Call StepExecution.onResume in parallel to the extent possible

Author: jglick

src/main/java/org/jenkinsci/plugins/workflow/flow/FlowExecutionList.java

@@ -23,13 +23,20 @@
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.CancellationException;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import java.util.logging.Logger;
+import org.jenkinsci.plugins.workflow.graph.FlowNode;
+import org.jenkinsci.plugins.workflow.graphanalysis.LinearBlockHoppingScanner;
 
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.Beta;
@@ -259,29 +266,19 @@ public void onResumed(@NonNull FlowExecution e) {
             Futures.addCallback(e.getCurrentExecutions(false), new FutureCallback<List<StepExecution>>() {
                 @Override
                 public void onSuccess(@NonNull List<StepExecution> result) {
-                    try {
-                        if (e.isComplete()) {
-                            // WorkflowRun.onLoad will not fireResumed if the execution was already complete when loaded,
-                            // and CpsFlowExecution should not then complete until afterStepExecutionsResumed, so this is defensive.
-                            return;
-                        }
-                        FlowExecutionList list = FlowExecutionList.get();
-                        FlowExecutionOwner owner = e.getOwner();
-                        if (!list.runningTasks.contains(owner)) {
-                            LOGGER.log(Level.WARNING, "Resuming {0}, which is missing from FlowExecutionList ({1}), so registering it now.", new Object[] {owner, list.runningTasks.getView()});
-                            list.register(owner);
-                        }
-                        LOGGER.log(Level.FINE, "Will resume {0}", result);
-                        for (StepExecution se : result) {
-                            try {
-                                se.onResume();
-                            } catch (Throwable x) {
-                                se.getContext().onFailure(x);
-                            }
-                        }
-                    } finally {
-                        e.afterStepExecutionsResumed();
+                    if (e.isComplete()) {
+                        // WorkflowRun.onLoad will not fireResumed if the execution was already complete when loaded,
+                        // and CpsFlowExecution should not then complete until afterStepExecutionsResumed, so this is defensive.
+                        return;
                     }
+                    FlowExecutionList list = FlowExecutionList.get();
+                    FlowExecutionOwner owner = e.getOwner();
+                    if (!list.runningTasks.contains(owner)) {
+                        LOGGER.log(Level.WARNING, "Resuming {0}, which is missing from FlowExecutionList ({1}), so registering it now.", new Object[] {owner, list.runningTasks.getView()});
+                        list.register(owner);
+                    }
+                    LOGGER.log(Level.FINE, "Will resume {0}", result);
+                    new ParallelResumer(result, e::afterStepExecutionsResumed).run();
                 }
 
                 @Override
@@ -294,7 +291,90 @@ public void onFailure(@NonNull Throwable t) {
                     e.afterStepExecutionsResumed();
                 }
 
-            }, Timer.get()); // We always hold RunMap and WorkflowRun locks here, so we resume steps on a different thread to avoid potential deadlocks. See JENKINS-67351.
+            }, MoreExecutors.directExecutor());
         }
     }
+
+    /** Calls {@link StepExecution#onResume} for each step in a running build.
+     * Does so in parallel, but always completing enclosing blocks before the enclosed step.
+     * A simplified version of https://stackoverflow.com/a/67449067/12916, since this should be a tree not a general DAG.
+     */
+    private static final class ParallelResumer {
+
+        private final Runnable onCompletion;
+        /** Step nodes mapped to the step execution. Entries removed when they are ready to be resumed. */
+        private final Map<FlowNode, StepExecution> nodes = new HashMap<>();
+        /** Step nodes currently being resumed. Removed after resumption completes. */
+        private final Set<FlowNode> processing = new HashSet<>();
+        /** Step nodes mapped to the nearest enclosing step node (no entry if at root). */
+        private final Map<FlowNode, FlowNode> enclosing = new HashMap<>();
+
+        ParallelResumer(Collection<StepExecution> executions, Runnable onCompletion) {
+            this.onCompletion = onCompletion;
+            // First look up positions in the flow graph, so that we can compute dependencies:
+            for (StepExecution se : executions) {
+                try {
+                    FlowNode n = se.getContext().get(FlowNode.class);
+                    if (n != null) {
+                        nodes.put(n, se);
+                    } else {
+                        LOGGER.warning(() -> "Could not find FlowNode for " + se + " so it will not be resumed");
+                    }
+                } catch (IOException | InterruptedException x) {
+                    LOGGER.log(Level.WARNING, "Could not look up FlowNode for " + se + " so it will not be resumed", x);
+                }
+            }
+            for (FlowNode n : nodes.keySet()) {
+                LinearBlockHoppingScanner scanner = new LinearBlockHoppingScanner();
+                scanner.setup(n);
+                for (FlowNode parent : scanner) {
+                    if (parent != n && nodes.containsKey(parent)) {
+                        enclosing.put(n, parent);
+                        break;
+                    }
+                }
+            }
+        }
+
+        synchronized void run() {
+            LOGGER.fine(() -> "Checking status with nodes=" + nodes + " enclosing=" + enclosing + " processing=" + processing);
+            if (nodes.isEmpty()) {
+                if (processing.isEmpty()) {
+                    LOGGER.fine("Done");
+                    onCompletion.run();
+                }
+                return;
+            }
+            Map<FlowNode, StepExecution> ready = new HashMap<>();
+            for (Map.Entry<FlowNode, StepExecution> entry : nodes.entrySet()) {
+                FlowNode n = entry.getKey();
+                FlowNode parent = enclosing.get(n);
+                if (parent == null || !nodes.containsKey(parent)) {
+                    ready.put(n, entry.getValue());
+                }
+            }
+            LOGGER.fine(() -> "Ready to resume: " + ready);
+            nodes.keySet().removeAll(ready.keySet());
+            for (Map.Entry<FlowNode, StepExecution> entry : ready.entrySet()) {
+                FlowNode n = entry.getKey();
+                StepExecution exec = entry.getValue();
+                processing.add(n);
+                Timer.get().submit(() -> {
+                    LOGGER.fine(() -> "About to resume " + n + " ~ " + exec);
+                    try {
+                        exec.onResume();
+                    } catch (Throwable x) {
+                        exec.getContext().onFailure(x);
+                    }
+                    LOGGER.fine(() -> "Finished resuming " + n + " ~ " + exec);
+                    synchronized (ParallelResumer.this) {
+                        processing.remove(n);
+                        run();
+                    }
+                });
+            }
+        }
+
+    }
+
 }