Possible deadlock in thread safe algorithms

[sidml]

When I try replacing CXXGRAPH::Graph with CXXGRAPH::Graph_TS in the dijkstra/bellman-ford tests, the algorithm seems to freeze. It could be because of possible deadlock while calling thread safe functions like getNodeSet. The algorithm has already acquired the lock, so when getNodeSet again tries to acquire lock, it results in a dead-lock.
It will be great if someone can investigate and correct the issue.

[ZigRazor]

This issue should be closed with #93