Chapter 3 Processes

Chapter 3: Processes
Chapter 3: Processes
3.2
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts - 7
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Chapter 3: Processes
Chapter 3: Processes
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
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
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
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
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
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
3.3
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Process Concept
Process Concept
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


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Batch system – jobs
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Time-shared systems – user programs or tasks
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 jobprocess

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!"
#
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
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program counter
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stack
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data section
3.4
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Process in Memory
Process in Memory
3.5
Silberschatz, Galvin and Gagne ©2005
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Process State
Process State
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$state
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new: The process is being created
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running: Instructions are being executed
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waiting: The process is waiting for some event to occur
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ready: The process is waiting to be assigned to a processor
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terminated: The process has finished execution
3.6
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Diagram of Process State
Diagram of Process State
3.7
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Process Control Block (PCB)
Process Control Block (PCB)
%

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
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
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&
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&
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'
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
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(
3.8
Silberschatz, Galvin and Gagne ©2005
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Process Control Block (PCB)
Process Control Block (PCB)
3.9
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CPU Switch From Process to Process
CPU Switch From Process to Process
3.10
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Process Scheduling Queues
Process Scheduling Queues
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Job queue!
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Ready queue!
$%
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Device queues!%
(
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#
3.11
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Ready Queue And Various I/O Device Queues
Ready Queue And Various I/O Device Queues
3.12
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts - 7
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Representation of Process Scheduling
Representation of Process Scheduling
3.13

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Schedulers
Schedulers
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Long-term scheduler)*+!
%
#
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Short-term scheduler)&+!
%
&
3.14
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Operating System Concepts - 7
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Addition of Medium Term Scheduling
Addition of Medium Term Scheduling
3.15
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Schedulers (Cont.)
Schedulers (Cont.)
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 #

)+⇒)+
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, #
)$+⇒)%+
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degree of
multiprogramming
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
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I/O-bound process – spends more time doing I/O than
computations, many short CPU bursts
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CPU-bound process – spends more time doing computations;
few very long CPU bursts
3.16
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Context Switch
Context Switch
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-&%$

%
■
%"
% %%
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%
3.17
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Process Creation
Process Creation
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$%$
$

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.
●
Parent and children share all resources
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Children share subset of parent’s resources
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Parent and child share no resources
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/
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Parent and children execute concurrently
●
Parent waits until children terminate
3.18
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Process Creation (Cont.)
Process Creation (Cont.)
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
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Child duplicate of parent
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Child has a program loaded into it
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&01
●
fork system call creates new process
●
exec system call used after a fork to replace the process’
memory space with a new program
3.19
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Process Creation
Process Creation
3.20
Silberschatz, Galvin and Gagne ©2005
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C Program Forking Separate Process
C Program Forking Separate Process

)+
2
3"
(4 4(
5 )+"
)67+2(44(
)$89 98+"
):+"
;
)557+2(44(
)8((8$88$0&,,+"
;
2(44(
(4%%
4(
%)0&,,+"
)88+"
)7+"
;
;
3.21
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A tree of processes on a typical Solaris
A tree of processes on a typical Solaris
3.22
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Process Termination
Process Termination
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 
)exit+
●
Output data from child to parent (via wait)
●
Process’ resources are deallocated by operating system
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
)abort+
●
Child has exceeded allocated resources
●
Task assigned to child is no longer required
●
If parent is exiting

Some operating system do not allow child to continue if its
parent terminates
–
All children terminated - cascading termination
3.23
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Cooperating Processes
Cooperating Processes
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Independent<<

■
Cooperating<<

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
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Information sharing
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Computation speed-up
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Modularity
●
Convenience
3.24
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts - 7
th
Edition, Feb 7, 2006
Producer-Consumer Problem
Producer-Consumer Problem
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$producer
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consumer
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unbounded-buffer places no practical limit on the size of the
buffer
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bounded-buffer assumes that there is a fixed buffer size
3.25
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts - 7
th
Edition, Feb 7, 2006
Bounded-Buffer – Shared-Memory Solution
Bounded-Buffer – Shared-Memory Solution
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
#define BUFFER_SIZE 10
typedef struct {
. . .
} item;
item buffer[BUFFER_SIZE];
int in = 0;
int out = 0;
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