/
multisem.go
54 lines (49 loc) · 1.08 KB
/
multisem.go
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package semutil
import (
"context"
)
// MultiSem is a semaphore that is made out of multiple underlying semaphores.
// The semaphores are attempted one at a time.
type MultiSem struct {
sems []Semaphore
}
// NewMultiSem creates a new MultiSem.
func NewMultiSem(sems ...Semaphore) Semaphore {
if len(sems) == 0 {
panic("no semaphores passed")
}
return &MultiSem{
sems: sems,
}
}
// Acquire acquires a semaphore. If all semaphores are starved, it only blocks
// on the last semaphore.
func (ms *MultiSem) Acquire(ctx context.Context, n int64) (ReleaseFun, error) {
select {
case <-ctx.Done():
return nil, ctx.Err()
default:
}
for _, sem := range ms.sems {
rel, ok := sem.TryAcquire(n)
if ok {
return rel, nil
}
}
lastSem := ms.sems[len(ms.sems)-1]
rel, err := lastSem.Acquire(ctx, n)
if err != nil {
return nil, err
}
return rel, nil
}
// TryAcquire acquires a semaphore, but does not block.
func (ms *MultiSem) TryAcquire(n int64) (ReleaseFun, bool) {
for _, sem := range ms.sems {
rel, ok := sem.TryAcquire(n)
if ok {
return rel, true
}
}
return nil, false
}