期末复习操作系统课件ch32.pptxVIP

Chapter3:ProcessmanagementpartIISemaphoreDefinitionPandVoperationMutexusingPandVoperationProcessSychronizationSynchronizationusingPandVoperationTypicalProblems

SemaphoreItincludingtwopartsAinteger,itsinitialvalue=0andaqueuepointer

PandVoperationonSemaphorePoperation:sem-lIfsem=0after(sem-1),thenitreturn,theprocesscontinueexecutingIfsem0after(sem-1),thentheprocessbeblockedandputtotheblockqueue.

Voperationsem+1;Ifsem0after(sem+1),theprocesscontinueexecutingIfsem=0after(sem+1),thenawakeaprocessintheblockingqueue

HowtoimplementPandVoperation

MutexusingPandVoperationP1P2P(sem)P(sem)SSV(sem)V(sem)

SynchronizationAnsynchronizationexamplePrivateandpublicSemaphore

SynchronizationusingPandVThreesteps:DecidinghowmanysemaphoreshoulduseInitializethesemaphoreUsingPandVoperation

TypicalproblemsOneproducerandoneconsumerandonebufferMultiproducersandmulticonsumersBarbershopproblemDining-PhilosophersProblem

P：

i=0;

while(true){

producing;

P(S1);

putintoBuffer[i];

V(S2);

i=(i+1)%n;};Q：j=0;while(true){P(S2);takefromBuffer[j];V(S1);consuming;j=(j+1)%n;};

MultiproducerandconsumersShareddata

semaphorefull,empty,mutex;

Initially:

full=0,empty=n,mutex=1

Producer(i){while(true){

producing;

P(empty);

P(mutex);putintoBuffer[i];i=(i+1)%n;V(mutex);

V(full);

}}

consumer(j){while(true){P(full);P(mutex);takefromBuffer[j];j=(j+1)%n;V(mutex);V(empty);consuming;}}

Ifweexchangethepositionofp(empty)andp(mutex),whatwillhappen?

Producer(i){while(true){

producing;

P(mutex);P(empty);

putintoBuffer[i];i=(i+1)%n;V(full);V(mutex);

}}

consumer(j){while(t