mongodb bulk calls flush concurrently

[jipperinbham]

while doing some integration testing, it was seen that the bulk process was logging a lot of the following:

ERRO[0906] flush error, E11000 duplicate key error index: enron.enron.$_id_ dup key: { : ObjectId('5658643c414f0983b634e231') }
  collection=enron

After taking a look at what could have caused this, it appears as though the 2 second timer can call flushAll at the same time that the manual flush is called here.