Download Implementing Processes, Threads, and Resources

Slide 6-1
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-2
Implementing
Processes, Threads,
and Resources
Copyright © 2004 Pearson Education, Inc.
6
Operating Systems: A Modern Perspective, Chapter 6
Processes
•
•
•
•
Process Concept
Process Scheduling
Operating on Processes
Threads
• Internet Links to Multi-threads:
– IBM
– Tom Wagner Site
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-3
Process Concept
• An operating system executes a variety of programs:
– Batch systems -- Jobs
– Time-Shared system -- user programs or tasks
• A Process -- a program in execution
• A Process -- a schedulable unit of computation
• There may be several processes executing the same
program at the same time.
E.g. several users running vi at the same time:
– Each instance of vi creates a separate process.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-4
Implementing the Process Abstraction
Pi CPU
Pj CPU
Pi Executable
Memory
Pj Executable
Memory
Pk CPU
…
Pk Executable
Memory
OS Address
Space
CPU
ALU
Control
Unit
Pi Address
Space
Pk Address
Space
…
Pj Address
Space
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Machine Executable Memory
OS interface
Slide 6-5
External View of the Process Manager
Application
Program
Device Mgr
UNIX
Memory Mgr
File Mgr
exec()
Memory Mgr
File Mgr
Process Mgr
Device Mgr
wait()
CreateThread()
CloseHandle() CreateProcess()
WaitForSingleObject()
Process Mgr
fork()
Windows
Hardware
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-6
Slide 6-7
Process Manager
• In a multi-programmed OS, several processes
can be “executed at the same time”.
• The Process Manager is that part of the OS
that is responsible for managing all the
processes on the system.
• When the computer is powered on, there is only
one program in execution: the initial process.
• The initial process creates the OS, which can
then create other processes as needed.
• A process can create another process with a
system call (e.g. fork in UNIX).
• The created process is called a child process
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Manager
Slide 6-8
• When a process is created, it specifies to the
Process Manager its resource needs (e.g.
memory requirements, files etc.)
• The Process Manager allocates the needed
resources and causes the process to be executed.
• The process manager is responsible
– for monitoring the state of each process executing on
the system
– process scheduling on CPU
– process synchronization and deadlock
– protection & security
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Manager Responsibilities
Slide 6-9
• Define & implement the essential characteristics of a
process and thread
– Algorithms to define the behavior
– Data structures to preserve the state of the execution
• Define what “things” threads in the process can reference –
the address space (most of the “things” are memory
locations)
• Manage the resources used by the processes/threads
• Tools to create/destroy/manipulate processes & threads
• Tools to time-multiplex the CPU – Scheduling the
(Chapter 7)
• Tools to allow threads to synchronization the operation
with one another (Chapters 8-9)
• Mechanisms to handle deadlock (Chapter 10)
• Mechanisms to handle protection (Chapter 14)
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-10
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Model
Slide 6-11
• A process is composed of the following
elements:
– a program (code)
– The data operated on by the process
– A set of resources to provide an environment
for execution
– A Process Descriptor: a record kept by the
OS to keep track of the progress of each
process.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Modern Processes and Threads
Thrdj in Pi
Thrdk in Pi
…
Pi CPU
…
…
OS interface
…
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Operating Systems: A Modern Perspective, Chapter 6
Slide 6-12
Slide 6-13
Processes &Threads
Stack
State
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Static data
Map
Operating Systems: A Modern Perspective, Chapter 6
Program
Map
Resources
Address Space
Stack
State
Process Address Space
• A process address
space includes:
– program code
– data section
– stack section
• Process Descriptor is kept
in OS space.
Copyright © 2004 Pearson Education, Inc.
Stack Section
Data Section
Program text
Main Memory
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-14
Slide 6-15
The Address Space
Address
Space
Address
Binding
Executable
Memory
Process
Files
Other objects
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Building the Address Space
• Some parts are built into the environment
– Files
– System services
• Some parts are imported at runtime
– Mailboxes
– Network connections
• Memory addresses are created at compile
(and run) time
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-16
Slide 6-17
Tracing the Hardware Process
Hardware process progress
Machine is
Powered up
Bootstap
Process Interrupt
Loader Manager Handler P1
Load the kernel
Initialization
Execute a thread
Schedule
Pn
…
Service an interrupt
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P,2
Operating Systems: A Modern Perspective, Chapter 6
The Abstract Machine Interface
Slide 6-18
Application Program
Abstract Machine Instructions
Trap
Instruction
User Mode
Instructions
fork()
open()
OS
User Mode
Instructions
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Supervisor Mode
Instructions
Operating Systems: A Modern Perspective, Chapter 6
create()
Context Switch
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Operating Systems: A Modern Perspective, Chapter 6
Slide 6-19
Slide 6-20
Context Switching
Executable Memory
Initialization
Interrupt
1
Process
Manager
7
8
Interrupt
Handler
2
4
3
P1
9
5
P2
6
Pn
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Descriptors
Slide 6-21
• OS creates/manages process abstraction
• Descriptor is data structure for each process
–
–
–
–
–
–
Register values
Logical state
Type & location of resources it holds
List of resources it needs
Security keys
etc. (see Table 6.3 and the source code of your
favorite OS)
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Descriptor
Slide 6-22
Contains information associated with a process:
• PID
• Process state
• Owner
• Parent process
• List of child processes
• list of allocated resources
• list of open files
• ….
• Copy of CPU registers at the last time the
process executed on the CPU
Process Descriptor Table
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Operating Systems: A Modern Perspective, Chapter 6
Windows NT Process Descriptor
EPROCESS
KPROCESS
NT Kernel
NT Executive
Copyright © 2004 Pearson Education, Inc.
…
uint32
uint32
…
Byte
…
void
…
KernelTime;
UserTime;
state;
*UniqueProcessId;
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-23
Windows NT Process Descriptor (2)
 Kernel process object including:





Pointer to the page directory
Kernel & user time
Process base priority
Process state
List of the Kernel thread descriptors that are
using this process
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-24
Windows NT Process Descriptor (3)









Slide 6-25
Parent identification
Exit status
Creation and termination times.
Memory status
Security information
executable image
Process priority class used by the thread scheduler.
A list of handles used by this process
A pointer to Win32-specific information
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Windows NT Thread Descriptor
EPROCESS
KPROCESS
ETHREAD
KTHREAD
NT Kernel
NT Executive
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Operating Systems: A Modern Perspective, Chapter 6
Slide 6-26
Creating a Process in UNIX
pid = fork();
UNIX kernel
Process Table
…
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Process Descriptor
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-27
Process Model CONTD
Slide 6-28
Process creation/initialization:
– Process Descriptor is created and initialized
– Resources needed by the process are allocated (e.g.
files, memory to store code, data, and stack).
– Process may inherent some resources from its
parent (e.g. open files, etc.)
– Process Descriptor must reflect all allocated
resources
– Process is loaded in memory, into its Address Space,
ready to begin execution
– From then on, process competes for CPU and other
resources with other processes.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Creation
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-29
Process Creation
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-30
Process Termination
Slide 6-31
• Process executes last statement and asks the
operating system to delete it
– process resources are de-allocated by the operating
system
• A process may be terminated by another process
– A parent terminates the execution of its children
• When a process exits what happens to its children?
– do not allow a child to exist if its parent has terminated
==> cascaded termination (VMS)
– allow children to exist after parent ==> orphan
processes (UNIX )
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-32
Creating a Process in NT
CreateProcess(…);
Win32 Subsystem
ntCreateProcess(…);
…
ntCreateThread(…);
NT Executive
Handle Table
NT Kernel
…
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Process Descriptor
Operating Systems: A Modern Perspective, Chapter 6
Windows NT Handles
Application
Handle
User Space
Supervisor Space
Executive Object
Kernel
Object
NT Executive
NT Kernel
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-33
Slide 6-34
Simple State Diagram
Request
Done
Running
Request
Schedule
Start
Allocate
Blocked
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Ready
Operating Systems: A Modern Perspective, Chapter 6
Process Model CONTD
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Operating Systems: A Modern Perspective, Chapter 6
Slide 6-35
Process Scheduling Queues
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Operating Systems: A Modern Perspective, Chapter 6
Slide 6-36
UNIX State Transition Diagram
Request
Wait by
parent
Done
Running
zombie
Sleeping
Schedule
Request
I/O Request
Start
Allocate
Runnable
I/O Complete
Uninterruptible
Sleep
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Resume
Traced or Stopped
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-37
Slide 6-38
Windows NT Thread States
CreateThread
Initialized
Activate
Dispatch
Exit
Wait
Running
Waiting
Ready
Wait Complete
Wait Complete
Transition
Preempt
Reinitialize
Select
Terminated
Dispatch
Standby
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Model CONTD
Slide 6-39
• Each process uses resources as it executes; main
memory, I/O devices, files, and the CPU
• The CPU is also a hardware resource
• During execution a process may request other
resources (e.g. more memory) and may release some
of its resources ==> dynamic allocation/de-allocation
• When a process can NOT get its requested resources it
gets blocked in a queue waiting for that resource.
• Multiprogramming: While one process uses the CPU,
the remaining are using I/O resources or waiting for a
resource (I/O or CPU) to be available.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Resources
Resource: Anything that a process can request, then be
blocked because that thing is not available.
R = {Rj | 0  j < m} = resource types
C = {cj  0 |  RjR (0  j < m)} = units of Rj available
Reusable resource: After a unit of the resource has been
allocated, it must ultimately be released back to the
system. E.g., CPU, primary memory, disk space, … The
maximum value for cj is the number of units of that
resource
Consumable resource: There is no need to release a
resource after it has been acquired. E.g., a message,
input data, … Notice that cj is unbounded.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-40
Using the Model
Slide 6-41
• There is a resource manager, Mgr(Rj) for every Rj
• Process pi can request units of Rj if it is currently running
pi can only request ni  cj units of reusable Rj
pi can request unbounded # of units of consumable Rj
•Mgr(Rj) can allocate units of Rj to pi
request
Mgr(Rj)
Process
allocate
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
A Generic Resource Manager
Resource Manager
Policy
Blocked Processes
ProcessProcess
Process
request()
Process
release()
Resource Pool
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-42
Process Hierarchies
Slide 6-43
• Parent-child relationship may be significant:
parent controls children’s execution
Done
Request
Running
Yield
Request
Schedule
Suspend
Ready-Active
Activate
Allocate
Suspend
Blocked-Active
Suspend
Start
Ready-Suspended
Allocate
Blocked-Suspended
Activate
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-44
Process Manager Overview
Program
Process
Abstract Computing Environment
File
Manager
Process
Deadlock
Description
Protection
Synchronization
Device
Manager
Devices
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Memory
Manager
Memory
Scheduler
CPU
Operating Systems: A Modern Perspective, Chapter 6
Resource
Resource
Resource
Manager
Manager
Manager
Other H/W
Slide 6-45
UNIX Organization
Process
Process
Libraries
Process
File
Manager
System Call Interface
Process
Deadlock
Description
Protection
Synchronization
Device
Manager
Memory
Manager
Scheduler
Monolithic Kernel
Devices
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Memory
CPU
Operating Systems: A Modern Perspective, Chapter 6
Resource
Resource
Resource
Manager
Manager
Manager
Other H/W
Slide 6-46
Windows NT Organization
T
Process
T
T
T
Process
Process
T
T
T
T
T
Libraries
Subsystem
Subsystem
Subsystem
User
NT Executive
NT Kernel
Hardware Abstraction Layer
Processor(s)
Copyright © 2004 Pearson Education, Inc.
Main Memory
Operating Systems: A Modern Perspective, Chapter 6
I/O Subsystem
Devices
UNIX Processes
• Each process has its own address space
– subdivided into code, data & stack
– a.out file describes the address apace
• OS creates a Process Descriptor to
manage each process. The collection of
all Process Descriptors is referred to as
the Process Descriptor Table
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-47
Slide 6-48
UNIX Processes
• Each process is assigned a unique process ID
(PID)
• The PID is essentially a pointer into the Process
Table of the OS.
• A process can use the system call getpid() to
obtain its own PID
• Each process has one parent process (the
process that created it), except for process 1
• Process 1 ( the init process) is the ancestor of
all other processes
• a process can use the system call getppid()
to obtain the PID of it parent (i.e. PPID)
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
UNIX Processes
Slide 6-49
• When Unix is first started, it has only one
process. The process is called "init", and its
PID is 1.
• The "init" process creates other operating
system processes to do OS functions
• For each port supporting user logins (e.g. a
terminal), init creates a process running the
getty program.
• The getty process waits for a user to begin
using the port.
• When the port begins to be used, getty creates a
new process to run the login program.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-50
UNIX Processes
• The login process prompts the user for
username and password, reads the username
and password and verifies by looking up the
/etc/passwd file.
• If login successful, the login process changes
directory to the user's directory and creates a
new process running the shell program
specified in the user's entry of the /etc/passwd
file.
• The shell process displays a "shell prompt" on
the terminal and waits for the user to type a
command.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
UNIX Processes
• When the user types a command, the shell
process, reads it, parses it, verifies it, and
creates a new process running the program
specified in the command. In the mean time,
the shell process gets suspended until the
command process finishes.
• When the command process is done, the shell
process is resumed again.
• When the user logs out, the shell process is
terminated and the login process is resumed,
etc. etc. etc.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-51
UNIX Processes
• UNIX fork creates a process
• UNIX wait allows a process to wait for
a child to terminate
• UNIX exec allows a child to run a new
program
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-52
Creating Processes
Slide 6-53
• UNIX fork() creates a process
fork( ) creates a child process that is identical to
its parent, except that it has:
– a different and unique PID
– a different PPID
• fork()
– creates a new address space for the child process
– copies code, data and stack into new address space
– provides child with access to open files of parent.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Creation: fork
Slide 6-54
int pid;
pid = fork();
• the fork is called by the parent but returns in
both the parent and the child
– In the parent, it returns the PID of the child process
– in the child it returns 0
• If fork() fails no child is created and -1 is
returned to the parent.
• After the child is created, the parent and the
child processes execute concurrently starting
from the instruction following the fork.
• Since only one can be using CPU at a time,
either may go first.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Process Creation: fork
Slide 6-55
int pid;
pid = fork( );
if ( pid == 0 )
{
/* code for child here */
exit(0);
}
if (pid < 0)
{
/* fork failed... Put error handling
code here */
}
/*remaining code for parent goes here */
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-56
#include <stdio.h>
int main( )
{ int pid;
if ( (pid = fork( ) ) == 0 )
{ printf(“I am the child, my pid=%d and my
parent pid=%d\n”, getpid( ), getppid( ) );
exit(0);
}
if (pid < 0)
{ fprintf(stderr, “fork failed\n”)
exit(1);
}
printf(“I am the parent, my pid=%d\n”, getpid( ) );
}
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Example: Chain of Processes
#include <stdio.h>
int i, n, pid;
for (i=1, i < n; ++i )
if ( ( pid=fork() ) != 0)
break;
fprintf(stdout,”This is process %d with
parent %d\n”, getpid(),getppid() );
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-57
Example: a fan of processes
#include <stdio.h>
int i, n, pid;
for (i=1, i<n; ++i)
if ( (pid=fork()) == 0)
break;
fprintf(stdout,”This is process %d with
parent %d\n”, getpid(),getppid() );
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-58
Synchronization of Parent and
Child
Slide 6-59
• What happens to the parent after it creates a child?
– They both execute concurrently
• If parent wants to wait until the child terminates
before proceeding further it executes a wait()
or waitpid() system call.
• When a process is terminated (with exit( ) ), a
signal is sent to its parent notifying it of the
termination.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
exit( )
Slide 6-60
• void exit(int status)
• exit( ) closes all process' file descriptors, deallocates code, data, and stack, and then terminates
the process.
• It sends a signal to the parent process telling of its
termination status and waits until the parent
accepts the signal.
• A process that is waiting for its parent to accept its
termination is called a "zombie"
• A parent accepts a child's termination by executing
wait( ).
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Synch. of Parent and Child
Slide 6-61
int pid;
pid = fork( );
if ( pid == 0 )
{
/* child executes this part
concurrently with parent */
exit(0);
}
/*parent works concurrently with
child and independent of each
other*/
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Synch. of Parent and Child
int pid;
pid = fork( );
if ( pid == 0 )
{
/* child executes this part
concurrently with parent */
exit(0);
}
wait(...); /* parent waits for
child*/
/*parent proceeds*/
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-62
Synch. of Parent and Child
• If a parent terminates without waiting for a
child, child becomes an orphan and is
adopted by the system init process by
setting their PPID to 1.
• init periodically executes wait( ) to remove
zombies from the system.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-63
Wait()
Slide 6-64
#include <sys/wait.h>
int wait(int *status);
1. if there are no child processes, wait returns
with
-1 (an error)
2. if one or more processes are already in the
zombie state, wait selects an arbitrary one,
stores its status in status , and returns its
PID
3. otherwise, wait sleeps until one of the child
processes terminates and then goes to step 2
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Child Executing a Different
Program
Slide 6-65
• Parent process calls fork to create a child process
• child process calls an exec system call.
• The exec system call replaces the address space of
the child with a new program
• several exec calls:
execv, execvp, etc.
int execv(char *filename, char *argv[ ]);
• filename is the name of an executable file
• argv is the command-line arguments for the
executable program.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Example:Parent
Slide 6-66
main( ) {
int pid;
/*code to set up the argv array for the child here*/
pid = fork();
if (pid==0)
{
execv(child_prog, argv);
/* execv does not return unless there is an error*/
fprintf(stderr,”error in the exec…terminating child..”);
exit(1);
}
wait( );
/*parent waits for child to terminate*/
…….}
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Example:Child
File child_prog.c:
main( )
{
/* code to be executed by child process */
}
• child_prog.c must be compiled into an executable
file.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-67
Slide 6-68
Threads (read Chap2)
• A thread (or lightweight process) is a basic unit
of computation. It uses less state and less
resources than heavyweight process
• In a system that supports threads, each
(heavyweight) process consist of one or more
threads.
• A traditional process is a process with one
thread.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Threads
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-69
Threads
• Each thread has its own
–
–
–
–
thread ID
program counter
stack space
possibly some of its own data
• A thread shares with its sibling threads:
– code section
– data section
– operating system resources (e.g. open files, CPU)
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-70
POSIX Threads
Slide 6-71
• DEC Unix conforms to the POSIX standard
==> # include <pthread.h>
• When a thread is created it is assigned a thread ID,
a stack, a starting address for execution.
• pthread_create(ChildID, Thread_attributes,
function_name, arguments)
–
–
–
–
ChildID is the returned child ID
Thread_attributes: set to NULL for default attributes
function_name: function to be executed by the thread
arguments: a pointer to the argument to be passed to the
function
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Why threads?
Slide 6-72
• Reduced context switching overhead
• An application that needs to block occasionally
waiting for I/O (e.g. disk): While one thread waits, a
second thread can run and do other computation==>
better performance for the application.
• Windowing systems:
– heavyweight process: physical screen manager
– a thread for each window: all threads share the same
physical screen.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Threads for a windows system
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6
Slide 6-73
Slide 6-74
Why threads?
• Since sibling threads use same data segment, data
sharing among cooperating threads is easily achieved
+ Applications that require sharing a common buffer (e.g.
producer-consumer) can benefit from thread utilization.
– no protection between threads: synchronization among
threads when accessing shared data must be enforced by the
programmer.
• Threads can be used in multiprocessor systems (each
thread runs on a separate processor, they all share
same address space on a shared memory).
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 6