聊聊machinery的TaskProcessor

序

本文主要研究一下machinery的TaskProcessor

TaskProcessor

// TaskProcessor - can process a delivered task
// This will probably always be a worker instance
type TaskProcessor interface {
    Process(signature *tasks.Signature) error
    CustomQueue() string
    PreConsumeHandler() bool
}

TaskProcessor接口定義了Process、CustomQueue、PreConsumeHandler方法

Worker

// Worker represents a single worker process
type Worker struct {
    server            *Server
    ConsumerTag       string
    Concurrency       int
    Queue             string
    errorHandler      func(err error)
    preTaskHandler    func(*tasks.Signature)
    postTaskHandler   func(*tasks.Signature)
    preConsumeHandler func(*Worker) bool
}

// CustomQueue returns Custom Queue of the running worker process
func (worker *Worker) CustomQueue() string {
    return worker.Queue
}

// Process handles received tasks and triggers success/error callbacks
func (worker *Worker) Process(signature *tasks.Signature) error {
    // If the task is not registered with this worker, do not continue
    // but only return nil as we do not want to restart the worker process
    if !worker.server.IsTaskRegistered(signature.Name) {
        return nil
    }

    taskFunc, err := worker.server.GetRegisteredTask(signature.Name)
    if err != nil {
        return nil
    }

    // Update task state to RECEIVED
    if err = worker.server.GetBackend().SetStateReceived(signature); err != nil {
        return fmt.Errorf("Set state to 'received' for task %s returned error: %s", signature.UUID, err)
    }

    // Prepare task for processing
    task, err := tasks.NewWithSignature(taskFunc, signature)
    // if this failed, it means the task is malformed, probably has invalid
    // signature, go directly to task failed without checking whether to retry
    if err != nil {
        worker.taskFailed(signature, err)
        return err
    }

    // try to extract trace span from headers and add it to the function context
    // so it can be used inside the function if it has context.Context as the first
    // argument. Start a new span if it isn't found.
    taskSpan := tracing.StartSpanFromHeaders(signature.Headers, signature.Name)
    tracing.AnnotateSpanWithSignatureInfo(taskSpan, signature)
    task.Context = opentracing.ContextWithSpan(task.Context, taskSpan)

    // Update task state to STARTED
    if err = worker.server.GetBackend().SetStateStarted(signature); err != nil {
        return fmt.Errorf("Set state to 'started' for task %s returned error: %s", signature.UUID, err)
    }

    //Run handler before the task is called
    if worker.preTaskHandler != nil {
        worker.preTaskHandler(signature)
    }

    //Defer run handler for the end of the task
    if worker.postTaskHandler != nil {
        defer worker.postTaskHandler(signature)
    }

    // Call the task
    results, err := task.Call()
    if err != nil {
        // If a tasks.ErrRetryTaskLater was returned from the task,
        // retry the task after specified duration
        retriableErr, ok := interface{}(err).(tasks.ErrRetryTaskLater)
        if ok {
            return worker.retryTaskIn(signature, retriableErr.RetryIn())
        }

        // Otherwise, execute default retry logic based on signature.RetryCount
        // and signature.RetryTimeout values
        if signature.RetryCount > 0 {
            return worker.taskRetry(signature)
        }

        return worker.taskFailed(signature, err)
    }

    return worker.taskSucceeded(signature, results)
}

//SetPreConsumeHandler sets a custom handler for the end of a job
func (worker *Worker) SetPreConsumeHandler(handler func(*Worker) bool) {
    worker.preConsumeHandler = handler
}

Worker實現了TaskProcessor接口，其Process方法先經過worker.server.GetRegisteredTask獲取taskFunc，而後經過signature更新state爲RECEIVED，以後設置爲STARTED，以後執行task.Call()，最後根據結果更新task爲failed或者success

小結

machinery的TaskProcessor接口定義了Process、CustomQueue、PreConsumeHandler方法。Worker實現了TaskProcessor接口，其Process方法先經過worker.server.GetRegisteredTask獲取taskFunc，而後經過signature更新state爲RECEIVED，以後設置爲STARTED，以後執行task.Call()，最後根據結果更新task爲failed或者success。

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• machinery