Add topological sort and cycle detection
This commit is contained in:
Abdelrahman Said
+149
-29
@@ -6,6 +6,8 @@
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#include <stdlib.h>
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#include <string.h>
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wp_intern WpLogger _log = { .name = wpStr8LitRo("dag_man") };
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/* ---------------------------------------------------------------------------
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* Pool allocator (arena-backed, intrusive free list)
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* -------------------------------------------------------------------------*/
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@@ -63,6 +65,7 @@ typedef struct {
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u64 index;
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u64 generation;
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} PrNodeId;
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typedef PrNodeId *PrNodeIdArray;
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typedef struct {
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union {
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@@ -124,6 +127,11 @@ wp_intern void prGraphInit(PrGraph *graph, WpAllocator *allocator, u64 capacity)
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graph->max_count_ever = 0;
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graph->count = 0;
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if (!graph->nodes || !graph->vertices) {
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graph->capacity = 0;
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return;
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}
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prPoolInit(&graph->vertex_pool, allocator, sizeof(PrEdgeVertex));
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memset(graph->nodes, 0, capacity * sizeof(PrNode));
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memset(graph->vertices, 0, capacity * sizeof(PrEdgeVertex));
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@@ -134,40 +142,73 @@ wp_intern void prGraphInit(PrGraph *graph, WpAllocator *allocator, u64 capacity)
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}
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}
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wp_intern void prGraphAddEdge(PrGraph *graph, PrNodeId from, PrNodeId to) {
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if (!prGraphIsActiveNode(graph, from) || !prGraphIsActiveNode(graph, to)) { return; }
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if (from.index == to.index) { return; }
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/* ---------------------------------------------------------------------------
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* Kahn's algorithm — topological sort / cycle detection
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*
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* Returns a WpArray of PrNodeId (sorted topologically). If the result count
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* is less than graph->count, the graph contains a cycle.
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* -------------------------------------------------------------------------*/
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PrEdgeVertex *edge = (PrEdgeVertex *)prPoolAlloc(&graph->vertex_pool);
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wp_intern PrNodeId *prGraphTopologicalSort(PrGraph *graph, const WpAllocator *allocator) {
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if (graph->count == 0) { return NULL; }
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if (!graph->nodes || graph->capacity == 0) { return NULL; }
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PrEdgeVertex *src = &graph->vertices[from.index];
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PrEdgeVertex *dst = &graph->vertices[to.index];
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PrNodeIdArray result = wpArrayAllocCapacity(PrNodeId, allocator, graph->count, WP_ARRAY_INIT_NONE);
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if (!result) { return NULL; }
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edge->source = from;
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edge->target = to;
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edge->next_forward = src->next_forward;
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edge->next_backward = dst->next_backward;
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src->next_forward = edge;
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dst->next_backward = edge;
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WpAllocator local_arena = wpMemArenaAllocatorInitZero(KiB(16));
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WpU64Array in_degree = wpArrayAllocCapacity(u64, &local_arena, graph->capacity, WP_ARRAY_INIT_FILLED);
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if (!in_degree) { return result; }
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memset(in_degree, 0, wpArrayCapacity(in_degree) * sizeof(u64));
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for (u64 i = 0; i < graph->max_count_ever; i++) {
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PrNodeId id = prGraphGetNode(graph, i);
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if (!prGraphIsActiveNode(graph, id)) { continue; }
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PrEdgeVertex *vertex = &graph->vertices[i];
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PrEdgeVertex *curr = vertex->next_forward;
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while (curr) {
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in_degree[curr->target.index]++;
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curr = curr->next_forward;
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}
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}
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WpQueue queue = wpQueueAlloc(u64, &local_arena, graph->count);
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for (u64 i = 0; i < graph->max_count_ever; i++) {
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PrNodeId id = prGraphGetNode(graph, i);
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if (!prGraphIsActiveNode(graph, id)) { continue; }
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if (in_degree[i] == 0) {
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wpQueuePush(u64, &queue, &i);
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}
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}
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while (queue.count > 0) {
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u64 *node_idx = wpQueuePop(u64, &queue);
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if (!node_idx) { break; }
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PrNodeId id = prGraphGetNode(graph, *node_idx);
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wpArrayAppendCapped(PrNodeId, result, &id);
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PrEdgeVertex *vertex = &graph->vertices[*node_idx];
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PrEdgeVertex *curr = vertex->next_forward;
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while (curr) {
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u64 target_idx = curr->target.index;
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if (in_degree[target_idx] > 0) {
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in_degree[target_idx]--;
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if (in_degree[target_idx] == 0) {
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wpQueuePush(u64, &queue, &target_idx);
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}
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}
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curr = curr->next_forward;
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}
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}
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return result;
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}
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wp_intern PrNodeId prGraphAddNode(PrGraph *graph, PrNodeType type) {
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u64 idx = graph->free_head;
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if (idx == INVALID_NODE_INDEX) { return INVALID_NODE_ID; }
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PrNode *node = &graph->nodes[idx];
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graph->free_head = node->next_free;
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node->next_free = INVALID_NODE_INDEX;
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node->type = type;
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memset(&node->params, 0, sizeof(node->params));
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graph->count++;
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if (idx + 1 > graph->max_count_ever) { graph->max_count_ever = idx + 1; }
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return (PrNodeId){ .index = idx, .generation = node->generation };
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}
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/* --- edge management -------------------------------------------------- */
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wp_intern void _unlinkForward(PrGraph *graph, PrNodeId from, PrEdgeVertex *edge) {
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if (!prGraphIsActiveNode(graph, from)) { return; }
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@@ -211,6 +252,55 @@ wp_intern void _unlinkBackward(PrGraph *graph, PrNodeId to, PrEdgeVertex *edge)
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}
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}
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wp_intern void prGraphAddEdge(PrGraph *graph, PrNodeId from, PrNodeId to) {
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if (!prGraphIsActiveNode(graph, from) || !prGraphIsActiveNode(graph, to)) { return; }
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if (from.index == to.index) { return; }
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PrEdgeVertex *edge = (PrEdgeVertex *)prPoolAlloc(&graph->vertex_pool);
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if (!edge) { return; }
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edge->source = from;
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edge->target = to;
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/* Link into adjacency chains */
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PrEdgeVertex *src = &graph->vertices[from.index];
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PrEdgeVertex *dst = &graph->vertices[to.index];
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edge->next_forward = src->next_forward;
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edge->next_backward = dst->next_backward;
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src->next_forward = edge;
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dst->next_backward = edge;
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/* Check whether the new edge created a cycle */
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WpAllocator scratch = wpMemArenaAllocatorInitZero(KiB(16));
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PrNodeIdArray sorted = prGraphTopologicalSort(graph, &scratch);
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u64 sorted_count = sorted ? wpArrayCount(sorted) : 0;
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if (sorted_count < graph->count) {
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_unlinkForward(graph, from, edge);
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_unlinkBackward(graph, to, edge);
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prPoolFree(&graph->vertex_pool, edge);
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}
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wpMemArenaAllocatorDestroy(&scratch);
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}
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wp_intern PrNodeId prGraphAddNode(PrGraph *graph, PrNodeType type) {
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u64 idx = graph->free_head;
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if (idx == INVALID_NODE_INDEX) { return INVALID_NODE_ID; }
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PrNode *node = &graph->nodes[idx];
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graph->free_head = node->next_free;
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node->next_free = INVALID_NODE_INDEX;
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node->type = type;
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memset(&node->params, 0, sizeof(node->params));
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graph->count++;
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if (idx + 1 > graph->max_count_ever) { graph->max_count_ever = idx + 1; }
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return (PrNodeId){ .index = idx, .generation = node->generation };
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}
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wp_intern void prGraphRemoveNode(PrGraph *graph, PrNodeId id) {
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if (!prGraphIsActiveNode(graph, id)) { return; }
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@@ -297,6 +387,10 @@ wp_intern void prGraphDump(const PrGraph *graph) {
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i32 main(void) {
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WpAllocator arena = wpMemArenaAllocatorInitZero(MiB(16));
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if (wpMemAllocatorInvalid(&arena)) {
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wpLogFatal(&_log, wpStr8Lit("arena init failed"));
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return 1;
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}
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PrGraph graph = {0};
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prGraphInit(&graph, &arena, 128);
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@@ -349,6 +443,32 @@ i32 main(void) {
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printf("\n");
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prGraphDump(&graph);
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printf("\n=== Try adding cycle 8→1 (should be rejected) ===\n");
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prGraphAddEdge(&graph, n8, n1);
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printf("\n=== Try adding 8→1 again (still rejected) ===\n");
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prGraphAddEdge(&graph, n8, n1);
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printf("\n=== Try adding cycle 7→2 (should be rejected) ===\n\n");
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prGraphAddEdge(&graph, n7, n2);
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prGraphDump(&graph);
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printf("\n=== Topological sort ===\n");
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PrNodeId *sorted = prGraphTopologicalSort(&graph, &arena);
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if (sorted) {
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u64 n = wpArrayCount(sorted);
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printf(" count: %llu / %llu active\n",
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(unsigned long long)n,
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(unsigned long long)graph.count);
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for (u64 i = 0; i < n; i++) {
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printf(" [%llu] idx=%llu gen=%llu\n",
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(unsigned long long)i,
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(unsigned long long)sorted[i].index,
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(unsigned long long)sorted[i].generation);
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}
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}
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wpMemArenaAllocatorDestroy(&arena);
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return 0;
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