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locks.go
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locks.go
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// Copyright 2016, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package topo
import (
"encoding/json"
"flag"
"fmt"
"os"
"os/user"
"sync"
"time"
log "github.com/golang/glog"
"golang.org/x/net/context"
"github.com/youtube/vitess/go/trace"
)
// This file contains utility methods and definitions to lock
// keyspaces and shards.
var (
// DefaultLockTimeout is a good value to use as a default for
// locking a shard / keyspace.
DefaultLockTimeout = 30 * time.Second
// LockTimeout is the command line flag that introduces a shorter
// timeout for locking topology structures.
LockTimeout = flag.Duration("lock_timeout", DefaultLockTimeout, "timeout for acquiring topology locks")
)
// Lock describes a long-running lock on a keyspace or a shard.
// It needs to be public as we JSON-serialize it.
type Lock struct {
// Action and the following fields are set at construction time.
Action string
HostName string
UserName string
Time string
// Status is the current status of the Lock.
Status string
}
// newLock creates a new Lock.
func newLock(action string) *Lock {
l := &Lock{
Action: action,
HostName: "unknown",
UserName: "unknown",
Time: time.Now().Format(time.RFC3339),
Status: "Running",
}
if h, err := os.Hostname(); err == nil {
l.HostName = h
}
if u, err := user.Current(); err == nil {
l.UserName = u.Username
}
return l
}
// ToJSON returns a JSON representation of the object.
func (l *Lock) ToJSON() (string, error) {
data, err := json.MarshalIndent(l, "", " ")
if err != nil {
return "", fmt.Errorf("cannot JSON-marshal node: %v", err)
}
return string(data), nil
}
// lockInfo is an individual info structure for a lock
type lockInfo struct {
lockPath string
actionNode *Lock
}
// locksInfo is the structure used to remember which locks we took
type locksInfo struct {
// mu protects the following members of the structure.
// Safer to be thread safe here, in case multiple go routines
// lock different things.
mu sync.Mutex
// info contans all the locks we took. It is indexed by
// keyspace (for keyspaces) or keyspace/shard (for shards).
info map[string]*lockInfo
}
// Context glue
type locksKeyType int
var locksKey locksKeyType
// LockKeyspace will lock the keyspace, and return:
// - a context with a locksInfo structure for future reference.
// - an unlock method
// - an error if anything failed.
//
// We lock a keyspace for the following operations to be guaranteed
// exclusive operation:
// * changing a keyspace sharding info fields (is this one necessary?)
// * changing a keyspace 'ServedFrom' field (is this one necessary?)
// * resharding operations:
// * horizontal resharding: includes changing the shard's 'ServedType',
// as well as the associated horizontal resharding operations.
// * vertical resharding: includes changing the keyspace 'ServedFrom'
// field, as well as the associated vertical resharding operations.
// * 'vtctl SetShardServedTypes' emergency operations
// * 'vtctl SetShardTabletControl' emergency operations
// * 'vtctl SourceShardAdd' and 'vtctl SourceShardDelete' emergency operations
// * keyspace-wide schema changes
func (ts Server) LockKeyspace(ctx context.Context, keyspace, action string) (context.Context, func(*error), error) {
i, ok := ctx.Value(locksKey).(*locksInfo)
if !ok {
i = &locksInfo{
info: make(map[string]*lockInfo),
}
ctx = context.WithValue(ctx, locksKey, i)
}
i.mu.Lock()
defer i.mu.Unlock()
// check that we're not already locked
if _, ok = i.info[keyspace]; ok {
return nil, nil, fmt.Errorf("lock for keyspace %v is already held", keyspace)
}
// lock
l := newLock(action)
lockPath, err := l.lockKeyspace(ctx, ts, keyspace)
if err != nil {
return nil, nil, err
}
// and update our structure
i.info[keyspace] = &lockInfo{
lockPath: lockPath,
actionNode: l,
}
return ctx, func(finalErr *error) {
i.mu.Lock()
defer i.mu.Unlock()
if _, ok := i.info[keyspace]; !ok {
if *finalErr != nil {
log.Errorf("trying to unlock keyspace %v multiple times", keyspace)
} else {
*finalErr = fmt.Errorf("trying to unlock keyspace %v multiple times", keyspace)
}
return
}
err := l.unlockKeyspace(ctx, ts, keyspace, lockPath, *finalErr)
if *finalErr != nil {
if err != nil {
// both error are set, just log the unlock error
log.Errorf("unlockKeyspace(%v) failed: %v", keyspace, err)
}
} else {
*finalErr = err
}
delete(i.info, keyspace)
}, nil
}
// CheckKeyspaceLocked can be called on a context to make sure we have the lock
// for a given keyspace.
func CheckKeyspaceLocked(ctx context.Context, keyspace string) error {
// extract the locksInfo pointer
i, ok := ctx.Value(locksKey).(*locksInfo)
if !ok {
return fmt.Errorf("keyspace %v is not locked (no locksInfo)", keyspace)
}
i.mu.Lock()
defer i.mu.Unlock()
// find the individual entry
_, ok = i.info[keyspace]
if !ok {
return fmt.Errorf("keyspace %v is not locked (no lockInfo in map)", keyspace)
}
// TODO(alainjobart): check the lock server implementation
// still holds the lock. Will need to look at the lockInfo struct.
// and we're good for now.
return nil
}
// lockKeyspace will lock the keyspace in the topology server.
// unlockKeyspace should be called if this returns no error.
func (l *Lock) lockKeyspace(ctx context.Context, ts Server, keyspace string) (lockPath string, err error) {
log.Infof("Locking keyspace %v for action %v", keyspace, l.Action)
ctx, cancel := context.WithTimeout(ctx, *LockTimeout)
defer cancel()
span := trace.NewSpanFromContext(ctx)
span.StartClient("TopoServer.LockKeyspaceForAction")
span.Annotate("action", l.Action)
span.Annotate("keyspace", keyspace)
defer span.Finish()
j, err := l.ToJSON()
if err != nil {
return "", err
}
return ts.LockKeyspaceForAction(ctx, keyspace, j)
}
// unlockKeyspace unlocks a previously locked keyspace.
func (l *Lock) unlockKeyspace(ctx context.Context, ts Server, keyspace string, lockPath string, actionError error) error {
// Detach from the parent timeout, but copy the trace span.
// We need to still release the lock even if the parent
// context timed out.
ctx = trace.CopySpan(context.TODO(), ctx)
ctx, cancel := context.WithTimeout(ctx, DefaultLockTimeout)
defer cancel()
span := trace.NewSpanFromContext(ctx)
span.StartClient("TopoServer.UnlockKeyspaceForAction")
span.Annotate("action", l.Action)
span.Annotate("keyspace", keyspace)
defer span.Finish()
// first update the actionNode
if actionError != nil {
log.Infof("Unlocking keyspace %v for action %v with error %v", keyspace, l.Action, actionError)
l.Status = "Error: " + actionError.Error()
} else {
log.Infof("Unlocking keyspace %v for successful action %v", keyspace, l.Action)
l.Status = "Done"
}
j, err := l.ToJSON()
if err != nil {
return err
}
return ts.UnlockKeyspaceForAction(ctx, keyspace, lockPath, j)
}
// LockShard will lock the shard, and return:
// - a context with a locksInfo structure for future reference.
// - an unlock method
// - an error if anything failed.
//
// We are currently only using this method to lock actions that would
// impact each-other. Most changes of the Shard object are done by
// UpdateShardFields, which is not locking the shard object. The
// current list of actions that lock a shard are:
// * all Vitess-controlled re-parenting operations:
// * InitShardMaster
// * PlannedReparentShard
// * EmergencyReparentShard
// * operations that we don't want to conflict with re-parenting:
// * DeleteTablet when it's the shard's current master
//
func (ts Server) LockShard(ctx context.Context, keyspace, shard, action string) (context.Context, func(*error), error) {
i, ok := ctx.Value(locksKey).(*locksInfo)
if !ok {
i = &locksInfo{
info: make(map[string]*lockInfo),
}
ctx = context.WithValue(ctx, locksKey, i)
}
i.mu.Lock()
defer i.mu.Unlock()
// check that we're not already locked
mapKey := keyspace + "/" + shard
if _, ok = i.info[mapKey]; ok {
return nil, nil, fmt.Errorf("lock for shard %v/%v is already held", keyspace, shard)
}
// lock
l := newLock(action)
lockPath, err := l.lockShard(ctx, ts, keyspace, shard)
if err != nil {
return nil, nil, err
}
// and update our structure
i.info[mapKey] = &lockInfo{
lockPath: lockPath,
actionNode: l,
}
return ctx, func(finalErr *error) {
i.mu.Lock()
defer i.mu.Unlock()
if _, ok := i.info[mapKey]; !ok {
if *finalErr != nil {
log.Errorf("trying to unlock shard %v/%v multiple times", keyspace, shard)
} else {
*finalErr = fmt.Errorf("trying to unlock shard %v/%v multiple times", keyspace, shard)
}
return
}
err := l.unlockShard(ctx, ts, keyspace, shard, lockPath, *finalErr)
if *finalErr != nil {
if err != nil {
// both error are set, just log the unlock error
log.Warningf("unlockShard(%s/%s) failed: %v", keyspace, shard, err)
}
} else {
*finalErr = err
}
delete(i.info, mapKey)
}, nil
}
// CheckShardLocked can be called on a context to make sure we have the lock
// for a given shard.
func CheckShardLocked(ctx context.Context, keyspace, shard string) error {
// extract the locksInfo pointer
i, ok := ctx.Value(locksKey).(*locksInfo)
if !ok {
return fmt.Errorf("shard %v/%v is not locked (no locksInfo)", keyspace, shard)
}
i.mu.Lock()
defer i.mu.Unlock()
// func the individual entry
mapKey := keyspace + "/" + shard
_, ok = i.info[mapKey]
if !ok {
return fmt.Errorf("shard %v/%v is not locked (no lockInfo in map)", keyspace, shard)
}
// TODO(alainjobart): check the lock server implementation
// still holds the lock. Will need to look at the lockInfo struct.
// and we're good for now.
return nil
}
// lockShard will lock the shard in the topology server.
// UnlockShard should be called if this returns no error.
func (l *Lock) lockShard(ctx context.Context, ts Server, keyspace, shard string) (lockPath string, err error) {
log.Infof("Locking shard %v/%v for action %v", keyspace, shard, l.Action)
ctx, cancel := context.WithTimeout(ctx, *LockTimeout)
defer cancel()
span := trace.NewSpanFromContext(ctx)
span.StartClient("TopoServer.LockShardForAction")
span.Annotate("action", l.Action)
span.Annotate("keyspace", keyspace)
span.Annotate("shard", shard)
defer span.Finish()
j, err := l.ToJSON()
if err != nil {
return "", err
}
return ts.LockShardForAction(ctx, keyspace, shard, j)
}
// unlockShard unlocks a previously locked shard.
func (l *Lock) unlockShard(ctx context.Context, ts Server, keyspace, shard string, lockPath string, actionError error) error {
// Detach from the parent timeout, but copy the trace span.
// We need to still release the lock even if the parent context timed out.
ctx = trace.CopySpan(context.TODO(), ctx)
ctx, cancel := context.WithTimeout(ctx, DefaultLockTimeout)
defer cancel()
span := trace.NewSpanFromContext(ctx)
span.StartClient("TopoServer.UnlockShardForAction")
span.Annotate("action", l.Action)
span.Annotate("keyspace", keyspace)
span.Annotate("shard", shard)
defer span.Finish()
// first update the actionNode
if actionError != nil {
log.Infof("Unlocking shard %v/%v for action %v with error %v", keyspace, shard, l.Action, actionError)
l.Status = "Error: " + actionError.Error()
} else {
log.Infof("Unlocking shard %v/%v for successful action %v", keyspace, shard, l.Action)
l.Status = "Done"
}
j, err := l.ToJSON()
if err != nil {
return err
}
return ts.UnlockShardForAction(ctx, keyspace, shard, lockPath, j)
}