I am attempting the multi-threaded bank transfer problem. However, I am having issues with correctly synchronizing the threads. Periodically after a thread performs a transfer between accounts it will test to ensure no money has been gained or loss altogether.
When a thread enters the test method it is supposed to set a flag that will prevent any other thread from entering the tranfer method, then wait until all threads currently performing transfers to end.
public void transfer(int from, int to, int amount) {
//finish running all threads' current transactions before test
accounts[from].waitForAvailableFunds(amount);
if (!open) return;
//checks to see if any thread is currently testing
//if so, wait
while(flag) {
try {
wait();
} catch (InterruptedException e) { /*ignore*/ }
}
//do not execute these two statements when a thread
//is performing a test
if (accounts[from].withdraw(amount)) {
accounts[to].deposit(amount);
}
if (shouldTest() && !flag) test();
}
//only one thread can perform a test at any given moment
public synchronized void test() {
//when test starts set a flag telling threads to
//not begin any new transfers
flag = true;
//wait for all threads currently performing transfers
//to finish current transfer before continuing
int sum = 0;
for (int i = 0; i < accounts.length; i++) {
System.out.printf("%s %s%n",
Thread.currentThread().toString(),accounts[i].toString());
sum += accounts[i].getBalance();
}
System.out.println(Thread.currentThread().toString() +
" Sum: " + sum);
if (sum != numAccounts * initialBalance) {
System.out.println(Thread.currentThread().toString() +
" Money was gained or lost");
System.exit(1);
} else {
System.out.println(Thread.currentThread().toString() +
" The bank is in balance");
}
//reset flag and notify threads test is complete.
flag = false;
notifyAll();
}
Firstly, I'm not even positive I have set the flag and waiting correctly. Secondly, how do I have the thread that entered the test method wait for all other threads that are already performing tranfers to complete the current transfer.
Thanks
