Java semaphore to syncronize printing to screen
- by Travis Griswald
I'm currently stuck on a bit of homework and was wondering if anyone could help -
I have to use semaphores in java to syncronize printing letters from 2 threads - one printing "A" and one printing "B". I cannot print out more than 2 of the same character in a row, so output should look like
AABABABABABBABABABABAABBAABBABABA
At the moment I have 3 semaphores, a binary mutex set to 1, and a counting semaphore, and my thread classes look something like this -
public void run() {
while (true) {
Time.delay(RandomGenerator.integer(0,20));
Semaphores.mutex.down ();
System.out.println (produce());
if (printCount > 1)
{ printCount = 0;
Semaphores.mutex.up ();
Semaphores.printB.up();
}
}
}
public String produce() {
printCount++;
return "A";
}
public void run() {
while (true) {
Time.delay(RandomGenerator.integer(0,20));
Semaphores.mutex.down ();
System.out.println (produce());
if (printCount > 1)
{ printCount = 0;
Semaphores.mutex.up ();
Semaphores.printA.up();
}
}
}
public String produce() {
printCount++;
return "B";
}
Yet whatever I try it either deadlocks, or it seems to be working only printing 2 in a row at most, but always seems to print 3 in a row every now and again!
Any help is much appreciated, not looking code or anything just a few pointers if possible :)
