Here, the apply method is modified to update the data and update the counter. If the counter is less than 10, put the vertex back on the global graph lab work queue so that it gets updated again at some point in the future. This process ensures that each vertex is updated 10 times.

Why would we want to do this? Imagine that we want to iterate PageRank 10 times. Then with the use of this counter variable, every node will be updated exactly 10 times.