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- stats: fix read-write race

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* periodicFlush() operation doesn't result in an inconsistent state at any time
* stats readers use the last unit ID properly, excluding the possibility
 when unit ID could be changed, but this unit isn't yet created
This commit is contained in:
Simon Zolin 2019-11-11 16:18:20 +03:00
parent 2a6e9f3c11
commit f64868472a
1 changed files with 22 additions and 19 deletions
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41
stats/stats_unit.go
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@ -207,6 +207,13 @@ func btoi(b []byte) uint64 {
}
// Flush the current unit to DB and delete an old unit when a new hour is started
// If a unit must be flushed:
// . lock DB
// . atomically set a new empty unit as the current one and get the old unit
// This is important to do it inside DB lock, so the reader won't get inconsistent results.
// . write the unit to DB
// . remove the stale unit from DB
// . unlock DB
func (s *statsCtx) periodicFlush() {
for {
s.unitLock.Lock()
@ -222,12 +229,13 @@ func (s *statsCtx) periodicFlush() {
continue
}
tx := s.beginTxn(true)
nu := unit{}
s.initUnit(&nu, id)
u := s.swapUnit(&nu)
udb := serialize(u)
tx := s.beginTxn(true)
if tx == nil {
continue
}
@ -455,15 +463,20 @@ func (s *statsCtx) Update(e Entry) {
s.unitLock.Unlock()
}
func (s *statsCtx) loadUnits(lastID uint32) []*unitDB {
func (s *statsCtx) loadUnits() ([]*unitDB, uint32) {
tx := s.beginTxn(false)
if tx == nil {
return nil
return nil, 0
}
s.unitLock.Lock()
curUnit := serialize(s.unit)
curID := s.unit.id
s.unitLock.Unlock()
units := []*unitDB{} //per-hour units
firstID := lastID - s.limit + 1
for i := firstID; i != lastID; i++ {
firstID := curID - s.limit + 1
for i := firstID; i != curID; i++ {
u := s.loadUnitFromDB(tx, i)
if u == nil {
u = &unitDB{}
@ -474,20 +487,13 @@ func (s *statsCtx) loadUnits(lastID uint32) []*unitDB {
_ = tx.Rollback()
s.unitLock.Lock()
cu := serialize(s.unit)
cuID := s.unit.id
s.unitLock.Unlock()
if cuID != lastID {
units = units[1:]
}
units = append(units, cu)
units = append(units, curUnit)
if len(units) != int(s.limit) {
log.Fatalf("len(units) != s.limit: %d %d", len(units), s.limit)
}
return units
return units, firstID
}
/* Algorithm:
@ -521,9 +527,7 @@ func (s *statsCtx) loadUnits(lastID uint32) []*unitDB {
func (s *statsCtx) getData(timeUnit TimeUnit) map[string]interface{} {
d := map[string]interface{}{}
lastID := s.conf.UnitID()
firstID := lastID - s.limit + 1
units := s.loadUnits(lastID)
units, firstID := s.loadUnits()
if units == nil {
return nil
}
@ -699,8 +703,7 @@ func (s *statsCtx) getData(timeUnit TimeUnit) map[string]interface{} {
}
func (s *statsCtx) GetTopClientsIP(limit uint) []string {
lastID := s.conf.UnitID()
units := s.loadUnits(lastID)
units, _ := s.loadUnits()
if units == nil {
return nil
}