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race condition on the servers field in the cluster connection object #312

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Merged
merged 1 commit into from
Jun 2, 2021
Merged

race condition on the servers field in the cluster connection object #312

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40 changes: 21 additions & 19 deletions cluster/cluster.go
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Original file line number Diff line number Diff line change
Expand Up @@ -126,28 +126,32 @@ func (c *clusterConnection) Do(ctx context.Context, req driver.Request) (driver.
timeout = c.defaultTimeout
}

serverCount := len(c.servers)
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@informalict informalict Jun 2, 2021

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here it is the race condition because c.servers can be written from the other place like UpdateEndpoints

var specificServer driver.Connection
var server driver.Connection
var serverCount int
var durationPerRequest time.Duration

if v := ctx.Value(keyEndpoint); v != nil {
if endpoint, ok := v.(string); ok {
// Override pool to only specific server if it is found
if s, ok := c.getSpecificServer(endpoint); ok {
server = s
durationPerRequest = timeout
serverCount = 1
specificServer = s
}
}
}

timeoutDivider := math.Max(1.0, math.Min(3.0, float64(serverCount)))
attempt := 1
s := specificServer
if s == nil {
s = c.getCurrentServer()
if server == nil {
server, serverCount = c.getCurrentServer()
timeoutDivider := math.Max(1.0, math.Min(3.0, float64(serverCount)))
durationPerRequest = time.Duration(float64(timeout) / timeoutDivider)
}

attempt := 1
for {
// Send request to specific endpoint with a 1/3 timeout (so we get 3 attempts)
serverCtx, cancel := context.WithTimeout(ctx, time.Duration(float64(timeout)/timeoutDivider))
resp, err := s.Do(serverCtx, req)
serverCtx, cancel := context.WithTimeout(ctx, durationPerRequest)
resp, err := server.Do(serverCtx, req)
cancel()

isNoLeaderResponse := false
Expand All @@ -162,8 +166,8 @@ func (c *clusterConnection) Do(ctx context.Context, req driver.Request) (driver.
err = aerr
}
}

}

if !isNoLeaderResponse || !followLeaderRedirect {
if err == nil {
// We're done
Expand All @@ -189,15 +193,13 @@ func (c *clusterConnection) Do(ctx context.Context, req driver.Request) (driver.

// Failed, try next server
attempt++
if specificServer != nil {
if attempt > serverCount {
// A specific server was specified, no failover.
return nil, driver.WithStack(err)
}
if attempt > len(c.servers) {
// or
// We've tried all servers. Giving up.
return nil, driver.WithStack(err)
}
s = c.getNextServer()
server = c.getNextServer()
}
}

Expand Down Expand Up @@ -321,11 +323,11 @@ func (c *clusterConnection) Protocols() driver.ProtocolSet {
return result
}

// getCurrentServer returns the currently used server.
func (c *clusterConnection) getCurrentServer() driver.Connection {
// getCurrentServer returns the currently used server and number of servers.
func (c *clusterConnection) getCurrentServer() (driver.Connection, int) {
c.mutex.RLock()
defer c.mutex.RUnlock()
return c.servers[c.current]
return c.servers[c.current], len(c.servers)
}

// getSpecificServer returns the server with the given endpoint.
Expand Down