Add a separate allow_gc flag for the Scans.

theano/gof/link.py

@@ -9,6 +9,8 @@ from theano.gof import utils
 from theano.gof import graph
 from theano.gof.type import Type
 
+from .utils import MethodNotDefined, undef
+
 __excepthook = sys.excepthook
 
 
@@ -181,6 +183,12 @@ raise_with_op.print_thunk_trace = False
 class Linker(object):
     """WRITEME"""
 
+    def clone(allow_gc=undef):
+        new = copy(self)
+        if allow_gc is not undef:
+            new.allow_gc = allow_gc
+        return new
+
     def make_thunk(self):
         """
         This function must return a triplet (function, input_variables, output_variables)
@@ -689,6 +697,11 @@ class WrapLinker(Linker):
             wrapper=self.wrapper)
         return other
 
+    def clone(allow_gc=undef):
+        return self.__class__(
+            linkers=[l.clone(allow_gc=allow_gc)],
+            wrapper=self.wrapper)
+
     def accept(self, fgraph, no_recycling=None):
         """
         @type fgraph: gof.FunctionGraph

theano/gof/utils.py

@@ -39,6 +39,11 @@ def hashtype(self):
     return hash(t.__name__) ^ hash(t.__module__)
 
 
+# Object to mark that a parameter is undefined (useful in cases where
+# None is a valid value with defined semantics)
+undef = object()
+
+
 class MethodNotDefined(Exception):
     """
     To be raised by functions defined as part of an interface.

theano/scan_module/scan_op.py

@@ -22,17 +22,12 @@ import numpy
 import theano
 from theano.compat import exc_message
 from theano.compile import function, Param, Out
-from theano import compile
-from theano import gradient
-from theano.gof.python25 import any, OrderedDict
+from theano import compile, config, gradient, gof, tensor
 from theano.gof import PureOp, Apply
-from theano import gof
+from theano.gof.python25 import any, OrderedDict
 from theano.tensor import TensorType
-from theano import tensor
 from theano.tensor.opt import Shape_i
-from theano.gradient import grad_undefined
-from theano.gradient import DisconnectedType
-from theano.gradient import NullType
+from theano.gradient import grad_undefined, DisconnectedType, NullType
 from theano.compile.profiling import ScanProfileStats
 
 from theano.scan_module import scan_utils
@@ -42,11 +37,18 @@ from theano.scan_module.scan_utils import safe_new, forced_replace
 _logger = logging.getLogger('theano.scan_module.scan_op')
 
 
+from theano.configparser import AddConfigVar, BoolParam
+AddConfigVar('scan.allow_gc',
+             "Allow/disallow gc inside of Scan",
+             BoolParam(False))
+
+
 class Scan(PureOp):
     def __init__(self,
                  inputs,
                  outputs,
                  info,
+                 allow_gc=None
                 ):
         """
         :param inputs: inputs of the inner function of scan
@@ -55,9 +57,13 @@ class Scan(PureOp):
             the scan op (like number of different types of
             arguments, name, mode, if it should run on GPU or
             not, etc.)
+        :param allow_gc: Use the gc in the inner function or not
+            (independant of the outer function)
         """
         if 'gpua' not in info:
             info['gpua'] = False
+        if allow_gc is None:
+            allow_gc = config.scan.allow_gc
         # adding properties into self
         self.inputs = inputs
         self.outputs = outputs
@@ -113,6 +119,9 @@ class Scan(PureOp):
             else:
                 self.mode_instance.message = "Scan sub profile"
         else:
+            mode_instance = mode_instance.__type__(
+                optimizer=mode_instance.provided_optimizer,
+                linker=mode_instance.provided_linker.clone(allow_gc=allow_gc))
             self.mode_instance = mode_instance
 
         if not hasattr(self, 'name') or self.name is None:
@@ -426,10 +435,10 @@ class Scan(PureOp):
         if not 'destroy_map' in other.info:
             other.info['destroy_map'] = OrderedDict()
         keys_to_check = ['truncate_gradient', 'profile',
-                         'n_seqs', 'tap_array', 'name',
+                         'n_seqs', 'tap_array',
                          'as_while', 'n_mit_sot', 'destroy_map',
                          'n_nit_sot', 'n_shared_outs',
-                         'n_sit_sot', 'gpu', 'n_mit_mot_outs',
+                         'n_sit_sot', 'gpu', 'gpua', 'n_mit_mot_outs',
                          'n_mit_mot', 'mit_mot_out_slices']
         # This are some safety checks ( namely that the inner graph has the
         # same number of inputs and same number of outputs )