I am new to go, but have worked with concurrency before. I am having an issue sharing a slice between multiple goroutines not containing the same data between all of the goroutines. I use a mutex as well to lock the struct when I modify the slice, but it doesn't seem to help. I have attached my code and would like to know what I am doing wrong, thanks for any help!
type State struct {
waiting int32
processing int32
completed int32
}
type Scheduler struct {
sync.Mutex
items chan interface{}
backPressure []interface{}
capacity int
canceler context.CancelFunc
state State
}
func NewScheduler(capacity int, handler func(interface {}) (interface{}, error)) Scheduler {
ctx, cancel := context.WithCancel(context.Background())
state := State{}
atomic.StoreInt32(&state.waiting, 0)
atomic.StoreInt32(&state.processing, 0)
atomic.StoreInt32(&state.completed, 0)
scheduler := Scheduler{
items: make(chan interface{}, capacity),
backPressure: make([]interface{}, 0),
capacity: capacity,
canceler: cancel,
state: state,
}
scheduler.initializeWorkers(ctx, handler)
return scheduler
}
func (s *Scheduler) initializeWorkers(ctx context.Context, handler func(interface {}) (interface{}, error)) {
for i := 0; i < 5; i++ {
go s.newWorker(ctx, handler)
}
}
func (s *Scheduler) newWorker(ctx context.Context, handler func(interface {}) (interface{}, error)) {
backoff := 0
for {
select {
case <-ctx.Done():
return
case job := <- s.items:
atomic.AddInt32(&s.state.waiting, -1)
atomic.AddInt32(&s.state.processing, 1)
job, _ = handler(job)
backoff = 0
atomic.AddInt32(&s.state.processing, -1)
atomic.AddInt32(&s.state.completed, 1)
default:
backoff += 1
s.CheckBackPressure()
time.Sleep(time.Duration(backoff * 10) * time.Millisecond)
}
}
}
func (s *Scheduler) AddItem(item interface{}) {
atomic.AddInt32(&s.state.waiting, 1)
if len(s.items) < s.capacity {
select {
case s.items <- item:
return
}
}
s.Lock()
defer s.Unlock()
s.backPressure = append(s.backPressure, item)
fmt.Printf("new backpressure len %v
", len(s.backPressure))
return
}
func (s *Scheduler) Process() {
var wg sync.WaitGroup
wg.Add(1)
go func() {
defer wg.Done()
for {
if atomic.LoadInt32(&s.state.waiting) == 0 && atomic.LoadInt32(&s.state.processing) == 0 {
return
}
runtime.Gosched()
}
}()
wg.Wait()
}
func (s *Scheduler) CheckBackPressure() {
s.Lock()
defer s.Unlock()
if len(s.backPressure) == 0 || s.capacity <= len(s.items) {
fmt.Printf("backpressure = %d :: len = %d cap = %d
", len(s.backPressure), len(s.items), s.capacity)
return
}
fmt.Printf("releasing backpressure
")
job, tmp := s.backPressure[0], s.backPressure[1:]
s.backPressure = tmp
s.items <- job
return
}
func (s *Scheduler) Stop() {
s.canceler()
}
This is the code that I am using to test the functionality:
type Job struct {
Value int
}
func TestSchedulerExceedingCapacity(t *testing.T) {
handler := func (ptr interface{}) (interface{}, error) {
job, ok := (ptr).(*Job)
if ok != true {
return nil, errors.New("failed to convert job")
}
// simulate work
time.Sleep(50 * time.Millisecond)
return job, nil
}
scheduler := NewScheduler(5, handler)
for i := 0; i < 25; i++ {
scheduler.AddItem(&(Job { Value: i }))
}
fmt.Printf("PROCESSING
")
scheduler.Process()
fmt.Printf("FINISHED
")
}
When I update the slice that holds the back pressure, it seems to indicate that it was correctly updated by printing new backpressure len 1
for 1-16.
However, when I check the back pressure from the worker, it indicates that the backpressure slice is empty. backpressure = 0 :: len = 0 cap = 5
.
Also "releasing backpressure" is never printed to stdout either.
Here is some additional output...
=== RUN TestSchedulerExceedingCapacity
new backpressure len 1
new backpressure len 2
new backpressure len 3
new backpressure len 4
new backpressure len 5
new backpressure len 6
new backpressure len 7
new backpressure len 8
backpressure = 0 :: len = 0 cap = 5
new backpressure len 9
new backpressure len 10
new backpressure len 11
new backpressure len 12
new backpressure len 13
new backpressure len 14
new backpressure len 15
new backpressure len 16
PROCESSING
backpressure = 0 :: len = 0 cap = 5
backpressure = 0 :: len = 0 cap = 5
backpressure = 0 :: len = 0 cap = 5
...
If I don't kill the test it indefinitely prints backpressure = 0 :: len = 0 cap = 5
I am assuming that I am not correctly synchronizing the changes, I would REALLY appreciate any insights, thanks!