Merge pull request #1887 from cfromknecht/parallel-chain-watcher-start

contractcourt/chain_arbitrator: parallel chain watcher start

contractcourt/chain_arbitrator.go

@@ -1,6 +1,7 @@
 package contractcourt
 
 import (
+	"errors"
 	"fmt"
 	"sync"
 	"sync/atomic"
@@ -14,6 +15,9 @@ import (
 	"github.com/lightningnetwork/lnd/lnwire"
 )
 
+// ErrChainArbExiting signals that the chain arbitrator is shutting down.
+var ErrChainArbExiting = errors.New("ChainArbitrator exiting")
+
 // ResolutionMsg is a message sent by resolvers to outside sub-systems once an
 // outgoing contract has been fully resolved. For multi-hop contracts, if we
 // resolve the outgoing contract, we'll also need to ensure that the incoming
@@ -423,15 +427,49 @@ func (c *ChainArbitrator) Start() error {
 		)
 	}
 
-	// Finally, we'll launch all the goroutines for each watcher and
+	// Now, we'll start all chain watchers in parallel to shorten start up
-	// arbitrator so they can carry out their duties.
+	// duration. In neutrino mode, this allows spend registrations to take
+	// advantage of batch spend reporting, instead of doing a single rescan
+	// per chain watcher.
+	//
+	// NOTE: After this point, we Stop the chain arb to ensure that any
+	// lingering goroutines are cleaned up before exiting.
+	watcherErrs := make(chan error, len(c.activeWatchers))
+	var wg sync.WaitGroup
 	for _, watcher := range c.activeWatchers {
-		if err := watcher.Start(); err != nil {
+		wg.Add(1)
+		go func(w *chainWatcher) {
+			defer wg.Done()
+			select {
+			case watcherErrs <- w.Start():
+			case <-c.quit:
+				watcherErrs <- ErrChainArbExiting
+			}
+		}(watcher)
+	}
+
+	// Once all chain watchers have been started, seal the err chan to
+	// signal the end of the err stream.
+	go func() {
+		wg.Wait()
+		close(watcherErrs)
+	}()
+
+	// Handle all errors returned from spawning our chain watchers. If any
+	// of them failed, we will stop the chain arb to shutdown any active
+	// goroutines.
+	for err := range watcherErrs {
+		if err != nil {
+			c.Stop()
 			return err
 		}
 	}
+
+	// Finally, we'll launch all the goroutines for each arbitrator so they
+	// can carry out their duties.
 	for _, arbitrator := range c.activeChannels {
 		if err := arbitrator.Start(); err != nil {
+			c.Stop()
 			return err
 		}
 	}
@@ -573,7 +611,7 @@ func (c *ChainArbitrator) ForceCloseContract(chanPoint wire.OutPoint) (*wire.Msg
 		closeTx: respChan,
 	}:
 	case <-c.quit:
-		return nil, fmt.Errorf("ChainArbitrator shutting down")
+		return nil, ErrChainArbExiting
 	}
 
 	// We'll await two responses: the error response, and the transaction
@@ -584,14 +622,14 @@ func (c *ChainArbitrator) ForceCloseContract(chanPoint wire.OutPoint) (*wire.Msg
 			return nil, err
 		}
 	case <-c.quit:
-		return nil, fmt.Errorf("ChainArbitrator shutting down")
+		return nil, ErrChainArbExiting
 	}
 
 	var closeTx *wire.MsgTx
 	select {
 	case closeTx = <-respChan:
 	case <-c.quit:
-		return nil, fmt.Errorf("ChainArbitrator shutting down")
+		return nil, ErrChainArbExiting
 	}
 
 	// We'll attempt to disable the channel in the background to