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Merge pull request #160 from slingamn/cache.4
fix a race in regenerateMembersCache
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commit
d5832bf765
@ -19,20 +19,21 @@ import (
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// Channel represents a channel that clients can join.
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type Channel struct {
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flags ModeSet
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lists map[Mode]*UserMaskSet
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key string
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members MemberSet
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membersCache []*Client // allow iteration over channel members without holding the lock
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name string
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nameCasefolded string
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server *Server
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createdTime time.Time
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stateMutex sync.RWMutex
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topic string
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topicSetBy string
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topicSetTime time.Time
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userLimit uint64
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flags ModeSet
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lists map[Mode]*UserMaskSet
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key string
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members MemberSet
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membersCache []*Client // allow iteration over channel members without holding the lock
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membersCacheMutex sync.Mutex // tier 2; see `regenerateMembersCache`
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name string
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nameCasefolded string
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server *Server
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createdTime time.Time
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stateMutex sync.RWMutex
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topic string
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topicSetBy string
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topicSetTime time.Time
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userLimit uint64
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}
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// NewChannel creates a new channel from a `Server` and a `name`
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@ -67,10 +68,15 @@ func NewChannel(s *Server, name string, addDefaultModes bool) *Channel {
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}
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func (channel *Channel) regenerateMembersCache() {
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// this is eventually consistent even without holding the writable Lock()
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// this is eventually consistent even without holding stateMutex.Lock()
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// throughout the update; all updates to `members` while holding Lock()
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// have a serial order, so the call to `regenerateMembersCache` that
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// happens-after the last one will see *all* the updates
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// happens-after the last one will see *all* the updates. then,
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// `membersCacheMutex` ensures that this final read is correctly paired
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// with the final write to `membersCache`.
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channel.membersCacheMutex.Lock()
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defer channel.membersCacheMutex.Unlock()
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channel.stateMutex.RLock()
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result := make([]*Client, len(channel.members))
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i := 0
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