the executing state, it might also be invoked on up-to-date
nodes when using Configure().
"""
-
T = self.tm.trace
if T: T.write(self.trace_message('Task.failed_stop()', self.node))
# Invoke will_not_build() to clean-up the pending children
# list.
- self.tm.will_not_build(self.targets)
+ self.tm.will_not_build(self.targets, lambda n: n.set_state(NODE_FAILED))
# Tell the taskmaster to not start any new tasks
self.tm.stop()
T = self.tm.trace
if T: T.write(self.trace_message('Task.failed_continue()', self.node))
- self.tm.will_not_build(self.targets)
-
+ self.tm.will_not_build(self.targets, lambda n: n.set_state(NODE_FAILED))
+
def make_ready_all(self):
"""
Marks all targets in a task ready for execution.
t.set_state(NODE_EXECUTING)
for s in t.side_effects:
s.set_state(NODE_EXECUTING)
- else:
+ else:
for t in self.targets:
# We must invoke visited() to ensure that the node
# information has been computed before allowing the
targets = set(self.targets)
+ pending_children = self.tm.pending_children
parents = {}
for t in targets:
# A node can only be in the pending_children set if it has
if T: T.write(self.trace_message('Task.postprocess()',
t,
'removing'))
+ pending_children.discard(t)
for p in t.waiting_parents:
parents[p] = parents.get(p, 0) + 1
for p in s.waiting_s_e:
if p.ref_count == 0:
self.tm.candidates.append(p)
- self.tm.pending_children.discard(p)
for p, subtract in parents.items():
p.ref_count = p.ref_count - subtract
'adjusting parent ref count'))
if p.ref_count == 0:
self.tm.candidates.append(p)
- self.tm.pending_children.discard(p)
for t in targets:
t.postprocess()
def no_next_candidate(self):
"""
Stops Taskmaster processing by not returning a next candidate.
-
+
Note that we have to clean-up the Taskmaster candidate list
because the cycle detection depends on the fact all nodes have
been processed somehow.
while self.candidates:
candidates = self.candidates
self.candidates = []
- self.will_not_build(candidates, lambda n: n.state < NODE_UP_TO_DATE)
+ self.will_not_build(candidates)
return None
+ def _validate_pending_children(self):
+ """
+ Validate the content of the pending_children set. Assert if an
+ internal error is found.
+
+ This function is used strictly for debugging the taskmaster by
+ checking that no invariants are violated. It is not used in
+ normal operation.
+
+ The pending_children set is used to detect cycles in the
+ dependency graph. We call a "pending child" a child that is
+ found in the "pending" state when checking the dependencies of
+ its parent node.
+
+ A pending child can occur when the Taskmaster completes a loop
+ through a cycle. For example, lets imagine a graph made of
+ three node (A, B and C) making a cycle. The evaluation starts
+ at node A. The taskmaster first consider whether node A's
+ child B is up-to-date. Then, recursively, node B needs to
+ check whether node C is up-to-date. This leaves us with a
+ dependency graph looking like:
+
+ Next candidate \
+ \
+ Node A (Pending) --> Node B(Pending) --> Node C (NoState)
+ ^ |
+ | |
+ +-------------------------------------+
+
+ Now, when the Taskmaster examines the Node C's child Node A,
+ it finds that Node A is in the "pending" state. Therefore,
+ Node A is a pending child of node C.
+
+ Pending children indicate that the Taskmaster has potentially
+ loop back through a cycle. We say potentially because it could
+ also occur when a DAG is evaluated in parallel. For example,
+ consider the following graph:
+
+
+ Node A (Pending) --> Node B(Pending) --> Node C (Pending) --> ...
+ | ^
+ | |
+ +----------> Node D (NoState) --------+
+ /
+ Next candidate /
+
+ The Taskmaster first evaluates the nodes A, B, and C and
+ starts building some children of node C. Assuming, that the
+ maximum parallel level has not been reached, the Taskmaster
+ will examine Node D. It will find that Node C is a pending
+ child of Node D.
+
+ In summary, evaluating a graph with a cycle will always
+ involve a pending child at one point. A pending child might
+ indicate either a cycle or a diamond-shaped DAG. Only a
+ fraction of the nodes ends-up being a "pending child" of
+ another node. This keeps the pending_children set small in
+ practice.
+
+ We can differentiate between the two cases if we wait until
+ the end of the build. At this point, all the pending children
+ nodes due to a diamond-shaped DAG will have been properly
+ built (or will have failed to build). But, the pending
+ children involved in a cycle will still be in the pending
+ state.
+
+ The taskmaster removes nodes from the pending_children set as
+ soon as a pending_children node moves out of the pending
+ state. This also helps to keep the pending_children set small.
+ """
+
+ for n in self.pending_children:
+ assert n.state in (NODE_PENDING, NODE_EXECUTING), \
+ (str(n), StateString[n.state])
+ assert len(n.waiting_parents) != 0, (str(n), len(n.waiting_parents))
+ for p in n.waiting_parents:
+ assert p.ref_count > 0, (str(n), str(p), p.ref_count)
+
+
def trace_message(self, message):
return 'Taskmaster: %s\n' % message
node = node.disambiguate()
state = node.get_state()
+ # For debugging only:
+ #
+ # try:
+ # self._validate_pending_children()
+ # except:
+ # self.ready_exc = sys.exc_info()
+ # return node
+
if CollectStats:
if not hasattr(node, 'stats'):
node.stats = Stats()
exc_value = sys.exc_info()[1]
e = SCons.Errors.ExplicitExit(node, exc_value.code)
self.ready_exc = (SCons.Errors.ExplicitExit, e)
- if T: T.write('Taskmaster: SystemExit\n')
+ if T: T.write(self.trace_message(' SystemExit'))
return node
except Exception, e:
# We had a problem just trying to figure out the
node.set_state(NODE_FAILED)
if S: S.child_failed = S.child_failed + 1
- if T: T.write('Taskmaster:****** <%-10s %-3s %s>\n' %
- (StateString[node.get_state()], node.ref_count, repr(str(node))))
+ if T: T.write(self.trace_message('****** %s\n' % self.trace_node(node)))
continue
if children_not_ready:
if T: T.write(self.trace_message(' adjusting ref count: %s, child %s' %
(self.trace_node(node), repr(str(child)))))
+ if T:
+ for pc in children_pending:
+ T.write(self.trace_message(' adding %s to the pending children set\n' %
+ self.trace_node(pc)))
self.pending_children = self.pending_children | children_pending
-
+
continue
# Skip this node if it has side-effects that are
if S: S.build = S.build + 1
if T: T.write(self.trace_message('Evaluating %s\n' %
self.trace_node(node)))
+
+ # For debugging only:
+ #
+ # try:
+ # self._validate_pending_children()
+ # except:
+ # self.ready_exc = sys.exc_info()
+ # return node
+
return node
return None
return task
- def will_not_build(self, nodes, mark_fail=lambda n: n.state != NODE_FAILED):
+ def will_not_build(self, nodes, node_func=lambda n: None):
"""
- Perform clean-up about nodes that will never be built.
+ Perform clean-up about nodes that will never be built. Invokes
+ a user defined function on all of these nodes (including all
+ of their parents).
"""
+ T = self.trace
+
pending_children = self.pending_children
- to_visit = set()
- for node in nodes:
- # Set failure state on all of the parents that were dependent
- # on this failed build.
- if mark_fail(node):
- node.set_state(NODE_FAILED)
- parents = node.waiting_parents
- to_visit = to_visit | parents
- pending_children = pending_children - parents
+ to_visit = set(nodes)
+ pending_children = pending_children - to_visit
+ if T:
+ for n in nodes:
+ T.write(self.trace_message(' removing %s from the pending children set\n' %
+ self.trace_node(n)))
try:
while 1:
try:
to_visit.remove(node)
else:
break
- if mark_fail(node):
- node.set_state(NODE_FAILED)
- parents = node.waiting_parents
- to_visit = to_visit | parents
- pending_children = pending_children - parents
+
+ node_func(node)
+
+ # Prune recursion by flushing the waiting children
+ # list immediately.
+ parents = node.waiting_parents
+ node.waiting_parents = set()
+
+ to_visit = to_visit | parents
+ pending_children = pending_children - parents
+
+ if T:
+ for p in parents:
+ T.write(self.trace_message(' removing %s from the pending children set\n' %
+ self.trace_node(p)))
except KeyError:
# The container to_visit has been emptied.
pass
else:
desc = desc + \
" Internal Error: no cycle found for node %s (%s) in state %s\n" % \
- (node, repr(node), StateString[node.get_state()])
+ (node, repr(node), StateString[node.get_state()])
raise SCons.Errors.UserError, desc
projects / scons.git / commitdiff