/*
software architecture design patterns in java
by partha kuchana
auerbach publications
*/
public class readwritelocktest {
public static void main(string[] args) {
item item = new item("compscience-i");
new membertransaction("member1", item, "statuscheck");
new membertransaction("member2", item, "statuscheck");
new membertransaction("member3", item, "checkout");
new membertransaction("member4", item, "checkout");
new membertransaction("member5", item, "checkout");
new membertransaction("member6", item, "statuscheck");
}
}
class item {
private string name;
private readwritelock rwlock;
private string status;
public item(string n) {
name = n;
rwlock = new readwritelock();
status = "n";
}
public void checkout(string member) {
rwlock.getwritelock();
status = "y";
system.out.println(member + " has been issued a write lock-chkout");
rwlock.done();
}
public string getstatus(string member) {
rwlock.getreadlock();
system.out.println(member + " has been issued a read lock");
rwlock.done();
return status;
}
public void checkin(string member) {
rwlock.getwritelock();
status = "n";
system.out.println(member + " has been issued a write lock-chkin");
rwlock.done();
}
}
class readwritelock {
private object lockobj;
private int totalreadlocksgiven;
private boolean writelockissued;
private int threadswaitingforwritelock;
public readwritelock() {
lockobj = new object();
writelockissued = false;
}
/*
* a read lock can be issued if there is no currently issued write lock and
* there is no thread(s) currently waiting for the write lock
*/
public void getreadlock() {
synchronized (lockobj) {
while ((writelockissued) || (threadswaitingforwritelock != 0)) {
try {
lockobj.wait();
} catch (interruptedexception e) {
//
}
}
//system.out.println(" read lock issued");
totalreadlocksgiven++;
}
}
/*
* a write lock can be issued if there is no currently issued read or write
* lock
*/
public void getwritelock() {
synchronized (lockobj) {
threadswaitingforwritelock++;
while ((totalreadlocksgiven != 0) || (writelockissued)) {
try {
lockobj.wait();
} catch (interruptedexception e) {
//
}
}
//system.out.println(" write lock issued");
threadswaitingforwritelock--;
writelockissued = true;
}
}
//used for releasing locks
public void done() {
synchronized (lockobj) {
//check for errors
if ((totalreadlocksgiven == 0) && (!writelockissued)) {
system.out.println(" error: invalid call to release the lock");
return;
}
if (writelockissued)
writelockissued = false;
else
totalreadlocksgiven--;
lockobj.notifyall();
}
}
}
class membertransaction extends thread {
private string name;
private item item;
private string operation;
public membertransaction(string n, item i, string p) {
name = n;
item = i;
operation = p;
start();
}
public void run() {
//all members first read the status
item.getstatus(name);
if (operation.equals("checkout")) {
system.out.println("/n" + name + " is ready to checkout the item.");
item.checkout(name);
try {
sleep(1);
} catch (interruptedexception e) {
//
}
item.checkin(name);
}
}
}
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