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worker.go
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worker.go
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package machinery
import (
"errors"
"fmt"
"reflect"
"runtime/debug"
"github.com/RichardKnop/machinery/v1/backends"
"github.com/RichardKnop/machinery/v1/logger"
"github.com/RichardKnop/machinery/v1/signatures"
"github.com/RichardKnop/machinery/v1/utils"
)
// Worker represents a single worker process
type Worker struct {
server *Server
ConsumerTag string
}
// Launch starts a new worker process. The worker subscribes
// to the default queue and processes incoming registered tasks
func (worker *Worker) Launch() error {
cnf := worker.server.GetConfig()
broker := worker.server.GetBroker()
logger.Get().Printf("Launching a worker with the following settings:")
logger.Get().Printf("- Broker: %s", cnf.Broker)
logger.Get().Printf("- ResultBackend: %s", cnf.ResultBackend)
logger.Get().Printf("- Exchange: %s", cnf.Exchange)
logger.Get().Printf("- ExchangeType: %s", cnf.ExchangeType)
logger.Get().Printf("- DefaultQueue: %s", cnf.DefaultQueue)
logger.Get().Printf("- BindingKey: %s", cnf.BindingKey)
errorsChan := make(chan error)
go func() {
for {
retry, err := broker.StartConsuming(worker.ConsumerTag, worker)
if retry {
logger.Get().Printf("Going to retry launching the worker. Error: %v", err)
} else {
errorsChan <- err // stop the goroutine
return
}
}
}()
return <-errorsChan
}
// Quit tears down the running worker process
func (worker *Worker) Quit() {
worker.server.GetBroker().StopConsuming()
}
// Process handles received tasks and triggers success/error callbacks
func (worker *Worker) Process(signature *signatures.TaskSignature) 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
}
task, err := worker.server.GetRegisteredTask(signature.Name)
if err != nil {
return nil
}
backend := worker.server.GetBackend()
// Update task state to RECEIVED
if err = backend.SetStateReceived(signature); err != nil {
return fmt.Errorf("Set State Received: %v", err)
}
// Get task args and reflect them to proper types
reflectedTask := reflect.ValueOf(task)
reflectedArgs, err := ReflectArgs(signature.Args)
if err != nil {
worker.finalizeError(signature, err)
return fmt.Errorf("Reflect task args: %v", err)
}
// Update task state to STARTED
if err = backend.SetStateStarted(signature); err != nil {
return fmt.Errorf("Set State Started: %v", err)
}
// Call the task passing in the correct arguments
results, err := TryCall(reflectedTask, reflectedArgs)
if err != nil {
return worker.finalizeError(signature, err)
}
return worker.finalizeSuccess(signature, results[0])
}
// Task succeeded, update state and trigger success callbacks
func (worker *Worker) finalizeSuccess(signature *signatures.TaskSignature, result reflect.Value) error {
// Update task state to SUCCESS
backend := worker.server.GetBackend()
taskResult := CreateTaskResult(result)
if err := backend.SetStateSuccess(signature, taskResult); err != nil {
return fmt.Errorf("Set State Success: %v", err)
}
logger.Get().Printf("Processed %s. Result = %v", signature.UUID, taskResult.Value)
// Trigger success callbacks
for _, successTask := range signature.OnSuccess {
if signature.Immutable == false {
// Pass results of the task to success callbacks
args := append([]signatures.TaskArg{{
Type: taskResult.Type,
Value: taskResult.Value,
}}, successTask.Args...)
successTask.Args = args
}
worker.server.SendTask(successTask)
}
// If the task was not part of a group, just return
if signature.GroupUUID == "" {
return nil
}
// Check if all task in the group has completed
groupCompleted, err := worker.server.GetBackend().GroupCompleted(
signature.GroupUUID,
signature.GroupTaskCount,
)
if err != nil {
return fmt.Errorf("GroupCompleted: %v", err)
}
// If the group has not yet completed, just return
if !groupCompleted {
return nil
}
// Defer purging of group meta queue if we are using AMQP backend
if worker.hasAMQPBackend() {
defer worker.server.backend.PurgeGroupMeta(signature.GroupUUID)
}
// There is no chord callback, just return
if signature.ChordCallback == nil {
return nil
}
// Trigger chord callback
shouldTrigger, err := worker.server.backend.TriggerChord(signature.GroupUUID)
if err != nil {
return fmt.Errorf("TriggerChord: %v", err)
}
// Chord has already been triggered
if !shouldTrigger {
return nil
}
// Get task states
taskStates, err := worker.server.GetBackend().GroupTaskStates(
signature.GroupUUID,
signature.GroupTaskCount,
)
if err != nil {
return nil
}
// Append group tasks' return values to chord task if it's not immutable
for _, taskState := range taskStates {
if !taskState.IsSuccess() {
return nil
}
if signature.ChordCallback.Immutable == false {
// Pass results of the task to the chord callback
signature.ChordCallback.Args = append(signature.ChordCallback.Args, signatures.TaskArg{
Type: taskState.Result.Type,
Value: taskState.Result.Value,
})
}
}
// Send the chord task
_, err = worker.server.SendTask(signature.ChordCallback)
if err != nil {
return err
}
return nil
}
// Task failed, update state and trigger error callbacks
func (worker *Worker) finalizeError(signature *signatures.TaskSignature, err error) error {
// Update task state to FAILURE
backend := worker.server.GetBackend()
if err1 := backend.SetStateFailure(signature, err.Error()); err1 != nil {
return fmt.Errorf("Set State Failure: %v", err1)
}
logger.Get().Printf("Failed processing %s. Error = %v", signature.UUID, err)
// Trigger error callbacks
for _, errorTask := range signature.OnError {
// Pass error as a first argument to error callbacks
args := append([]signatures.TaskArg{{
Type: "string",
Value: err.Error(),
}}, errorTask.Args...)
errorTask.Args = args
worker.server.SendTask(errorTask)
}
return nil
}
// Returns true if the worker uses AMQP backend
func (worker *Worker) hasAMQPBackend() bool {
_, ok := worker.server.backend.(*backends.AMQPBackend)
return ok
}
// ReflectArgs converts []TaskArg to []reflect.Value
func ReflectArgs(args []signatures.TaskArg) ([]reflect.Value, error) {
argValues := make([]reflect.Value, len(args))
for i, arg := range args {
argValue, err := utils.ReflectValue(arg.Type, arg.Value)
if err != nil {
return nil, err
}
argValues[i] = argValue
}
return argValues, nil
}
// TryCall attempts to call the task with the supplied arguments.
//
// `err` is set in the return value in two cases:
// 1. The reflected function invocation panics (e.g. due to a mismatched
// argument list).
// 2. The task func itself returns a non-nil error.
func TryCall(f reflect.Value, args []reflect.Value) (results []reflect.Value, err error) {
defer func() {
// Recover from panic and set err.
if e := recover(); e != nil {
switch e := e.(type) {
default:
err = errors.New("Invoking task caused a panic")
case error:
err = e
case string:
err = errors.New(e)
}
// Print stack trace
logger.Get().Printf("%s", debug.Stack())
}
}()
results = f.Call(args)
// If an error was returned by the task func, propagate it
// to the caller via err.
if !results[1].IsNil() {
return nil, results[1].Interface().(error)
}
return results, err
}
// CreateTaskResult ...
func CreateTaskResult(value reflect.Value) *backends.TaskResult {
return &backends.TaskResult{
Type: reflect.TypeOf(value.Interface()).String(),
Value: value.Interface(),
}
}