Transcript Processes

Review
What is an operating system
• The first program
• A program that lets you run other programs
• A program that provides controlled access to resources:
– CPU
– Memory
– Display, keyboard, mouse
– Persistent storage
– Network
Tanenbaum & Bo, Modern Operating
Systems:4th ed., (c) 2013 Prentice-Hall, Inc.
All rights reserved.
Operating System Structure
www.cs rutgers.edu/~pxk
kernel
• Core component of the operating
system: the central program that
manages resources and scheduling
– Controls execution of programs
– Schedules
– Allocates memory
– Allows programs to controlled access to
devices
Processor Modes
• Mode bit: Supervisor or User mode
• Supervisor mode
– Can execute all machine instructions
– Can reference all memory locations
• User mode
– Can only execute a subset of instructions
– Can only reference a subset of memory
locations
Operating Systems: A Modern
Perspective, Chapter 3
System Calls
other stuff
Kernel portion
of address space
kernel stack
kernel text
trap into kernel
User portion of
address space
write(fd, buf, len)
Interrupt Vector
• Table set up by OS kernel; pointers to code to
run on different events
System Boot
In the beginning…
• Memory is initialized
• Initial program loaded from boot device
– Early days switches
– ROM
• BIOS : Basic Input/Output System
– Low level software for accessing basic I/O
– Code to load stage 1 boot loader
When the computer is booted:
• BIOS is started
– Checks RAM size
– Checks devices present
– Determines the boot device
• Typically one of several disks tagged as such
– Reads block 0 from that device into memory at a
fixed location and jumps there.
First Stage of Boot Loader
• This first block(0) is called the Master Boot
Record (MBR)
• Contains first stage of boot loader
• Contains a program that normally examines
the partition table at the end of sector
– Loads the Volume Boot Record (VBR)
Second Stage of Boot Loader
• The secondary boot loader is read from the
partition identified in the VBR
• The loader reads in the operating system from
the active partition and starts it.
• May offer user a choice of operating systems
Transfer of Control
• When the boot loader finishes loading the OS,
it transfer control to it
• The OS will initialize itself and load various
modules as needed.
• The OS queries the BIOS to get information
about the devices.
Good-bye BIOS
• Univided Extensible Firmware Interface (UEFI)
– Or EFI
• Created for 32bit and 64 bit architectures
• Goal
– Create a successor to BIOS
• Not restrictions in addressing
UEFI
• BIOS Components preserved
– Power management
– System management (date, etc)
• Support for larger disks
• No need to start up in 16-bit (real) mode
– Access to all memory
• Boot manager lets you select OS
– No need for MBR
Processes
Main Points
• Process Concept
• Creating and managing processes
– fork, exec, wait
• Communicating between processes
• Example: implementing a shell
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
Process vs. Program
• Program
– Code and static data stored in a file
• Process is an instance of an executing program.
–
–
–
–
Has its own address pace
Memory map
Open files/ pending signals
Processor state
• Program counter
• CPU registers
• Relationship:
– Many processes can be running the same program
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
Operating System View of Process
• At start of process, the Operating System’s
duties include:
– Load program into memory
– Allocate memory for program data
– Set up kernel bookkeeping:

Process ID

Priority

User IDs

Process State

Address of executing
instruction

Address of return instruction
Typical Process Layout
• Libraries provide the
glue between user
processes and the OS
– libc linked in with all C
programs
– Provides cout, malloc,
and a whole slew of
other routines necessary
for programs
Activation Records
Stack
OBJECT1
OBJECT2
Heap
HELLO WORLD
GO BIG RED CS!
Data
cout.write( “string”, size) {
create the string to be printed
SYSCALL 80
}
malloc() { … }
strcmp() { … }
Library
Text
main() {
cout <<“HELLO WORLD”;
!
Program
Stack and Stack Frames
square (int x)
STACK
{ return x*x }
doCalc(int val)
{
printf (“square is %d\n”,
square(val) }
Frame for square
Frame for doCalc
main (int x, int y)
{ key = 9999
doCalc (key) }
Frame for main
Frames for C run-time start up
functions
Process in Memory
Supervisor and User Memory
Supervisor
Process
Supervisor
Space
User
Process
User
Space
Operating Systems: A Modern
Perspective, Chapter 3
Full System Layout
• The OS is omnipresent and
steps in where necessary to
aid application execution
Kernel Activation Records
USER OBJECT1
OBJECT2
LINUX
syscall_entry_point() { … }
– Typically resides in high
memory
• When an application needs
to perform a privileged
operation, it needs to
invoke the OS
OS Stack
OS Heap
OS Data
OS Text
Activation Records
OBJECT1
OBJECT2
HELLO WORLD
GO BIG RED CS!
printf(char * fmt, …) {
Stack
Heap
Data
Library
main() { … }
Program
The Process Model
One physical program counter
Figure 2-1. (a) Multiprogramming of four programs in
memory.
Tanenbaum & Bo,Modern Operating Systems:4th ed., (c) 2013 Prentice-Hall, Inc. All rights reserved.
Processes in a Multitasking
Environment
• Each process has a unique identifier PID
• Asynchronous events(interrupts) may occur
• Processes may have requests running that take a long
time
• OS Goal:
• Always have some process running.
• Context saving/switching
• Processes may be suspended and resumed
• Need to save/restore state about process
The Process Model
A logical program counter
stored in the process and
loaded into physical
counter
Figure 2-1. (b) Conceptual model of
four independent, sequential processes.
Tanenbaum & Bo,Modern Operating Systems:4th ed., (c) 2013 Prentice-Hall, Inc. All rights reserved.
Diagram of Process State
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
Process Concept
• Process: an instance of a program, running
with limited rights
– Process control block: the data structure the OS
uses to keep track of a process
– Two parts to a process:
• Thread: a sequence of instructions within a process
– Potentially many threads per process (for now 1:1)
– Thread aka lightweight process
• Address space: set of rights of a process
– Memory that the process can access
– Other permissions the process has (e.g., which procedure calls
it can make, what files it can access)
Process Control Block (PCB)
Process Control Blocks
PID
Terminated children
Link
Return code
PID
Terminated children
Link
Return code
PID
Terminated children
Link
Return code
Process Control
Block
Process Control Block (PCB)
Bookkeeping/Management of a process
Includes:
•
•
•
•
•
•
•
•
•
Process ID
Program Counter
CPU Registers
CPU scheduling information
Priority
Process state
Memory management information
Accounting information
List of I/O devices allocated to process
PCB
Figure 2-4. Some of the fields of a typical process table entry.
Tanenbaum & Bo,Modern Operating Systems:4th ed., (c) 2013 Prentice-Hall, Inc. All rights reserved.
Environment Variables
• Every process has an environment block that contains a
set of environment variables and their values.
• There are two types of environment variables:
• user environment variables (set for each
user)
• system environment variables (set for
everyone)
• Some library functions allow their behavior to change
based on environment variables.
Microsoft Developer Resources
http://linuxcourse.rutgers.edu/rute/node12.html
Diagram of Process State
Process Creation
Four principal events that cause processes to be
created:
1. System initialization.
2. Execution of a process creation system call by
a running process.
3. A user request to create a new process.
4. Initiation of a batch job.
Tanenbaum & Bo,Modern Operating
Systems:4th ed., (c) 2013 Prentice-Hall, Inc.
All rights reserved.
Process Creation
 Parent process create children processes,
which, in turn create other processes, forming a tree of
processes
 UNIX examples
 fork system call creates new process
Child process is almost an exact duplicate of parent process
 exec system call used after a fork to replace the
process’ memory space with a new program
Process Creation (Cont)
• Generally, process identified and managed via a process
identifier (pid)
• Resource sharing
– Parent and children share all resources
– Children share subset of parent’s resources
– Parent and child share no resources
• Execution
– Parent and children execute concurrently
– Parent waits until children terminate
• Address space
– Child duplicate of parent
– Child has a program loaded into it
UNIX Process Management
• UNIX fork – system call to create a copy of the
current process, and start it running
– No arguments!
• UNIX exec – system call to change the program
being run by the current process
• UNIX wait – system call to wait for a process to
finish
• UNIX signal – system call to send a notification
to another process
Process Creation
Parent my
perform other
actions here
Child statuses
passed to
parent
Memory of
parent copied
to child
Kernel restarts
parent
C Program Forking Separate Process
#include < iostream>
# include <sys/types.h>
#include <unistd.h>
int main()
{
pid_t pid;
/* fork another process */
pid = fork();
if (pid < 0) { /* error occurred */
cout << “ Fork Failed” << endl;
exit(-1);
}
else if (pid == 0) { /* child process */
execlp("/bin/ls", "ls", NULL);
}
else { /* parent process */
/* parent will wait for the child to complete */
wait (NULL);
cout << Child Complete << endl;
exit(0);
}
}
UNIX Process Management
Question: What does this code print?
int child_pid = fork();
if (child_pid == 0) {
// I'm the child process
cout << “ I am process “ << getpid() << endl;
return 0;
} else {
// I'm the parent process
cout << “ I am parent of process “<<child_pid<<endl;
return 0;
}
Implementing UNIX fork
Steps to implement UNIX fork
– Create and initialize the process control block
(PCB) in the kernel
– Create a new address space
– Initialize the address space with a copy of the
entire contents of the address space of the parent
– Inherit the execution context of the parent (e.g.,
any open files)
– Inform the scheduler that the new process is
ready to run
Implementing UNIX exec
• Steps to implement UNIX fork
– Load the program into the current address space
– Copy arguments into memory in the address
space
– Initialize the hardware context to start execution
at ``start''
Windows CreateProcess
• System call to create a new process to run a
program
– Create and initialize the process control block (PCB) in
the kernel
– Create and initialize a new address space
– Load the program into the address space
– Copy arguments into memory in the address space
– Initialize the hardware context to start execution at
``start'’
– Inform the scheduler that the new process is ready to
run
Windows CreateProcess API
(simplified)
if (!CreateProcess(
NULL,
// No module name (use command line)
argv[1],
// Command line
NULL,
// Process handle not inheritable
NULL,
// Thread handle not inheritable
FALSE,
// Set handle inheritance to FALSE
0,
// No creation flags
NULL,
// Use parent's environment block
NULL,
// Use parent's starting directory
&si,
// Pointer to STARTUPINFO structure
&pi )
// Pointer to PROCESS_INFORMATION structure
)
Diagram of Process State
System Call Using the trap Instruction
…
fork();
…
Trap Table
fork() {
…
trap
N_SYS_FORK()
…
}
Kernel
sys_fork()
sys_fork() {
/* system function */
…
return;
}
Operating Systems: A Modern
Perspective, Chapter 3
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
• Time dependent on hardware support
CPU Switch From Process to Process
CPU Switch From Process to Process
Diagram of Process State
Process Termination
Typical conditions which terminate a process:
1. Normal exit (voluntary).
2. Error exit (voluntary).
3. Fatal error (involuntary).
4. Killed by another process (involuntary).
Tanenbaum & Bo,Modern Operating
Systems:4th ed., (c) 2013 Prentice-Hall, Inc.
All rights reserved.
Process Termination
• Process executes last statement and asks the
operating system to delete it (exit)
– Output data from child to parent (via wait)
– Process’ resources are deallocated by operating
system
• Parent may terminate execution of children
processes (abort)
– Child has exceeded allocated resources
– Task assigned to child is no longer required
– If parent is exiting
• Some operating system do not allow child to continue if its
parent terminates
– All children terminated - cascading termination
Process Termination
Parent Process
It is useful for the parent to know how and when the child
terminates
 Waiting on a child process:
Wait() system call waits for one (any one) of the child processes to
end
Returns the process ID (PID) of the child being terminated
Returns status of the child
Kernel adds the process CPU times and resource statistic to the
running total for all children of the parent process
Releases resources held by child to system pool
SIGCHLD signal
Q.E.D.
Orphans and Zombies
Orphan
 Parents ends before Child process
 Who becomes the parent?
INIT, the ancestor of all processes. INIT will periodically clean up
orphans
Zombie
 Child terminates before the parent performs wait()
Kernel turns process into ZOMBIE
 Most resources held by child are returned to the system pool
 Un-killable processes – Are waiting for their parent to issue
wait()
Wait for parents to exit when they will become orphans
 Big problem for daemons.
The UNIX Architecture
Interactive User
Libraries
Commands
Application
Programs
…
OS System Call Interface
…
Device Driver
Operating Systems: A Modern
Perspective, Chapter 3
Trap Table
Driver Interface
Device Driver
Device Driver
Monolithic Kernel Module
•Process Management
•Memory Management
•File Management
•Device Mgmt Infrastructure
Introduction to Interprocess
Communcaiton
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
– Data Transfer
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
Examples of IPC System
PIPES
 Data streaming
 Direct communication
 Used to connect 2 processes
 Ordinary pipes
Producer – Consumer fashion
Cannot be accessed outside the process that creates it.
Usually Parent – Child communication
Deleted when process terminates
 Named pipes
 Alias: FIFO in unix
 Appear as typical files in the system
Pipes
•
•
•
•
2 processes set up pipes in advance
Communication is in one direction
Byte stream
… show example
Implementing a shell
System Call : fork()
• Create a child process
• Returns to both the child and parent
System Call : exec()
• Run application in current process
exec(prog, args)
Execl( pathname, arg[0], arg[1]…. 0)
Excelp(arg[0], arg[1]…. 0)
http://www.yolinux.com/TUTORIALS/ForkExecPr
ocesses.html
System Call: wait()
• Pause until child process has exited
wait(): Blocks calling process until the child process
terminates. If child process has already teminated,
the wait() call returns immediately. if the calling
process has multiple child processes, the function
returns when one returns.
waitpid(): Options available to block calling process
for a particular child process not the first one
• http://www.yolinux.com/TUTORIALS/ForkExecProcesse
s.html
System call : system()
• Invokes the command processor to execute
a command.
• Uses fork() exec() and wait()
• The call "blocks" and waits for the task to be
performed before continuing.
system(“ls –l”);
UNIX Signal
• Facility for one process to send another
instant notification
• Send an interrupt to a process
signal(processID, type)
• Signal Handling example
– http://www.yolinux.com/TUTORIALS/C++Signals.h
tml
System Call : dup2()
• Replace the tofileDesc file descriptor with a
copy of the fromfiledesc file descriptor. Used
for replacing stdin or stdout or both in a child
process
dup2(fromFileDesc, toFileDesc)
• Example:
http://www.cs.loyola.edu/~jglenn/702/S2005/Exam
ples/pipe.html
Shell
• A shell is a job control system
– Allows programmer to create and manage a set of
programs to do some task
– Windows, MacOS, Linux all have shells
• Example: to compile a C program
cc –c sourcefile1.c
cc –c sourcefile2.c
ln –o program sourcefile1.o sourcefile2.o
Implementing a Shell
char *prog, **args;
int child_pid;
// Read and parse the input a line at a time
while (readAndParseCmdLine(&prog, &args)) {
child_pid = fork(); // create a child process
if (child_pid == 0) {
exec(prog, args);
// I'm the child process. Run program
// NOT REACHED
} else {
wait(child_pid);
// I'm the parent, wait for child
return 0;
}
}
POSIX
• POSIX, an acronym for "Portable Operating
System Interface", is a family of standards
specified by the IEEE for maintaining
compatibility between operating systems.
POSIX defines the application programming
interface (API), along with command line
shells and utility interfaces, for software
compatibility with variants of Unix and other
operating systems.
http://en.wikipedia.org/wiki/POSIX