Looking at the picture below, I noticed that Maven sometimes prints 3 angled brackets (">>>" or "<<<") when invoking particular goals.
What do these angled brackets mean?
All other goal invocations are preceded by 3 hyphens ("---"). My guess is that goals (in this case, the devserver_stop goal) preceded by angled brackets are executed asynchronously. If that's the case, how can I make these goals be executed synchronously?
You are close - the >>> means it is going to fork a new execution of Maven. I couldn't find much detail, but you can look here http://books.sonatype.com/mvnref-book/reference/writing-plugins-sect-plugins-lifecycle.html. I think it's still synchronous from Maven's point of view, but just in a separate execution.
The plugin you're talking about spawns its own threads, so is inherently asynchronous, but that's not to do with Maven.
You can see the configuration of the appengine plugin here http://code.google.com/p/appengine-maven-plugin/source/browse/src/main/java/com/google/appengine/devappserver/DevAppServerAsyncStart.java - it's the @execute phase="package" that means it forks.
