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oracle.go
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oracle.go
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/*
* Copyright (C) 2017 Dgraph Labs, Inc. and Contributors
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package posting
import (
"context"
"github.com/dgraph-io/dgraph/protos/intern"
"github.com/dgraph-io/dgraph/x"
)
var o *oracle
func Oracle() *oracle {
return o
}
func init() {
o = new(oracle)
o.init()
}
type oracle struct {
x.SafeMutex
commits map[uint64]uint64
aborts map[uint64]struct{}
maxpending uint64
// Used for waiting logic.
waiters map[uint64][]chan struct{}
}
func (o *oracle) init() {
o.commits = make(map[uint64]uint64)
o.aborts = make(map[uint64]struct{})
o.waiters = make(map[uint64][]chan struct{})
}
func (o *oracle) Done(startTs uint64) {
o.Lock()
defer o.Unlock()
delete(o.commits, startTs)
delete(o.aborts, startTs)
}
func (o *oracle) CommitTs(startTs uint64) uint64 {
o.RLock()
defer o.RUnlock()
return o.commits[startTs]
}
func (o *oracle) addToWaiters(startTs uint64) (chan struct{}, bool) {
o.Lock()
defer o.Unlock()
if o.maxpending >= startTs {
return nil, false
}
ch := make(chan struct{})
o.waiters[startTs] = append(o.waiters[startTs], ch)
return ch, true
}
func (o *oracle) MaxPending() uint64 {
o.RLock()
defer o.RUnlock()
return o.maxpending
}
func (o *oracle) CurrentState() *intern.OracleDelta {
od := new(intern.OracleDelta)
od.Commits = make(map[uint64]uint64)
o.RLock()
defer o.RUnlock()
for startTs := range o.aborts {
od.Aborts = append(od.Aborts, startTs)
}
for startTs, commitTs := range o.commits {
od.Commits[startTs] = commitTs
}
return od
}
func (o *oracle) WaitForTs(ctx context.Context, startTs uint64) error {
ch, ok := o.addToWaiters(startTs)
if !ok {
return nil
}
select {
case <-ch:
return nil
case <-ctx.Done():
return ctx.Err()
}
}
func (o *oracle) ProcessOracleDelta(od *intern.OracleDelta) {
o.Lock()
defer o.Unlock()
for startTs, commitTs := range od.Commits {
o.commits[startTs] = commitTs
}
for _, startTs := range od.Aborts {
o.aborts[startTs] = struct{}{}
}
if od.MaxPending <= o.maxpending {
return
}
for startTs, toNotify := range o.waiters {
if startTs > od.MaxPending {
continue
}
for _, ch := range toNotify {
close(ch)
}
delete(o.waiters, startTs)
}
o.maxpending = od.MaxPending
}