Golang Datastore.GetMulti方法代碼示例

func gatherTasks(ds appwrap.Datastore, job JobInfo) ([]JobTask, error) {
	taskKeys := makeTaskKeys(ds, job.FirstTaskId, job.TaskCount)
	tasks := make([]JobTask, len(taskKeys))

	i := 0
	for i < len(taskKeys) {
		last := i + 100
		if last > len(taskKeys) {
			last = len(taskKeys)
		}

		if err := ds.GetMulti(taskKeys[i:last], tasks[i:last]); err != nil {
			return nil, err
		}

		i = last
	}

	return tasks, nil
}

// check if the specified job has completed. it should currently be at expectedStage, and if it's been completed
// we advance it to next stage. if it's already at nextStage another process has beaten us to it so we're done
//
// caller needs to check the stage in the final job; if stageChanged is true it will be either nextStage or StageFailed.
// If StageFailed then at least one of the underlying tasks failed and the reason will appear as a taskError{} in err
func jobStageComplete(c context.Context, ds appwrap.Datastore, jobKey *datastore.Key, taskKeys []*datastore.Key, expectedStage, nextStage JobStage) (stageChanged bool, job JobInfo, finalErr error) {
	last := len(taskKeys)
	tasks := make([]JobTask, 100)
	for last > 0 {
		first := last - 100
		if first < 0 {
			first = 0
		}

		taskCount := last - first

		if err := ds.GetMulti(taskKeys[first:last], tasks[0:taskCount]); err != nil {
			finalErr = err
			return
		} else {
			for i := 0; i < taskCount; i++ {
				if tasks[i].Status == TaskStatusFailed {
					logInfo(c, "failed tasks found")
					nextStage = StageFailed
					last = -1
					finalErr = taskError{tasks[i].Info}
					break
				} else if tasks[i].Status != TaskStatusDone {
					return
				}
			}

			if last >= 0 {
				last = first
			}
		}
	}

	// running this in a transaction ensures only one process advances the stage
	if transErr := runInTransaction(ds, func(ds appwrap.Datastore) error {
		job = JobInfo{}
		if err := ds.Get(jobKey, &job); err != nil {
			return err
		}

		if job.Stage != expectedStage {
			// we're not where we expected, so advancing this isn't our responsibility
			stageChanged = false
			return errMonitorJobConflict
		}

		job.Stage = nextStage
		job.UpdatedAt = time.Now()

		_, err := ds.Put(jobKey, &job)
		stageChanged = (err == nil)
		return err
	}); transErr != nil {
		finalErr = transErr
	}

	if finalErr != nil {
		logCritical(c, "taskComplete failed: %s", finalErr)
	} else {
		logInfo(c, "task is complete")
	}

	return
}