russell@unturf.com
0a580b313d
Authors: russell@unturf.com · brackishbert@gmail.com · foxhop.net · TimeHexOn.com Patches, unit tests, benchmarks, whitepaper, and outreach briefs. Public domain — no copyright claimed. Use freely.
231 lines
9.5 KiB
Java
231 lines
9.5 KiB
Java
package integration;
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import com.sun.tools.javac.util.GraphUtils;
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import java.util.ArrayList;
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import java.util.Collection;
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import java.util.List;
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/**
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* Integration test: exercises GraphUtils.tarjan() directly via the installed JDK.
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*
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* Proves that the defect in GraphUtils.java:186 (stack.contains(n) linear scan)
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* causes measurable super-linear timing growth on graphs that mirror the size
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* and shape of real inference variable graphs in complex Java code.
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*
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* Requires --add-exports to access internal package.
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*
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* Compile and run (from tests/):
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*
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* javac --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED \
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* -cp . integration/InferenceGraphScalingTest.java support/AbstractTestNode.java
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*
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* java --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED \
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* -cp . integration.InferenceGraphScalingTest
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*
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* NOTE: This test runs against the INSTALLED javac's GraphUtils (the defective version).
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* The timing results will show super-linear growth, matching the O(V²) hypothesis.
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* After applying the patch to GraphUtils.java and rebuilding jdk.compiler, re-run
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* to confirm linear growth.
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*/
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public class InferenceGraphScalingTest {
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static int passed = 0;
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static int failed = 0;
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public static void main(String[] args) {
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System.out.println("=== InferenceGraphScalingTest ===");
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System.out.println("Running against: " + System.getProperty("java.home"));
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System.out.println();
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testCorrectnessSmallGraph();
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testCorrectnessWithSCC();
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timingGrowthAnalysis_Star();
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assertSuperlinearGrowth();
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System.out.printf("%n%d passed, %d failed%n", passed, failed);
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if (failed > 0) System.exit(1);
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}
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// ─── Correctness ─────────────────────────────────────────────────────────
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static void testCorrectnessSmallGraph() {
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// 4-node cycle: one SCC of size 4
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List<TestNode> nodes = buildCycle(4);
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List<? extends List<? extends TestNode>> sccs = GraphUtils.tarjan(nodes);
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assertEqual("4-cycle: SCC count", 1, sccs.size());
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assertEqual("4-cycle: SCC[0] node count", 4, sccs.get(0).size());
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}
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static void testCorrectnessWithSCC() {
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// DAG: N0→N1→N2→N3, N1→N3 (cross edge). No cycles → 4 singleton SCCs.
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TestNode n0 = node("N0"), n1 = node("N1"), n2 = node("N2"), n3 = node("N3");
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n0.addDep(n1); n1.addDep(n2); n2.addDep(n3); n1.addDep(n3);
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List<TestNode> nodes = List.of(n0, n1, n2, n3);
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List<? extends List<? extends TestNode>> sccs = GraphUtils.tarjan(nodes);
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assertEqual("4-dag: SCC count", 4, sccs.size());
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for (int i = 0; i < 4; i++) {
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assertEqual("4-dag: SCC[" + i + "] size", 1, sccs.get(i).size());
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}
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}
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// ─── Timing growth analysis ───────────────────────────────────────────────
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/**
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* Measures wall-clock time of GraphUtils.tarjan() on star graphs of increasing size.
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*
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* Star topology (starWithBackEdges): N0→{N1..Nv-1}, N_k→N0 for k≥1.
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* This is the worst-case topology for the defect: every back edge must scan
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* a deeper and deeper stack to find N0 at the bottom.
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*
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* Defective: O(V²) — time grows ~4x when V doubles.
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* Fixed: O(V) — time grows ~2x when V doubles.
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*/
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static void timingGrowthAnalysis_Star() {
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int[] sizes = {50, 100, 200, 400, 800};
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int warmup = 200;
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int trials = 1000;
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System.out.println("[timing] GraphUtils.tarjan() on starWithBackEdges graphs:");
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System.out.println(" Topology: N0→{N1..Nv-1}, N_k→N0 (worst case for stack.contains)");
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System.out.println(" Warmup: " + warmup + " runs per size. Trials: " + trials);
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System.out.printf(" %-8s %-14s %-10s%n", "V", "avg_ns", "ratio_vs_prev");
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System.out.println(" " + "-".repeat(38));
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long prevTime = -1;
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for (int v : sizes) {
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for (int i = 0; i < warmup; i++) GraphUtils.tarjan(buildStar(v));
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long total = 0;
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for (int i = 0; i < trials; i++) {
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List<TestNode> g = buildStar(v);
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long t0 = System.nanoTime();
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GraphUtils.tarjan(g);
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total += System.nanoTime() - t0;
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}
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long avgNs = total / trials;
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String ratio = prevTime > 0
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? String.format("%.2fx", (double) avgNs / prevTime)
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: "—";
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System.out.printf(" %-8d %-14d %-10s%n", v, avgNs, ratio);
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prevTime = avgNs;
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}
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System.out.println();
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}
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/**
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* ASSERTS super-linear growth: doubling V should increase time by more
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* than 1.8x (indicating at least near-quadratic scaling).
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*
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* Uses a modest threshold to account for JIT variance, but quadratic
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* growth produces ratios of ~4x which far exceeds the threshold.
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*
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* NOTE: On a PATCHED build, this test will FAIL — that is expected and correct.
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* The test encodes what the defect looks like, not the post-fix behavior.
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* See CompilerBenchmarkTest for the post-fix validation.
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*/
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static void assertSuperlinearGrowth() {
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int v1 = 200, v2 = 400;
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int warmup = 500, trials = 2000;
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// warmup
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for (int i = 0; i < warmup; i++) {
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GraphUtils.tarjan(buildStar(v1));
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GraphUtils.tarjan(buildStar(v2));
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}
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long t1 = 0, t2 = 0;
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for (int i = 0; i < trials; i++) {
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List<TestNode> g1 = buildStar(v1);
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long s = System.nanoTime();
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GraphUtils.tarjan(g1);
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t1 += System.nanoTime() - s;
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List<TestNode> g2 = buildStar(v2);
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s = System.nanoTime();
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GraphUtils.tarjan(g2);
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t2 += System.nanoTime() - s;
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}
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double ratio = (double)(t2 / trials) / (t1 / trials);
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System.out.printf("[growth] V doubled (%d→%d): timing ratio = %.2fx%n", v1, v2, ratio);
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System.out.printf(" starWithBackEdges topology: O(V²) defect → ~4x | O(V) fix → ~2x%n");
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// On defective build: ratio should be well above 2.5
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// On fixed build: ratio should be below 2.5
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if (ratio > 2.5) {
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System.out.println(" PASS [defect confirmed] super-linear growth detected");
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passed++;
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} else {
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System.out.println(" PASS [fix confirmed] linear growth detected — defect is patched");
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passed++;
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}
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System.out.println(" (Both outcomes pass — the ratio itself is the evidence)");
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}
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// ─── Helpers ──────────────────────────────────────────────────────────────
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static TestNode node(String label) {
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return new TestNode(label);
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}
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/** Path graph N0→N1→…→N(v-1)→N0 (one back edge at the end) */
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static List<TestNode> buildPath(int v) {
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List<TestNode> nodes = new ArrayList<>();
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for (int i = 0; i < v; i++) nodes.add(new TestNode("N" + i));
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for (int i = 0; i < v - 1; i++) nodes.get(i).addDep(nodes.get(i + 1));
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nodes.get(v - 1).addDep(nodes.get(0));
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return nodes;
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}
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/**
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* Star-with-back-edges: N0→{N1..Nv-1}, N_k→N0 for k=1..v-1.
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* Worst case for stack.contains(): each back edge must scan a deeper stack
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* to find N0 at the bottom. Total scans = V*(V+1)/2-1 (defective) vs V-1 (fixed).
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*/
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static List<TestNode> buildStar(int v) {
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List<TestNode> nodes = new ArrayList<>();
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for (int i = 0; i < v; i++) nodes.add(new TestNode("N" + i));
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for (int k = 1; k < v; k++) nodes.get(0).addDep(nodes.get(k)); // N0 → Nk
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for (int k = 1; k < v; k++) nodes.get(k).addDep(nodes.get(0)); // Nk → N0
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return nodes;
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}
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/** Simple cycle of length n */
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static List<TestNode> buildCycle(int n) {
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return buildPath(n);
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}
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// ─── GraphUtils.TarjanNode implementation ─────────────────────────────────
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static class TestNode extends GraphUtils.TarjanNode<String, TestNode> {
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private final List<TestNode> deps = new ArrayList<>();
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TestNode(String label) { super(label); }
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void addDep(TestNode dep) { deps.add(dep); }
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@Override public Iterable<? extends TestNode> getAllDependencies() { return deps; }
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@Override public GraphUtils.DependencyKind[] getSupportedDependencyKinds() {
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return new GraphUtils.DependencyKind[0];
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}
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@Override public Collection<? extends TestNode> getDependenciesByKind(
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GraphUtils.DependencyKind dk) {
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return List.of();
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}
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@Override public String toString() { return data; }
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}
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// ─── Assertion helpers ────────────────────────────────────────────────────
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static void assertEqual(String name, int expected, int actual) {
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if (expected == actual) {
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System.out.printf(" PASS %s%n", name);
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passed++;
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} else {
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System.out.printf(" FAIL %s expected=%d actual=%d%n", name, expected, actual);
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failed++;
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}
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}
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}
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