Skip to content

Commit

Permalink
Non-recursive implementation of DependencyGraph to avoid stack overfl…
Browse files Browse the repository at this point in the history 
…ow (#590)
  • Loading branch information
@ThomasHaas
ThomasHaas authored Dec 12, 2023
1 parent c73aa37 commit c8111be
Showing 1 changed file with 116 additions and 47 deletions.
163 changes: 116 additions & 47 deletions dartagnan/src/main/java/com/dat3m/dartagnan/utils/dependable/DependencyGraph.java
View file
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
import java.util.function.Function;

public class DependencyGraph<T> {

//TODO: Maybe add a way to enable Identity-based hashmaps
private final Map<T, Node> nodeMap;
private List<Node> nodeList;
Expand Down Expand Up @@ -80,12 +81,12 @@ private Node getNodeInternal(T item) {
}

private void initializeNodes() {
Queue<Node> workingQueue = new ArrayDeque<>(nodeMap.values());
final Queue<Node> workingQueue = new ArrayDeque<>(nodeMap.values());
while (!workingQueue.isEmpty()) {
Node node = workingQueue.remove();
final Node node = workingQueue.remove();
for (T dependency : dependencyMap.apply(node.content)) {
boolean isNew = !nodeMap.containsKey(dependency);
Node depNode = getNodeInternal(dependency);
final boolean isNew = !nodeMap.containsKey(dependency);
final Node depNode = getNodeInternal(dependency);
node.dependencies.add(depNode);
depNode.dependents.add(node);
if (isNew) {
Expand All @@ -105,9 +106,11 @@ private void tarjan() {
topIndex = -1;
stack.clear();

final Deque<StackFrame> recursionStack = new ArrayDeque<>();
for (Node node : nodeMap.values()) {
if (!node.wasVisited()) {
strongConnect(node);
recursionStack.push(new StackFrame(node, node.getDependents().iterator()));
strongConnect(recursionStack);
}
}

Expand All @@ -118,47 +121,86 @@ private void tarjan() {

// Create sorted list of all nodes
// and sort their dependencies/dependents as well
Comparator<Node> cmp = Comparator.comparingInt(Node::getTopologicalIndex);
final Comparator<Node> cmp = Comparator.comparingInt(Node::getTopologicalIndex);
nodeList = ImmutableList.sortedCopyOf(cmp, nodeMap.values());
for (Node node : nodeList){
node.getDependencies().sort(cmp);
node.getDependents().sort(cmp);
}

Collections.reverse(sccs);

}

private void strongConnect(Node v) {
v.index = index;
v.lowlink = index;
stack.push(v);
v.isOnStack = true;
index++;
/*
A non-recursive implementation of the recursive DFS-based algorithm
found at the bottom of this class.
*/
private void strongConnect(Deque<StackFrame> recursionStack) {
Node lastVisited = null;
while (!recursionStack.isEmpty()) {
final StackFrame frame = recursionStack.getLast();
final Node v = frame.node;
final Iterator<Node> successorsToProcess = frame.iterator;

if (!v.wasVisited()) {
// Start of recursion
v.index = index;
v.lowlink = index;
stack.push(v);
v.isOnStack = true;
index++;
} else {
// Recursion in progress (we returned from a deeper recursion level)
assert (lastVisited != null);
v.lowlink = Math.min(v.lowlink, lastVisited.lowlink);
}

for (Node w : v.getDependents()) {
if (!w.wasVisited()) {
strongConnect(w);
v.lowlink = Math.min(v.lowlink, w.lowlink);
boolean recursionDone = true;
while (successorsToProcess.hasNext()) {
final Node w = successorsToProcess.next();
if (!w.wasVisited()) {
// Prepare for recursive call
recursionStack.addLast(new StackFrame(w, w.getDependents().iterator()));
recursionDone = false;
break;
} else if (w.isOnStack) {
v.lowlink = Math.min(v.lowlink, w.index);
}
}
else if (w.isOnStack) {
v.lowlink = Math.min(v.lowlink, w.index);

if (!recursionDone) {
// Recurse deeper
continue;
}

if (v.lowlink == v.index) {
final Set<Node> scc = new HashSet<>();
sccs.add(scc);
v.topologicalIndex = ++topIndex;
Node w;
do {
w = stack.pop();
w.isOnStack = false;
scc.add(w);
w.scc = scc;
w.topologicalIndex = v.getTopologicalIndex();
} while (w != v);
}

// Recursion done
recursionStack.removeLast();
lastVisited = v;
}
}

// Used to implement DFS recursion-free
private class StackFrame {
private final Node node;
private final Iterator<Node> iterator;

if (v.lowlink == v.index) {
Set<Node> scc = new HashSet<>();
sccs.add(scc);
v.topologicalIndex = ++topIndex;
Node w;
do {
w = stack.pop();
w.isOnStack = false;
scc.add(w);
w.scc = scc;
w.topologicalIndex = v.getTopologicalIndex();
} while (w != v);
public StackFrame(Node node, Iterator<Node> iterator) {
this.node = node;
this.iterator = iterator;
}
}

Expand Down Expand Up @@ -186,22 +228,11 @@ private Node(T content) {
}

public T getContent() { return content; }
public int getTopologicalIndex() { return topologicalIndex; }

public List<Node> getDependents() {
return dependents;
}

public List<Node> getDependencies() {
return dependencies;
}

public Set<Node> getSCC() {
return scc;
}

public int getTopologicalIndex() {
return topologicalIndex;
}
public List<Node> getDependents() { return dependents; }
public List<Node> getDependencies() { return dependencies; }
public Set<Node> getSCC() { return scc; }

@Override
public int hashCode() {
Expand All @@ -216,7 +247,7 @@ public boolean equals(Object obj) {
} else if (obj == null || obj.getClass() != getClass()) {
return false;
}
Node node = (Node)obj;
final Node node = (Node)obj;
return node.content.equals(this.content);
}

Expand All @@ -225,4 +256,42 @@ public String toString() {
return content.toString();
}
}

// -------------------------------------------------------------------
// -------- Original (recursive) strongConnect implementation --------
// -------------------------------------------------------------------
/*
private void strongConnect(Node v) {
v.index = index;
v.lowlink = index;
stack.push(v);
v.isOnStack = true;
index++;
for (Node w : v.getDependents()) {
if (!w.wasVisited()) {
strongConnect(w);
v.lowlink = Math.min(v.lowlink, w.lowlink);
} else if (w.isOnStack) {
v.lowlink = Math.min(v.lowlink, w.index);
}
}
if (v.lowlink == v.index) {
Set<Node> scc = new HashSet<>();
sccs.add(scc);
v.topologicalIndex = ++topIndex;
Node w;
do {
w = stack.pop();
w.isOnStack = false;
scc.add(w);
w.scc = scc;
w.topologicalIndex = v.getTopologicalIndex();
} while (w != v);
}
}
*/
// -------------------------------------------------------------------
}

0 comments on commit c8111be

Please sign in to comment.