According to the documentation,
Shared MCR Instance — When using MATLAB Builder NE, you can create a shared MCR instance, also known as a singleton. The builder creates a single MCR instance for each MATLAB Builder NE component in an application. You can reuse this instance by sharing it among all subsequent class instances within the component. Such sharing results in more efficient memory usage and eliminates the MCR startup cost in each subsequent class instantiation. All class instances share a single MATLAB workspace and share global variables in the MATLAB files used to build the component.
Don't create or use non-constant static state anywhere (in M, C++ or Java code). Code that uses global variables, for example, will likely yield unexpected results if other applications share the MCR's global resources.
