Add --max-workers and heuristics for parallel operations

add a global flag for --max-workers so users can limit the number
of parallel operations for a given function.  also, when not limited
by max-workers, we implement a heuristic function that returns the
number of preferred parallel workers based on the number of CPUs and
the given operation.

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

1 files changed, 91 insertions, 0 deletions

diff --git a/cmd/podman/shared/parallel.go b/cmd/podman/shared/parallel.go
new file mode 100644
index 000000000..03eba2f0b
--- /dev/null
+++ b/cmd/podman/shared/parallel.go
@@ -0,0 +1,91 @@
+package shared
+
+import (
+	"runtime"
+	"sync"
+)
+
+type pFunc func() error
+
+// ParallelWorkerInput is a struct used to pass in a slice of parallel funcs to be
+// performed on a container ID
+type ParallelWorkerInput struct {
+	ContainerID  string
+	ParallelFunc pFunc
+}
+
+type containerError struct {
+	ContainerID string
+	Err         error
+}
+
+// ParallelWorker is a "threaded" worker that takes jobs from the channel "queue"
+func ParallelWorker(wg *sync.WaitGroup, jobs <-chan ParallelWorkerInput, results chan<- containerError) {
+	for j := range jobs {
+		err := j.ParallelFunc()
+		results <- containerError{ContainerID: j.ContainerID, Err: err}
+		wg.Done()
+	}
+}
+
+// ParallelExecuteWorkerPool takes container jobs and performs them in parallel.  The worker
+// int determines how many workers/threads should be premade.
+func ParallelExecuteWorkerPool(workers int, functions []ParallelWorkerInput) map[string]error {
+	var (
+		wg sync.WaitGroup
+	)
+
+	resultChan := make(chan containerError, len(functions))
+	results := make(map[string]error)
+	paraJobs := make(chan ParallelWorkerInput, 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 ParallelWorker(&wg, paraJobs, resultChan)
+	}
+
+	// Add jobs to the workers
+	for _, j := range functions {
+		j := j
+		wg.Add(1)
+		paraJobs <- j
+	}
+
+	close(paraJobs)
+	wg.Wait()
+
+	close(resultChan)
+	for ctrError := range resultChan {
+		results[ctrError.ContainerID] = ctrError.Err
+	}
+
+	return results
+}
+
+// Parallelize provides the maximum number of parallel workers (int) as calculated by a basic
+// heuristic. This can be overriden by the --max-workers primary switch to podman.
+func Parallelize(job string) int {
+	numCpus := runtime.NumCPU()
+	switch job {
+	case "stop":
+		if numCpus <= 2 {
+			return 4
+		} else {
+			return numCpus * 3
+		}
+	case "rm":
+		if numCpus <= 3 {
+			return numCpus * 3
+		} else {
+			return numCpus * 4
+		}
+	case "ps":
+		return 8
+	}
+	return 3
+}