This page explains the various phases comprising Iterator::run_iterator(). Prior to Iterator construction, when command-line options are parsed, Boolean run mode flags corresponding to PRERUN, RUN, and POSTRUN are set in ParallelLibrary. If the user didn't specify any specific run modes, the default is for all three to be true (all phases will execute).

Iterator is constructed.

When called, run_iterator() sequences:

initialize_run(): unconditionally called, virtual. Performs common initialization such as allocating workspaces, setting communicators and evaluation counts. When re-implementing this virtual, a derived class must call its nearest parent's initialize_run(), typically before performing its own implementation steps.
Not implemented: pre-run input
IF PRERUN, invoke pre_run(): virtual function; default no-op. Purpose: derived classes should implement pre_run() if they are able to generate all parameter sets (variables) at once, separate from run(). Derived implementations should call their nearest parent's pre_run(), typically before performing their own steps.
IF PRERUN, invoke pre_output(): non-virtual function; if user requested, output variables to file.
Not implemented: run input
IF RUN, invoke virtual function run(). Purpose: at a minimum, evaluate parameter sets through computing responses; for iterators without pre/post capability, their entire implementation is in run() and this is a reasonable default for new Iterators.
Not implemented: run output
IF POSTRUN, invoke post_input(): virtual function, default only print helpful message on mode. Purpose: derived iterators supporting post-run input from file must implement to read file and populate variables/responses (and possibly best points) appropriately. Implementations must check if the user requested file input.
IF POSTRUN, invoke post_run(): virtual function. Purpose: generate statistics / final results. Any analysis that can be done solely on tabular data read by post_input() can be done here. Derived re-implementations should call their nearest parent's post-run(), typically after performing their specific post-run activities.
Not implemented: post-run output
finalize_run(): unconditionally called, virtual. Purpose: free workspaces. Default base class behavior is no-op, however, derived implementations should call their nearest parent's finalize_run after performing their specialized portions.

Iterator is destructed.