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executor.go
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executor.go
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package batch
import (
"context"
"time"
"github.com/treeverse/lakefs/pkg/logging"
)
// RequestBufferSize is the amount of requests users can dispatch that haven't been processed yet before
// dispatching new ones would start blocking.
const RequestBufferSize = 1 << 17
type Executer interface {
Execute() (interface{}, error)
}
type BatchTracker interface {
// Batched is called when a request is added to an existing batch.
Batched()
}
type BatchFn func() (interface{}, error)
func (b BatchFn) Execute() (interface{}, error) {
return b()
}
type DelayFn func(dur time.Duration)
type Batcher interface {
BatchFor(key string, dur time.Duration, exec Executer) (interface{}, error)
}
type nonBatchingExecutor struct {
}
func (n *nonBatchingExecutor) BatchFor(_ string, _ time.Duration, exec Executer) (interface{}, error) {
return exec.Execute()
}
type response struct {
v interface{}
err error
}
type request struct {
key string
timeout time.Duration
exec Executer
onResponse chan *response
}
type Executor struct {
// requests is the channel accepting inbound requests
requests chan *request
// execs is the internal channel used to dispatch the callback functions.
// Several requests with the same key in a given duration will trigger a single write to exec said key.
execs chan string
waitingOnKey map[string][]*request
Logger logging.Logger
Delay DelayFn
}
func NopExecutor() *nonBatchingExecutor {
return &nonBatchingExecutor{}
}
func NewExecutor(logger logging.Logger) *Executor {
return &Executor{
requests: make(chan *request, RequestBufferSize),
execs: make(chan string, RequestBufferSize),
waitingOnKey: make(map[string][]*request),
Logger: logger,
Delay: time.Sleep,
}
}
func (e *Executor) BatchFor(key string, timeout time.Duration, exec Executer) (interface{}, error) {
cb := make(chan *response)
e.requests <- &request{
key: key,
timeout: timeout,
exec: exec,
onResponse: cb,
}
response := <-cb
return response.v, response.err
}
func (e *Executor) Run(ctx context.Context) {
for {
select {
case <-ctx.Done():
return
case req := <-e.requests:
// see if we have it scheduled already
if _, exists := e.waitingOnKey[req.key]; !exists {
e.waitingOnKey[req.key] = []*request{req}
// this is a new key, let's fire a timer for it
go func(req *request) {
e.Delay(req.timeout)
e.execs <- req.key
}(req)
} else {
if b, ok := req.exec.(BatchTracker); ok {
b.Batched()
}
e.waitingOnKey[req.key] = append(e.waitingOnKey[req.key], req)
}
case execKey := <-e.execs:
// let's take all callbacks
waiters := e.waitingOnKey[execKey]
delete(e.waitingOnKey, execKey)
go func(key string) {
// execute and call all mapped callbacks
v, err := waiters[0].exec.Execute()
if e.Logger.IsTracing() {
e.Logger.WithFields(logging.Fields{
"waiters": len(waiters),
"key": key,
}).Trace("dispatched BatchFn")
}
for _, waiter := range waiters {
waiter.onResponse <- &response{v, err}
}
}(execKey)
}
}
}