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sem shovel=1; //铲子互斥

sem lock_hole;//树坑变量锁

sem lock_watered_hole;//未浇水变量锁

int critical_hole_count=0;//树坑数量

int un_wartered_hole=0;//记录已填土，没浇水的洞

void a(){

while(true){

wait(lock_hole);

if(critical_hole_count < 3){

wait(shovel);

while(++critical_hole_count<3);

signal(shovel);

signal(lock_hole);

}else{

signal(lock_hole);

}

}}

 

void b(){

while(true){

wait(lock_hole);

if(critical_hole_count >0){

wait(lock_watered_hole);

while(critical_hole_count > 0){

//plant

wait(shovel);

//fill

signal(shovel);

critical_hole_count--;

un_watered_hole++;

}

signal(lock_watered_hole);

signal(lock_hole);

}else{

signal(lock_hole)

}

}

}

 

void c(){

wait(lock_watered_hole){

if(un_watered_hole>0){

while(--un_watered_hole>0);//water

}

signal(lock_watered_hole)

}

}

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