TaskTree: Unwind execution properly on synchronous done

When task or group setup handler finishes synchronously
we may end up with mismatched execution order or may
grow call stack considerably. The fix is to detect
synchronous finishes and leave handling to the synchronous
caller.

Change-Id: Id72cf8cc98e2f53ff601a5e5226cd203a8470aaf
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/tasktree.cpp

@@ -9,6 +9,11 @@
 namespace Utils {
 namespace Tasking {
 
+static TaskAction toTaskAction(bool success)
+{
+    return success ? TaskAction::StopWithDone : TaskAction::StopWithError;
+}
+
 bool TreeStorageBase::isValid() const
 {
     return m_storageData && m_storageData->m_constructor && m_storageData->m_destructor;
@@ -144,13 +149,16 @@ public:
     TaskContainer(TaskTreePrivate *taskTreePrivate, TaskContainer *parentContainer,
                   const TaskItem &task);
     ~TaskContainer();
-    void start();
+    TaskAction start();
+    TaskAction startChildren();
     int selectChildren(); // returns the skipped child count
     void stop();
     bool isRunning() const;
     int taskCount() const;
-    void childDone(bool success);
+    int currentLimit() const;
-    void invokeEndHandler(bool success, bool propagateToParent = true);
+    TaskAction childDone(bool success);
+    void groupDone(bool success);
+    void invokeEndHandler(bool success);
     void resetSuccessBit();
     void updateSuccessBit(bool success);
 
@@ -170,8 +178,9 @@ public:
     GroupConfig m_groupConfig;
     QList<TaskNode *> m_children;
     QList<TaskNode *> m_selectedChildren;
-    int m_currentIndex = -1;
+    int m_doneCount = -1;
     bool m_successBit = true;
+    Guard m_startGuard;
 };
 
 class StorageActivator
@@ -200,7 +209,8 @@ public:
     {
     }
 
-    void start();
+    // If returned value != Start, childDone() needs to be called in parent container (in caller)
+    TaskAction start();
     void stop();
     bool isRunning() const;
     bool isTask() const;
@@ -210,6 +220,7 @@ private:
     const TaskItem::TaskHandler m_taskHandler;
     TaskContainer m_container;
     std::unique_ptr<TaskInterface> m_task;
+    Guard m_startGuard;
 };
 
 class TaskTreePrivate
@@ -227,7 +238,11 @@ public:
             QTC_ASSERT(m_storages.contains(it.key()), qWarning("The registered storage doesn't "
                        "exist in task tree. Its handlers will never be called."));
         }
-        m_root->start();
+        const TaskAction action = m_root->start();
+        if (action == TaskAction::StopWithDone)
+            emitDone();
+        else if (action == TaskAction::StopWithError)
+            emitError();
     }
     void stop() {
         QTC_ASSERT(m_root, return);
@@ -333,25 +348,21 @@ TaskContainer::~TaskContainer()
     deleteStorages();
 }
 
-void TaskContainer::start()
+TaskAction TaskContainer::start()
 {
-    m_currentIndex = 0;
+    m_doneCount = 0;
     m_groupConfig = {};
     m_selectedChildren.clear();
 
     createStorages();
-    {
+    if (m_groupHandler.m_setupHandler || m_groupHandler.m_dynamicSetupHandler) {
         StorageActivator activator(*this);
-        if (m_groupHandler.m_setupHandler) {
         GuardLocker locker(m_taskTreePrivate->m_guard);
+        if (m_groupHandler.m_setupHandler)
             m_groupHandler.m_setupHandler();
-        }
+        if (m_groupHandler.m_dynamicSetupHandler)
-
-        if (m_groupHandler.m_dynamicSetupHandler) {
-            GuardLocker locker(m_taskTreePrivate->m_guard);
             m_groupConfig = m_groupHandler.m_dynamicSetupHandler();
     }
-    }
 
     if (m_groupConfig.action == GroupAction::StopWithDone
         || m_groupConfig.action == GroupAction::StopWithError) {
@@ -359,7 +370,7 @@ void TaskContainer::start()
         const int skippedTaskCount = taskCount();
         m_taskTreePrivate->advanceProgress(skippedTaskCount);
         invokeEndHandler(success);
-        return;
+        return toTaskAction(success);
     }
 
     const int skippedTaskCount = selectChildren();
@@ -367,18 +378,40 @@ void TaskContainer::start()
 
     if (m_selectedChildren.isEmpty()) {
         invokeEndHandler(true);
-        return;
+        return TaskAction::StopWithDone; // TODO: take workflow policy into account?
     }
 
     resetSuccessBit();
 
-    const int childCount = m_selectedChildren.size();
+    GuardLocker locker(m_startGuard);
-    const int startCount = m_parallelLimit ? qMin(m_parallelLimit, childCount) : childCount;
+    return startChildren();
-    for (int i = 0; i < startCount; ++i) {
-        m_selectedChildren.at(i)->start();
-        if (!isRunning())
-            return;
 }
+
+TaskAction TaskContainer::startChildren()
+{
+    const int childCount = m_selectedChildren.size();
+    for (int i = m_doneCount; i < childCount; ++i) {
+        const int limit = currentLimit();
+        if (i >= limit)
+            break;
+
+        const TaskAction action = m_selectedChildren.at(i)->start();
+        if (action == TaskAction::Continue)
+            continue;
+
+        const TaskAction finalizeAction = childDone(action == TaskAction::StopWithDone);
+        if (finalizeAction == TaskAction::Continue)
+            continue;
+
+        int skippedTaskCount = 0;
+        // Skip scheduled but not run yet. The current (i) was already notified.
+        for (int j = i + 1; j < limit; ++j)
+            skippedTaskCount += m_selectedChildren.at(j)->taskCount();
+        m_taskTreePrivate->advanceProgress(skippedTaskCount);
+
+        return finalizeAction;
+    }
+    return TaskAction::Continue;
 }
 
 int TaskContainer::selectChildren()
@@ -403,21 +436,23 @@ void TaskContainer::stop()
     if (!isRunning())
         return;
 
-    if (m_parallelLimit) { // skip not started tasks
+    const int childCount = m_selectedChildren.size();
-        int skippedTaskCount = 0;
+    const int limit = currentLimit();
-        for (int i = m_currentIndex + m_parallelLimit; i < m_selectedChildren.size(); ++i)
-            skippedTaskCount += m_selectedChildren.at(i)->taskCount();
-        m_taskTreePrivate->advanceProgress(skippedTaskCount);
-    }
 
-    m_currentIndex = -1;
+    for (int i = m_doneCount; i < limit; ++i)
-    for (TaskNode *child : std::as_const(m_selectedChildren))
+        m_selectedChildren.at(i)->stop();
-        child->stop();
+
+    int skippedTaskCount = 0;
+    for (int i = limit; i < childCount; ++i)
+        skippedTaskCount += m_selectedChildren.at(i)->taskCount();
+
+    m_taskTreePrivate->advanceProgress(skippedTaskCount);
+    m_doneCount = -1;
 }
 
 bool TaskContainer::isRunning() const
 {
-    return m_currentIndex >= 0;
+    return m_doneCount >= 0;
 }
 
 int TaskContainer::taskCount() const
@@ -425,48 +460,43 @@ int TaskContainer::taskCount() const
     return m_taskCount;
 }
 
-void TaskContainer::childDone(bool success)
+int TaskContainer::currentLimit() const
+{
+    const int childCount = m_selectedChildren.size();
+    return  m_parallelLimit ? qMin(m_doneCount + m_parallelLimit, childCount) : childCount;
+}
+
+TaskAction TaskContainer::childDone(bool success)
 {
     if ((m_workflowPolicy == WorkflowPolicy::StopOnDone && success)
             || (m_workflowPolicy == WorkflowPolicy::StopOnError && !success)) {
         stop();
         invokeEndHandler(success);
-        return;
+        groupDone(success);
+        return toTaskAction(success);
     }
 
-    ++m_currentIndex;
+    ++m_doneCount;
     updateSuccessBit(success);
 
-    if (m_currentIndex == m_selectedChildren.size()) {
+    if (m_doneCount == m_selectedChildren.size()) {
         invokeEndHandler(m_successBit);
-        return;
+        groupDone(m_successBit);
+        return toTaskAction(m_successBit);
     }
 
     if (m_parallelLimit == 0)
-        return;
+        return TaskAction::Continue;
 
-    const int nextIndexToRun = m_currentIndex + m_parallelLimit - 1;
+    if (m_startGuard.isLocked())
-    if (nextIndexToRun < m_selectedChildren.size())
+        return TaskAction::Continue;
-        m_selectedChildren.at(nextIndexToRun)->start();
+
+    return startChildren();
 }
 
-void TaskContainer::invokeEndHandler(bool success, bool propagateToParent)
+void TaskContainer::groupDone(bool success)
 {
-    m_currentIndex = -1;
+    if (m_startGuard.isLocked())
-    m_successBit = success;
-    {
-        StorageActivator activator(*this);
-        if (success && m_groupHandler.m_doneHandler) {
-            GuardLocker locker(m_taskTreePrivate->m_guard);
-            m_groupHandler.m_doneHandler();
-        } else if (!success && m_groupHandler.m_errorHandler) {
-            GuardLocker locker(m_taskTreePrivate->m_guard);
-            m_groupHandler.m_errorHandler();
-        }
-    }
-    deleteStorages();
-
-    if (!propagateToParent)
         return;
 
     if (m_parentContainer) {
@@ -479,6 +509,23 @@ void TaskContainer::invokeEndHandler(bool success, bool propagateToParent)
         m_taskTreePrivate->emitError();
 }
 
+void TaskContainer::invokeEndHandler(bool success)
+{
+    m_doneCount = -1;
+    m_successBit = success;
+    const bool callDoneHandler = success && m_groupHandler.m_doneHandler;
+    const bool callErrorHandler = !success && m_groupHandler.m_errorHandler;
+    if (callDoneHandler || callErrorHandler) {
+        StorageActivator activator(*this);
+        GuardLocker locker(m_taskTreePrivate->m_guard);
+        if (callDoneHandler)
+            m_groupHandler.m_doneHandler();
+        else if (callErrorHandler)
+            m_groupHandler.m_errorHandler();
+    }
+    deleteStorages();
+}
+
 void TaskContainer::resetSuccessBit()
 {
     if (m_selectedChildren.isEmpty())
@@ -545,17 +592,14 @@ void TaskContainer::deactivateStorages()
         m_parentContainer->deactivateStorages();
 }
 
-void TaskNode::start()
+TaskAction TaskNode::start()
 {
-    if (!isTask()) {
+    if (!isTask())
-        m_container.start();
+        return m_container.start();
-        return;
+
-    }
+    const auto finalize = [this] {
-    const auto finalize = [this](bool success) {
         m_container.m_taskTreePrivate->advanceProgress(1);
         m_task.release()->deleteLater();
-        QTC_CHECK(m_container.m_parentContainer);
-        m_container.m_parentContainer->childDone(success);
     };
     m_task.reset(m_taskHandler.m_createHandler());
     {
@@ -566,25 +610,32 @@ void TaskNode::start()
             action = m_taskHandler.m_setupHandler(*m_task.get());
         }
         if (action != TaskAction::Continue) {
-            finalize(action == TaskAction::StopWithDone);
+            finalize();
-            return;
+            return action;
         }
     }
+    const std::shared_ptr<TaskAction> unwindAction = std::make_shared<TaskAction>(TaskAction::Continue);
     connect(m_task.get(), &TaskInterface::done, this, [=](bool success) {
-        {
+        const bool callDoneHandler = success && m_taskHandler.m_doneHandler;
+        const bool callErrorHandler = !success && m_taskHandler.m_errorHandler;
+        if (callDoneHandler || callErrorHandler) {
             StorageActivator activator(m_container);
-            if (success && m_taskHandler.m_doneHandler) {
             GuardLocker locker(m_container.m_taskTreePrivate->m_guard);
+            if (callDoneHandler)
                 m_taskHandler.m_doneHandler(*m_task.get());
-            } else if (!success && m_taskHandler.m_errorHandler) {
+            else if (callErrorHandler)
-                GuardLocker locker(m_container.m_taskTreePrivate->m_guard);
                 m_taskHandler.m_errorHandler(*m_task.get());
         }
-        }
+        finalize();
-        finalize(success);
+        if (m_startGuard.isLocked())
+            *unwindAction = toTaskAction(success);
+        else
+            m_container.m_parentContainer->childDone(success);
     });
 
+    GuardLocker locker(m_startGuard);
     m_task->start();
+    return *unwindAction;
 }
 
 void TaskNode::stop()
@@ -594,7 +645,7 @@ void TaskNode::stop()
 
     if (!m_task) {
         m_container.stop();
-        m_container.invokeEndHandler(false, false);
+        m_container.invokeEndHandler(false);
         return;
     }