Allow clearing MEX-file from memory
By default, MEX-files are unlocked, meaning you can clear them at any time. Calling mexLock locks a MEX-file so that you cannot clear it from memory. Call mexUnlock to remove the lock.
mexLock increments a lock count. If you called mexLock n times, call mexUnlock n times to unlock your MEX-file.
See the following examples in matlabroot/extern/examples/mex.