Download Chapter-3-OpratingSystemSupport

OPERATING SYSTEM SUPPORT
OPERATING SYSTEM
SUPPORT
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Introduction
The Operating System Layer
Protection
Processes and Threads
Communication and Invocation
Operating System Architecture
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OPERATING SYSTEM SUPPORT
Introduction
 Many distributed operating systems have
been investigated, but there are none in
general/wide use.
 But network operating system are in wide
use for various reasons both technical and
non-technical.
 Users have much invested in their
application software; they will not adopt a
new operating system that will not run their
applications.
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OPERATING SYSTEM SUPPORT
Introduction
 The second reason against the adoption of
distributed operating system is that users
tend to prefer to have a degree of
autonomy for their machines, even in a
organization.
 Unix and Windows are two examples of network
operating systems.
 Those have a networking capability built into
them and so can be used to access remote
resources using basic services such as rlogin
and telnet.
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OPERATING SYSTEM SUPPORT
Introduction
 The combination of middleware and
network operating systems provides an
acceptance balance between the
requirement of autonomy and network
transparency.
 The network operating systems allows
users to run their favorite word processor
and other standalone applications.
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OPERATING SYSTEM SUPPORT
The Operating System Layer
Applic ations, services
Middle w are
OS: kernel,
lib raries &
servers
OS1
Processes, threads,
communicatio n, ...
OS2
Processes, threads,
communicatio n, ...
Computer &
netw ork hardw are
Computer &
netw ork hardw are
Node 1
Node 2
Pla tform
Figure 1. System layers
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OPERATING SYSTEM SUPPORT
The Operating System Layer
 Figure 1 shows how the operating system
layer at each of two nodes supports a
common middleware layer in providing a
distributed infrastructure for applications
and services.
 Kernels and server processes are the
components that manage resources and
present clients with an interface to the
resources.
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OPERATING SYSTEM SUPPORT
The Operating System Layer
 The OS facilitates:
 Encapsulation
 Protection
 Concurrent processing
 Invocation mechanism is a means of
accessing an encapsulated resource.
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OPERATING SYSTEM SUPPORT
The Operating System Layer
Proc es s manager
Communic ation
manager
Thread manager
Memory manager
Supervisor
Figure 2. Core OS functionality
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OPERATING SYSTEM SUPPORT
Process Manager: handles the creation of and operations
upon processes.
Thread manager: Thread Creation, Synchronization and
Scheduling. Threads are schedulable activities attached to
processes
Communication Manager: manages communication between
threads attached to different processes on the same computer.
Communication between threads in remote processes.
Memory Manager: management of physical and virtual memory
Supervisor: Dispatching of interrupts, system call traps and
other exceptions; control of memory management unit and
hardware caches. Processor and floating point unit register
manipulations.
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OPERATING SYSTEM SUPPORT
Protection
Resources require protection from illegitimate
access
File protection by providing access privileges
Hardware supports to protect modules: hard lock
Kernel can control the memory management unit
and set of processor registers so that no other
code may access the machine’s physical
resources except in acceptable way.
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OPERATING SYSTEM SUPPORT
Processes and Threads
 Process
 A process consists of an execution
environment together with one or more
threads.
 A thread is the operating system
abstraction of an activity.
 An execution environment is the unit of
resource management: a collection of local
kernel managed resources to which its
threads have access.
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OPERATING SYSTEM SUPPORT
Processes and Threads
 An execution environment consists of :
 An address space
 Thread synchronization and communication
resources (e.g., semaphores, sockets)
 Higher-level resources (e.g., file systems,
windows)
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OPERATING SYSTEM SUPPORT
Processes and Threads
 Threads
 Threads are schedulable activities
attached to processes.
 The aim of having multiple threads of
execution is :
 To maximize degree of concurrent execution
between operations
 To enable the overlap of computation with
input and output
 To enable concurrent processing on
multiprocessors.
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OPERATING SYSTEM SUPPORT
Processes and Threads
 Threads can be helpful within servers:
 Concurrent processing of client’s requests
can reduce the tendency for servers to
become bottleneck.
• E.g. one thread can process a client’s request
while a second thread serving another request
waits for a disk access to complete.
 Processes vs. Threads
 Threads are “lightweight” processes,
 processes are expensive to create but
threads are easier to create and destroy.
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OPERATING SYSTEM SUPPORT
Processes and Threads
 Thread synchronization
 The main difficult issues in multi-threaded
programming are the sharing of objects
and the techniques used for thread
coordination and cooperation.
 Each thread’s local variables in methods
are private to it.
 Threads have private stack.
 Threads do not have private copies of
static (class) variables or object instance
variables.
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OPERATING SYSTEM SUPPORT
Processes and Threads
 Java provides the synchronized keyword
for thread coordination.
 any object can only be accessed through
one invocation of any of its synchronized
methods.
 an object can have synchronized and nonsynchronized methods.
 example
 synchronized addTo() and removeFrom()
methods to serialize requests in worker pool
example.
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OPERATING SYSTEM SUPPORT
Processes and Threads
 Threads can be blocked and woken up
 The thread awaiting a certain condition calls
an object’s wait() method.
 The other thread calls notify() or notifyAll()
to awake one or all blocked threads.
 example
 When a worker thread discovers that there
are no requests to process, it calls wait() on
the instance of Queue.
 When the I/O thread adds a request to the
queue, it calls the queue’s notify() method
to wake up the worker.
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OPERATING SYSTEM SUPPORT
Client and server with threads
Thread 2 makes
requests to server
Thread 1
generates
results
Input-output
Receipt &
queuing
T1
Requests
N threads
Client
Server
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OPERATING SYSTEM SUPPORT
Communication and Invocation
RMI, RPC, Events/Notifications Review
OS Communication: what, which protocols
Communication Primitive: doOperation,
getRequest and sendReply
Protocols and Openness: most OS in 1980s
incorporated their own network protocols tuned
to RPC interactions
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OPERATING SYSTEM SUPPORT
Invocation Performance
Client and Server may make many millions of
invocation related operations in their life times.
However the network bandwidth improves
invocation times have not decreased in
proportion.
NULL RPC is defined as an RPC without
parameters that executes a null procedure and
returns no values.
Its execution involves an exchange of
messages carrying some system data but not
user data.
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OPERATING SYSTEM SUPPORT
Invocation Performance
Null Invocation costs are important because
they measure a fixed overhead, the latency.
Invocation cost increase with the size of
arguments and results, but in many cases the
latency is significant compared with the
remainder of delay.
RPC bandwidth/throughput is also concern
when data has to be transferred in bulk.
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OPERATING SYSTEM SUPPORT
Invocation Performance
Marshalling: and unmarshalling which involve
copying and converting data become significant
when amount of data grows.
Data copying: message data is copied several
times in the course of RPC like from across the
user-kernel boundary, across each protocol
layer, between network interface and kernel
buffers.
Packet initialization: initializing protocol
headers and trailers including checksums
Thread Scheduling and Context switching
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OPERATING SYSTEM SUPPORT
Operating System Architecture
 The major kernel architectures:
 Monolithic kernels
 Micro-kernels
 Monolithic Kernels
 A monolithic kernel can contain some
server processes that execute within its
address space, including file servers and
some networking.
 The code that these processes execute is
part or the standard kernel configuration.
(Figure 5)
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Operating System Architecture
 Microkernel
 The microkernel appears as a layer
between hardware layer and a layer
consisting of major systems.
 If performance is the goal, rather than
portability, then middleware may use the
facilities of the microkernel directly.
(Figure 6)
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OPERATING SYSTEM SUPPORT
Operating System Architecture
S4
.......
S1
S1
Key:
Server:
S2
S3
S2
S3
S4
.......
.......
Monolithic Kernel
Kernel code and data:
Microkernel
Dy namic ally loaded s erv er program:
Figure 5. Monolithic kernel and microkernel
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Operating System Architecture
Middle w are
Language
support
subsystem
Language
support
subsystem
OS emula tio n
subsystem
....
Microkernel
Hardw are
The microkernel supports middleware via subsystems
Figure 6. The role of the microkernel
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Operating System Architecture
 Monolithic and Microkernel comparison
 The advantages of a microkernel
 extensibility
 Its ability to enforce modularity behind
memory protection boundaries.
 Its small kernel has less complexity.
 The advantages of a monolithic
 The relative efficiency with which operations
can be invoked because even invocation to
a separate user-level address space on the
same node is more costly.
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Operating System Architecture
 Hybrid Approaches
 Pure microkernel operating system such as
Chorus & Mach have changed over a time to
allow servers to be loaded dynamically into the
kernel address space or into a user-level
address space.
 In some operating system such as SPIN, the
kernel and all dynamically loaded modules
grafted onto the kernel execute within a single
address space.
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