Fix deploy --dry-run deadlock

Once we got over 1000 items in our deploy list, we deadlocked because nothing consumes the channel until we're done with the "queue everything up" loop, so we need to start consuming that list right away instead.  As long as it's part of our waitgroup, this should be fine and work correctly.

Author: tianon

cmd/deploy/main.go

@@ -22,8 +22,7 @@ func main() {
 		args = os.Args[1:]
 
 		// --dry-run
-		dryRun     bool
-		dryRunOuts chan chan []byte
+		dryRun bool
 
 		// --parallel
 		parallel bool
@@ -35,8 +34,6 @@ func main() {
 		switch arg {
 		case "--dry-run":
 			dryRun = true
-			// we want to allow parallel, but want the output to be in-order so we resynchronize output with a channel of channels (technically this also limits parallelization, but hopefully this limit is generous enough that it doesn't matter)
-			dryRunOuts = make(chan chan []byte, 1000)
 
 		case "--parallel":
 			parallel = true
@@ -68,6 +65,27 @@ func main() {
 	childMutexes := sync.Map{}
 	wg := sync.WaitGroup{}
 
+	var dryRunOuts chan chan []byte
+	if dryRun {
+		// we want to allow parallel, but want the output to be in-order so we resynchronize output with a channel of channels (technically this also limits parallelization, but hopefully this limit is generous enough that it doesn't matter)
+		dryRunOuts = make(chan chan []byte, 100000)
+
+		// we also have to start consuming that channel immediately, just in case we *do* hit that parallelization limit 🙈
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+
+			for dryRunOut := range dryRunOuts {
+				j, ok := <-dryRunOut
+				if !ok {
+					// (I think) this means we didn't output anything, so this should be all our "skips"
+					continue
+				}
+				fmt.Printf("%s\n", j)
+			}
+		}()
+	}
+
 	dec := json.NewDecoder(stdout)
 	for dec.More() {
 		var raw inputRaw
@@ -240,17 +258,7 @@ func main() {
 		}
 	}
 
-	if dryRun {
-		close(dryRunOuts)
-		for dryRunOut := range dryRunOuts {
-			j, ok := <-dryRunOut
-			if !ok {
-				// (I think) this means we didn't output anything, so this should be all our "skips"
-				continue
-			}
-			fmt.Printf("%s\n", j)
-		}
-	}
+	close(dryRunOuts)
 
 	wg.Wait()
 }