Fix ConcurrentModificationException when iterating through connection

[hovis]

Fix ConcurrentModificationException when iterating through connections returned by getConnections()

Description

Wrap new ArrayList(connections) in synchronized to avoid ConcurrentModificationException

Related Issue

Issue #921
Also related to #902

Motivation and Context

ConcurrentModificationException when looping connections and a connection is created/removed elsewhere at the same time.

How Has This Been Tested?

Tested in production with a tight loop iterating over connections gathering statistics whilst connections are made/removed elsewhere. No more cases of ConcurrentModificationException after the fix.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.