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1、应用类型知识要点一：进程同步问题整形信号量：未遵循“让权等待原则”wait(S): while S=0 do no-op; S:=S-1;signal(S): S:=S+1记录型信号量：执行wait操作时，信号量的值加1，信号量的值小于0时阻塞；执行signal操作时，信号量的值减1，信号量的值小于等于0时唤醒阻塞中的进程。type semaphore=record value:integer; L:list of process; endprocedure wait(S)var S:semaphore;beginS.value=S.value-1;if S.value0 then block
2、(S.L);endprocedure signal(S)var S:semaphore;beginS.value:=S.value+1;if S.valueSj，专门设置一初值为0的信号量，并在Si结束之后执行对该信号量的signal操作，而在Sj开始之前执行对该信号量的wait操作，这样便可保证程序段Si执行完后才执行程序段Sj。生产者-消费者问题主程序(n为常量)Var buffer:array0,n-1 of item;in, out: integer:=0,0;mutex,empty,full:semaphore:=1,n,0;beginparbeginproducer1;produc
3、eri;producerM;consumer1;consumerj;consumerN;parendend生产者子程序消费者子程序produceriVar nextp:item;beginrepeatProduce an item in nextp;wait(empty);wait(mutex);bufferin:=nextp;in=(in+1)mod n;signal(mutex);signal(full);until falseendconsumerjVar nextc:item;beginrepeatwait(full);wait(mutex);nextc:=bufferout;out:
4、=(out+1) mod n;signal(mutex);signal(empty);Consume the item in nextc;until falseend生产者子程序(基于AND信号量)消费者子程序(基于AND信号量)produceribeginrepeatProduce an item in nextp;Swait(empty, mutex);bufferin=nextp;in:=(in+1) mod n;Signal(mutex, full);until falseendconsumerjbeginrepeatSwait(full,mutex);nextc:=bufferout
5、;out:=(out+1) mod n;Ssignal(mutex, empty);Consume the item in nextc;until falseend读者-写者问题(读者优先)主程序Var readercount:integer:=0;rcmutex,wmutex:semaphore:=1,1;beginparbeginreader1;readeri;readerM;writer1;writerj;writerN;parendend读者readeribeginrepeatwait(rcmutex);if readercount=0 then wait(wmutex);reader
6、count:=readercount+1;signal(rcmutex);Perform read operation;wait(rcmutex);readercount:=readercount-1;if readercount=0 then signal(wmutex);signal(rcmutex);until falseend写者writerjbeginrepeatwait(wmutex);Perform write operation;signal(wmutex);until false;endreadercount:读者数rcmutex:读者进程中用于readercount变量的互
7、斥访问wmutex:用于读者与写者、写者与写者之间的互斥访问写者与第一个读者竞争wmutex。一旦读者获得wmutex，那么直到所有读者执行结束由最后一个读者释放，而每个写者执行结束都释放，所以读者优先写者执行。读者-写者问题(写者优先)主程序Var readercount,writercount:integer:=0,0;rcmutex,wcmutex,wmutex,S:semaphore:=1,1,1,1;beginparbeginreader1;readeri;readerM;writer1;writerj;writerN;parendend读者readeribeginrepeatwai
8、t(S);wait(rcmutex);if readercount=0 then wait(wmutex);readercount:=readercount+1;signal(rcmutex);signal(S);Perform read operation;wait(rcmutex);readercount:=readercount-1;if readercount=0 then signal(wmutex);signal(rcmutex);until false;end写者writerjbeginrepeatwait(wcmutex);if writercount=0 then wait(
9、S);writercount:=writercount+1;signal(wcmutex);wait(wmutex);Perform write operation;signal(wmutex);wait(wcmutex);writercount:=writercount-1;if writercount=0 then signal(S);signal(wcmutex);until falseendrcmutex:读者进程中用于readercount变量的互斥访问wcmutex:写者进程中用于writercount变量的互斥访问wmutex: 用于读者与写者、写者与写者之间的互斥访问读者与第一
10、个写者竞争S信号量。一旦读者获得S信号量，那么直到所有读者执行结束由最后一个写者释放，而每个读者执行结束都释放，所以写者优先读者执行。读者-写者问题(限定读者数)主程序Var RN:integer:=10;rmax,wmutex:semaphore:=RN,1;beginparbeginreader1;readeri;readerM;writer1;writerj;writerN;parendend读者readeribeginrepeat=Swait(rmax,1,1,wmutex,1,0);Swait(rmax,1,1);Swait(wmutex,1,0);Perform read oper
11、ation;Ssignal(rmax,1);until false;end写者writerjbeginrepeatSwait(wmutex,1,1, rmax,RN,0);Perform write operationSignal(wmutex);until falseendRN:限定最多同时读的读者数rmax:空位置的数目，即系统还允许执行读操作的读者数，超过这个数目后读者将等待wmutex: 用于读者与写者、写者与写者之间的互斥访问读者执行Swait(wmutex,1,0)保证无写者(wmutex值保持不改变)写者执行Swait(wmutex,1,1,rmax,RN,0)保证既无写者在写又无读者在读(rmax值保持不变)哲学家进餐问题主程序Var chopstick:array0,4 of semapho
