Outline
• Cross referenced Linux source code
• About Lab1
• Using the Operating Systems - continued
– The abstract model of computing
– Resources
• Files
– Processes and threads
– Objects
Linux Source Code
• Cross referenced Linux source code is
available at
– http://www.cs.fsu.edu/~baker/cis5930.B03/xref.html
• How the system calls are implemented in Linux
• Two examples
– fork
– execve
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Lab1
• Built-in commands
• Additional features for executing external
commands
• Submission
• Demonstration
• Grading
• Honor code
– You are allowed to use examples from this class
– But you are not allowed to submit other’s work
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Review: System Overview
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Review: Using the O.S.
• For a programmer, the operating system
interface is most important
– The functions provided by the OS
• System calls in the UNIX case
– Abstract resources that are available
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Resources
• A resource is any abstract machine entity that
– A process must request it from the OS
– The process must suspend its operations until the
entity is allocated to it
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Files
• A sequential file is a named, linear stream of
bytes
• An open file is an abstract resource
– The OS implements the abstraction by mapping
bytes in the stream to blocks of information
stored on the device
– It has a descriptor so that OS can keep track of its
status
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Files – cont.
• Files are more fundamental than other
resources
– They are the prevalent form by which information
is stored
– OS often takes the file as a primitive and then
model other resource abstractions after it
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Files – cont.
• File related system calls
–
–
–
–
–
–
open
close
read
write
lseek
fcntl
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Other Resources
• Processor is a resource
• Memory is a resource
• I/O devices
– Keyboard is a resource
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Other Resources – cont.
• UNIX treats all I/O devices as files
– Provides a similar interface
• open, close, read, write, seek, ioctl
– Special file descriptors
• 0 is the standard input
• 1 is the standard output
• 2 is the standard error
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Processes
• A process is a sequential program in
execution
–
–
–
–
The object program to be executed
The data on which the program will execute
Resources required by the program
The threads in the process
• The status of each thread’s execution
– Process state
– PC
– Register values
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Processes – cont.
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Processes – cont.
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Process States
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Processes – cont.
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Processes – cont.
• Differences between a process and its
corresponding program
– A program is a static entity made up instructions
– A process is a dynamic entity that executes a
program on a particular set of data
• It has its own status and resources
– Two or more processes could be executing the
same program
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Processes – cont.
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Threads
• A thread (or lightweight process) is an
execution engine component of a process; it
is a basic unit of CPU utilization
• It consists of:
– program counter
– register set
– stack space
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Threads – cont.
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Threads executing in two processes
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Threads – cont.
• A thread shares with its peer threads its:
–
–
–
–
code section
data section
operating-system resources
collectively known as a task
• A traditional or heavyweight process is equal
to a task with one thread
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UNIX Processes
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Threads – cont.
• Benefits of multithreading
– Improve application responsiveness
• Netscape uses multithreaded programming
–
–
–
–
Use multiprocessors efficiently
Improve program structure
Use fewer system resources
Faster to switch between threads than processes
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Threads in a spreadsheet program
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Disk server using threads
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Kinds of threads
• Lightweight processes
– threads implemented by the OS
• A process can implement user threads
– threads implemented (solely) by the user
– these are more efficient
– but if the OS blocks one of them, they are all
blocked
• Kernel threads are threads that run inside the
OS (a.k.a. the kernel)
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Thread Related Functions and System Calls
• POSIX Thread
– pthread_create
– pthread_join
– pthread_exit
• Solaris Thread
– thr_create
– thr_join
– thr_exit
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Objects
• Object-oriented design models
– A system is modeled as a set of autonomous
entities, called objects
• Each object responds to messages and interacts with
other objects through message passing
• Object-oriented Operating Systems
– A new mechanism to specify a system
• Specify the individual units of serial computation
• Specify the model of interactions among units
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Summary
• Operating systems provide a virtual
computing environment for application
programmers
– Functions provided by O.S.
– Abstract resources by O.S.
• Files
• Processes and threads
• Objects
– Programmers can develop applications more
efficiently
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Recitation Tomorrow
• We will first go over the requirement of Lab1
• Then we will take about how to implement
the built-in commands
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