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service.go
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service.go
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// Copyright 2019-present Open Networking Foundation.
//
// 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 (
"container/list"
lockapi "github.com/atomix/atomix-api/go/atomix/primitive/lock"
metaapi "github.com/atomix/atomix-api/go/atomix/primitive/meta"
"github.com/atomix/atomix-go-framework/pkg/atomix/errors"
"github.com/atomix/atomix-go-framework/pkg/atomix/storage/protocol/rsm"
)
func init() {
registerServiceFunc(newService)
}
func newService(context ServiceContext) Service {
return &lockService{
ServiceContext: context,
queue: list.New(),
watchers: make(map[ProposalID]Watcher),
timers: make(map[ProposalID]rsm.Timer),
}
}
// lockService is a state machine for a list primitive
type lockService struct {
ServiceContext
owner *LockRequest
queue *list.List
watchers map[ProposalID]Watcher
timers map[ProposalID]rsm.Timer
}
func (l *lockService) Backup(writer SnapshotWriter) error {
state := &LockState{
Owner: l.owner,
}
request := l.queue.Front()
for request != nil {
state.Requests = append(state.Requests, request.Value.(LockRequest))
request = request.Next()
}
return writer.WriteState(state)
}
func (l *lockService) Restore(reader SnapshotReader) error {
state, err := reader.ReadState()
if err != nil {
return err
}
l.owner = state.Owner
for _, request := range state.Requests {
l.queue.PushBack(request)
}
return nil
}
func (l *lockService) Lock(lock LockProposal) {
lockRequest := LockRequest{
ProposalID: lock.ID(),
SessionID: lock.Session().ID(),
}
if lock.Request().Timeout != nil {
expire := l.Scheduler().Time().Add(*lock.Request().Timeout)
lockRequest.Expire = &expire
}
if l.owner == nil {
// If the lock is not already owned, immediately grant the lock to the requester.
// Note that we still have to publish an event to the session. The event is guaranteed to be received
// by the client-side primitive after the LOCK response.
l.owner = &lockRequest
l.watchers[lock.ID()] = lock.Session().Watch(func(state SessionState) {
if state == SessionClosed {
l.unlock(lock.Session())
delete(l.watchers, lock.ID())
}
})
lock.Reply(&lockapi.LockResponse{
Lock: lockapi.Lock{
ObjectMeta: metaapi.ObjectMeta{
Revision: &metaapi.Revision{
Num: metaapi.RevisionNum(lock.ID()),
},
},
State: lockapi.Lock_LOCKED,
},
})
} else if lock.Request().Timeout != nil && int64(*lock.Request().Timeout) == 0 {
// If the timeout is 0, that indicates this is a tryLock request. Immediately fail the request.
lock.Fail(errors.NewTimeout("lock request timed out"))
} else if lock.Request().Timeout != nil {
// If a timeout exists, add the request to the queue and set a timer. Note that the lock request expiration
// time is based on the *state machine* time - not the system time - to ensure consistency across servers.
element := l.queue.PushBack(lockRequest)
l.timers[lock.ID()] = l.Scheduler().RunAt(*lockRequest.Expire, func() {
// When the lock request timer expires, remove the request from the queue and publish a FAILED
// event to the session. Note that this timer is guaranteed to be executed in the same thread as the
// state machine commands, so there's no need to use a lock here.
delete(l.timers, lock.ID())
l.queue.Remove(element)
lock.Fail(errors.NewTimeout("lock request timed out"))
})
l.watchers[lock.ID()] = lock.Session().Watch(func(state SessionState) {
if state == SessionClosed {
l.unlock(lock.Session())
delete(l.watchers, lock.ID())
}
})
} else {
// If the lock does not have an expiration, just add the request to the queue with no expiration.
l.queue.PushBack(lockRequest)
l.watchers[lock.ID()] = lock.Session().Watch(func(state SessionState) {
if state == SessionClosed {
l.unlock(lock.Session())
delete(l.watchers, lock.ID())
}
})
}
}
func (l *lockService) Unlock(unlock UnlockProposal) (*lockapi.UnlockResponse, error) {
if l.owner != nil {
// If the commit's session does not match the current lock holder, preserve the existing lock.
// If the current lock ID does not match the requested lock ID, preserve the existing lock.
// However, ensure the associated lock request is removed from the queue.
if unlock.Session().ID() != l.owner.SessionID {
return nil, errors.NewConflict("not the lock owner")
}
// The lock has been released. Populate the lock from the queue.
element := l.queue.Front()
if element != nil {
request := element.Value.(LockRequest)
l.queue.Remove(element)
// If the waiter has a lock timer, cancel the timer.
timer, ok := l.timers[request.ProposalID]
if ok {
timer.Cancel()
delete(l.timers, request.ProposalID)
}
lock, ok := l.Proposals().Lock().Get(request.ProposalID)
if ok {
l.owner = &request
lock.Reply(&lockapi.LockResponse{
Lock: lockapi.Lock{
ObjectMeta: metaapi.ObjectMeta{
Revision: &metaapi.Revision{
Num: metaapi.RevisionNum(lock.ID()),
},
},
State: lockapi.Lock_LOCKED,
},
})
return &lockapi.UnlockResponse{
Lock: lockapi.Lock{
ObjectMeta: metaapi.ObjectMeta{
Revision: &metaapi.Revision{
Num: metaapi.RevisionNum(lock.ID()),
},
},
State: lockapi.Lock_LOCKED,
},
}, nil
}
} else {
l.owner = nil
return &lockapi.UnlockResponse{
Lock: lockapi.Lock{
State: lockapi.Lock_UNLOCKED,
},
}, nil
}
}
return &lockapi.UnlockResponse{
Lock: lockapi.Lock{
State: lockapi.Lock_UNLOCKED,
},
}, nil
}
func (l *lockService) GetLock(get GetLockQuery) (*lockapi.GetLockResponse, error) {
if l.owner != nil {
return &lockapi.GetLockResponse{
Lock: lockapi.Lock{
ObjectMeta: metaapi.ObjectMeta{
Revision: &metaapi.Revision{
Num: metaapi.RevisionNum(l.owner.ProposalID),
},
},
State: lockapi.Lock_LOCKED,
},
}, nil
}
return &lockapi.GetLockResponse{
Lock: lockapi.Lock{
State: lockapi.Lock_UNLOCKED,
},
}, nil
}
func (l *lockService) unlock(session Session) {
// Remove all instances of the session from the queue.
element := l.queue.Front()
for element != nil {
next := element.Next()
lock := element.Value.(LockRequest)
if lock.SessionID == session.ID() {
l.queue.Remove(element)
timer, ok := l.timers[lock.ProposalID]
if ok {
timer.Cancel()
delete(l.timers, lock.ProposalID)
}
}
element = next
}
// If the removed session is the current holder of the lock, nullify the lock and attempt to grant it
// to the next waiter in the queue.
if l.owner != nil && l.owner.SessionID == session.ID() {
l.owner = nil
element := l.queue.Front()
if element != nil {
lock := element.Value.(LockRequest)
l.queue.Remove(element)
// If the waiter has a lock timer, cancel the timer.
timer, ok := l.timers[lock.ProposalID]
if ok {
timer.Cancel()
delete(l.timers, lock.ProposalID)
}
l.owner = &lock
proposal, ok := l.Proposals().Lock().Get(lock.ProposalID)
if ok {
proposal.Reply(&lockapi.LockResponse{
Lock: lockapi.Lock{
ObjectMeta: metaapi.ObjectMeta{
Revision: &metaapi.Revision{
Num: metaapi.RevisionNum(l.owner.ProposalID),
},
},
State: lockapi.Lock_LOCKED,
},
})
}
}
}
}