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Copy pathPQR.java
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133 lines (116 loc) · 3.13 KB
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/*
* Let P, Q, R share a buffer,
* P and Q form a pair of producer-consumer models,
* R is both producer and consumer,
* can write if the buffer is empty,
* can read if the buffer is not empty.
* Implement synchronization.
*/
public class PQR {
public static void main(String[] args) {
Semaphores semaphores = new Semaphores();
Thread p = new Thread(new P(semaphores));
Thread q = new Thread(new Q(semaphores));
Thread r = new Thread(new R(semaphores));
p.start();
q.start();
r.start();
}
}
class Semaphores {
public boolean full = false;
public boolean empty = true;
public boolean mutex = true;
public synchronized boolean pFull() {
if (full) {
full = false;
return true;
}
return false;
}
public synchronized boolean pEmpty() {
if (empty) {
empty = false;
return true;
}
return false;
}
public synchronized boolean pMutex() {
if (mutex) {
mutex = false;
return true;
}
return false;
}
public synchronized void vFull() {
full = true;
}
public synchronized void vEmpty() {
empty = true;
}
public synchronized void vMutex() {
mutex = true;
}
}
class P implements Runnable {
public Semaphores semaphores;
public P(Semaphores semaphores) {
this.semaphores = semaphores;
}
public void run() {
while (true) {
while (!semaphores.pEmpty()) {
}
while (!semaphores.pMutex()) {
}
System.out.println("P produces one.");
semaphores.vMutex();
semaphores.vFull();
}
}
}
class Q implements Runnable {
public Semaphores semaphores;
public Q(Semaphores semaphores) {
this.semaphores = semaphores;
}
public void run() {
while (true) {
while (!semaphores.pFull()) {
}
while (!semaphores.pMutex()) {
}
System.out.println("Q consumes one.");
semaphores.vMutex();
semaphores.vEmpty();
}
}
}
class R implements Runnable {
public Semaphores semaphores;
public R(Semaphores semaphores) {
this.semaphores = semaphores;
}
public void run() {
while (true) {
if (semaphores.empty) {
while (!semaphores.pEmpty()) {
}
while (!semaphores.pMutex()) {
}
System.out.println("R produces one.");
semaphores.vMutex();
semaphores.vFull();
}
if (semaphores.full) {
while (!semaphores.pFull()) {
}
while (!semaphores.pMutex()) {
}
System.out.println("R consumes one.");
semaphores.vMutex();
semaphores.vEmpty();
}
}
}
}