When you use callback routines, and invoke the parallel implementation of ILOG CPLEX optimizers, you need to be aware that the ILOG CPLEX environment passed to the callback routine corresponds to an individual ILOG CPLEX thread rather than to the original environment created. ILOG CPLEX frees this environment when finished with the thread. This does not affect most uses of the callback function. However, keep in mind that ILOG CPLEX associates problem objects, parameter settings, and message channels with the environment that specifies them. ILOG CPLEX therefore frees these items when it removes that environment; if the callback uses routines like CPXcreateprob, CPXcloneprob, or CPXgetchannels, those objects remain allocated only as long as the associated environment does. (You should not change parameters from within a callback.) So, applications that access ILOG CPLEX objects in the callback should use the original environment you created if they need to access these objects outside the scope of the callback function.