2.3 操作系统 李航 IPC

Process-IPC-part2李航funfind@Contents•Semaphore•Mutexes•Monitors•MessagePassing•BarriersSemaphore#defineN1OO/*numberofslotsinthebuffer*/typedefintsemaphore;semaphoremutex=1;semaphoreempty=N;、semaphorefull=O;voidproducer(void)intitem;while(TRUE)(item=produce—item();down(&empty);down(&mutex);insert—item(item);up(&mutex);up(&full);voidconsumer(void)intitem;/*semaphoresareaspecialkindofint*//*controlsaccesstocriticalregion*//*countsemptybufferslots*//*countsfullbufferslots*/、/*TRUEistheconstant1*/generatesomethingtoputinbuffer*/r^decrementemptycount*/</*e^tercriticalregion*//*purmewiteminbuffer*/>/*ieavebqticalregion*/ncremeoffullslots*/KeyIdea:仓库没有空槽位不能再生产，仓库没有产品不能再消费；向仓库中虹放置产品或取产品是原子操作’while(TRUE)(down(&full);down(&mutex);item=remove_item();up(&mutex);up(&empty);consume_item(item);}/*infiniteloop*//*decrementfullcount*//*entercriticalregion*//*takeitemfrombuffer*//*leavecriticalregion*//*incrementcountofemptyslots*./*dosomethingwiththeitem*/Mutex•SimplifiedSemaphore◦whereonlytwostatesexist:•lock&unlockThreadcallDescriptionPthreadmutexinitCreateamutexPthreadmutexdestroyDestroyanexistingmutexPthreadmutexlockAcquirealockorblockPthreadmutextrylockAcquirealockorfailPthreadmutexunlockReleasealockMutex•PossibleImplementationmutex_lock:TSLREGISTER,MUTEXCMPREGISTER,#。JZEokCALLthread-yieldJMPmutex_lockok:RETcopymutextoregisterandsetmutexto1wasmutexzero?ifitwaszero,mutexwasunlocked,soreturnmutexisbusy;scheduleanotherthreadtryagainIreturntocaller;criticalregionenteredmutex_unlock:MOVEMUTEX,#0RETstorea0inmutexreturntocallerMutex•ConditionalVariablesBuffer大小为1。值为正数，0表示现在buffer为空若没有cond_wait.那么producer发现buffer不为空，就得释放锁，然后又加锁进入忙等待状态，直至buffer为空。Mutex•What'sthedifferenceofmutex&semaphore?◦Onlythedifferenceindefinition?◦ImplementationDifferencesMonitor•Semaphoreproblem。easytodeadlock•Solution。Highlevelabstraction•Monitor:Amonitorisacollectionofprocedures,variables,anddatastructuresthatareallgroupedtogetherinaspecialkindofmoduleorpackage.Processesmaycalltheproceduresinamonitorwhenevertheywantto,buttheycannotdirectlyaccessthemonitor'sinternaldatastructuresfromproceduresdeclaredoutsidethemonitor.•ImportantFeature:Onlyoneprocesscanbeactiveinamonitoratanyinstant.Monitormonitorexampleintegerz;conditionc\procedureproducer^);end;procedureconsumer^);••・end;endmonitor;MutualExclusionwithBusywaitingmonitorProducerConsumercondition/mZ/,empty,integercount',procedureinsert(item:integer)-,beginifcount=Nthenyvait(full);insert_item(item);count:=count+1;ifcount=1thensignalfempty)end;functionremove',integer,beginifcount=0thenwait(e“?p邛丿；remove=removecount:=count

一1;ifcount=N-Ithensignal的〃)end;count:=0;endmonitor;procedureproducer,beginwhiletruedobeginitem=produceProducerConsumer.insert(item)endend;procedureconsumer,beginwhiletruedobeginitem=ProducerConsumer.remove;consume_item(item)endend;MonitorExample—PseudoPascalpublicclassProducerconsumer{staticfinalintN=100;//constantgivingthebuffersizestaticproducerp=newproducer();Hinstantiateanewproducerthreadstaticconsumerc=newconsumer();Hinstantiateanewconsumerthreadstaticourmonitormon=newourmonitor();//instantiateanewmonitorpublicstaticvoidmain(Stringargs[])(р.start();//starttheproducerthreadс.start();//starttheconsumerthreadstaticclassproducerextendsThread(publicvoidrun()(//runmethodcontainsthethreadcodeintitem;while(true)(〃

producerloopitem=produceitem();mon.insert(item);privateintproduceitem()(...}//actuallyproducestaticclassconsumerextendsThread(publicvoidrun()(runmethodcontainsthethreadcodeintitem;while(true){//consumerloop|item=mon.remove();consumeitem(item);privatevoidconsumeitem(intitem)(...}//actuallyconsumestaticclassourmonitor(Hthisisamonitorprivateintbuffer[]=newint[N];privateintcount=0,Io=0,hi=0;〃

countersandindicespublicsynchronizedvoidinsert(intval)(if(count==N)gotosleep();//ifthebufferisfull,gotosleepbuffer[hi]=val;Hinsertanitemintothebufferhi=(hi+1)%N;//slottoplacenextitemincount=count+1;//onemoreiteminthebuffernowif(count=1)notify();//ifconsumerwassleeping,wakeituppublicsynchronizedintremove(){intval;if(count=0)gotosleep();IIifthebufferisempty,gotosleepval=buffer[Io];II

fetchanitemfromthebufferlo=(lo+1)%N;II

slottofetchnextitemfromcount=count-1;II

onefewitemsinthebufferif(count=N-1)notify();//ifproducerwassleeping,wakeitupreturnval;privatevoidgotosleep()(try{wait();}catch(InterruptedExceptionexc){)；MonitorJavaExampleMessagePassing#defineN100voidproducer(void){intitem;messagem;while(TRUE)(item=produce_item();receive(consumer,&m);build_message(&m,item);send(consumer,&m);}}voidconsumer(void){intitem,i;messagem;for(i=0;ivN;i++)send(producer,while(TRUE)(receive(producer,&m);item=extract_item(&