seba-365 - implemented dep
Change-Id: Ia6226d50e7615935a0c8876809a687427ff88c22
diff --git a/vendor/golang.org/x/sync/semaphore/semaphore.go b/vendor/golang.org/x/sync/semaphore/semaphore.go
new file mode 100644
index 0000000..ac53e73
--- /dev/null
+++ b/vendor/golang.org/x/sync/semaphore/semaphore.go
@@ -0,0 +1,127 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package semaphore provides a weighted semaphore implementation.
+package semaphore // import "golang.org/x/sync/semaphore"
+
+import (
+ "container/list"
+ "context"
+ "sync"
+)
+
+type waiter struct {
+ n int64
+ ready chan<- struct{} // Closed when semaphore acquired.
+}
+
+// NewWeighted creates a new weighted semaphore with the given
+// maximum combined weight for concurrent access.
+func NewWeighted(n int64) *Weighted {
+ w := &Weighted{size: n}
+ return w
+}
+
+// Weighted provides a way to bound concurrent access to a resource.
+// The callers can request access with a given weight.
+type Weighted struct {
+ size int64
+ cur int64
+ mu sync.Mutex
+ waiters list.List
+}
+
+// Acquire acquires the semaphore with a weight of n, blocking until resources
+// are available or ctx is done. On success, returns nil. On failure, returns
+// ctx.Err() and leaves the semaphore unchanged.
+//
+// If ctx is already done, Acquire may still succeed without blocking.
+func (s *Weighted) Acquire(ctx context.Context, n int64) error {
+ s.mu.Lock()
+ if s.size-s.cur >= n && s.waiters.Len() == 0 {
+ s.cur += n
+ s.mu.Unlock()
+ return nil
+ }
+
+ if n > s.size {
+ // Don't make other Acquire calls block on one that's doomed to fail.
+ s.mu.Unlock()
+ <-ctx.Done()
+ return ctx.Err()
+ }
+
+ ready := make(chan struct{})
+ w := waiter{n: n, ready: ready}
+ elem := s.waiters.PushBack(w)
+ s.mu.Unlock()
+
+ select {
+ case <-ctx.Done():
+ err := ctx.Err()
+ s.mu.Lock()
+ select {
+ case <-ready:
+ // Acquired the semaphore after we were canceled. Rather than trying to
+ // fix up the queue, just pretend we didn't notice the cancelation.
+ err = nil
+ default:
+ s.waiters.Remove(elem)
+ }
+ s.mu.Unlock()
+ return err
+
+ case <-ready:
+ return nil
+ }
+}
+
+// TryAcquire acquires the semaphore with a weight of n without blocking.
+// On success, returns true. On failure, returns false and leaves the semaphore unchanged.
+func (s *Weighted) TryAcquire(n int64) bool {
+ s.mu.Lock()
+ success := s.size-s.cur >= n && s.waiters.Len() == 0
+ if success {
+ s.cur += n
+ }
+ s.mu.Unlock()
+ return success
+}
+
+// Release releases the semaphore with a weight of n.
+func (s *Weighted) Release(n int64) {
+ s.mu.Lock()
+ s.cur -= n
+ if s.cur < 0 {
+ s.mu.Unlock()
+ panic("semaphore: bad release")
+ }
+ for {
+ next := s.waiters.Front()
+ if next == nil {
+ break // No more waiters blocked.
+ }
+
+ w := next.Value.(waiter)
+ if s.size-s.cur < w.n {
+ // Not enough tokens for the next waiter. We could keep going (to try to
+ // find a waiter with a smaller request), but under load that could cause
+ // starvation for large requests; instead, we leave all remaining waiters
+ // blocked.
+ //
+ // Consider a semaphore used as a read-write lock, with N tokens, N
+ // readers, and one writer. Each reader can Acquire(1) to obtain a read
+ // lock. The writer can Acquire(N) to obtain a write lock, excluding all
+ // of the readers. If we allow the readers to jump ahead in the queue,
+ // the writer will starve — there is always one token available for every
+ // reader.
+ break
+ }
+
+ s.cur += w.n
+ s.waiters.Remove(next)
+ close(w.ready)
+ }
+ s.mu.Unlock()
+}