go 64 lines · 9 steps

A priority job queue with Go's container/heap

Implementing heap.Interface turns a slice of jobs into a priority queue ordered by priority then arrival time.

Explained by highlit
Intermediate priority-queue heap interfaces data-structures scheduling
1package scheduler
2 
3import (
4 "container/heap"
5 "time"
6)
7 
8type Job struct {
9 ID string
10 Priority int
11 Enqueued time.Time
12 Payload []byte
13 index int
14}
15 
16type JobQueue []*Job
17 
18func (q JobQueue) Len() int { return len(q) }
19 
20func (q JobQueue) Less(i, j int) bool {
21 if q[i].Priority != q[j].Priority {
22 return q[i].Priority > q[j].Priority
23 }
24 return q[i].Enqueued.Before(q[j].Enqueued)
25}
26 
27func (q JobQueue) Swap(i, j int) {
28 q[i], q[j] = q[j], q[i]
29 q[i].index = i
30 q[j].index = j
31}
32 
33func (q *JobQueue) Push(x any) {
34 job := x.(*Job)
35 job.index = len(*q)
36 *q = append(*q, job)
37}
38 
39func (q *JobQueue) Pop() any {
40 old := *q
41 n := len(old)
42 job := old[n-1]
43 old[n-1] = nil
44 job.index = -1
45 *q = old[:n-1]
46 return job
47}
48 
49func (q *JobQueue) Enqueue(job *Job) {
50 job.Enqueued = time.Now()
51 heap.Push(q, job)
52}
53 
54func (q *JobQueue) Dequeue() (*Job, bool) {
55 if q.Len() == 0 {
56 return nil, false
57 }
58 return heap.Pop(q).(*Job), true
59}
60 
61func (q *JobQueue) Reprioritize(job *Job, priority int) {
62 job.Priority = priority
63 heap.Fix(q, job.index)
64}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Satisfying heap.Interface lets the standard library manage ordering while you own the storage.
  2. 2A tie-breaker in Less gives you stable, fair ordering — here oldest job wins on equal priority.
  3. 3Tracking each element's index enables O(log n) removal and reprioritization, not just push and pop.

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