diff options
Diffstat (limited to 'vendor/golang.org/x/sync/semaphore/semaphore.go')
-rw-r--r-- | vendor/golang.org/x/sync/semaphore/semaphore.go | 131 |
1 files changed, 0 insertions, 131 deletions
diff --git a/vendor/golang.org/x/sync/semaphore/semaphore.go b/vendor/golang.org/x/sync/semaphore/semaphore.go deleted file mode 100644 index e9d2d79a9..000000000 --- a/vendor/golang.org/x/sync/semaphore/semaphore.go +++ /dev/null @@ -1,131 +0,0 @@ -// 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" - "sync" - - // Use the old context because packages that depend on this one - // (e.g. cloud.google.com/go/...) must run on Go 1.6. - // TODO(jba): update to "context" when possible. - "golang.org/x/net/context" -) - -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 only until 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() -} |