信号量机制

信号量机制：1，整型信号量（P，V操作wait(S)=S-1 ,signal(S)=s+1）2，记录型信号量(wait(S) : S.value:=S.value-1;if S.value<0 then block(S.L) signal(S) S.value:=S.value+1;

if S.value<=0 then wakeup(S.L);) /Var a,b,c:semaphore:=0,0,0;begin parbegin

begin S1:signal(a);signal(b);end;;begin wait(a);S2;signal(c);end;

Pruduce an item nextp;wait(empty);wait(mutex);buffer(in):=nextp;

in:=(in+1)mod n;signal(mutex);signal(full);until false;end

Consumer:begin/repeat/wait(full);wait(mutex);nextc:=buffer(out);out:=(out+1)mod

n;signal(mutex);signal(empty);consumer the item in nextc;until false;end