replace async client API / federator msg processing with worker pools (#497)

* replace async client API / federator msg processing with worker pools
* appease our lord-and-saviour, the linter

internal/worker/workers.go

@@ -0,0 +1,69 @@
+package worker
+
+import (
+	"context"
+	"errors"
+	"runtime"
+
+	"codeberg.org/gruf/go-runners"
+	"github.com/sirupsen/logrus"
+)
+
+// Worker represents a proccessor for MsgType objects, using a worker pool to allocate resources.
+type Worker[MsgType any] struct {
+	workers runners.WorkerPool
+	process func(context.Context, MsgType) error
+}
+
+// New returns a new Worker[MsgType] with given number of workers and queue size
+// (see runners.WorkerPool for more information on args). If args < 1 then suitable
+// defaults are determined from the runtime's GOMAXPROCS variable.
+func New[MsgType any](workers int, queue int) *Worker[MsgType] {
+	if workers < 1 {
+		workers = runtime.GOMAXPROCS(0)
+	}
+	if queue < 1 {
+		queue = workers * 100
+	}
+	return &Worker[MsgType]{
+		workers: runners.NewWorkerPool(workers, queue),
+		process: nil,
+	}
+}
+
+// Start will attempt to start the underlying worker pool, or return error.
+func (w *Worker[MsgType]) Start() error {
+	if w.process == nil {
+		return errors.New("nil Worker.process function")
+	}
+	if !w.workers.Start() {
+		return errors.New("failed to start Worker pool")
+	}
+	return nil
+}
+
+// Stop will attempt to stop the underlying worker pool, or return error.
+func (w *Worker[MsgType]) Stop() error {
+	if !w.workers.Stop() {
+		return errors.New("failed to stop Worker pool")
+	}
+	return nil
+}
+
+// SetProcessor will set the Worker's processor function, which is called for each queued message.
+func (w *Worker[MsgType]) SetProcessor(fn func(context.Context, MsgType) error) {
+	if w.process != nil {
+		logrus.Panic("Worker.process is already set")
+	}
+	w.process = fn
+}
+
+// Queue will queue provided message to be processed with there's a free worker.
+func (w *Worker[MsgType]) Queue(msg MsgType) {
+	logrus.Tracef("queueing %[1]T message; %+[1]v", msg)
+	w.workers.Enqueue(func(ctx context.Context) {
+		if err := w.process(ctx, msg); err != nil {
+			logrus.Error(err)
+		}
+	})
+}