creational/object-pool: reimplement the object pool pattern

creational/object-pool.md

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+# Object Pool Pattern
+
+The object pool creational design pattern is used to prepare and keep multiple
+instances according to the demand expectation.
+
+## Implementation
+
+```go
+package pool
+
+type Pool chan *Object
+
+func New(total int) *Pool {
+	p := make(chan *Object, total)
+
+	for i := 0; i < total; i++ {
+		p <- new(Object)
+	}
+
+	return p
+}
+```
+
+## Usage
+
+Given below is a simple lifecycle example on an object pool.
+
+```go
+p := pool.New(2)
+
+select {
+case obj := <-p:
+	obj.Do( /*...*/ )
+
+	p <- obj
+default:
+	// No more objects left retry later or fail
+	return
+}
+```
+
+## Rules of Thumb
+
+- Object pool pattern is useful in cases where object initialization is more
+  expensive than the object maintenance.
+- If there are spikes in demand as opposed to a steady demand, the maintenance
+  overhead might overweigh the benefits of an object pool.
+- It has positive effects on performance due to object being initialized beforehand.