mmap() to memory-map a file pointer to the shared memory object  Reading and writing to shared memory is done by using the pointer returned by mmap(). Operating System Concepts – 10th Edition 3.48 Silberschatz, Galvin and Gagne ©2018  IPC POSIX Producer Operating System Concepts – 10th Edition 3.49 Silberschatz, Galvin and Gagne ©2018  IPC POSIX Consumer Operating System Concepts – 10th Edition 3.50 Silberschatz, Galvin and Gagne ©2018  Examples of IPC Systems - Mach Mach communication is message based  Even system calls are messages  Each task gets two ports at creation- Kernel and Notify  Messages are sent and received using the mach_msg() function  Ports needed for communication, created via mach_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 – 10th Edition 3.51 Silberschatz, Galvin and Gagne ©2018  Mach Messages #include struct message { mach_msg_header_t header; int data; }; mach port t client; mach port t server; Operating System Concepts – 10th Edition 3.52 Silberschatz, Galvin and Gagne ©2018  Mach Message Passing - Client Operating System Concepts – 10th Edition 3.53 Silberschatz, Galvin and Gagne ©2018  Mach Message Passing - Server Operating System Concepts – 10th Edition 3.54 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 – 10th Edition 3.55 Silberschatz, Galvin and Gagne ©2018  Local Procedure Calls in Windows Operating System Concepts – 10th Edition 3.56 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 – 10th Edition 3.57 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 – 10th Edition 3.58 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 – 10th Edition 3.59 Silberschatz, Galvin and Gagne ©2018  Communications in Client-Server Systems Sockets Remote Procedure Calls Operating System Concepts – 10th Edition 3.60 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 – 10th Edition 3.61 Silberschatz, Galvin and Gagne ©2018  Socket Communication Operating System Concepts – 10th Edition 3.62 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 – 10th Edition 3.63 Silberschatz, Galvin and Gagne ©2018  Sockets in Java The equivalent Date client Operating System Concepts – 10th Edition 3.64 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 – 10th Edition 3.65 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 – 10th Edition 3.66 Silberschatz, Galvin and Gagne ©2018  Execution of RPC Operating System Concepts – 10th Edition 3.67 Silberschatz, Galvin and Gagne ©2018  End of Chapter 3 Operating System Concepts – 10th Edition Silberschatz, Galvin and Gagne ©2018