chapter 3 process description design and control principles · process description and control....
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Seventh EditionBy William Stallings
Operating Systems:Internals
and Design
Principles
Chapter 3Process Description and Control
Structure of Process Structure of Process Images in Virtual MemoryImages in Virtual Memory
Structure of Process Structure of Process Images in Virtual MemoryImages in Virtual Memory
How to do SWITCH???
1.Mode Switch2.Context Switch3.Process Switch
Context Switch
save the context of the processor
save the context of the processor
update the process control block of the process currently in the Running state
update the process control block of the process currently in the Running state
move the process control block of this
process to the appropriate queue
move the process control block of this
process to the appropriate queue
select another process for execution
select another process for execution
update the process control block of the
process selected
update the process control block of the
process selected
update memory management data
structures
update memory management data
structures
restore the context of the processor to
that which existed at the time the selected
process was last switched out
restore the context of the processor to
that which existed at the time the selected
process was last switched out
If the currently running process is to be moved to another state (Ready, Blocked, etc.), then the OS must make substantial changes in its environment
Mode Switch
If no interrupts are pending the processor:
If no interrupts are pending the processor:
proceeds to the fetch stage and fetches the next instruction of the current
program in the current process
If an interrupt is pending the processor:
If an interrupt is pending the processor:
Saves the context of the current program being executed.
switches from user mode to kernel mode so that the interrupt processing code may
include privileged instructions
sets the program counter to the starting address of an interrupt handler program
Process Switch
A process switch may occur any time that the OS has gained control from the currently running process.Possible events giving OS control are:
• Due to some sort of event that is external to and independent of the currently running process
– clock interrupt– I/O interrupt– memory fault
• Time slice– the maximum amount of
time that a process can execute before being interrupted
• An error or exception condition generated within the currently running process
• OS determines if the condition is fatal– moved to the Exit state and
a process switch occurs– action will depend on the
nature of the error
Process Switch
A process switch may occur any time that the OS has gained control from the currently running process.Steps:
1. Save the Current state 2. Give control the new process3. Restore the previous state.
What is the difference between Mode switch and Process switch?
Types of Kernel
Non-Process Kernel
Exe within User-process
Process –based Kernel
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 via parallel sub-tasks– Modularity by dividing system functions into separate
processes – Convenience - even an individual may want to edit,
print and compile in parallel
Seventh EditionBy William Stallings
Operating Systems:Internals
and Design
Principles
Chapter 4Process and
Threads
Process and ThreadsProcessØThe unit or resource allocation and a unit of protectionØThe key states for a Process are:qRunningqReadyqBlockedqSuspendedqExit
ØProcess operations are:■ Create ■ Terminate ■ Spawn.
ThreadØThe unit of dispatching is referred to as a thread or lightweight processØThe key states for a thread are:qRunningqReadyqBlocked
ØThread operations associated with a change in thread state are:
n Spawnn Blockn Unblockn Finish
Process has PCB and Address spaceThread has TCB and Stacks
Process has PCB and Address spaceThread has TCB and Stacks
Benefits of THREADS
Takes less time to create a new thread than a process
Less time to terminate a thread than a process
Switching between two threads takes less timethan switching between processes
Threads enhance efficiency in communicationbetween programs
Types of Threads
Kernel level Thread (KLT)
User Level Thread (ULT)
ComparisonKLTs
1. Kernel is aware of the presence of KLT
2. Thread management is done by the kernel
3. If one thread in a process is blocked, the kernel can schedule another thread of the same process
ULTs
1. The kernel is not aware of the existence of threads
2. All thread management is done by the application (Thread Library; A package of routines for ULT)
3. In a typical OS many system calls are blocking as a result, when a ULT executes a system call, not only is that thread blocked, but all of the threads within the process are blocked
Difference and Similarities
KLTs
4. Can run on specific OS
5. The kernel can simultaneously schedule multiple threads from the same process on multiple processors
6. The transfer of control from one thread to another within the same process requires a mode switch to the kernel
7. Examples are:Windows NT
ULTs
4. ULTs can run on any OS
5. In a pure ULT strategy, a multithreaded application cannottake advantage of multiprocessing (multi-processor or multi-core)
6. Thread switching does not require kernel mode privileges
7. Examples are:DCE Thread library
Relationships Between ULTStates and Process States
Relationships Between ULTStates and Process States
Combined Approaches
Thread creation is donein the user space
Bulk of scheduling andsynchronization of threads is by the application
Solaris is an example
Solaris Process
• includes the user’s address space, stack, and process control blockProcessProcess
• a user-created unit of execution within a processUser-level Threads
User-level Threads
• a mapping between ULTs and kernel threadsLightweight
Processes (LWP)Lightweight
Processes (LWP)
• fundamental entities that can be scheduled and dispatched to run on one of the system processorsKernel ThreadsKernel Threads
Processes and Threadsin Solaris
Processes and Threadsin Solaris
A Lightweight Process (LWP) Data Structure Includes:
A Lightweight Process (LWP) Data Structure Includes:
1. An LWP identifier2. The priority of this LWP 3. A signal mask 4. Saved values of user-level registers 5. The kernel stack for this LWP6. Resource usage and profiling data7. Pointer to the corresponding kernel
thread8. Pointer to the process structure
User-Level Threads
Thread management is done by user-level threads library without the intervention of the kernel§ Fast to create and manage§ If the kernel is single threaded, any user-level thread performing a blocking system call willcause the entire process to be blocked
User thread libraries§ POSIX Pthreads§ Mach C-threads§ Solaris 2 UI-threads
Kernel-Level ThreadsSupported by the Kernel§Slower to create and manage than user threads§If thread performs a blocking system call, the kernel can schedule another thread in the application for execution§In multi-processor environments, the kernel can schedule threads on multiple processors
Examples- Windows 95/98/NT/2000- Solaris- Tru64 UNIX- BeOS- Linux
Relationship Between Threads and ProcessesRelationship Between Threads and Processes
Implementation of Threads in Java
public class Mythread{public static void main(String args[]){
SomeThread p1=new SomeThread(1);p1.start();
SomeThread p2=new SomeThread(2);p2.start();
SomeThread p3=new SomeThread(3);p3.start();
}}
class SomeThread extends Thread{
int myId;SomeThread(int id)
{this.myId=id;
}public void run(){
int i;for(i=1;i<10;i++)System.out.println
("Thread" + myId + ":" + i);}
}
Java Threads
Java threads may be created by extending the Thread class orimplementing the Runnable interface
Java threads are managed by the JVM
Thread Run Trace
Thread2:1Thread2:2Thread3:1Thread3:2Thread3:3Thread3:4Thread3:5Thread3:6Thread3:7
Thread3:8Thread3:9Thread1:1Thread2:3Thread2:4Thread2:5Thread1:2Thread1:3Thread2:6
Thread1:4Thread1:5Thread2:7Thread1:6Thread1:7Thread2:8Thread1:8Thread1:9Thread2:9
Summary
User-level threadscreated and managed by a threads library that runs in the user space of a processa mode switch is not required to switch from one thread to anotheronly a single user-level thread within a process can execute at a timeif one thread blocks, the entire process is blocked
Kernel-level threadsthreads within a process that are maintained by the kernela mode switch is required to switch from one thread to anothermultiple threads within the same process can execute in parallel on a multiprocessorblocking of a thread does not block the entire process
Process/related to resource ownership
Thread/related to program execution