Add "tumble" distributed transaction processing service for appengine.

appengine/tumble/fire_tasks.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package tumble
+
+import (
+        "fmt"
+        "net/http"
+
+        "github.com/julienschmidt/httprouter"
+        "github.com/luci/gae/service/taskqueue"
+        "github.com/luci/luci-go/common/clock"
+        "github.com/luci/luci-go/common/errors"
+        "github.com/luci/luci-go/common/logging"
+        "golang.org/x/net/context"
+)
+
+func fireTasks(c context.Context, shards map[uint64]struct{}) bool {
+        if len(shards) == 0 {
+                return true
+        }
+
+        tq := taskqueue.Get(c)
+
+        cfg := GetConfig(c)
+
+        trf := cfg.TemporalRoundFactor
+        eta := clock.Now(c).UTC().Add(cfg.TemporalMinDelay + trf).Round(trf)
+        tasks := make([]*taskqueue.Task, 0, len(shards))
+
+        for shard := range shards {
+                tasks = append(tasks, &taskqueue.Task{
+                        Name: fmt.Sprintf("%d_%d", eta.Unix(), shard),
+
+                        Path: cfg.ProcessURL(eta, shard),
+
+                        ETA: eta,
+
+                        // TODO(riannucci): Tune RetryOptions?
+                })
+        }
+
+        err := tq.AddMulti(tasks, cfg.Name)
+        if err != nil {
+                if merr, ok := err.(errors.MultiError); ok {
+                        lme := errors.NewLazyMultiError(len(merr))
+                        for i, err := range merr {
+                                if err == taskqueue.ErrTaskAlreadyAdded {
+                                        continue
+                                }
+                                lme.Assign(i, err)
+                        }
+                        err = lme.Get()
+                }
+                if err != nil {
+                        logging.Warningf(c, "attempted to fire tasks %v, but failed: %s", shards, err)
+                }
+        }
+        return err == nil
+}
+
+// FireAllTasks fires off 1 task per shard to ensure that no tumble work
+// languishes forever. This may not be needed in a constantly-loaded system with
+// good tumble key distribution.
+func FireAllTasks(c context.Context) error {
+        num := GetConfig(c).NumShards
+        shards := make(map[uint64]struct{}, num)
+        for i := uint64(0); i < num; i++ {
+                shards[i] = struct{}{}
+        }
+
+        err := error(nil)
+        if !fireTasks(c, shards) {
+                err = errors.New("unable to fire all tasks")
+        }
+
+        return err
+}
+
+// FireAllTasksHandler is a http handler suitable for installation into
+// a httprouter. It expects `logging` and `luci/gae` services to be installed
+// into the context.
+//
+// FireAllTasksHandler verifies that it was called within an Appengine Cron
+// request, and then invokes the FireAllTasks function.
+func FireAllTasksHandler(c context.Context, rw http.ResponseWriter, r *http.Request, _ httprouter.Params) {
+        if err := FireAllTasks(c); err != nil {
+                rw.WriteHeader(http.StatusInternalServerError)
+                fmt.Fprintf(rw, "fire_all_tasks failed: %s", err)
+        } else {
+                rw.Write([]byte("ok"))
+        }
+}