读者与写者问题

1:利用记录型信号量解决：

Varrmutex,wmutex ：semaphore:=1,1;

         Readcount :integer:=0;

         begin

         parbegin

         Readercont:begin

                            repeat

                                     wait(rmutex);

                                     ifreadcount=0  then wait(wmutex);                                                                                   

      Readcount:Readcount+1;

                                     signal(rmutex);

                                               readoperation;

                                     wait(rmutex);

                                     Readcount:Readcount-1;

                                     If  Readcount=0 then signal(wmutex);

                                     Signal(rmutex);

                            until false;

                                              

writer:begin

                   wait(wmutex);

                            writer operation

                   signal(wmutex)

         until false

end

parend

end

 

1:利用信号量集机制解决：（即改为允许多个读者同时读,控制读者的数目）

 

VarReadcount :integer;

R,W:semaphore:=Readcount,1;//学者与读者的互斥信号量

begin

         parbegin

         reder:begin

                   repeat

                            Swait(R,1,1);

                            Swait(W,1,0);

                                     Readoperation;

                            Signal(R,1);

                   until false;

         end

writer:begin

         repeat

         Swait(W,1,1;R,Readcount,0);

         Writer operation

         Signal(W,1);

untilfalse;

end

parend

end

parendend

参考文献：计算机操作系统