Resolving code review comments.

concepts/actor/actor_overview.md

@@ -1,6 +1,6 @@
 # Introduction to Actors
-Actors is an application pattern based on the Virtual Actor pattern. 
-Dapr programming model enables writing the actor pattern. The Actors API provides a single-threaded programming model built on the scalability and reliability guarantees.
+
+Dapr runtime provides an actor implementation which is based on Virtual Actor pattern. The Dapr Actors API provides a single-threaded programming model leveraging the scalability and reliability guarantees provided by underlying platform on which Dapr is running.
 
 ## What are Actors?
 
@@ -20,24 +20,23 @@ Although the actor design pattern can be a good fit to a number of distributed s
 
 # Actors in Dapr
 
-Every actor is defined as an instance of an actor type, identical to the way a .NET object is an instance of a .NET type. For example, there may be an actor type that implements the functionality of a calculator and there could be many actors of that type that are distributed on various nodes across a cluster. Each such actor is uniquely identified by an actor ID.
+Every actor is defined as an instance of an actor type, identical to the way an object is an instance of a class. For example, there may be an actor type that implements the functionality of a calculator and there could be many actors of that type that are distributed on various nodes across a cluster. Each such actor is uniquely identified by an actor ID.
 
 # Actor Lifetime
 
 Dapr actors are virtual, meaning that their lifetime is not tied to their in-memory representation. As a result, they do not need to be explicitly created or destroyed. The Dapr Actors runtime automatically activates an actor the first time it receives a request for that actor ID. If an actor is not used for a period of time, the Dapr Actors runtime garbage-collects the in-memory object. It will also maintain knowledge of the actor's existence should it need to be reactivated later. For more details, see Actor lifecycle and garbage collection.
 
-This virtual actor lifetime abstraction carries some caveats as a result of the virtual actor model, and in fact the Reliable Actors implementation deviates at times from this model.
+This virtual actor lifetime abstraction carries some caveats as a result of the virtual actor model, and in fact the Dapr Actors implementation deviates at times from this model.
 
-An actor is automatically activated (causing an actor object to be constructed) the first time a message is sent to its actor ID. After some period of time, the actor object is garbage collected. In the future, using the actor ID again, causes a new actor object to be constructed. An actor's state outlives the object's lifetime when storing the state in Dapr.
+An actor is automatically activated (causing an actor object to be constructed) the first time a message is sent to its actor ID. After some period of time, the actor object is garbage collected. In the future, using the actor ID again, causes a new actor object to be constructed. An actor's state outlives the object's lifetime as state is stored in configured state provider for Dapr runtime.
 
 # Distribution and failover
 To provide scalability and reliability, actors instances are distributed throughout the cluster and automatically migrates them from failed nodes to healthy ones as required.
 
-Actors are distributed across the pods of the Actor Service, and those pods are distributed across the nodes in a cluster. Each service partition contains a set of actors
+Actors are distributed across the pods of the Actor Service, and those pods are distributed across the nodes in a cluster. Each service instance contains a set of actors.
 
 The Dapr Actor runtime manages distribution scheme and key range settings for you. This simplifies some choices but also carries some consideration:
 
-* Dapr Actors is using the range partitioning scheme.
 * By default, actors are randomly placed into pods resulting in uniform distribution.
 * Because actors are randomly placed, it should be expected that actor operations will always require network communication, including serialization and deserialization of method call data, incurring latency and overhead.
 
@@ -49,12 +48,10 @@ You can interact with Dapr to invoke the actor method by calling Http/gRPC endpo
 POST/GET/PUT/DELETE http://localhost:3500/v1.0/actors/<actorType>/<actorId>/method/<method>
 ```
 
-If you want to pass the method parameters, then you can pass in request body.
+You can provide any data for actor method in the request body and response for the request would be in response body which is data from actor call.
 
 Refer [dapr spec](/dapr/spec/blob/master/actors.md) for more details.
 
-Since Method invocations and their responses ultimately result in network requests across the cluster, so the arguments and the result types of the tasks that they return must be serializable.
-
 ### Concurrency
 
 The Dapr Actors runtime provides a simple turn-based access model for accessing actor methods. This means that no more than one thread can be active inside an actor object's code at any time. Turn-based access greatly simplifies concurrent systems as there is no need for synchronization mechanisms for data access. It also means systems must be designed with special considerations for the single-threaded access nature of each actor instance.
@@ -63,7 +60,13 @@ A single actor instance cannot process more than one request at a time. An actor
 
 Actors can deadlock on each other if there is a circular request between two actors while an external request is made to one of the actors simultaneously. The Dapr actor runtime will automatically time out on actor calls and throw an exception to the caller to interrupt possible deadlock situations.
 
+![](../../images/actors_communication.png)
+
 ### Turn-based access
 A turn consists of the complete execution of an actor method in response to a request from other actors or clients, or the complete execution of a timer/reminder callback. Even though these methods and callbacks are asynchronous, the Dapr Actors runtime does not interleave them. A turn must be fully finished before a new turn is allowed. In other words, an actor method or timer/reminder callback that is currently executing must be fully finished before a new call to a method or callback is allowed. A method or callback is considered to have finished if the execution has returned from the method or callback and the task returned by the method or callback has finished. It is worth emphasizing that turn-based concurrency is respected even across different methods, timers, and callbacks.
 
-The Dapr Actors runtime enforces turn-based concurrency by acquiring a per-actor lock at the beginning of a turn and releasing the lock at the end of the turn. Thus, turn-based concurrency is enforced on a per-actor basis and not across actors. Actor methods and timer/reminder callbacks can execute simultaneously on behalf of different actors.
+The Dapr Actors runtime enforces turn-based concurrency by acquiring a per-actor lock at the beginning of a turn and releasing the lock at the end of the turn. Thus, turn-based concurrency is enforced on a per-actor basis and not across actors. Actor methods and timer/reminder callbacks can execute simultaneously on behalf of different actors.
+
+The following example illustrates the above concepts. Consider an actor type that implements two asynchronous methods (say, Method1 and Method2), a timer, and a reminder. The diagram below shows an example of a timeline for the execution of these methods and callbacks on behalf of two actors (ActorId1 and ActorId2) that belong to this actor type.
+
+![](../../images/actors_concurrency.png)