Deadlock when third party media employs external lock and ICE is active

[nanang]

ICE transport holds mutex, i.e: group lock, in sending operation and invoking receiving callbacks. If application (e.g: third party media implementation) employs its own mutex, deadlock will potentially occur when the lock order between app mutex and ICE group lock is not uniform.

As described in Group Lock wiki page, external mutex can be synchronized by chaining the external mutex to the group lock. However, currently ICE group lock is not exported so application cannot chain its mutex into ICE group lock.

[ming]

In 4606:

Fixed #1674: Deadlock when third party media employs external lock and ICE is active