wave9 complete: 458/207 — airflow/argo/pytorch-0003/tf/jax/pyg/grpc/thrift + graphhopper/valhalla
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130
defects/argo-workflows/patch/argo-0001-get-task-linear-scan.md
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130
defects/argo-workflows/patch/argo-0001-get-task-linear-scan.md
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# argo-0001 — O(N) Linear Scan in GetTask() Called Inside DAG Execution Loop
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**Severity:** HIGH
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**Complexity:** O(N·D) → O(D) per execution cycle, overall O(N²) → O(N)
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**CWE:** CWE-407 (Algorithmic Complexity)
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## Affected File
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`workflow/controller/dag.go` lines 83–89
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## Defective Code
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```go
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// dagContext holds context information about this context's DAG
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type dagContext struct {
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// tasks are all the tasks in the template
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tasks []wfv1.DAGTask // <-- stored as a SLICE
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...
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}
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// GetTask returns the DAGTask for the given taskName.
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// Called from: resolveDependencies, assessDAGPhase, executeDAG task loop,
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// ancestry.go GetTaskDependencies, validate.go
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func (d *dagContext) GetTask(ctx context.Context, taskName string) *wfv1.DAGTask {
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for _, task := range d.tasks { // O(N) linear scan
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if task.Name == taskName {
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return &task
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}
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}
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panic("target " + taskName + " does not exist")
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}
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```
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**Why it is O(N²):** `GetTask()` is called multiple times per task during
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`executeDAG()`, which itself iterates over all tasks (or target tasks). The
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outer loop runs once per task being executed. Each call to `GetTask()` scans
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the entire `tasks` slice. For a DAG with N tasks, this yields O(N²) total
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comparisons per reconciliation cycle.
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### Call graph (defective paths)
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```
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executeDAG()
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└── for _, taskName := range targetTasks [O(N) tasks]
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├── GetTask(taskName) [O(N) each]
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├── GetTask(taskName).Hooks → GetTask(taskName) [O(N) each]
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└── GetTask(taskName).GetExitHook(...) [O(N) each]
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assessDAGPhase()
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└── for _, depName := range targetTasks [O(N)]
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└── GetTask(depName) [O(N) each]
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ancestry.go:GetTaskAncestry()
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└── recursive DFS over all ancestors
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└── GetTaskDependencies → resolveDependencies
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└── GetTask(taskName) [O(N) each]
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ancestry.go:getTaskDependsLogic()
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└── for _, dependency := range dagTask.Dependencies [O(D)]
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└── GetTask(dependency) [O(N) each]
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```
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Note: `dagValidationContext.GetTask()` in `validate.go:1315` correctly uses a
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`map[string]wfv1.DAGTask` for O(1) lookup. The runtime `dagContext` uses a
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slice — this discrepancy is the defect.
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## Fixed Code
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### Step 1: Add a task lookup map to `dagContext`
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```go
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type dagContext struct {
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boundaryName string
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boundaryID string
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tasks []wfv1.DAGTask
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taskByName map[string]*wfv1.DAGTask // <-- add this field
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...
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}
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```
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### Step 2: Populate the map in `executeDAG` where dagContext is constructed
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```go
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dagCtx := &dagContext{
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boundaryName: nodeName,
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boundaryID: node.ID,
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tasks: tmpl.DAG.Tasks,
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visited: make(map[string]bool),
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tmpl: tmpl,
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wf: woc.wf,
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tmplCtx: tmplCtx,
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dependencies: make(map[string][]string),
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dependsLogic: make(map[string]string),
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log: woc.log,
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}
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// Build O(1) task lookup map
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dagCtx.taskByName = make(map[string]*wfv1.DAGTask, len(tmpl.DAG.Tasks))
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for i := range dagCtx.tasks {
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dagCtx.taskByName[dagCtx.tasks[i].Name] = &dagCtx.tasks[i]
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}
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```
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### Step 3: Replace GetTask body
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```go
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func (d *dagContext) GetTask(ctx context.Context, taskName string) *wfv1.DAGTask {
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if task, ok := d.taskByName[taskName]; ok {
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return task
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}
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panic("target " + taskName + " does not exist")
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}
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```
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## Complexity Analysis
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| Version | GetTask | Per executeDAG cycle | N=500 tasks |
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|---------|---------|---------------------|-------------|
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| Defective | O(N) | O(N²) | ~125,000 compares |
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| Fixed | O(1) | O(N) | ~500 lookups |
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For a DAG with 500 tasks, the fixed version performs 250× fewer operations per
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reconciliation cycle.
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## Trigger Path
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Every time Argo's workflow controller reconciles a running DAG workflow, it
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calls `executeDAG()` → `executeDAGTask()` for each pending task. With N=500 tasks
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and 3 `GetTask()` calls per task in the hot path, each reconciliation does 750×500=375,000
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string comparisons instead of 750 map lookups. At 1 reconcile/second for a
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long-running workflow, this adds seconds of unnecessary CPU per minute.
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245
defects/argo-workflows/unit/ArgoGetTaskAlgorithm.java
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245
defects/argo-workflows/unit/ArgoGetTaskAlgorithm.java
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package unit;
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import java.util.*;
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/**
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* argo-0001 — O(N) linear GetTask() scan inside O(N) DAG execution loop
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*
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* Simulates the defective GetTask() from:
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* workflow/controller/dag.go:83-89
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*
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* Defect: dagContext stores tasks as []DAGTask (slice). GetTask(name) does
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* linear scan. Called O(N) times per executeDAG() cycle → O(N²) total.
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*
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* Fix: Build a map[string]*DAGTask at dagContext construction time → O(1) lookup.
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*
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* The unit test simulates:
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* 1. A DAGContext with N tasks (stored as list in defective, map in fixed)
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* 2. An executeDAG loop that calls GetTask() once per targetTask
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* 3. Counts total comparisons to confirm O(N²) vs O(N)
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*/
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public class ArgoGetTaskAlgorithm {
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static int opCount = 0;
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static void check(String desc, boolean cond) {
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System.out.println((cond ? "PASS" : "FAIL") + ": " + desc);
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if (!cond) throw new AssertionError("FAIL: " + desc);
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}
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// -----------------------------------------------------------------------
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// Simulated DAGTask
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// -----------------------------------------------------------------------
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static class DAGTask {
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final String name;
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final List<String> dependencies;
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DAGTask(String name, List<String> deps) {
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this.name = name;
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this.dependencies = deps;
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}
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}
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// -----------------------------------------------------------------------
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// DEFECTIVE: tasks stored as List<DAGTask>, GetTask does linear scan
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// -----------------------------------------------------------------------
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static class DefectiveDagContext {
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final List<DAGTask> tasks;
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DefectiveDagContext(List<DAGTask> tasks) {
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this.tasks = new ArrayList<>(tasks);
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}
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DAGTask getTask(String taskName) {
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for (DAGTask task : tasks) { // O(N) scan
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opCount++;
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if (task.name.equals(taskName)) {
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return task;
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}
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}
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throw new RuntimeException("task not found: " + taskName);
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}
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// Simulates executeDAG: for each target task, call getTask() 3 times
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// (matches the 3 GetTask calls on lines 292, 300, 307 in dag.go)
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void executeDAG(List<String> targetTasks) {
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for (String taskName : targetTasks) {
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getTask(taskName); // line 292: task := dagCtx.GetTask(ctx, taskName)
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getTask(taskName); // line 300: dagCtx.GetTask(ctx, taskName).Hooks
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getTask(taskName); // line 307: dagCtx.GetTask(ctx, taskName).GetExitHook(...)
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}
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}
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}
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// -----------------------------------------------------------------------
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// FIXED: tasks stored as Map<String, DAGTask>, GetTask does O(1) lookup
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// -----------------------------------------------------------------------
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static class FixedDagContext {
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final List<DAGTask> tasks;
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final Map<String, DAGTask> taskByName;
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FixedDagContext(List<DAGTask> tasks) {
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this.tasks = new ArrayList<>(tasks);
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this.taskByName = new HashMap<>(tasks.size() * 2);
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for (DAGTask t : tasks) {
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this.taskByName.put(t.name, t);
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}
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}
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DAGTask getTask(String taskName) {
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opCount++; // count each lookup
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DAGTask task = taskByName.get(taskName);
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if (task == null) throw new RuntimeException("task not found: " + taskName);
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return task;
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}
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void executeDAG(List<String> targetTasks) {
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for (String taskName : targetTasks) {
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getTask(taskName);
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getTask(taskName);
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getTask(taskName);
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}
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}
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}
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// Build N tasks (all as target tasks — worst case: getTask scans entire list)
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static List<DAGTask> buildTasks(int n) {
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List<DAGTask> tasks = new ArrayList<>(n);
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for (int i = 0; i < n; i++) {
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tasks.add(new DAGTask("task-" + i, Collections.emptyList()));
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}
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return tasks;
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}
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public static void main(String[] args) {
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int passed = 0;
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int total = 0;
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// ------------------------------------------------------------------
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// Test 1: Correctness — both return same task
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// ------------------------------------------------------------------
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total++;
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{
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List<DAGTask> tasks = buildTasks(10);
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DefectiveDagContext def = new DefectiveDagContext(tasks);
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FixedDagContext fix = new FixedDagContext(tasks);
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opCount = 0;
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DAGTask defTask = def.getTask("task-7");
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opCount = 0;
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DAGTask fixTask = fix.getTask("task-7");
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check("Correctness: both find task-7", defTask.name.equals("task-7") && fixTask.name.equals("task-7"));
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passed++;
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}
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// ------------------------------------------------------------------
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// Test 2: Op-count for getTask on last element — defective is O(N)
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// ------------------------------------------------------------------
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total++;
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{
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int n = 100;
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List<DAGTask> tasks = buildTasks(n);
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DefectiveDagContext def = new DefectiveDagContext(tasks);
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FixedDagContext fix = new FixedDagContext(tasks);
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opCount = 0;
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def.getTask("task-99"); // last element -> worst case: N comparisons
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long defOps = opCount;
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opCount = 0;
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fix.getTask("task-99");
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long fixOps = opCount;
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System.out.printf(" Single getTask (last of N=%d): defective=%d ops, fixed=%d ops%n",
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n, defOps, fixOps);
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check("Defective getTask(last) scans all N elements", defOps == n);
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check("Fixed getTask is O(1)", fixOps == 1);
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passed += 2;
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total++;
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}
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// ------------------------------------------------------------------
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// Test 3: executeDAG op-count ratio — O(N²) vs O(N)
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// ------------------------------------------------------------------
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total++;
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{
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int n = 300;
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List<DAGTask> tasks = buildTasks(n);
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List<String> targetTasks = new ArrayList<>();
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for (DAGTask t : tasks) targetTasks.add(t.name);
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DefectiveDagContext def = new DefectiveDagContext(tasks);
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FixedDagContext fix = new FixedDagContext(tasks);
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opCount = 0;
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def.executeDAG(targetTasks);
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long defOps = opCount;
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opCount = 0;
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fix.executeDAG(targetTasks);
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long fixOps = opCount;
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double ratio = (double) defOps / fixOps;
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System.out.printf(" executeDAG N=%d: defective=%d ops, fixed=%d ops, ratio=%.1fx%n",
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n, defOps, fixOps, ratio);
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// Defective: 3 calls × avg N/2 scans × N tasks = 3N²/2
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// Fixed: 3 calls × 1 lookup × N tasks = 3N
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// Expected ratio ≈ N/2 = 150 for N=300; require >= 50x conservatively
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check("Op-count ratio >= 50x for executeDAG N=" + n, ratio >= 50.0);
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passed++;
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}
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// ------------------------------------------------------------------
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// Test 4: Quadratic growth — ops at N=200 should be ~4x ops at N=100
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// ------------------------------------------------------------------
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total++;
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{
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List<DAGTask> tasks100 = buildTasks(100);
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List<DAGTask> tasks200 = buildTasks(200);
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List<String> target100 = new ArrayList<>(); for (DAGTask t : tasks100) target100.add(t.name);
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List<String> target200 = new ArrayList<>(); for (DAGTask t : tasks200) target200.add(t.name);
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opCount = 0;
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new DefectiveDagContext(tasks100).executeDAG(target100);
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long ops100 = opCount;
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opCount = 0;
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new DefectiveDagContext(tasks200).executeDAG(target200);
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long ops200 = opCount;
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double growthRatio = (double) ops200 / ops100;
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System.out.printf(" Defective growth (200 vs 100): %.2fx (expected ~4x for O(N²))%n",
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growthRatio);
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check("Defective shows quadratic growth (ratio >= 3.5x)", growthRatio >= 3.5);
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passed++;
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}
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// ------------------------------------------------------------------
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// Test 5: Linear growth for fixed
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// ------------------------------------------------------------------
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total++;
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{
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List<DAGTask> tasks100 = buildTasks(100);
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List<DAGTask> tasks200 = buildTasks(200);
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List<String> target100 = new ArrayList<>(); for (DAGTask t : tasks100) target100.add(t.name);
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List<String> target200 = new ArrayList<>(); for (DAGTask t : tasks200) target200.add(t.name);
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opCount = 0;
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new FixedDagContext(tasks100).executeDAG(target100);
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long ops100 = opCount;
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opCount = 0;
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new FixedDagContext(tasks200).executeDAG(target200);
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long ops200 = opCount;
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double growthRatio = (double) ops200 / ops100;
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System.out.printf(" Fixed growth (200 vs 100): %.2fx (expected ~2x for O(N))%n",
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growthRatio);
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check("Fixed shows linear growth (ratio < 3.0x)", growthRatio < 3.0);
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passed++;
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}
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System.out.printf("%n%d/%d PASS%n", passed, total);
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}
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}
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