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vendor/go.mongodb.org/mongo-driver/internal/semaphore.go

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+// Copyright (C) MongoDB, Inc. 2017-present.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
+package internal
+
+import (
+	"context"
+	"errors"
+)
+
+// NewSemaphore creates a new semaphore.
+func NewSemaphore(slots uint64) *Semaphore {
+	ch := make(chan struct{}, slots)
+	for i := uint64(0); i < slots; i++ {
+		ch <- struct{}{}
+	}
+
+	return &Semaphore{
+		permits: ch,
+	}
+}
+
+// Semaphore is a synchronization primitive that controls access
+// to a common resource.
+type Semaphore struct {
+	permits chan struct{}
+}
+
+// Len gets the number of permits available.
+func (s *Semaphore) Len() uint64 {
+	return uint64(len(s.permits))
+}
+
+// Wait waits until a resource is available or until the context
+// is done.
+func (s *Semaphore) Wait(ctx context.Context) error {
+	select {
+	case <-s.permits:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
+// Release releases a resource back into the pool.
+func (s *Semaphore) Release() error {
+	select {
+	case s.permits <- struct{}{}:
+	default:
+		return errors.New("internal.Semaphore.Release: attempt to release more resources than are available")
+	}
+
+	return nil
+}