provide a way for running critical region

Sometime we need to execute a piece of code against the repository that must not be executed concurrently. A typical use case is the allocation of folder hierarchies when we're importing documents.

The main problem comes with the transaction isolation. The container is injecting a transaction in the thread, which forbid the thread to see the changes achieved by other threads until the transaction commit.

We may work-around this by providing a runner that will

• acquire a document lock
• enter the critical section
• reset the transaction context (commit, disassociate session, start)
• release the document lock