Add pkg/leak, to help find leaks.

Change-Id: I52b15f168f63c5ac40c40f258d1f3ff2ffd4965e

pkg/leak/leak.go

@@ -0,0 +1,63 @@
+/*
+Copyright 2013 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 leak
+
+import (
+	"bytes"
+	"fmt"
+	"log"
+	"runtime"
+)
+
+// A Checker checks for leaks.
+type Checker struct {
+	pc []uintptr // nil once closed
+}
+
+// NewChecker returns a Checker, remembering the stack trace.
+func NewChecker() *Checker {
+	pc := make([]uintptr, 50)
+	ch := &Checker{pc[:runtime.Callers(0, pc)]}
+	runtime.SetFinalizer(ch, (*Checker).finalize)
+	return ch
+}
+
+func (c *Checker) Close() {
+	if c != nil {
+		c.pc = nil
+	}
+}
+
+func (c *Checker) finalize() {
+	if c == nil || c.pc == nil {
+		return
+	}
+	nTestLeaks++ // for testing
+	var buf bytes.Buffer
+	buf.WriteString("Leak at:\n")
+	for _, pc := range c.pc {
+		f := runtime.FuncForPC(pc)
+		if f == nil {
+			break
+		}
+		file, line := f.FileLine(f.Entry())
+		fmt.Fprintf(&buf, "  %s:%d\n", file, line)
+	}
+	log.Println(buf.String())
+}
+
+var nTestLeaks int

pkg/leak/leak_test.go

@@ -0,0 +1,48 @@
+/*
+Copyright 2013 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 leak
+
+import (
+	"runtime"
+	"testing"
+)
+
+func TestLeak(t *testing.T) {
+	testLeak(t, false, 1)
+}
+
+func TestNoLeak(t *testing.T) {
+	testLeak(t, true, 0)
+}
+
+func testLeak(t *testing.T, close bool, want int) {
+	c := make(chan bool)
+	go func() {
+		ch := NewChecker()
+		if close {
+			ch.Close()
+		}
+		c <- true
+	}()
+	<-c
+	leak0 := nTestLeaks
+	runtime.GC()
+	leaks := nTestLeaks - leak0
+	if leaks != want {
+		t.Errorf("got %d leaks; want %d", want)
+	}
+}