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Emulate a TryLock using atomic.CompareAndSwap 

Prevent possible queueing behind serverConfigLock in the event that a server fails on a busy host.
This commit is contained in:
Sean Chittenden 2016-02-24 19:11:16 -08:00
parent 102dcafe76
commit c980d492c6
1 changed files with 10 additions and 2 deletions
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12
consul/server_manager/server_manager.go
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@ -98,6 +98,10 @@ type ServerManager struct {
// cluster and limit the rate at which it rebalances server
// connections
clusterInfo ConsulClusterInfo
// notifyFailedServersBarrier is acts as a barrier to prevent
// queueing behind serverConfigLog and acts as a TryLock().
notifyFailedBarrier int32
}
// AddServer takes out an internal write lock and adds a new server. If the
@ -207,10 +211,14 @@ func NewServerManager(logger *log.Logger, shutdownCh chan struct{}, cci ConsulCl
func (sm *ServerManager) NotifyFailedServer(server *server_details.ServerDetails) {
serverCfg := sm.getServerConfig()
if len(serverCfg.servers) > 0 && serverCfg.servers[0] == server {
// Use atomic.CAS to emulate a TryLock().
if len(serverCfg.servers) > 0 && serverCfg.servers[0] == server &&
atomic.CompareAndSwapInt32(&sm.notifyFailedBarrier, 0, 1) {
defer atomic.StoreInt32(&sm.notifyFailedBarrier, 0)
// Grab a lock, retest, and take the hit of cycling the first
// server to the end.
sm.serverConfigLock.Lock() // FIXME(sean@): wtb TryLock
sm.serverConfigLock.Lock()
defer sm.serverConfigLock.Unlock()
serverCfg = sm.getServerConfig()