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Use a semaphore instead of WaitGroup for FlatMap parallelism. #168

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Use a semaphore instead of WaitGroup for FlatMap parallelism. #168

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25 changes: 8 additions & 17 deletions flatmap.go
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Original file line number Diff line number Diff line change
@@ -1,9 +1,10 @@
package rxgo

import (
"sync"
"context"

"github.com/reactivex/rxgo/handlers"
"golang.org/x/sync/semaphore"
)

// transforms emitted items into observables and flattens them into single observable.
Expand Down Expand Up @@ -32,36 +33,26 @@ func (o *observable) flatMap(
}

func flatObservedSequence(out chan interface{}, o Observable, apply func(interface{}) Observable, maxInParallel uint) {
var (
sequence Observable
wg sync.WaitGroup
count uint
)
ctx := context.TODO()
sem := semaphore.NewWeighted(int64(maxInParallel))

defer close(out)
emissionObserver := newFlattenEmissionObserver(out)

count = 0

for {
element, err := o.Next()
if err != nil {
break
}
sequence = apply(element)
count++
wg.Add(1)
sequence := apply(element)
sem.Acquire(ctx, 1)
go func() {
defer wg.Done()
defer sem.Release(1)
sequence.Subscribe(emissionObserver).Block()
}()

if count%maxInParallel == 0 {
wg.Wait()
}
}

wg.Wait()
sem.Acquire(ctx, int64(maxInParallel))
}

func newFlattenEmissionObserver(out chan interface{}) Observer {
Expand Down