Synchronized collections are broken in their design and, even worst, they currently don't fullfil their contract, i.e., most of the methods aren't synchronized!

Here is a comment in SynchronizedMap that should definitely make you nervous:

todo: also add all other methods.

Similar comments can be found in the other Synchronized collection traits.

Furthermore, these traits are broken in design as ticket #6087 demonstrates.

For the above reasons, I'd highly recommend to 1) add the missing synchronized methods, and 2) deprecate all Synchronized collection traits before shipping 2.11.

However, I realize that providing synchronized collections may still be desiderable (not everyone may be happy to migrate toward a concurrent collection - though, I'd like to know what's the argument for that). For this reason, I think we could provide Synchronized wrappers like Java does. This won't help people that were mixing a Synchronized trait with other collection traits, but I really don't see how we could allow that, and still prevent users from shooting themselves in the foot. If you have a great idea, please do share it.

This ticket is based on the following discussion https://groups.google.com/forum/#!topic/scala-internals/1gCbqTRCxAQ