# A counter on which threads can wait until its value is 0
class SynchronizedCounter

	# The starting value, always starts with 0
	private var c = 0

	private var cond = new PthreadCond
	private var mutex = new Mutex

	# Increment the counter atomically
	fun increment do
		mutex.lock
		c += 1
		mutex.unlock
	end

	# Decrement the counter atomically,
	# signals to waiting thread(s) if `c == 0`
	fun decrement do
		mutex.lock
		c -= 1
		if c == 0 then
			cond.signal
		end
		mutex.unlock
	end

	# Block until `c == 0`
	fun wait do
		mutex.lock
		while c != 0 do cond.wait(mutex)
		mutex.unlock
	end
end