Join

The next pattern I want to present is Join. This is a very simple pattern that starts multiple tasks in parallel. In the Parallel Programming Library, Join is implemented as a class method of the TParallel class. To execute three methods, Task1, Task2, and Task3, in parallel, you simply call TParallel.Join with the parameters collected in an array:

TParallel.Join([Task1, Task2, Task3]);

This is equivalent to the following implementation, which uses tasks:

var
  tasks: array [1..3] of ITask;
tasks[1] := TTask.Run(Task1);
tasks[2] := TTask.Run(Task2);
tasks[3] := TTask.Run(Task3);

Although the approaches work the same way, that doesn’t mean that Join is implemented in this way. Rather than that, it uses a pattern that I haven’t yet covered, a parallel for to run tasks in parallel.

Join starts tasks but doesn’t wait for them to complete. It returns an ITask interface representing a new, composite task, which only exits when all of its...