EECS 3221:
OPERATING SYSTEM FUNDAMENTALS
Hamzeh Khazaei
Department of Electrical Engineering and Computer Science
Week 2, Module 2: Processes
January 21, 2021
Operating System Concepts 10th Edition 3.1 Silberschatz et al 2018 updated by Khazaei @ 2021
1
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 et al 2018 updated by Khazaei @ 2021
2
1
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
4 Function parameters, return addresses, local variables
! Data section containing global variables
! Heap containing memory dynamically allocated during run time
Operating System Concepts 10th Edition 3.3 Silberschatz et al 2018 updated by Khazaei @ 2021
3
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 3.4 Silberschatz et al 2018 updated by Khazaei @ 2021
4
2
Process in Memory
Operating System Concepts 10th Edition 3.5 Silberschatz et al 2018 updated by Khazaei @ 2021
5
Memory Layout of a C Program
Operating System Concepts 10th Edition 3.6 Silberschatz et al 2018 updated by Khazaei @ 2021
6
3
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 3.7 Silberschatz et al 2018 updated by Khazaei @ 2021
7
Diagram of Process State
Operating System Concepts 10th Edition 3.8 Silberschatz et al 2018 updated by Khazaei @ 2021
8
4
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 3.9 Silberschatz et al 2018 updated by Khazaei @ 2021
9
Threads
! So far, process has a single thread of execution
! Consider having multiple program counters per process
! Multiple locations can execute at once
4 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 3.10 Silberschatz et al 2018 updated by Khazaei @ 2021
10
5
Process Representation in Linux (PCB)
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;/* list of open files */
struct mm_struct *mm;/* address space of this process */
Operating System Concepts 10th Edition 3.11 Silberschatz et al 2018 updated by Khazaei @ 2021
/* process identifier */
/* state of the process */ /* scheduling information */ /* this processs parent */ /* this processs children */
11
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 3.12 Silberschatz et al 2018 updated by Khazaei @ 2021
12
6
Ready and Wait Queues
Operating System Concepts 10th Edition 3.13 Silberschatz et al 2018 updated by Khazaei @ 2021
13
Representation of Process Scheduling
Operating System Concepts 10th Edition 3.14 Silberschatz et al 2018 updated by Khazaei @ 2021
14
7
CPU Switch From Process to Process
A context switch occurs when the CPU switches from one process to another.
Operating System Concepts 10th Edition 3.15 Silberschatz et al 2018 updated by Khazaei @ 2021
15
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 PCBethe longer the context switch
! Time dependent on hardware support
! Some hardware provides multiple sets of registers per CPUe
multiple contexts loaded at once
Operating System Concepts 10th Edition 3.16 Silberschatz et al 2018 updated by Khazaei @ 2021
16
8
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 3.17 Silberschatz et al 2018 updated by Khazaei @ 2021
17
Operations on Processes
! System must provide mechanisms for:
! process creation
! process termination
Operating System Concepts 10th Edition 3.18 Silberschatz et al 2018 updated by Khazaei @ 2021
18
9
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 parents resources
! Parent and child share no resources
! Execution options
! Parent and children execute concurrently
! Parent waits until children terminate
Operating System Concepts 10th Edition 3.19 Silberschatz et al 2018 updated by Khazaei @ 2021
19
A Tree of Processes in Linux
Operating System Concepts 10th Edition 3.20 Silberschatz et al 2018 updated by Khazaei @ 2021
20
10
Process Creation (Cont.)
! Address space
! Child duplicate of parent
! Child has a program loaded into it
! UNIX examples
! fork()systemcallcreatesnewprocess
! exec()systemcallusedafterafork()toreplacetheprocess memory space with a new program
! Parent process calls wait() for the child to terminate
Operating System Concepts 10th Edition 3.21 Silberschatz et al 2018 updated by Khazaei @ 2021
21
C Program Forking Separate Process
Operating System Concepts 10th Edition 3.22 Silberschatz et al 2018 updated by Khazaei @ 2021
22
11
Creating a Separate Process via Windows API
Operating System Concepts 10th Edition 3.23 Silberschatz et al 2018 updated by Khazaei @ 2021
23
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())
! Processresources 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 3.24 Silberschatz et al 2018 updated by Khazaei @ 2021
24
12
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 t pid;
int status;
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 3.25 Silberschatz et al 2018 updated by Khazaei @ 2021
25
Zombie process
Operating System Concepts 10th Edition 3.26 Silberschatz et al 2018 updated by Khazaei @ 2021
26
13
Orphan Process
Operating System Concepts 10th Edition 3.27 Silberschatz et al 2018 updated by Khazaei @ 2021
27
Android Process Importance Hierarchy
! Mobile operating systems often must 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 3.28 Silberschatz et al 2018 updated by Khazaei @ 2021
28
14
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
4 RunsinsandboxrestrictingdiskandnetworkI/O,minimizingeffectof security exploits
! Plug-in process for each type of plug-in
Operating System Concepts 10th Edition 3.29 Silberschatz et al 2018 updated by Khazaei @ 2021
29
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 3.30 Silberschatz et al 2018 updated by Khazaei @ 2021
30
15
Communications Models
(a) Shared memory (b) Message passing
Operating System Concepts 10th Edition 3.31 Silberschatz et al 2018 updated by Khazaei @ 2021
31
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 et al 2018 updated by Khazaei @ 2021
32
16
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 et al 2018 updated by Khazaei @ 2021
33
!
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 et al 2018 updated by Khazaei @ 2021
!
34
17
item next_produced;
while (true) {
/* produce an item in next produced */ while (((in + 1) % BUFFER_SIZE) == out)
; /* do nothing */ buffer[in] = next_produced; in = (in + 1) % BUFFER_SIZE;
}
Operating System Concepts 10th Edition 3.35 Silberschatz et al 2018 updated by Khazaei @ 2021
35
item next_consumed;
while (true) {
while (in == out)
}
; /* do nothing */
next_consumed = buffer[out];
out = (out + 1) % BUFFER_SIZE;
/* consume the item in next consumed */
Operating System Concepts 10th Edition 3.36 Silberschatz et al 2018 updated by Khazaei @ 2021
36
18
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 et al 2018 updated by Khazaei @ 2021
37
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 et al 2018 updated by Khazaei @ 2021
38
19
Message Passing (Cont.)
! Implementation of communication link ! Physical:
4 Shared memory 4 Hardware bus 4 Network
! Logical:
4 Direct or indirect
4 Synchronous or asynchronous 4 Automatic or explicit buffering
Operating System Concepts 10th Edition 3.39 Silberschatz et al 2018 updated by Khazaei @ 2021
39
Direct Communication
! Processes must name each other explicitly:
! send(P,message)sendamessagetoprocessP
! receive(Q,message)receiveamessagefromprocessQ
! 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 et al 2018 updated by Khazaei @ 2021
40
20
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 et al 2018 updated by Khazaei @ 2021
41
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 et al 2018 updated by Khazaei @ 2021
42
21
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 et al 2018 updated by Khazaei @ 2021
43
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 et al 2018 updated by Khazaei @ 2021
44
22
Buffering
! Queue of messages attached to the link.
! Implemented in one of three ways
1. Zerocapacitynomessagesarequeuedonalink. Sender must wait for receiver (rendezvous)
2. Boundedcapacityfinitelengthofnmessages Sender must wait if link full
3. Unboundedcapacityinfinitelength Sender never waits
Operating System Concepts 10th Edition 3.45 Silberschatz et al 2018 updated by Khazaei @ 2021
45
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 3.46 Silberschatz et al 2018 updated by Khazaei @ 2021
46
23
IPC POSIX Producer
Operating System Concepts 10th Edition 3.47 Silberschatz et al 2018 updated by Khazaei @ 2021
47
IPC POSIX Consumer
Operating System Concepts 10th Edition 3.48 Silberschatz et al 2018 updated by Khazaei @ 2021
48
24
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 3.51 Silberschatz et al 2018 updated by Khazaei @ 2021
51
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 3.52 Silberschatz et al 2018 updated by Khazaei @ 2021
52
25
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 3.53 Silberschatz et al 2018 updated by Khazaei @ 2021
53
Communications in Client-Server Systems
! Sockets
! Remote Procedure Calls
Operating System Concepts 10th Edition 3.54 Silberschatz et al 2018 updated by Khazaei @ 2021
54
26
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 3.55 Silberschatz et al 2018 updated by Khazaei @ 2021
55
Operating System Concepts 10th Edition 3.56 Silberschatz et al 2018 updated by Khazaei @ 2021
56
27
Sockets in Java
! Three types of sockets
! Connection-oriented (TCP)
! Connectionless (UDP)
4 MulticastSocket class data can be sent to multiple recipients
! Consider this Date server in Java:
Operating System Concepts 10th Edition 3.57
Silberschatz et al 2018 updated by Khazaei @ 2021
57
Sockets in Java
The equivalent Date client
Operating System Concepts 10th Edition 3.58 Silberschatz et al 2018 updated by Khazaei @ 2021
58
28
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 3.59 Silberschatz et al 2018 updated by Khazaei @ 2021
59
Remote Procedure Calls (Cont.)
! Data representation handled via External Data Representation (XDR) 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
! Why do we need a matchmaker?
Operating System Concepts 10th Edition 3.60 Silberschatz et al 2018 updated by Khazaei @ 2021
60
29
Execution of RPC
Operating System Concepts 10th Edition 3.61 Silberschatz et al 2018 updated by Khazaei @ 2021
61
End of Chapter 3 Any Question?
Operating System Concepts 10th Edition Silberschatz et al 2018 updated by Khazaei @ 2020
62
30
Reviews
There are no reviews yet.