Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 68 insertions, 0 deletions

diff --git a/pkg/p9/pool.go b/pkg/p9/pool.go
new file mode 100644
index 000000000..9a508b898
--- /dev/null
+++ b/pkg/p9/pool.go
@@ -0,0 +1,68 @@
+// Copyright 2018 Google Inc.
+//
+// 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
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package p9
+
+import (
+	"sync"
+)
+
+// pool is a simple allocator.
+//
+// It is used for both tags and FIDs.
+type pool struct {
+	mu sync.Mutex
+
+	// cache is the set of returned values.
+	cache []uint64
+
+	// start is the starting value (if needed).
+	start uint64
+
+	// max is the current maximum issued.
+	max uint64
+
+	// limit is the upper limit.
+	limit uint64
+}
+
+// Get gets a value from the pool.
+func (p *pool) Get() (uint64, bool) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	// Anything cached?
+	if len(p.cache) > 0 {
+		v := p.cache[len(p.cache)-1]
+		p.cache = p.cache[:len(p.cache)-1]
+		return v, true
+	}
+
+	// Over the limit?
+	if p.start == p.limit {
+		return 0, false
+	}
+
+	// Generate a new value.
+	v := p.start
+	p.start++
+	return v, true
+}
+
+// Put returns a value to the pool.
+func (p *pool) Put(v uint64) {
+	p.mu.Lock()
+	p.cache = append(p.cache, v)
+	p.mu.Unlock()
+}