7장: 동기화 예제

Semaphore nFullSlots = 0; -> 지금 있는 것들의 개수 Semaphore nEmptySlots = N; -> 가능한 room의 개수 Semaphore mutex = 1; Producer(item){ nEmptySlots.wait(); // wait until space mutex.wait(); //mutex Enqueue(item); mutex.signal(); nFullSlots.signal(); // tell consumer there is more data } Consumer(){ nFullSlots.wait(); // check if there's data mutex.wait(); item = Dequeue(); mutex.signal(); nEmptySlots.signal(); // tell producer need more return item; }

Producer(item){ mutex.wait(); nEmptySlots.wait(); Enqueue(item); mutex.signal(); nFullSlots.signal(); // tell consumer there is more data } Consumer(){ nFullSlots.wait(); // check if there's data mutex.wait(); item = Dequeue(); mutex.signal(); nEmptySlots.signal(); // tell producer need more return item; }

semaphore rw_mutex = 1; // reader와 writer 간의 mutex, writer들 간의 mutex semaphore mutex = 1; // read_count를 갱신할 때 상호 배제를 보장하기 위함. int read_count = 0; //Writer while(true){ wait(rw_mutex); signal(rw_mutex); } //Reader while(true){ wait(mutex) read_count ++; if(read_count == 1){ wait(rw_mutex); } signal(mutex); //reading wait(mutex); read_count --; if(read_count == 0){ signal(rw_mutex); } signal(mutex); }

semaphore chopstick[5]; while(true){ //think wait(chopstick[i]); wait(chopstick[i+1] % 5); // eat signal(chopstick[i]); signal(chopstick[i+1%5]); //think }

monitor DiningPhilosophers { enums{THINKING, HUNGRY, EATING} state[5]; condition self[5]; void pickup(int i){ state[i] = HUNGRY; test(i); if(state[i]!=EATING) self[i].wait(); //자기 자신을 대기 시킨다. } void putdown(int i){ state[i] = THINKING; test((i+4)%5); test((i+1)%5); } void test(int i){ if((state[i+4]%5 != EATING) && (state[i+1]%5 != EATING) && state[i]==HUNGRY){ state[i] = EATING; self[i].signal(); // 남이 풀어준다. } } initialization_code(){ for(int i=0; i<5; i++) state[i] = THINKING; } }

#include <pthread.h> pthrad_mutex_t mutex; pthread_mutex_init(&mutex, NULL); pthrad_mutex_lock(&mutex); //critical section pthread_mutex_unlock(&mutex);

#include<semaphore.h> sem_t *sem //create semaphore and initialize to 1 sem = sem_open("SEM"., O_CREAT, 0666, 1);//SEM이라는 이름, O_CREAT: 존재하지 않을 경우 생성, 0666을 통해 다른 프로세스에 읽기 및 쓰기 접근 권한, 1로 초기화 sem_wait(sem); //critical section sem_post(sem); //무명 세마포 sem_init(&sem, 0, 1) //플래그로 0을 전달하면 세마포를 만든 프로세스에 속하는 스레드만 이 세마포를 공유할 수 있다.

pthread_mutex_t mutex; pthread_cond_t cond_var; pthread_mutex_init(&mutex, NULL); pthread_cond_init(&cond_var, NULL); pthread_mutex_lock(&mutex); while(a!=b) pthread_cond_wait(&cond_var, &mutex); pthread_mutex_unlock(&mutex);

pthread_mutex_lock(&mutex); a = b; pthread_cond_signal(&cond_var); pthread_mutex_unlock(&mutex);

public class BoundedBuffer<E>{ private static final inti BUFFER_SIZE = 5; private int count, in, out; private E[] buffer; public BoundedBuffeR(){ count = 0; in = 0; out = 0; buffer = (E[]) new Object[BUFFER_SIZE]; } public synchronized void insert(E item){ while(count == BUFFER_SIZE){ try { wait(); } catch(InterruptedException ie){} } buffer[in] = item; in = (in + 1) % BUFFER_SIZE; count ++; notify(); } public synchronized E remove(){ E item; while(count == 0){ try{ wait(); } catch (InterruptedException ie){} } item = buffer[out]; out = (out + 1) % BUFFER_SIZE; count --; notify(); return item; } }

Lock key = new ReentrantLock(); key.lock(); try{ //critical section }finally { key.unlock(); }

Semaphore sem = new Semaphore(1); try{ sem.acquire(); } catch(InterruptedException ie){} finally{ sem.release(); }

Lock key = new ReentrantLock(); Condition condVar = key.newCondition(); Lock lock = new ReentrantLock(); Condition[] condVars = new Condition[5]; for(int i=0; i<5; i++) condVars[i] = lock.newcondition(); public void doWork(int threadNumber){ lock.lock(); try{ if(threadNumber != turn) condVars[threadNumber].await(); turn = (turn + 1) % 5; condVars[turn].signal(); }catch(InterruptedException ie){ } finally { lock.unlock(); } }