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remove registeredChannelsMutex

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This moves channel registration to an eventual consistency model,
where the in-memory datastructures (Channel and ChannelManager)
are the exclusive source of truth, and updates to them get persisted
asynchronously to the DB.
This commit is contained in:
Shivaram Lingamneni 2017-11-08 22:19:50 -05:00
parent d5832bf765
commit d4cb15354f
7 changed files with 318 additions and 247 deletions
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25
irc/channelmanager.go
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@ -59,11 +59,21 @@ func (cm *ChannelManager) Join(client *Client, name string, key string) error {
cm.Lock()
entry := cm.chans[casefoldedName]
if entry == nil {
entry = &channelManagerEntry{
channel: NewChannel(server, name, true),
pendingJoins: 0,
// XXX give up the lock to check for a registration, then check again
// to see if we need to create the channel. we could solve this by doing LoadChannel
// outside the lock initially on every join, so this is best thought of as an
// optimization to avoid that.
cm.Unlock()
info := client.server.channelRegistry.LoadChannel(casefoldedName)
cm.Lock()
entry = cm.chans[casefoldedName]
if entry == nil {
entry = &channelManagerEntry{
channel: NewChannel(server, name, true, info),
pendingJoins: 0,
}
cm.chans[casefoldedName] = entry
}
cm.chans[casefoldedName] = entry
}
entry.pendingJoins += 1
cm.Unlock()
@ -85,7 +95,12 @@ func (cm *ChannelManager) maybeCleanup(entry *channelManagerEntry, afterJoin boo
if afterJoin {
entry.pendingJoins -= 1
}
if entry.channel.IsEmpty() && entry.pendingJoins == 0 {
// TODO(slingamn) right now, registered channels cannot be cleaned up.
// this is because once ChannelManager becomes the source of truth about a channel,
// we can't move the source of truth back to the database unless we do an ACID
// store while holding the ChannelManager's Lock(). This is pending more decisions
// about where the database transaction lock fits into the overall lock model.
if !entry.channel.IsRegistered() && entry.channel.IsEmpty() && entry.pendingJoins == 0 {
// reread the name, handling the case where the channel was renamed
casefoldedName := entry.channel.NameCasefolded()
delete(cm.chans, casefoldedName)