COP 4600 Operating Systems Fall 2010 - PowerPoint Presentation

Slide1

COP 4600 Operating Systems Fall 2010

Dan C. Marinescu

Office: HEC 439 B

Office hours:

Tu-Th

3:30-4:30 PMSlide2

Last time:

Presentation of the paper “Programming with Threads” by Andrew

BirellThread coordination with a bounded buffer. WAITNOTIFYToday:Thread coordination with a bounded buffer. AWAITADVANCESEQUENCETICKETSemaphoresDeadlock and Wait for GraphsEnforced modularity on the Intel x86 architectureVirtual MachinesNext TimeScheduling Algorithms

Lecture 22 – Thursday November 4, 2010

Lecture 22

2Slide3

Coordination with bounded buffer

WAIT and NOTIFY can be used to coordinate the SEND and RECIVE systems calls.

This solution creates problems when a NOTIFY is sent before the WAIT. The thread in the WAITING state will never wake up. Lecture 223Slide4

Lecture 22

4Slide5

Lecture 22

5Slide6

AWAIT - ADVANCE solution

A new state, WAITING and two

before-or-after actions that take a RUNNING thread into the WAITING state and back to RUNNABLE state.eventcount  variables with an integer value shared between threads and the thread manager; they are like events but have a value. A thread in the WAITING state waits for a particular value of the eventcount AWAIT(eventcount,value)If eventcount >value  the control is returned to the thread calling AWAIT and this thread will continue executionIf eventcount ≤value  the state of the thread calling AWAIT is changed to WAITING and the thread is suspended.ADVANCE(eventcount) increments the

eventcount by one then

searches the thread_table

for threads waiting for this

eventcount

if it finds a thread and the

eventcount

exceeds the value the thread is waiting for then the state of the thread is changed to RUNNABLE

Lecture 22

6Slide7

Implementation of AWAIT and ADVANCE

Lecture 22

7Slide8

Lecture 22

8Slide9

Solution for a single sender and multiple receivers

Lecture 22

9Slide10

Supporting multiple senders: the sequencer

Sequencer

 shared variable supporting thread sequence coordination -it allows threads to be ordered and is manipulated using two before-or-after actions.TICKET(sequencer)  returns a negative value which increases by one at each call. Two concurrent threads calling TICKET on the same sequencer will receive different values based upon the timing of the call, the one calling first will receive a smaller value.READ(sequencer)  returns the current value of the sequencer Lecture 2210Slide11

Multiple sender solution; only the SEND must be modified

Lecture 22

11Slide12

Semaphores

Introduced by

Dijkstra in 1965Does not require busy waiting Semaphore S – integer variableTwo standard operations modify S: wait() and signal()Originally called P() and V()Less complicatedCan only be accessed via two indivisible (atomic) operationswait (S) { while S <= 0 ; // no-op

S--; }

signal (S) {

S++;

}

12

Lecture 22Slide13

Lecture 22

13Slide14

Lecture 22

14Slide15

Lecture 22

15

Simultaneous conditions for deadlockMutual exclusion: only one process at a time can use a resource.Hold and wait: a process holding at least one resource is waiting to acquire additional resources held by other processes.No preemption: a resource can be released only voluntarily by the process holding it (presumably after that process has finished).Circular wait: there exists a set {P0, P1, …, P0} of waiting processes such that P0 is waiting for a resource that is held by P1, P1

is waiting for a resource that is held by P2, …, Pn

–1 is waiting for a resource that is held by P

n

, and

P

0

is waiting for a resource that is held by

P

0

.Slide16

Wait for graphs

Lecture 22

16Slide17

Evolution of modularity for the Intel architecture x86

Real and Virtual Address Space

The address space size determined by the number of address bits: 24 for 80286 a 16 bit processor  modularity enforced through segmentation 32 for 80386 a 32 bit processor  each segment could have up to 232 byteswithin each segment support for virtual memoryBackward compatibility17Lecture 22Slide18

Lecture 22

18Slide19

19

Lecture 22Slide20

The increase in the number of lines of operating systems source code

(millions)20Lecture 22Slide21

Virtual machines

First commercial product

 IBM VM 370 originally developed as CP-67Advantages:One could run multiple guest operating systems on the same machineAn error in one guest operating system does not bring the machine downAn ideal environment for developing operating systems21Lecture 22