Stop containers in parallel fashion

Prior, we were stopping containers serially.  So if a container had a default
timeout of 10 seconds and there were five containers being stopped, the operation
would take roughly 50 seconds.  If we stop these containers in parallel, the operation
should be roughly 10 seconds and change which is a significant speed up at scale.

Signed-off-by: baude <bbaude@redhat.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/cmd/podman/utils.go b/cmd/podman/utils.go
index 89ec48dbe..1b767532e 100644
--- a/cmd/podman/utils.go
+++ b/cmd/podman/utils.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	gosignal "os/signal"
+	"sync"
 
 	"github.com/containers/libpod/libpod"
 	"github.com/docker/docker/pkg/signal"
@@ -215,3 +216,50 @@ func getPodsFromContext(c *cli.Context, r *libpod.Runtime) ([]*libpod.Pod, error
 	}
 	return pods, lastError
 }
+
+type pFunc func() error
+
+type workerInput struct {
+	containerID  string
+	parallelFunc pFunc
+}
+
+// worker is a "threaded" worker that takes jobs from the channel "queue"
+func worker(wg *sync.WaitGroup, jobs <-chan workerInput, results map[string]error) {
+	for j := range jobs {
+		err := j.parallelFunc()
+		results[j.containerID] = err
+		wg.Done()
+	}
+}
+
+// parallelExecuteWorkerPool takes container jobs and performs them in parallel.  The worker
+// int is determines how many workers/threads should be premade.
+func parallelExecuteWorkerPool(workers int, functions []workerInput) map[string]error {
+	var (
+		wg sync.WaitGroup
+	)
+	results := make(map[string]error)
+	paraJobs := make(chan workerInput, len(functions))
+
+	// If we have more workers than functions, match up the number of workers and functions
+	if workers > len(functions) {
+		workers = len(functions)
+	}
+
+	// Create the workers
+	for w := 1; w <= workers; w++ {
+		go worker(&wg, paraJobs, results)
+	}
+
+	// Add jobs to the workers
+	for _, j := range functions {
+		j := j
+		wg.Add(1)
+		paraJobs <- j
+	}
+
+	close(paraJobs)
+	wg.Wait()
+	return results
+}