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dendrite/internal/mutex.go
Kegsay f8d3a762c4
Add a per-room mutex to federationapi when processing transactions (#1810)
* Add a per-room mutex to federationapi when processing transactions

This has numerous benefits:
 - Prevents us doing lots of state resolutions in busy rooms. Previously, room forks would always result
   in a state resolution being performed immediately, without checking if we were already doing this in
   a different transaction. Now they will queue up, resulting in fewer calls to `/state_ids`, `/g_m_e`, etc.
 - Prevents memory usage from growing too large as a result and potentially OOMing.

And costs:
 - High traffic rooms will be slightly slower due to head-of-line blocking from other servers,
   though this has always been an issue as roomserver has a per-room mutex already.

* Fix unit tests

* Correct mutex lock ordering
2021-03-30 10:01:32 +01:00

38 lines
706 B
Go

package internal
import "sync"
type MutexByRoom struct {
mu *sync.Mutex // protects the map
roomToMu map[string]*sync.Mutex
}
func NewMutexByRoom() *MutexByRoom {
return &MutexByRoom{
mu: &sync.Mutex{},
roomToMu: make(map[string]*sync.Mutex),
}
}
func (m *MutexByRoom) Lock(roomID string) {
m.mu.Lock()
roomMu := m.roomToMu[roomID]
if roomMu == nil {
roomMu = &sync.Mutex{}
}
m.roomToMu[roomID] = roomMu
m.mu.Unlock()
// don't lock inside m.mu else we can deadlock
roomMu.Lock()
}
func (m *MutexByRoom) Unlock(roomID string) {
m.mu.Lock()
roomMu := m.roomToMu[roomID]
if roomMu == nil {
panic("MutexByRoom: Unlock before Lock")
}
m.mu.Unlock()
roomMu.Unlock()
}