Address supervisor code re-factoring feedback from Robin

src/Pipe.h

@@ -66,32 +66,72 @@ private:
 	int status_flags[2];
 };
 
+/**
+ * A pair of pipes that can be used for bi-directinoal IPC.
+ */
 class PipePair {
 public:
 
+	/**
+	 * Create a pair of pipes
+	 * @param flags  file descriptor flags to set on pipes
+	 * @status_flags  descriptor status flags to set on pipes
+	 * @fds  may be supplied to open existing file descriptors rather
+	 * than create ones from a new pair of pipes.  Should point to memory
+	 * containing four consecutive file descriptors, "read" end and "write" end
+	 * of the first pipe followed by the "read" end and "write" end of the
+	 * second pipe.
+	 */
 	PipePair(int flags, int status_flags, int* fds = nullptr);
 
+	/**
+	 * @return the pipe used for receiving input
+	 */
 	Pipe& In()
 		{ return pipes[swapped]; }
 
+	/**
+	 * @return the pipe used for sending output
+	 */
 	Pipe& Out()
 		{ return pipes[!swapped]; }
 
+	/**
+	 * @return the pipe used for receiving input
+	 */
 	const Pipe& In() const
 		{ return pipes[swapped]; }
 
+	/**
+	 * @return the pipe used for sending output
+	 */
 	const Pipe& Out() const
 		{ return pipes[!swapped]; }
 
+	/**
+	 * @return a file descriptor that may used for receiving messages by
+	 * polling/reading it.
+	 */
 	int InFD() const
 		{ return In().ReadFD(); }
 
+	/**
+	 * @return a file descriptor that may be used for sending messages by
+	 * writing to it.
+	 */
 	int OutFD() const
 		{ return Out().WriteFD(); }
 
+	/**
+	 * Swaps the meaning of the pipes in the pair.  E.g. call this after
+	 * fork()'ing so that the child process uses the right pipe for
+	 * reading/writing.
+	 */
 	void Swap()
 		{ swapped = ! swapped; }
 
+private:
+
 	Pipe pipes[2];
 	bool swapped = false;
 };