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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc.core;
import java.util.Objects;
import java.util.Queue;
/**
* @author <a href="mailto:havardpe@yahoo-inc.com">Haavard Pettersen</a>
* @author Simon Thoresen Hult
*/
class ScheduledQueue {
public static final int MILLIS_PER_SLOT = 2;
public static final int NUM_SLOTS = 1024;
public static final int SLOT_MASK = NUM_SLOTS - 1; // bitmask to modulo NUM_SLOTS
public static final int ITER_SHIFT = Integer.numberOfTrailingZeros(NUM_SLOTS); // number of bits to shift off SLOT_MASK
private final Entry[] slots = new Entry[NUM_SLOTS + 1];
private final int[] counts = new int[NUM_SLOTS + 1];
private int currIter = 0;
private int currSlot = 0;
private long nextTick;
public ScheduledQueue(long currentTimeMillis) {
this.nextTick = currentTimeMillis + MILLIS_PER_SLOT;
}
public Entry newEntry(Object payload) {
Objects.requireNonNull(payload, "payload");
return new Entry(payload);
}
public synchronized void drainTo(long currentTimeMillis, Queue<Object> out) {
if (slots[NUM_SLOTS] == null && currentTimeMillis < nextTick) {
return;
}
drainTo(NUM_SLOTS, 0, out);
while (currentTimeMillis >= nextTick) {
if (++currSlot >= NUM_SLOTS) {
currSlot = 0;
currIter++;
}
drainTo(currSlot, currIter, out);
nextTick += MILLIS_PER_SLOT;
}
}
private void drainTo(int slot, int iter, Queue<Object> out) {
int cnt = counts[slot];
Entry entry = slots[slot];
for (int i = 0; i < cnt; i++) {
Entry next = entry.next;
if (entry.iter == iter) {
linkOut(entry);
out.add(entry.payload);
}
entry = next;
}
}
synchronized int queueSize() {
int sum = 0;
for (int cnt : counts) {
sum += cnt;
}
return sum;
}
private synchronized void scheduleAt(Entry entry, long expireAtMillis) {
if (entry.next != null) {
linkOut(entry);
}
long delayMillis = expireAtMillis - nextTick;
if (delayMillis < 0) {
entry.slot = NUM_SLOTS;
entry.iter = 0;
} else {
long ticks = 1 + (int)((delayMillis + MILLIS_PER_SLOT / 2) / MILLIS_PER_SLOT);
entry.slot = (int)((ticks + currSlot) & SLOT_MASK);
entry.iter = currIter + (int)((ticks + currSlot) >> ITER_SHIFT);
}
linkIn(entry);
}
private synchronized void unschedule(Entry entry) {
if (entry.next != null) {
linkOut(entry);
}
}
private void linkIn(Entry entry) {
Entry head = slots[entry.slot];
if (head == null) {
entry.next = entry;
entry.prev = entry;
slots[entry.slot] = entry;
} else {
entry.next = head;
entry.prev = head.prev;
head.prev.next = entry;
head.prev = entry;
}
++counts[entry.slot];
}
private void linkOut(Entry entry) {
Entry head = slots[entry.slot];
if (entry.next == entry) {
slots[entry.slot] = null;
} else {
entry.prev.next = entry.next;
entry.next.prev = entry.prev;
if (head == entry) {
slots[entry.slot] = entry.next;
}
}
entry.next = null;
entry.prev = null;
--counts[entry.slot];
}
public class Entry {
private final Object payload;
private int slot;
private int iter;
private Entry next;
private Entry prev;
private Entry(Object payload) {
this.payload = payload;
}
public void scheduleAt(long expireAtMillis) {
ScheduledQueue.this.scheduleAt(this, expireAtMillis);
}
public void unschedule() {
ScheduledQueue.this.unschedule(this);
}
}
}
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