/
queue.go
170 lines (143 loc) · 3.04 KB
/
queue.go
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package crawler
import (
"context"
"encoding/json"
"fmt"
"sync"
"github.com/planetlabs/go-stac/internal/normurl"
"golang.org/x/sync/errgroup"
)
type taskType string
const (
resourceTask = taskType("resource")
collectionsTask = taskType("collections")
childrenTask = taskType("children")
featuresTask = taskType("features")
)
var validTaskTypes = map[taskType]bool{
resourceTask: true,
collectionsTask: true,
childrenTask: true,
featuresTask: true,
}
type Task struct {
entry *normurl.Locator
resource *normurl.Locator
taskType taskType
}
func (t *Task) Entry() string {
if t.entry == nil {
return ""
}
return t.entry.String()
}
func (t *Task) Resource() string {
if t.resource == nil {
return ""
}
return t.resource.String()
}
func (t *Task) new(resource *normurl.Locator, taskType taskType) *Task {
return &Task{
entry: t.entry,
resource: resource,
taskType: taskType,
}
}
type jsonTask struct {
Entry *normurl.Locator
Resource *normurl.Locator
Type string
}
func (t *Task) UnmarshalJSON(data []byte) error {
var jt jsonTask
if err := json.Unmarshal(data, &jt); err != nil {
return err
}
t.entry = jt.Entry
if t.entry == nil {
return fmt.Errorf("missing entry")
}
t.resource = jt.Resource
if t.resource == nil {
return fmt.Errorf("missing resource")
}
t.taskType = taskType(jt.Type)
if !validTaskTypes[t.taskType] {
return fmt.Errorf("invalid task type: %s", t.taskType)
}
return nil
}
func (t *Task) MarshalJSON() ([]byte, error) {
jt := jsonTask{
Entry: t.entry,
Resource: t.resource,
Type: string(t.taskType),
}
return json.Marshal(jt)
}
type Handler func(task *Task) error
type Queue interface {
Add(tasks []*Task) error
Handle(handler Handler)
Wait() error
}
// NewMemoryQueue is used if a custom queue is not provided for a crawl.
//
// The crawl will stop if the provided context is cancelled. The limit is used
// to control the number of resources that will be visited concurrently.
func NewMemoryQueue(ctx context.Context, limit int) Queue {
group, ctx := errgroup.WithContext(ctx)
group.SetLimit(limit)
return &memoryQueue{
ctx: ctx,
group: group,
mutex: &sync.Mutex{},
buffer: []*Task{},
handler: nil,
}
}
type memoryQueue struct {
ctx context.Context
group *errgroup.Group
mutex *sync.Mutex
buffer []*Task
handler Handler
}
func (q *memoryQueue) Add(tasks []*Task) error {
q.mutex.Lock()
q.buffer = append(q.buffer, tasks...)
q.mutex.Unlock()
q.process()
return nil
}
func (q *memoryQueue) Handle(handler Handler) {
q.handler = handler
q.process()
}
func (q *memoryQueue) Wait() error {
return q.group.Wait()
}
func (q *memoryQueue) process() {
if q.handler == nil || len(q.buffer) == 0 {
return
}
q.mutex.Lock()
count := 0
for _, task := range q.buffer {
task := task
added := q.group.TryGo(func() error {
defer q.process()
return q.handler(task)
})
if !added {
break
}
count += 1
}
if count > 0 {
q.buffer = q.buffer[count:]
}
q.mutex.Unlock()
}
var _ Queue = (*memoryQueue)(nil)