UE4 Twitch 2016 05-05: Unreal Message Bus Overview

UE4 Twitch Stream 5/5/2016Unreal Message Bus Overview

Gerke Max [email protected]

@gmpreussner

Process

MessageEndpoints

Message Bus

Message Bus:Framework for exchanging commands, events, documents, or any other data

inside UStructs between endpoints

USTRUCT()struct FHelloMessage{ GENERATED_BODY()

UPROPERTY(EditAnywhere, Category=“Message”) FString HelloText;

FHelloMessage(const FString& InText) : HelloText(InText) { }};

Declare a message type (you can also use any existing UStruct, such as FVector or FColor)

Process

SenderEndpoint = FMessageEndpoint::Builder(“FMySender”, MessageBus);

ReceiverEndpoint = FMessageEndpoint::Builder(“FMyReceiver”, MessageBus) .Handling<FHelloMessage>(this, &FMyReceiver::HandleHelloMessage);

Create a sender endpoint

Create a receiver endpoint

Message Endpoints:Helper classes for sending and receiving

messages on the message bus

Process

Subscribers

Publisher



if (ReceiverEndpoint.IsValid()){ ReceiverEndpoint->Subscribe<FHelloMessage>();}

SenderEndpoint.Publish(new FHelloMessage(TEXT(“Hey there!”)));

void FMyReceiver::HandleHelloMessage(const FHelloMessage& Message, const TSharedRef<IMessageContextRef>& Context){ GLog->Log(*Message.HelloText); // prints “Hey there!” }

Subscribe receiver to FHelloMessage messages

Publish a message to all subscribers

Handle received FHelloMessage

Publish-Subscribe:Messages are sent to all endpoints that

subscribed to that message type

Process

Responder

Requester



if (ReceiverEndpoint.IsValid()){ ReeiverEndpoint->Subscribe<FHelloMessage>();}

SenderEndpoint.Publish(new FHelloMessage(TEXT(“Hey there!”)));

void FMyReceiver::HandleHelloMessage(const FHelloMessage& Message, const TSharedRef<IMessageContextRef>& Context){ SenderEndpoint->Send(new FReplyMessage(TEXT(“O hai!”)), Context->GetSender());}

Send back a response

Request-Response:Messages are sent directly to one or more

recipients using their message address

Process Process

Message Bridge

Message Bridges:Connect two message buses in separate processes via some transport technology

Process Process

UDPTCP

HTTPNamed PipesShared Mem

ZeroMQRabbitMQ

etc.

Message Bridges:Connect two message buses in separate processes via some transport technology

Computer

Computer

Computer

Process Process Process

Process

Internet(via Message Tunnel)

UE4 Instance3DStudio MaxMayaBuild FarmHardware I/Oetc.

The following slides explain UE4’s layered architecture for device managementas a more complex example use case for how the Messaging system can be usedto simplify the process of writing distributed applications.

The diagrams show how the same code architecture is being used to support anumber of different hardware configurations.

The last slide shows how the function calls flow through the various layers. Notethat some of this code has changed over the course of the last year. The intent isto demonstrate how interprocess communication can be implemented, and howfunction calls change to messages and back to function calls.

Use

r PC

Host

PC

ITargetDevice

ITargetDeviceService

ITargetDeviceProxy

Devi

ce

Application

Platform specific interfaces

Platform agnostic interfaces

Physical Tier

Legend:

Target Device ManagementUses a multi-layered multi-tier

architecture instead of having the application talk directly to the devices

MessageBus

Platform SDK

Devi

ce Daemon

Use

r PC

Host

PC

ITargetDevice


ITargetDeviceProxy

MessageBus

IPP

Application

Message Bus

Use

r PC

Host

PC

ITargetDevice


ITargetDeviceProxy

Devi

ce

Application

Platform specific interfaces

Platform agnostic interfaces

Physical Tier

Legend:

• Target devices are usually connectedto some host computer and communicatevia some platform SDK

Example: XBoxOne, PS4

• Some target devices can be deployed towithout a host computer if they have anetwork connection

Example: Windows, Mac, iPad, iPhone

MessageBus

Platform SDK

Use

r / H

ost P

C

ITargetDevice


ITargetDeviceProxy

Devi

ce

MessageBus

Platform SDK

Application

Use

r PC

Host

PC

/ Dev

ice

ITargetDevice


ITargetDeviceProxy

MessageBus

Application

Use

r PC

/ Hos

t PC

/ Dev

ice

ITargetDevice


ITargetDeviceProxy

MessageBus

Application

Use

r PC

Host

PC

ITargetDevice


ITargetDeviceProxy

Devi

ce

MessageBus

Platform SDK

Application

• Target device is another computer

Example: Deploying to another PC

• Target device is the local computer

Example: Deploying to your own PC

• Target device is another deviceconnected to the local PC

Example: iPhone, iPad on yourown computer

• Target device is another deviceconnected to another PC

Example: iPhone, iPad on someoneelse’s computer

Application ILauncher

Launch()

FLauncherWorker

Run()

ITargetDeviceProxy

PerformTask()

FLauncherDeployToDeviceTask

DeployApp(TransactionId)


targetdevice.deploy.file

targetdevice.deploy.commit

ITargetDevice

LocalFile

Cache

Deploy(Directory)

IPP iOS Device

Copy FilesDeploy Files

targetdevice.deploy.finished (AppId)

OnDeployCommitted(TransactionId, AppId)

Deploy

Launch

FLauncherLaunchTask

PerformTask()LaunchApp(AppId)

targetdevice.launchLaunch(AppId)

Launch Daemon

iosdaemon.launch [Url]

iosdaemon.launch .successtargetdevice.launch.finished

return AppId DeviceFile

System

Message Bus

Function Call

Vendor Specific

Legend:

UE4 Twitch 2016 05-05: Unreal Message Bus Overview

Software

Transcript of UE4 Twitch 2016 05-05: Unreal Message Bus Overview