聊聊machinery的TaskState

序

本文主要研究一下machinery的TaskState

TaskState

const (
    // StatePending - initial state of a task
    StatePending = "PENDING"
    // StateReceived - when task is received by a worker
    StateReceived = "RECEIVED"
    // StateStarted - when the worker starts processing the task
    StateStarted = "STARTED"
    // StateRetry - when failed task has been scheduled for retry
    StateRetry = "RETRY"
    // StateSuccess - when the task is processed successfully
    StateSuccess = "SUCCESS"
    // StateFailure - when processing of the task fails
    StateFailure = "FAILURE"
)

type TaskState struct {
    TaskUUID  string        `bson:"_id"`
    TaskName  string        `bson:"task_name"`
    State     string        `bson:"state"`
    Results   []*TaskResult `bson:"results"`
    Error     string        `bson:"error"`
    CreatedAt time.Time     `bson:"created_at"`
    TTL       int64         `bson:"ttl,omitempty"`
}

type TaskResult struct {
    Type  string      `bson:"type"`
    Value interface{} `bson:"value"`
}

// NewPendingTaskState ...
func NewPendingTaskState(signature *Signature) *TaskState {
    return &TaskState{
        TaskUUID:  signature.UUID,
        TaskName:  signature.Name,
        State:     StatePending,
        CreatedAt: time.Now().UTC(),
    }
}

// NewReceivedTaskState ...
func NewReceivedTaskState(signature *Signature) *TaskState {
    return &TaskState{
        TaskUUID: signature.UUID,
        State:    StateReceived,
    }
}

// NewStartedTaskState ...
func NewStartedTaskState(signature *Signature) *TaskState {
    return &TaskState{
        TaskUUID: signature.UUID,
        State:    StateStarted,
    }
}

// NewSuccessTaskState ...
func NewSuccessTaskState(signature *Signature, results []*TaskResult) *TaskState {
    return &TaskState{
        TaskUUID: signature.UUID,
        State:    StateSuccess,
        Results:  results,
    }
}

// NewFailureTaskState ...
func NewFailureTaskState(signature *Signature, err string) *TaskState {
    return &TaskState{
        TaskUUID: signature.UUID,
        State:    StateFailure,
        Error:    err,
    }
}

// NewRetryTaskState ...
func NewRetryTaskState(signature *Signature) *TaskState {
    return &TaskState{
        TaskUUID: signature.UUID,
        State:    StateRetry,
    }
}

// IsCompleted returns true if state is SUCCESS or FAILURE,
// i.e. the task has finished processing and either succeeded or failed.
func (taskState *TaskState) IsCompleted() bool {
    return taskState.IsSuccess() || taskState.IsFailure()
}

// IsSuccess returns true if state is SUCCESS
func (taskState *TaskState) IsSuccess() bool {
    return taskState.State == StateSuccess
}

// IsFailure returns true if state is FAILURE
func (taskState *TaskState) IsFailure() bool {
    return taskState.State == StateFailure
}

TaskState定義了PENDING、RECEIVED、STARTED、RETRY、SUCCESS、FAILURE狀態；TaskState定義了TaskUUID、TaskName、State、Results、Error、CreatedAt、TTL屬性；它提供了NewPendingTaskState、NewReceivedTaskState、NewStartedTaskState、NewSuccessTaskState、NewFailureTaskState、NewRetryTaskState方法來根據Signature來建立不一樣state的TaskState；另外還提供了IsCompleted、IsSuccess、IsFailure方法

Signature

// Signature represents a single task invocation
type Signature struct {
    UUID           string
    Name           string
    RoutingKey     string
    ETA            *time.Time
    GroupUUID      string
    GroupTaskCount int
    Args           []Arg
    Headers        Headers
    Priority       uint8
    Immutable      bool
    RetryCount     int
    RetryTimeout   int
    OnSuccess      []*Signature
    OnError        []*Signature
    ChordCallback  *Signature
    //MessageGroupId for Broker, e.g. SQS
    BrokerMessageGroupId string
    //ReceiptHandle of SQS Message
    SQSReceiptHandle string
    // StopTaskDeletionOnError used with sqs when we want to send failed messages to dlq,
    // and don't want machinery to delete from source queue
    StopTaskDeletionOnError bool
    // IgnoreWhenTaskNotRegistered auto removes the request when there is no handeler available
    // When this is true a task with no handler will be ignored and not placed back in the queue
    IgnoreWhenTaskNotRegistered bool
}

// Arg represents a single argument passed to invocation fo a task
type Arg struct {
    Name  string      `bson:"name"`
    Type  string      `bson:"type"`
    Value interface{} `bson:"value"`
}

// Headers represents the headers which should be used to direct the task
type Headers map[string]interface{}

// NewSignature creates a new task signature
func NewSignature(name string, args []Arg) (*Signature, error) {
    signatureID := uuid.New().String()
    return &Signature{
        UUID: fmt.Sprintf("task_%v", signatureID),
        Name: name,
        Args: args,
    }, nil
}

Signature表明對task的調用，它定義了UUID、Name、RoutingKey、ETA、GroupUUID、GroupTaskCount、Args、Headers、Priority、Immutable、RetryCount、RetryTimeout、OnSuccess、OnError、ChordCallback、BrokerMessageGroupId、SQSReceiptHandle、StopTaskDeletionOnError、IgnoreWhenTaskNotRegistered屬性

Backend

// Backend represents a Redis result backend
type Backend struct {
    common.Backend
    host     string
    password string
    db       int
    pool     *redis.Pool
    // If set, path to a socket file overrides hostname
    socketPath string
    redsync    *redsync.Redsync
    redisOnce  sync.Once
    common.RedisConnector
}

// SetStatePending updates task state to PENDING
func (b *Backend) SetStatePending(signature *tasks.Signature) error {
    conn := b.open()
    defer conn.Close()

    taskState := tasks.NewPendingTaskState(signature)
    return b.updateState(conn, taskState)
}

// SetStateReceived updates task state to RECEIVED
func (b *Backend) SetStateReceived(signature *tasks.Signature) error {
    conn := b.open()
    defer conn.Close()

    taskState := tasks.NewReceivedTaskState(signature)
    b.mergeNewTaskState(conn, taskState)
    return b.updateState(conn, taskState)
}

// SetStateStarted updates task state to STARTED
func (b *Backend) SetStateStarted(signature *tasks.Signature) error {
    conn := b.open()
    defer conn.Close()

    taskState := tasks.NewStartedTaskState(signature)
    b.mergeNewTaskState(conn, taskState)
    return b.updateState(conn, taskState)
}

// SetStateRetry updates task state to RETRY
func (b *Backend) SetStateRetry(signature *tasks.Signature) error {
    conn := b.open()
    defer conn.Close()

    taskState := tasks.NewRetryTaskState(signature)
    b.mergeNewTaskState(conn, taskState)
    return b.updateState(conn, taskState)
}

// SetStateSuccess updates task state to SUCCESS
func (b *Backend) SetStateSuccess(signature *tasks.Signature, results []*tasks.TaskResult) error {
    conn := b.open()
    defer conn.Close()

    taskState := tasks.NewSuccessTaskState(signature, results)
    b.mergeNewTaskState(conn, taskState)
    return b.updateState(conn, taskState)
}

// SetStateFailure updates task state to FAILURE
func (b *Backend) SetStateFailure(signature *tasks.Signature, err string) error {
    conn := b.open()
    defer conn.Close()

    taskState := tasks.NewFailureTaskState(signature, err)
    b.mergeNewTaskState(conn, taskState)
    return b.updateState(conn, taskState)
}

// GetState returns the latest task state
func (b *Backend) GetState(taskUUID string) (*tasks.TaskState, error) {
    conn := b.open()
    defer conn.Close()

    return b.getState(conn, taskUUID)
}

此Backend是基於Redis實現的，它提供了SetStatePending、SetStateReceived、SetStateStarted、SetStateRetry、SetStateSuccess、SetStateFailure、GetState方法

小結

machinery的TaskState定義了PENDING、RECEIVED、STARTED、RETRY、SUCCESS、FAILURE狀態；TaskState定義了TaskUUID、TaskName、State、Results、Error、CreatedAt、TTL屬性；它提供了NewPendingTaskState、NewReceivedTaskState、NewStartedTaskState、NewSuccessTaskState、NewFailureTaskState、NewRetryTaskState方法來根據Signature來建立不一樣state的TaskState；另外還提供了IsCompleted、IsSuccess、IsFailure方法。

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