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Diffstat (limited to 'devtools/server/docs')
| -rw-r--r-- | devtools/server/docs/actor-e10s-handling.md | 106 | ||||
| -rw-r--r-- | devtools/server/docs/actor-hierarchy.md | 129 | ||||
| -rw-r--r-- | devtools/server/docs/actor-registration.md | 41 | ||||
| -rw-r--r-- | devtools/server/docs/protocol.js.md | 651 |
4 files changed, 927 insertions, 0 deletions
diff --git a/devtools/server/docs/actor-e10s-handling.md b/devtools/server/docs/actor-e10s-handling.md new file mode 100644 index 000000000..ad6919ffd --- /dev/null +++ b/devtools/server/docs/actor-e10s-handling.md @@ -0,0 +1,106 @@ +# How to handle E10S in actors + +In multi-process environments, most devtools actors are created and initialized in the child content process, to be able to access the resources they are exposing to the toolbox. But sometimes, these actors need to access things in the parent process too. Here's why and how. + +## Use case and examples + +Some actors need to exchange messages between the parent and the child process (typically when some components aren't available in the child process). + +E.g. the **director-manager** needs to ask the list of installed **director scripts** from +the **director-registry** running in the parent process. + +To that end, there's a parent/child setup mechanism at `DebuggerServer` level that can be used. + +When the actor is loaded for the first time in the `DebuggerServer` running in the child process, it may decide to run a setup procedure to load a module in the parent process with which to communicate. + +E.g. in the **director-registry**: + +``` + const {DebuggerServer} = require("devtools/server/main"); + + // Setup the child<->parent communication only if the actor module + // is running in a child process. + if (DebuggerServer.isInChildProcess) { + setupChildProcess(); + } + + function setupChildProcess() { + // `setupInParent` is defined on DebuggerServerConnection, + // your actor receive a reference to one instance in its constructor. + conn.setupInParent({ + module: "devtools/server/actors/director-registry", + setupParent: "setupParentProcess" + }); + // ... + } +``` + +The `setupChildProcess` helper defined and used in the previous example uses the `DebuggerServerConnection.setupInParent` to run a given setup function in the parent process Debugger Server, e.g. in the **director-registry** module. + +With this, the `DebuggerServer` running in the parent process will require the requested module (**director-registry**) and call its `setupParentProcess` function (which should be exported on the module). + +The `setupParentProcess` function will receive a parameter that contains a reference to the **MessageManager** and a prefix that should be used to send/receive messages between the child and parent processes. + +See below an example implementation of a `setupParent` function in the parent process: + +``` +exports.setupParentProcess = function setupParentProcess({ mm, prefix }) { + // Start listening for messages from the actor in the child process. + setMessageManager(mm); + + function handleChildRequest(msg) { + switch (msg.json.method) { + case "get": + return doGetInParentProcess(msg.json.args[0]); + break; + case "list": + return doListInParentProcess(); + break; + default: + console.error("Unknown method name", msg.json.method); + throw new Error("Unknown method name"); + } + } + + function setMessageManager(newMM) { + if (mm) { + // Remove listener from old message manager + mm.removeMessageListener("debug:some-message-name", handleChildRequest); + } + // Switch to the new message manager for future use + // Note: Make sure that any other functions also use the new reference. + mm = newMM; + if (mm) { + // Add listener to new message manager + mm.addMessageListener("debug:some-message-name", handleChildRequest); + } + } + + return { + onBrowserSwap: setMessageManager, + onDisconnected: () => setMessageManager(null), + }; +}; +``` + +The server will call the `onDisconnected` method returned by the parent process setup flow to give the actor modules the chance to cleanup their handlers registered on the disconnected message manager. + +The server will call the `onBrowserSwap` method returned by the parent process setup flow to notify actor modules when the message manager for the target frame has changed. The parent process code should remove any message listeners from the previous message manager and add them to the new one. + +## Summary of the setup flow + +In the child process: + +* The `DebuggerServer` loads an actor module, +* the actor module checks `DebuggerServer.isInChildProcess` to know whether it runs in a child process or not, +* the actor module then uses the `DebuggerServerConnection.setupInParent` helper to start setting up a parent-process counterpart, +* the `DebuggerServerConnection.setupInParent` helper asks the parent process to run the required module's setup function, +* the actor module uses the `DebuggerServerConnection.parentMessageManager.sendSyncMessage` and `DebuggerServerConnection.parentMessageManager.addMessageListener` helpers to send or listen to message. + +In the parent process: + +* The DebuggerServer receives the `DebuggerServerConnection.setupInParent` request, +* tries to load the required module, +* tries to call the `module[setupParent]` function with the frame message manager and the prefix as parameters `{ mm, prefix }`, +* the `setupParent` function then uses the mm to subscribe the message manager events, +* the `setupParent` function returns an object with `onDisconnected` and `onBrowserSwap` methods which the server can use to notify the module of various lifecycle events diff --git a/devtools/server/docs/actor-hierarchy.md b/devtools/server/docs/actor-hierarchy.md new file mode 100644 index 000000000..28ddd97c4 --- /dev/null +++ b/devtools/server/docs/actor-hierarchy.md @@ -0,0 +1,129 @@ +# How actors are organized + +To start with, actors are living within /devtools/server/actors/ folder. +They are organized in a hierarchy for easier lifecycle/memory management: +once a parent is removed from the pool, its children are removed as well. +(See actor-registration.md for more information about how to implement one) + +The overall hierarchy of actors looks like this: + + RootActor: First one, automatically instantiated when we start connecting. + | Mostly meant to instantiate new actors. + | + |--> Global-scoped actors: + | Actors exposing features related to the main process, + | that are not specific to any particular context (document, tab, app, + | add-on, or worker). + | A good example is the preference actor. + | + \--> "TabActor" (or alike): + | Actors meant to designate one context (document, tab, app, + | add-on, or worker) and track its lifetime. Generally, there is + | one of these for each thing you can point a toolbox at. + | + \--> Tab-scoped actors: + Actors exposing one particular feature set, this time, + specific to a given context (document, tab, app, add-on, or + worker). Examples include the console and inspector actors. + These actors may extend this hierarchy by having their + own children, like LongStringActor, WalkerActor, etc. + +## RootActor + +The root actor is special. It is automatically created when a client connects. +It has a special `actorID` which is unique and is "root". +All other actors have an `actorID` which is computed dynamically, +so that you need to ask an existing actor to create an Actor +and returns its `actorID`. That's the main role of RootActor. + + RootActor (root.js) + | + |-- BrowserTabActor (webbrowser.js) + | Targets tabs living in the parent process when e10s (multiprocess) + | is turned off for this tab. + | Returned by "listTabs" or "getTab" requests. + | + |-- RemoteBrowserActor (webbrowser.js) + | Targets tabs living in the child process when e10s (multiprocess) is + | turned on for this tab. Note that this is just a proxy for ContentActor, + | that lives in the child process. + | Returned by "listTabs" or "getTab" requests. + | | + | \-> ContentActor (childtab.js) + | Targets tabs living out-of-process (e10s) or apps (on firefox OS). + | Returned by "connect" on RemoteBrowserActor (for tabs) or + | "getAppActor" on the Webapps actor (for apps). + | + |-- WorkerActor (worker.js) + | Targets a worker (applies to various kinds like web worker, service + | worker, etc.). + | Returned by "listWorkers" request to the root actor to get all workers. + | Returned by "listWorkers" request to a BrowserTabActor to get workers for + | a specific tab. + | Returned by "listWorkers" request to a ChildProcessActor to get workers + | for the chrome of the child process. + | + |-- ChromeActor (chrome.js) + | Targets all resources in the parent process of firefox + | (chrome documents, JSM, JS XPCOM, etc.). + | Returned by "getProcess" request without any argument. + | + |-- ChildProcessActor (child-process.js) + | Targets the chrome of the child process (e10s). + | Returned by "getProcess" request with a id argument, + | matching the targeted process. + | + \-- BrowserAddonActor (addon.js) + Targets the javascript of add-ons. + Returned by "listAddons" request. + +## "TabActor" + +Those are the actors exposed by the root actors which are meant to track the +lifetime of a given context: tab, app, process, add-on, or worker. It also +allows to fetch the tab-scoped actors connected to this context. Actors like +console, inspector, thread (for debugger), styleinspector, etc. Most of them +inherit from TabActor (defined in webbrowser.js) which is document centric. It +automatically tracks the lifetime of the targeted document, but it also tracks +its iframes and allows switching the context to one of its iframes. For +historical reasons, these actors also handle creating the ThreadActor, used to +manage breakpoints in the debugger. All the other tab-scoped actors are created +when we access the TabActor's grip. We return the tab-scoped actors `actorID` in +it. Actors inheriting from TabActor expose `attach`/`detach` requests, that +allows to start/stop the ThreadActor. + +The tab-scoped actors expect to find the following properties on the "TabActor": + - threadActor: + ThreadActor instance for the given context, + only defined once `attach` request is called, or on construction. + - isRootActor: (historical name) + Always false, except on ChromeActor. + Despite the attribute name, it is being used to accept all resources + (like chrome one) instead of limiting only to content resources. + - makeDebugger: + Helper function used to create Debugger object for the targeted context. + (See actors/utils/make-debugger.js for more info) + +In addition to this, the actors inheriting from TabActor, expose many other +attributes and events: + - window: + Reference to the window global object currently targeted. + It can change over time if we switch context to an iframe, so it + shouldn't be stored in a variable, but always retrieved from the actor. + - windows: + List of all document globals including the main window object and all iframes. + - docShell: + DocShell reference for the targeted context. + - docShells: + List of all docshells for the targeted document and all its iframes. + - chromeEventHandler: + The chrome event handler for the current context. Allows to listen to events + that can be missing/cancelled on this document itself. + +See TabActor documentation for events definition. + +## Tab-scoped actors + +Each of these actors focuses on providing one particular feature set, specific +to one context, that can be a web page, an app, a top level firefox window, a +process, an add-on, or a worker. diff --git a/devtools/server/docs/actor-registration.md b/devtools/server/docs/actor-registration.md new file mode 100644 index 000000000..8d79d9372 --- /dev/null +++ b/devtools/server/docs/actor-registration.md @@ -0,0 +1,41 @@ +# How to register an actor + +## Tab actors vs. global actors + +Tab actors are the most common types of actors. That's the type of actors you will most probably be adding. + +Tab actors target a document, this could be a tab in Firefox, an app on B2G or a remote document in Firefox for Android/Safari/Chrome for Android (via Valence). + +Global actors however are for the rest, for things not related to any particular document but instead for things global to the whole Firefox/B2G/Chrome/Safari intance the toolbox is connected to (e.g. the preference actor). + +## The DebuggerServer.registerModule function + +To register a tab actor: + +``` +DebuggerServer.registerModule("devtools/server/actors/webconsole", { + prefix: "console", + constructor: "WebConsoleActor", + type: { tab: true } +}); +``` + +To register a global actor: + +``` +DebuggerServer.registerModule("devtools/server/actors/addons", { + prefix: "addons", + constructor: "AddonsActor", + type: { global: true } +}); +``` + +If you are adding a new built-in devtools actor, you should be registering it using `DebuggerServer.registerModule` in `addBrowserActors` or `addTabActors` in `/devtools/server/main.js`. + +If you are adding a new actor from an add-on, you should call `DebuggerServer.registerModule` directly from your add-on code. + +## A note about lazy registration + +The `DebuggerServer` loads and creates all of the actors lazily to keep the initial memory usage down (which is extremely important on lower end devices). + +It becomes especially important when debugging apps on b2g or pages with e10s when there are more than one process, because that's when we need to spawn a `DebuggerServer` per process (it may not be immediately obvious that the server in the main process is mostly only here for piping messages to the actors in the child process). diff --git a/devtools/server/docs/protocol.js.md b/devtools/server/docs/protocol.js.md new file mode 100644 index 000000000..e033bf142 --- /dev/null +++ b/devtools/server/docs/protocol.js.md @@ -0,0 +1,651 @@ +Writing an Actor +================ + +A Simple Hello World +-------------------- + +Here's a simple Hello World actor. It is a global actor (not associated with a given browser tab). +It has two parts: a spec and an implementation. The spec would go somewhere like +`devtools/shared/specs/hello-world.js` and would look like: + + const {Arg, RetVal, generateActorSpec} = require("devtools/shared/protocol"); + + const helloWorldSpec = generateActorSpec({ + typeName: "helloWorld", // I'll explain types later, I promise. + + methods: { + sayHello: { + // The request packet template. There are no arguments, so + // it is empty. The framework will add the "type" and "to" + // request properties. + request: {}, + + // The response packet template. The return value of the function + // will be plugged in where the RetVal() appears in the template. + response: { + greeting: RetVal("string") // "string" is the return value type. + } + }, + }, + }); + + // Expose the spec so it can be imported by the implementation. + exports.helloWorldSpec = helloWorldSpec; + +The actor implementation would go somewhere like +`devtools/server/actors/hello-world.js` and would look like: + + const protocol = require("devtools/shared/protocol"); + const {helloWorldSpec} = require("devtools/shared/specs/hello-world"); + + const HelloActor = protocol.ActorClassWithSpec(helloWorldSpec, { + initialize: function (conn) { + protocol.Actor.prototype.initialize.call(this, conn); // This is the worst part of heritage. + }, + + sayHello: function () { + return "hello"; + }, + }); + + // You also need to export the actor class in your module for discovery. + exports.HelloActor = HelloActor; + +To activate your actor, register it in the `addBrowserActors` method in `server/main.js`. +The registration code would look something like this: + + this.registerModule("devtools/server/actors/hello-world", { + prefix: "hello", + constructor: "HelloActor", + type: { global: true } + }); + +Your spec allows the actor to support a `sayHello` request. +A request/reply will look like this: + + -> { to: <actorID>, type: "sayHello" } + <- { from: <actorID>, greeting: "hello" } + +Now we can create a client side object. We call these *front* objects and +they typically go in `devtools/shared/fronts/`. + +Here's the front for the HelloActor: + + const HelloFront = protocol.FrontClassWithSpec(helloWorldSpec, { + initialize: function (client, form) { + protocol.Front.prototype.initialize.call(this, client, form); + // This call may not be required but it's a good idea. It will + // guarantee that your instance is managed in the pool. + this.manage(this); + } + }); + +Note that there is no `sayHello` method. The FrontClass will generate a method on the Front object that matches the method declaration in the Actor class. + +The generated methods will return a Promise. That promise will resolve to the RetVal of the actor method. + +So if we have a reference to a HelloFront object, we can issue a `sayHello` request: + + hello.sayHello().then(greeting => { + console.log(greeting); + }); + +How do you get an initial reference to the front? That's a bit tricky, but basically there are two ways: + +* Manually +* Magically + +Manually - If you're using a DebuggerClient instance, you can discover the actorID manually and create a Front for it: + + let hello = HelloFront(this.client, { actor: <hello actorID> }); + +Magically - Once you have an initial reference to a protocol.js object, it can return other protocol.js objects and fronts will automatically be created. + +Arguments +--------- + +`sayHello` has no arguments, so let's add a method that does take arguments. +Here's an adjustment to the spec: + + methods: { + echo: { + request: { echo: Arg(0, "string") }, + response: { echoed: RetVal("string") } + } + } + +Here's an adjustment to the implementation: + + echo: function (str) { + return str + "... " + str + "..."; + } + +This tells the library to place the 0th argument, which should be a string, in the `echo` property of the request packet. + + +This will generate a request handler whose request and response packets look like this: + + { to: <actorID>, type: "echo", echo: <str> } + { from: <actorID>, echoed: <str> } + +The client usage should be predictable: + + hello.echo("hello").then(str => { assert(str === "hello... hello...") }) + +The library tries hard to make using fronts feel like natural javascript (or as natural as you believe promises are, I guess). When building the response it will put the return value of the function where RetVal() is specified in the response template, and on the client side it will use the value in that position when resolving the promise. + +Returning JSON +-------------- + +Maybe your response is an object. Here's an example of a spec: + + methods: { + addOneTwice: { + request: { a: Arg(0, "number"), b: Arg(1, "number") }, + response: { ret: RetVal("json") } + } + } + +Here's an example implementation: + + addOneTwice: function (a, b) { + return { a: a + 1, b: b + 1 }; + } + +This will generate a response packet that looks like: + + { from: <actorID>, ret: { a: <number>, b: <number> } } + +That's probably unnecessary nesting (if you're sure you won't be returning an object with 'from' as a key!), so you can just replace `response` with: + + response: RetVal("json") + +and now your packet will look like: + + { from: <actorID>, a: <number>, b: <number> } + +Types and Marshalling +--------------------- + +Things have been pretty simple up to this point - all the arguments we've passed in have been javascript primitives. But for some types (most importantly Actor types, which I'll get to eventually), we can't just copy them into a JSON packet and expect it to work, we need to marshal things ourselves. + +Again, the protocol lib tries hard to provide a natural API to actors and clients, and sometime that natural API might involve object APIs. I'm going to use a wickedly contrived example, bear with me. Let's say I have a small object that contains a number and has a few methods associated with it: + + let Incrementor = function (i) { + this.value = value; + } + Incrementor.prototype = { + increment: function () { this.value++ }, + decrement: function () { this.value-- } + }; + + +and I want to return it from a backend function: + + // spec: + methods: { + getIncrementor: { + request: { number: Arg(0, "number") }, + response: { value: RetVal("incrementor") } // We'll define "incrementor" below. + } + } + + // implementation: + getIncrementor: function (i) { + return new Incrementor(i) + } + +I want that response to look like `{ from: <actorID>, value: <number> }`, but the client side needs to know to return an Incrementor, not a primitive number. So let's tell the protocol lib about Incrementors: + + protocol.types.addType("incrementor", { + // When writing to a protocol packet, just send the value + write: (v) => v.value, + + // When reading from a protocol packet, wrap with an Incrementor + // object. + read: (v) => new Incrementor(v) + }); + +And now our client can use the API as expected: + + front.getIncrementor(5).then(incrementor => { + incrementor.increment(); + assert(incrementor.value === 6); + }); + +You can do the same thing with arguments: + + // spec: + methods: { + passIncrementor: { + request: { Arg(0, "incrementor") }, + } + } + + // implementation: + passIncrementor: function (inc) { + w.increment(); + assert(incrementor.value === 6); + } + + front.passIncrementor(new Incrementor(5)); + +The library provides primitiive `boolean`, `number`, `string`, and `json` types. + +Moving right along, let's say you want to pass/return an array of Incrementors. You can just prepend `array:` to the type name: + + // spec: + methods: { + incrementAll: { + request: { incrementors: Arg(0, "array:incrementor") }, + response: { incrementors: RetVal("array:incrementor") } + } + } + + // implementation: + incrementAll: function (incrementors) { + incrementors.forEach(incrementor => { + incrementor.increment(); + } + return incrementors; + } + +You can use an iterator in place of an array as an argument or return value, and the library will handle the conversion automatically. + +Or maybe you want to return a dictionary where one item is a incrementor. To do this you need to tell the type system which members of the dictionary need custom marshallers: + + protocol.types.addDictType("contrivedObject", { + incrementor: "incrementor", + incrementorArray: "array:incrementor" + }); + + // spec: + methods: { + reallyContrivedExample: { + response: RetVal("contrivedObject") + } + } + + // implementations: + reallyContrivedExample: function () { + return { + /* a and b are primitives and so don't need to be called out specifically in addDictType */ + a: "hello", b: "world", + incrementor: new Incrementor(1), + incrementorArray: [new Incrementor(2), new Incrementor(3)] + } + } + + front.reallyContrivedExample().then(obj => { + assert(obj.a == "hello"); + assert(obj.b == "world"); + assert(incrementor.i == 1); + assert(incrementorArray[0].i == 2); + assert(incrementorArray[1].i == 3); + }); + +Nullables +--------- + +If an argument, return value, or dict property can be null/undefined, you can prepend `nullable:` to the type name: + + "nullable:incrementor", // Can be null/undefined or an incrementor + "array:nullable:incrementor", // An array of incrementors that can have holes. + "nullable:array:incrementor" // Either null/undefined or an array of incrementors without holes. + + +Actors +------ + +Probably the most common objects that need custom martialing are actors themselves. These are more interesting than the Incrementor object, but by default they're somewhat easy to work with. Let's add a ChildActor implementation that will be returned by the HelloActor (which is rapidly becoming the OverwhelminglyComplexActor): + + // spec: + const childActorSpec = generateActorSpec({ + actorType: "childActor", + methods: { + getGreeting: { + response: { greeting: RetVal("string") }, + } + } + }); + + // implementation: + const ChildActor = protocol.ActorClassWithSpec(childActorSpec, { + initialize: function (conn, id) { + protocol.Actor.prototype.initialize.call(this, conn); + this.greeting = "hello from " + id; + }, + getGreeting: function () { + return this.greeting; + }, + }); + + exports.ChildActor = ChildActor; + + const ChildFront = protocol.FrontClassWithSpec(childActorSpec, { + initialize: function (client, form) { + protocol.Front.prototype.initialize.call(this, client, form); + }, + }); + +The library will register a marshaller for the actor type itself, using typeName as its tag. + +So we can now add the following code to HelloActor: + + // spec: + methods: { + getChild: { + request: { id: Arg(0, "string") }, + response: { child: RetVal("childActor") } + } + } + + // implementation: + getChild: function (id) { + return ChildActor(this.conn, id); + } + + front.getChild("child1").then(childFront => { + return childFront.getGreeting(); + }).then(greeting => { + assert(id === "hello from child1"); + }); + +The conversation will look like this: + + { to: <actorID>, type: "getChild", id: "child1" } + { from: <actorID>, child: { actor: <childActorID> }} + { to: <childActorID>, type: "getGreeting" } + { from: <childActorID>, greeting: "hello from child1" } + +But the ID is the only interesting part of this made-up example. You're never going to want a reference to a ChildActor without checking its ID. Making an extra request just to get that id is wasteful. You really want the first response to look like `{ from: <actorID>, child: { actor: <childActorID>, greeting: "hello from child1" } }` + +You can customize the marshalling of an actor by providing a `form` method in the `ChildActor` class: + + form: function () { + return { + actor: this.actorID, + greeting: this.greeting + } + }, + +And you can demarshal in the `ChildFront` class by implementing a matching `form` method: + + form: function (form) { + this.actorID = form.actor; + this.greeting = form.greeting; + } + +Now you can use the id immediately: + + front.getChild("child1").then(child => { assert(child.greeting === "child1) }); + +You may come across a situation where you want to customize the output of a `form` method depending on the operation being performed. For example, imagine that ChildActor is a bit more complex, with a, b, c, and d members: + + ChildActor: + form: function () { + return { + actor: this.actorID, + greeting: this.greeting, + a: this.a, + b: this.b, + c: this.c, + d: this.d + } + } + ChildFront: + form: function (form) { + this.actorID = form.actorID; + this.id = form.id; + this.a = form.a; + this.b = form.b; + this.c = form.c; + this.d = form.d; + } + +And imagine you want to change 'c' and return the object: + + // Oops! If a type is going to return references to itself or any other + // type that isn't fully registered yet, you need to predeclare the type. + types.addActorType("childActor"); + + ... + + // spec: + methods: { + changeC: { + request: { newC: Arg(0) }, + response: { self: RetVal("childActor") } + } + } + + // implementation: + changeC: function (newC) { + c = newC; + return this; + } + + ... + + childFront.changeC('hello').then(ret => { assert(ret === childFront); assert(childFront.c === "hello") }); + +Now our response will look like: + + { from: <childActorID>, self: { actor: <childActorID>, greeting: <id>, a: <a>, b: <b>, c: "hello", d: <d> } + +But that's wasteful. Only c changed. So we can provide a *detail* to the type using `#`: + + response: { self: RetVal("childActor#changec") } + +and update our form methods to make use of that data: + + // In ChildActor: + form: function (detail) { + if (detail === "changec") { + return { actor: this.actorID, c: this.c } + } + // ... the rest of the form method stays the same. + } + + // In ChildFront: + form: function (form, detail) { + if (detail === "changec") { + this.actorID = form.actor; + this.c = form.c; + return; + } + // ... the rest of the form method stays the same. + } + +Now the packet looks like a much more reasonable `{ from: <childActorID>, self: { actor: <childActorID>, c: "hello" } }` + +Lifetimes +--------- + +No, I don't want to talk about lifetimes quite yet. + +Events +------ + +Your actor has great news! + +Actors are subclasses of jetpack `EventTarget`, so you can just emit events. +Here's how you'd set it up in a spec: + + events: { + "good-news": { + type: "goodNews", // event target naming and packet naming are at odds, and we want both to be natural! + news: Arg(0) + } + } + + methods: { + giveGoodNews: { + request: { news: Arg(0) } + } + } + +Here's how the implementation would look: + + const event = require("sdk/event/core"); + + // In your protocol.ActorClassWithSpec definition: + giveGoodNews: function (news) { + event.emit(this, "good-news", news); + } + +Now you can listen to events on a front: + + front.on("good-news", news => { + console.log(`Got some good news: ${news}\n`); + }); + front.giveGoodNews().then(() => { console.log("request returned.") }); + +You might want to update your front's state when an event is fired, before emitting it against the front. You can use `preEvent` in the front definition for that: + + countGoodNews: protocol.preEvent("good-news", function (news) { + this.amountOfGoodNews++; + }); + +You can have events wait until an asynchronous action completes before firing by returning a promise. If you have multiple preEvents defined for a specific event, and atleast one fires asynchronously, then all preEvents most resolve before all events are fired. + + countGoodNews: protocol.preEvent("good-news", function (news) { + return this.updateGoodNews().then(() => this.amountOfGoodNews++); + }); + +On a somewhat related note, not every method needs to be request/response. Just like an actor can emit a one-way event, a method can be marked as a one-way request. Maybe we don't care about giveGoodNews returning anything: + + // spec: + methods: { + giveGoodNews: { + request: { news: Arg(0, "string") }, + oneway: true + } + } + + // implementation: + giveGoodNews: function (news) { + emit(this, "good-news", news); + } + +Lifetimes +--------- + +No, let's talk about custom front methods instead. + +Custom Front Methods +-------------------- + +You might have some bookkeeping to do before issuing a request. Let's say you're calling `echo`, but you want to count the number of times you issue that request. Just use the `custom` tag in your front implementation: + + echo: custom(function (str) { + this.numEchos++; + return this._echo(str); + }, { + impl: "_echo" + }) + +This puts the generated implementation in `_echo` instead of `echo`, letting you implement `echo` as needed. If you leave out the `impl`, it just won't generate the implementation at all. You're on your own. + +Lifetimes +--------- + +OK, I can't think of any more ways to put this off. The remote debugging protocol has the concept of a *parent* for each actor. This is to make distributed memory management a bit easier. Basically, any descendents of an actor will be destroyed if the actor is destroyed. + +Other than that, the basic protocol makes no guarantees about lifetime. Each interface defined in the protocol will need to discuss and document its approach to lifetime management (although there are a few common patterns). + +The protocol library will maintain the child/parent relationships for you, but it needs some help deciding what the child/parent relationships are. + +The default parent of an object is the first object that returns it after it is created. So to revisit our earlier HelloActor `getChild` implementation: + + // spec: + methods: { + getChild: { + request: { id: Arg(0) }, + response: { child: RetVal("childActor") } + } + } + + // implementation: + getChild: function (id) { + return new ChildActor(this.conn, id); + } + +The ChildActor's parent is the HelloActor, because it's the one that created it. + +You can customize this behavior in two ways. The first is by defining a `marshallPool` property in your actor. Imagine a new ChildActor method: + + // spec: + methods: { + getSibling: { + request: { id: Arg(0) }, + response: { child: RetVal("childActor") } + } + } + + // implementation: + getSibling: function (id) { + return new ChildActor(this.conn, id); + } + +This creates a new child actor owned by the current child actor. But in this example we want all actors created by the child to be owned by the HelloActor. So we can define a `defaultParent` property that makes use of the `parent` proeprty provided by the Actor class: + + get marshallPool() { return this.parent } + +The front needs to provide a matching `defaultParent` property that returns an owning front, to make sure the client and server lifetimes stay synced. + +For more complex situations, you can define your own lifetime properties. Take this new pair of HelloActor methods: + + // When the "temp" lifetime is specified, look for the _temporaryParent attribute as the owner. + types.addLifetime("temp", "_temporaryParent"); + + // spec: + methods: { + getTemporaryChild: { + request: { id: Arg(0) }, + response: { + child: RetVal("temp:childActor") // use the lifetime name here to specify the expected lifetime. + } + }, + clearTemporaryChildren: { + oneway: true + } + } + + // implementation: + getTemporaryChild: function (id) { + if (!this._temporaryParent) { + // Create an actor to serve as the parent for all temporary children and explicitly + // add it as a child of this actor. + this._temporaryParent = this.manage(new Actor(this.conn)); + } + return new ChildActor(this.conn, id); + } + + clearTemporaryChildren: function () { + if (this._temporaryParent) { + this._temporaryParent.destroy(); + delete this._temporaryParent; + } + } + +This will require some matching work on the front: + + getTemporaryChild: protocol.custom(function (id) { + if (!this._temporaryParent) { + this._temporaryParent = this.manage(new Front(this.client)); + } + return this._getTemporaryChild(id); + }, { + impl: "_getTemporaryChild" + }), + + clearTemporaryChildren: protocol.custom(function (id) { + if (this._temporaryParent) { + this._temporaryParent.destroy(); + delete this._temporaryParent; + } + return this._clearTemporaryChildren(); + }, { + impl: "_clearTemporaryChildren" + }) |