Add concurrency patterns:generators

README.md

@@ -67,7 +67,7 @@ __Concurrency Patterns__:
 | [Bounded Parallelism](concurrency/bounded_parallelism.md) | Completes large number of independent tasks with resource limits |
 | TODO: [Broadcast](concurrency/broadcast.md) | Transfers a message to all recipients simultaneously |
 | TODO: [Coroutines](concurrency/coroutine.md) | Subroutines that allow suspending and resuming execution at certain locations |
-| TODO: [Generators](concurrency/generator.md) | Yields a sequence of values one at a time |
+| [Generators](concurrency/generator.md) | Yields a sequence of values one at a time |
 | TODO: [Reactor](concurrency/reactor.md) | Demultiplexes service requests delivered concurrently to a service handler and dispatches them syncronously to the associated request handlers |
 | [Parallelism](concurrency/parallelism.md) | Completes large number of independent tasks |
 | TODO: [Producer Consumer](concurrency/producer_consumer.md) | Separates tasks from task executions |

concurrency/generator.md

@@ -0,0 +1,6 @@
+# Generator Pattern
+
+[Generator](https://en.wikipedia.org/wiki/Generator_(computer_programming)) is a special routine that can be used to control the iteratoin behavior of a loop.
+
+# Implementation and Example
+With Go language, we can Implemente generator in two ways: channel and closure. Fibnacci example can be found in [generators.go](generators.go).

concurrency/generators.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"fmt"
+)
+
+//implement generator by closure
+func FibnacciClosure() func() (ret int) {
+	a, b := 0, 1
+	return func() (ret int) {
+		ret = b
+		a, b = b, a+b
+		return
+	}
+}
+
+//implement generator by channel
+func FibnacciChan(n int) chan int {
+	ret := make(chan int)
+
+	go func() {
+		a, b := 0, 1
+		for i := 0; i < n; i++ {
+			ret <- b
+			a, b = b, a+b
+		}
+		close(ret)
+	}()
+
+	return ret
+}
+
+func main() {
+	//closure
+	nextFib := FibnacciClosure()
+	for i := 0; i < 20; i++ {
+		fmt.Println(nextFib())
+	}
+
+	//channel
+	for i := range FibnacciChan(20) {
+		fmt.Println(i)
+	}
+}