3 files changed, 155 insertions, 0 deletions
diff --git a/pkg/pool/BUILD b/pkg/pool/BUILD
new file mode 100644
index 000000000..7b1c6b75b
--- /dev/null
+++ b/pkg/pool/BUILD
@@ -0,0 +1,25 @@
+load("//tools:defs.bzl", "go_library", "go_test")
+
+package(
+    default_visibility = ["//visibility:public"],
+    licenses = ["notice"],
+)
+
+go_library(
+    name = "pool",
+    srcs = [
+        "pool.go",
+    ],
+    deps = [
+        "//pkg/sync",
+    ],
+)
+
+go_test(
+    name = "pool_test",
+    size = "small",
+    srcs = [
+        "pool_test.go",
+    ],
+    library = ":pool",
+)
diff --git a/pkg/pool/pool.go b/pkg/pool/pool.go
new file mode 100644
index 000000000..a1b2e0cfe
--- /dev/null
+++ b/pkg/pool/pool.go
@@ -0,0 +1,66 @@
+// Copyright 2018 The gVisor Authors.
+//
+// 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 pool
+
+import (
+	"gvisor.dev/gvisor/pkg/sync"
+)
+
+// Pool is a simple allocator.
+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()
+}
diff --git a/pkg/pool/pool_test.go b/pkg/pool/pool_test.go
new file mode 100644
index 000000000..d928439c1
--- /dev/null
+++ b/pkg/pool/pool_test.go
@@ -0,0 +1,64 @@
+// Copyright 2018 The gVisor Authors.
+//
+// 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 pool
+
+import (
+	"testing"
+)
+
+func TestPoolUnique(t *testing.T) {
+	p := Pool{Start: 1, Limit: 3}
+	got := make(map[uint64]bool)
+
+	for {
+		n, ok := p.Get()
+		if !ok {
+			break
+		}
+
+		// Check unique.
+		if _, ok := got[n]; ok {
+			t.Errorf("pool spit out %v multiple times", n)
+		}
+
+		// Record.
+		got[n] = true
+	}
+}
+
+func TestExausted(t *testing.T) {
+	p := Pool{Start: 1, Limit: 500}
+	for i := 0; i < 499; i++ {
+		_, ok := p.Get()
+		if !ok {
+			t.Fatalf("pool exhausted before 499 items")
+		}
+	}
+
+	_, ok := p.Get()
+	if ok {
+		t.Errorf("pool not exhausted when it should be")
+	}
+}
+
+func TestPoolRecycle(t *testing.T) {
+	p := Pool{Start: 1, Limit: 500}
+	n1, _ := p.Get()
+	p.Put(n1)
+	n2, _ := p.Get()
+	if n1 != n2 {
+		t.Errorf("pool not recycling items")
+	}
+}