用信号量机制实现的写者优先的算法如

用信号量机制实现的写者优先的算法如 ：

Var Mut1,Mut2,Wmutex,Fmutex:Semaphore;

Rcount,Wcount:integer;

Mut1:=Mut2:=WMutex:=Fmutex:=1;

Rcount:=Wcount:=0;

//Fmutex --> 读者写者互斥

//WMutex --> 写者互斥

//Mut1 --> access to Rcount && 竞争Fmutex

//Mut2 --> access to Wcount

Writer:begin

Wait(Mut1);

Wcount:=Wcount+1；

If Wcount=1 then Wait(Fmutex); //如有读者，写者阻塞在此处 Signal(Mut1);

Wait(WMutex);

写操作；

Signal(Wmutex);

Wait(Mut1);

Wcount:=Wcount-1;

If Wcount=0 then Signal(Fmutex);

Signal(Mut1);

end

Reader:begin

Wait(Mut1); //读者需要先申请Mut1,如果有写者在等待Fmutex,则读者被阻塞，写者优先

Signal(Mut1); //立即释放Mut1，使写者可以随时申请到Mut1

Wait(Mut2);

Rcount:=Rcount+1;

If Rcount=1 then Wait(Fmutex); //第一个读者进入时，申请Fmutex；如有写者，第一个读者会阻塞在此处

Signal(Mut2);

读操作；

Wait(Mut2);

Rcount:=Rcount-1;

If Rcount=0 then Signal(Fmutex); //最后一个读者退出时，释放Fmutex Singal(Mut2);

end