title: What is execution context in Scala?
body: <p>I am new to Scala, and was trying to use some parallel constructs(<code>Future</code> in particular).</p>
  <p>I found there is an implicit parameter of type <code>ExecutionContext</code>. IMO, it is something similar to(and maybe more abstract than) the concept of thread pool. I have tried to learn it through <a href="http://docs.scala-lang.org/overviews/core/futures.html" rel="nofollow noreferrer">documentation</a>, but I cannot find any clear and detailed introduction about it.</p>
  <p>Could anyone please explain what exactly execution context is in Scala? And what is the purpose of introducing execution context to the language?</p>