Moved dataflow from pending

akka-docs/java/dataflow.rst

@@ -0,0 +1,189 @@
+Dataflow Concurrency (Java)
+===========================
+
+Introduction
+------------
+
+**IMPORTANT: As of Akka 1.1, Akka Future, CompletableFuture and DefaultCompletableFuture have all the functionality of DataFlowVariables, they also support non-blocking composition and advanced features like fold and reduce, Akka DataFlowVariable is therefor deprecated and will probably resurface in the following release as a DSL on top of Futures.**
+
+Akka implements `Oz-style dataflow concurrency <http://www.mozart-oz.org/documentation/tutorial/node8.html#chapter.concurrency>`_ through dataflow (single assignment) variables and lightweight (event-based) processes/threads.
+
+Dataflow concurrency is deterministic. This means that it will always behave the same. If you run it once and it yields output 5 then it will do that **every time**, run it 10 million times, same result. If it on the other hand deadlocks the first time you run it, then it will deadlock **every single time** you run it. Also, there is **no difference** between sequential code and concurrent code. These properties makes it very easy to reason about concurrency. The limitation is that the code needs to be side-effect free, e.g. deterministic. You can't use exceptions, time, random etc., but need to treat the part of your program that uses dataflow concurrency as a pure function with input and output.
+
+The best way to learn how to program with dataflow variables is to read the fantastic book `Concepts, Techniques, and Models of Computer Programming <http://www.info.ucl.ac.be/%7Epvr/book.html>`_. By Peter Van Roy and Seif Haridi.
+
+The documentation is not as complete as it should be, something we will improve shortly. For now, besides above listed resources on dataflow concurrency, I recommend you to read the documentation for the GPars implementation, which is heavily influenced by the Akka implementation:
+* `<http://gpars.codehaus.org/Dataflow>`_
+* `<http://www.gpars.org/guide/guide/7.%20Dataflow%20Concurrency.html>`_
+
+Dataflow Variables
+------------------
+
+Dataflow Variable defines three different operations:
+
+1. Define a Dataflow Variable
+
+.. code-block:: java
+
+  import static akka.dataflow.DataFlow.*;
+
+  DataFlowVariable<int> x = new DataFlowVariable<int>();
+
+2. Wait for Dataflow Variable to be bound
+
+.. code-block:: java
+
+  x.get();
+
+3. Bind Dataflow Variable
+
+.. code-block:: java
+
+  x.set(3);
+
+A Dataflow Variable can only be bound once. Subsequent attempts to bind the variable will throw an exception.
+
+You can also shutdown a dataflow variable like this:
+
+.. code-block:: java
+
+  x.shutdown();
+
+Threads
+-------
+
+You can easily create millions lightweight (event-driven) threads on a regular workstation.
+
+.. code-block:: java
+
+  import static akka.dataflow.DataFlow.*;
+  import akka.japi.Effect;
+
+  thread(new Effect() {
+    public void apply() { ... }
+  });
+
+You can also set the thread to a reference to be able to control its life-cycle:
+
+.. code-block:: java
+
+  import static akka.dataflow.DataFlow.*;
+  import akka.japi.Effect;
+
+  ActorRef t = thread(new Effect() {
+    public void apply() { ... }
+  });
+
+  ... // time passes
+
+  t.sendOneWay(new Exit()); // shut down the thread
+
+Examples
+--------
+
+Most of these examples are taken from the `Oz wikipedia page <http://en.wikipedia.org/wiki/Oz_%28programming_language%29>`_
+
+Simple DataFlowVariable example
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This example is from Oz wikipedia page: http://en.wikipedia.org/wiki/Oz_(programming_language).
+Sort of the "Hello World" of dataflow concurrency.
+
+Example in Oz:
+
+.. code-block:: ruby
+
+  thread
+    Z = X+Y     % will wait until both X and Y are bound to a value.
+    {Browse Z}  % shows the value of Z.
+  end
+  thread X = 40 end
+  thread Y = 2 end
+
+Example in Akka:
+
+.. code-block:: java
+
+  import static akka.dataflow.DataFlow.*;
+  import akka.japi.Effect;
+
+  DataFlowVariable<int> x = new DataFlowVariable<int>();
+  DataFlowVariable<int> y = new DataFlowVariable<int>();
+  DataFlowVariable<int> z = new DataFlowVariable<int>();
+
+  thread(new Effect() {
+    public void apply() {
+      z.set(x.get() + y.get());
+      System.out.println("z = " + z.get());
+    }
+  });
+
+  thread(new Effect() {
+    public void apply() {
+      x.set(40);
+    }
+  });
+
+  thread(new Effect() {
+    public void apply() {
+      y.set(40);
+    }
+  });
+
+Example on life-cycle management of DataFlowVariables
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Shows how to shutdown dataflow variables and bind threads to values to be able to interact with them (exit etc.).
+
+Example in Akka:
+
+.. code-block:: java
+  import static akka.dataflow.DataFlow.*;
+  import akka.japi.Effect;
+
+  // create four 'int' data flow variables
+  DataFlowVariable<int> x = new DataFlowVariable<int>();
+  DataFlowVariable<int> y = new DataFlowVariable<int>();
+  DataFlowVariable<int> z = new DataFlowVariable<int>();
+  DataFlowVariable<int> v = new DataFlowVariable<int>();
+
+  ActorRef main = thread(new Effect() {
+    public void apply() {
+      System.out.println("Thread 'main'")
+      if (x.get() > y.get()) {
+        z.set(x);
+        System.out.println("'z' set to 'x': " + z.get());
+      } else {
+        z.set(y);
+        System.out.println("'z' set to 'y': " + z.get());
+      }
+
+      // main completed, shut down the data flow variables
+      x.shutdown();
+      y.shutdown();
+      z.shutdown();
+      v.shutdown();
+    }
+  });
+
+  ActorRef setY = thread(new Effect() {
+    public void apply() {
+      System.out.println("Thread 'setY', sleeping...");
+      Thread.sleep(5000);
+      y.set(2);
+      System.out.println("'y' set to: " + y.get());
+    }
+  });
+
+  ActorRef setV = thread(new Effect() {
+    public void apply() {
+      System.out.println("Thread 'setV'");
+      y.set(2);
+      System.out.println("'v' set to y: " + v.get());
+    }
+  });
+
+  // shut down the threads
+  main.sendOneWay(new Exit());
+  setY.sendOneWay(new Exit());
+  setV.sendOneWay(new Exit());

akka-docs/java/index.rst

@@ -7,6 +7,7 @@ Java API
    untyped-actors
    typed-actors
    actor-registry
+   dataflow
    stm
    transactors
    remote-actors