sible using <code>take</code>.
 The class is lightweight enough to be suitable for transient use
 when processing groups of tasks.

 <p>

 <b>Usage Examples.</b>

 Suppose you have a set of solvers for a certain problem, each
 returning a value of some type <code>Result</code>, and would like to
 run them concurrently, processing the results of each of them that
 return a non-null value, in some method <code>use(Result r)</code>. You
 could write this as:

 <pre> <code>void solve(Executor e,
            Col