Document X::Proc::Async::AlreadyStarted

lib/Type/Proc/Async.pod

@@ -87,6 +87,11 @@ Initiates spawning of the external program. Returns a promise that will be
 kept with a L<Proc::Status|/type/Proc::Status> object once the external
 program exits, and that will be broken if the program cannot be started.
 
+If C<start> is called on a Proc::Async object on which it has already been
+called before, an exception of L<type
+X::Proc::Async::AlreadyStarted|/type/X::Proc::Async::AlreadyStarted> is
+thrown.
+
 =head2 method path
 
     method path(Proc::Async:D:)

lib/Type/X/Proc/Async/AlreadyStarted.pod

@@ -0,0 +1,17 @@
+=begin pod
+
+=TITLE class X::Proc::Async::AlreadyStarted
+
+=SUBTITLE Exception for when you call C<start> on an already started Proc::Async object
+
+    class X::Proc::Async::AlreadyStarted is Exception { ... }
+
+When you call C<start> twice on the same L<Proc::Async|/type/Proc::Async>
+object, the second invocation will die with an
+C<X::Proc::Async::AlreadyStarted> exception.
+
+    my $proc = Proc::Async.new("echo");
+    $proc.start;
+    $proc.start;    # Process has already been started
+
+=end pod