eth/downloader: wait for all fetcher goroutines to exit before termin…

…ating (#16509)

eth/downloader/downloader.go

@@ -135,9 +135,10 @@ type Downloader struct {
 	stateCh        chan dataPack // [eth/63] Channel receiving inbound node state data
 
 	// Cancellation and termination
-	cancelPeer string        // Identifier of the peer currently being used as the master (cancel on drop)
-	cancelCh   chan struct{} // Channel to cancel mid-flight syncs
-	cancelLock sync.RWMutex  // Lock to protect the cancel channel and peer in delivers
+	cancelPeer string         // Identifier of the peer currently being used as the master (cancel on drop)
+	cancelCh   chan struct{}  // Channel to cancel mid-flight syncs
+	cancelLock sync.RWMutex   // Lock to protect the cancel channel and peer in delivers
+	cancelWg   sync.WaitGroup // Make sure all fetcher goroutines have exited.
 
 	quitCh   chan struct{} // Quit channel to signal termination
 	quitLock sync.RWMutex  // Lock to prevent double closes
@@ -476,12 +477,11 @@ func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td *big.I
 // spawnSync runs d.process and all given fetcher functions to completion in
 // separate goroutines, returning the first error that appears.
 func (d *Downloader) spawnSync(fetchers []func() error) error {
-	var wg sync.WaitGroup
 	errc := make(chan error, len(fetchers))
-	wg.Add(len(fetchers))
+	d.cancelWg.Add(len(fetchers))
 	for _, fn := range fetchers {
 		fn := fn
-		go func() { defer wg.Done(); errc <- fn() }()
+		go func() { defer d.cancelWg.Done(); errc <- fn() }()
 	}
 	// Wait for the first error, then terminate the others.
 	var err error
@@ -498,12 +498,10 @@ func (d *Downloader) spawnSync(fetchers []func() error) error {
 	}
 	d.queue.Close()
 	d.Cancel()
-	wg.Wait()
 	return err
 }
 
-// Cancel cancels all of the operations and resets the queue. It returns true
-// if the cancel operation was completed.
+// Cancel cancels all of the operations and resets the queue.
 func (d *Downloader) Cancel() {
 	// Close the current cancel channel
 	d.cancelLock.Lock()
@@ -516,6 +514,7 @@ func (d *Downloader) Cancel() {
 		}
 	}
 	d.cancelLock.Unlock()
+	d.cancelWg.Wait()
 }
 
 // Terminate interrupts the downloader, canceling all pending operations.