CL 260449 lock retry

/*
Copyright 2013 The Go 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 lock

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"testing"
	"time"
)

func TestLock(t *testing.T) {
	testLock(t, false)
}

func TestLockPortable(t *testing.T) {
	return
	testLock(t, true)
}

func TestLockInChild(t *testing.T) {
	f := os.Getenv("TEST_LOCK_FILE")
	if f == "" {
		// not child
		return
	}
	lock := Lock
	if v, _ := strconv.ParseBool(os.Getenv("TEST_LOCK_PORTABLE")); v {
		lock = lockPortable
	}

	lk, err := lock(f)
	if err != nil {
		if v, _ := strconv.ParseBool(os.Getenv("TEST_LOCK_WAITRETRY")); v {
			for scan := bufio.NewScanner(os.Stdin); scan.Scan(); {
				lk, err = lock(f)
				if err != nil {
					log.Fatalf("2nd lock attempt failed: %v", err)
				}
				break
			}
		} else {
			log.Fatalf("Lock failed: %v", err)
		}
	}

	if v, _ := strconv.ParseBool(os.Getenv("TEST_LOCK_CRASH")); v {
		// Simulate a crash, or at least not unlocking the
		// lock.  We still exit 0 just to simplify the parent
		// process exec code.
		os.Exit(0)
	}
	lk.Close()
}

func testLock(t *testing.T, portable bool) {
	lock := Lock
	if portable {
		lock = lockPortable
	}

	td, err := ioutil.TempDir("", "")
	if err != nil {
		t.Fatal(err)
	}
	defer os.RemoveAll(td)

	path := filepath.Join(td, "foo.lock")

	retryC := make(chan struct{})
	childLock := func(crash, retry bool) error {
		cmd := exec.Command(os.Args[0], "-test.run=LockInChild$")
		cmd.Env = []string{"TEST_LOCK_FILE=" + path}
		if portable {
			cmd.Env = append(cmd.Env, "TEST_LOCK_PORTABLE=1")
		}
		if crash {
			cmd.Env = append(cmd.Env, "TEST_LOCK_CRASH=1")
		}
		if retry {
			cmd.Env = append(cmd.Env, "TEST_LOCK_WAITRETRY=1")
			var stdin, stderr, stdout bytes.Buffer
			cmd.Stdin = &stdin
			cmd.Stdout = &stdout
			cmd.Stderr = &stderr
			if err := cmd.Start(); err != nil {
				return fmt.Errorf("Child Process lock of %s failed to start: %v %s %s", path, err, stdout.String(), stderr.String())
			}
			<-retryC
			if _, err := io.Copy(&stdin, strings.NewReader("retry")); err != nil {
				return fmt.Errorf("failed to make child Process lock of %s retry a lock: %v %s %s", path, err, stdout.String(), stderr.String())
			}
			c := make(chan error)
			go func() {
				c <- cmd.Wait()
			}()
			select {
			case <-time.After(5*time.Second):
				return fmt.Errorf("timed out waiting for child Process retry lock of %s: %v %s %s", path, err, stdout.String(), stderr.String())
			case err := <-c:
				t.Logf("Child output: %q (err %v)", stdout.String(), err)
				if err != nil {
					return fmt.Errorf("Child Process retry lock of %s failed: %v %s %s", path, err, stdout.String(), stderr.String())
				}				
			}
			return nil
		}
		out, err := cmd.CombinedOutput()
		t.Logf("Child output: %q (err %v)", out, err)
		if err != nil {
			return fmt.Errorf("Child Process lock of %s failed: %v %s", path, err, out)
		}
		return nil
	}

	t.Logf("Locking in crashing child...")
	if err := childLock(true, false); err != nil {
		t.Fatalf("first lock in child process: %v", err)
	}

	t.Logf("Locking+unlocking in child...")
	if err := childLock(false, false); err != nil {
		t.Fatalf("lock in child process after crashing child: %v", err)
	}

	t.Logf("Locking in parent...")
	lk1, err := lock(path)
	if err != nil {
		t.Fatal(err)
	}

	t.Logf("Again in parent...")
	_, err = lock(path)
	if err == nil {
		t.Fatal("expected second lock to fail")
	}

	go func() {
		t.Logf("Locking in child...")
		if childLock(false, true) != nil {
			t.Fatalf("lock in child process should have failed, retried, and then succeeded: %v", err)
		}
	}()

	t.Logf("Unlocking lock in parent")
	if err := lk1.Close(); err != nil {
		t.Fatal(err)
	}
	retryC <- struct{}{}

	lk3, err := lock(path)
	if err != nil {
		t.Fatal(err)
	}
	lk3.Close()
}