save_state not working with multicore

[MihaiBabiac]

It's impossible to run the code with both --multicore and --save_state at the same time. The reason is that the code tries to pickle the process pool, which is not possible, leading to a crash.

See below my fix for this issue.

--- a/PonyGE2/src/utilities/algorithm/state.py
+++ b/PonyGE2/src/utilities/algorithm/state.py
@@ -1,6 +1,9 @@
 import pickle
 import random
 from os import path
+from multiprocessing import Pool
+
+from utilities.algorithm.initialise_run import pool_init
 
 
 def create_state(individuals):
@@ -32,6 +35,10 @@ def create_state(individuals):
     pickle_params = {param: (check_name(params[param]) if callable(
         params[param]) else params[param]) for param in params}
 
+    # the process pool is not picklable, so we don't save it
+    if "POOL" in pickle_params:
+        del pickle_params["POOL"]
+
     # Create a picklable version of the trackers module.
     pickle_trackers = {i: getattr(trackers, i) for i in dir(trackers)
                        if not i.startswith("__")}
@@ -123,6 +130,11 @@ def set_state(state):
     for param in state['params']:
         params[param] = state['params'][param]
 
+    if params['MULTICORE']:
+        # initialize pool if multi-core is enabled
+        params['POOL'] = Pool(processes=params['CORES'], initializer=pool_init,
+                              initargs=(params,))
+
     # Set correct param imports for specified function options, including
     # error metrics and fitness functions.
     set_param_imports()