Constructors in eigen_typekit are not thread-safe

[meyerj]

Currently constructors in package eigen_typekit have a local instance of the respective type which is initialized and returned by reference from the implemented operator(). This is not thread-safe at all because constructors are singletons registered once when the typekit is loaded.

Each call to operator() should therefore return a new instance by value.

[ahoarau]

Addressed in b8e97bc

[meyerj]

Thanks for the patch!

Some functors still have mutable ptr member variables with a single instance that gets overwritten and is returned by value for each invocation (and in some cases the ptr instance is unused now). That is better than to return by const reference, but not thread-safe if the constructors are invoked concurrently from different threads. I suggest to eliminate all member variables and only return new instances, either a temporary or an instance created as a local variable and returned by value.

[ahoarau]

I added the patch. Sorry I got confused by who was holding the data. Should be good for merge now

[meyerj]

Fixed in #26. Thanks to @ahoarau!