Shared/Util: Introduce a task scheduler which schedules task with c++11 techniques.

* Use std::function as callback (methods, lamdas & std::bind).
* Uses std::chrono::duration as duration type (Milliseconds, Seconds...)
  - With c++11 user defined literals we could just write "11s" for example (MSVS 2015, gcc & clang).
* Provides a lot of overloads for easier usage:
  - Static durations or random durations between min and max.
  - Named (with group ids - group id 0 is possible) or anonymous tasks.
  - Asynchronous tasks.
* Is adapted to the current needs of scripting:
  - Repeat tasks through the TaskContext
  - Schedule new tasks from the context.
  - Provides access to the times repeat counter of a task,
    this will help to schedule multi step events (dialogs for example).

See https://gist.github.com/Naios/6d143538abdc3d32fd2b for usage examples.

src/server/shared/PrecompiledHeaders/sharedPCH.h

@@ -6,3 +6,4 @@
 #include "SQLOperation.h"
 #include "Errors.h"
 #include "TypeList.h"
+#include "TaskScheduler.h"

src/server/shared/Utilities/TaskScheduler.cpp

@@ -0,0 +1,204 @@
+/*
+ * Copyright (C) 2008-2015 TrinityCore <http://www.trinitycore.org/>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "TaskScheduler.h"
+
+TaskScheduler& TaskScheduler::Update()
+{
+    _now = clock_t::now();
+    Dispatch();
+    return *this;
+}
+
+TaskScheduler& TaskScheduler::Update(size_t const milliseconds)
+{
+    return Update(std::chrono::milliseconds(milliseconds));
+}
+
+TaskScheduler& TaskScheduler::Async(std::function<void()> const& callable)
+{
+    _asyncHolder.push(callable);
+    return *this;
+}
+
+TaskScheduler& TaskScheduler::CancelAll()
+{
+    /// Clear the task holder
+    _task_holder.Clear();
+    _asyncHolder = AsyncHolder();
+    return *this;
+}
+
+TaskScheduler& TaskScheduler::CancelGroup(group_t const group)
+{
+    _task_holder.RemoveIf([group](TaskContainer const& task) -> bool
+    {
+        return task->IsInGroup(group);
+    });
+    return *this;
+}
+
+TaskScheduler& TaskScheduler::CancelGroupsOf(std::vector<group_t> const& groups)
+{
+    std::for_each(groups.begin(), groups.end(),
+        std::bind(&TaskScheduler::CancelGroup, this, std::placeholders::_1));
+
+    return *this;
+}
+
+TaskScheduler& TaskScheduler::InsertTask(TaskContainer task)
+{
+    _task_holder.Push(std::forward<TaskContainer>(task));
+    return *this;
+}
+
+void TaskScheduler::Dispatch()
+{
+    // Process all asyncs
+    while (!_asyncHolder.empty())
+    {
+        _asyncHolder.front()();
+        _asyncHolder.pop();
+    }
+
+    while (!_task_holder.IsEmpty())
+    {
+        if (_task_holder.First()->_end > _now)
+            break;
+
+        // Perfect forward the context to the handler
+        // Use weak references to catch destruction before callbacks.
+        TaskContext context(new TaskContextInstance(_task_holder.Pop(),
+            std::weak_ptr<TaskScheduler>(self_reference)));
+
+        // Invoke the context
+        context->Invoke();
+    }
+}
+
+void TaskScheduler::TaskQueue::Push(TaskContainer&& task)
+{
+    container.insert(task);
+}
+
+auto TaskScheduler::TaskQueue::Pop() -> TaskContainer
+{
+    TaskContainer result = *container.begin();
+    container.erase(container.begin());
+    return result;
+}
+
+auto TaskScheduler::TaskQueue::First() const -> TaskContainer const&
+{
+    return *container.begin();
+}
+
+void TaskScheduler::TaskQueue::Clear()
+{
+    container.clear();
+}
+
+void TaskScheduler::TaskQueue::RemoveIf(std::function<bool(TaskContainer const&)> const& filter)
+{
+    for (auto itr = container.begin(); itr != container.end();)
+        if (filter(*itr))
+            itr = container.erase(itr);
+        else
+            ++itr;
+}
+
+void TaskScheduler::TaskQueue::ModifyIf(std::function<bool(TaskContainer const&)> const& filter)
+{
+    std::vector<TaskContainer> cache;
+    for (auto itr = container.begin(); itr != container.end();)
+        if (filter(*itr))
+        {
+            cache.push_back(*itr);
+            itr = container.erase(itr);
+        }
+        else
+            ++itr;
+
+    container.insert(cache.begin(), cache.end());
+}
+
+bool TaskScheduler::TaskQueue::IsEmpty() const
+{
+    return container.empty();
+}
+
+TaskContextInstance& TaskContextInstance::Dispatch(std::function<TaskScheduler&(TaskScheduler&)> const& apply)
+{
+    if (auto const owner = _owner.lock())
+        apply(*owner);
+
+    return *this;
+}
+
+bool TaskContextInstance::IsInGroup(TaskScheduler::group_t const group) const
+{
+    return _task->IsInGroup(group);
+}
+
+TaskContextInstance& TaskContextInstance::SetGroup(TaskScheduler::group_t const group)
+{
+    _task->_group = group;
+    return *this;
+}
+
+TaskContextInstance& TaskContextInstance::ClearGroup()
+{
+    _task->_group = boost::none;
+    return *this;
+}
+
+TaskScheduler::repeated_t TaskContextInstance::GetRepeatCounter() const
+{
+    return _task->_repeated;
+}
+
+TaskContextInstance& TaskContextInstance::Async(std::function<void()> const& callable)
+{
+    return Dispatch(std::bind(&TaskScheduler::Async, std::placeholders::_1, callable));
+}
+
+TaskContextInstance& TaskContextInstance::CancelAll()
+{
+    return Dispatch(std::mem_fn(&TaskScheduler::CancelAll));
+}
+
+TaskContextInstance& TaskContextInstance::CancelGroup(TaskScheduler::group_t const group)
+{
+    return Dispatch(std::bind(&TaskScheduler::CancelGroup, std::placeholders::_1, group));
+}
+
+TaskContextInstance& TaskContextInstance::CancelGroupsOf(std::vector<TaskScheduler::group_t> const& groups)
+{
+    return Dispatch(std::bind(&TaskScheduler::CancelGroupsOf, std::placeholders::_1, groups));
+}
+
+void TaskContextInstance::AssertOnConsumed()
+{
+    // This was adapted to TC to prevent static analysis tools from complaining.
+    // If you encounter this assertion check if you repeat a TaskContext more then 1 time!
+    ASSERT(_task && "Bad task logic, task context was consumed already!");
+}
+
+void TaskContextInstance::Invoke()
+{
+    _task->_task(shared_from_this());
+}

src/server/shared/Utilities/TaskScheduler.h

@@ -0,0 +1,591 @@
+/*
+ * Copyright (C) 2008-2015 TrinityCore <http://www.trinitycore.org/>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _TASK_SCHEDULER_H_
+#define _TASK_SCHEDULER_H_
+
+#include <algorithm>
+#include <chrono>
+#include <vector>
+#include <queue>
+#include <memory>
+#include <utility>
+#include <set>
+
+#include <boost/optional.hpp>
+
+#include "Util.h"
+
+class TaskContextInstance;
+
+typedef std::shared_ptr<TaskContextInstance> TaskContext;
+
+/// The TaskScheduler class provides the ability to schedule std::function's in the near future.
+/// Use TaskScheduler::Update to update the scheduler.
+/// Popular methods are:
+/// * Schedule (Schedules a std::function which will be executed in the near future).
+/// * Schedules an asynchronous function which will be executed at the next update tick.
+/// * Cancel, Delay & Reschedule (Methods to manipulate already scheduled tasks).
+/// Tasks are organized in groups (uint), multiple tasks can have the same group id,
+/// you can provide a group or not, but keep in mind that you can only manipulate specific tasks through its group id!
+/// Tasks callbacks use the function signature void(TaskContext) where TaskContext provides
+/// access to the function schedule plan which makes it possible to repeat the task
+/// with the same duration or a new one.
+/// It also provides access to the repeat counter which is useful for task that repeat itself often
+/// but behave different every time (spoken event dialogs for example).
+class TaskScheduler
+{
+    friend class TaskContextInstance;
+
+    // Time definitions (use steady clock)
+    typedef std::chrono::steady_clock clock_t;
+    typedef clock_t::time_point timepoint_t;
+    typedef clock_t::duration duration_t;
+
+    // Task group type
+    typedef uint32 group_t;
+    // Task repeated type
+    typedef uint32 repeated_t;
+    // Task handle type
+    typedef std::function<void(TaskContext)> task_handler_t;
+
+    class Task
+    {
+        friend class TaskContextInstance;
+        friend class TaskScheduler;
+
+        timepoint_t _end;
+        duration_t _duration;
+        boost::optional<group_t> _group;
+        repeated_t _repeated;
+        task_handler_t _task;
+
+    public:
+        // All Argument construct
+        Task(timepoint_t const& end, duration_t const& duration, boost::optional<group_t> const& group,
+            repeated_t const repeated, task_handler_t const& task)
+                : _end(end), _duration(duration), _group(group), _repeated(repeated), _task(task) { }
+
+        // Minimal Argument construct
+        Task(timepoint_t const& end, duration_t const& duration, task_handler_t const& task)
+            : _end(end), _duration(duration), _group(boost::none), _repeated(0), _task(task) { }
+
+        // Copy construct
+        Task(Task const&) = delete;
+        // Move construct
+        Task(Task&&) = delete;
+        // Copy Assign
+        Task& operator= (Task const&) = default;
+        // Move Assign
+        Task& operator= (Task&& right) = delete;
+
+        // Order tasks by its end
+        inline bool operator< (Task const& other) const
+        {
+            return _end < other._end;
+        }
+
+        inline bool operator> (Task const& other) const
+        {
+            return _end > other._end;
+        }
+
+        // Compare tasks with its end
+        inline bool operator== (Task const& other)
+        {
+            return _end == other._end;
+        }
+
+        // Returns true if the task is in the given group
+        inline bool IsInGroup(group_t const group) const
+        {
+            return _group == group;
+        }
+    };
+
+    typedef std::shared_ptr<Task> TaskContainer;
+
+    /// Container which provides Task order, insert and reschedule operations.
+    struct Compare
+    {
+        bool operator() (TaskContainer const& left, TaskContainer const& right)
+        {
+            return (*left.get()) < (*right.get());
+        };
+    };
+
+    class TaskQueue
+    {
+        std::multiset<TaskContainer, Compare> container;
+
+    public:
+        // Pushes the task in the container
+        void Push(TaskContainer&& task);
+
+        /// Pops the task out of the container
+        TaskContainer Pop();
+
+        TaskContainer const& First() const;
+
+        void Clear();
+
+        void RemoveIf(std::function<bool(TaskContainer const&)> const& filter);
+
+        void ModifyIf(std::function<bool(TaskContainer const&)> const& filter);
+
+        bool IsEmpty() const;
+    };
+
+    /// Contains a self reference to track if this object was deleted or not.
+    std::shared_ptr<TaskScheduler> self_reference;
+
+    /// The current time point (now)
+    timepoint_t _now;
+
+    /// The Task Queue which contains all task objects.
+    TaskQueue _task_holder;
+
+    typedef std::queue<std::function<void()>> AsyncHolder;
+
+    /// Contains all asynchronous tasks which will be invoked at
+    /// the next update tick.
+    AsyncHolder _asyncHolder;
+
+public:
+    TaskScheduler() : self_reference(this, [](TaskScheduler const*) { }),
+        _now(clock_t::now()) { }
+
+    TaskScheduler(TaskScheduler const&) = delete;
+    TaskScheduler(TaskScheduler&&) = delete;
+    TaskScheduler& operator= (TaskScheduler const&) = delete;
+    TaskScheduler& operator= (TaskScheduler&&) = delete;
+
+    /// Update the scheduler to the current time.
+    TaskScheduler& Update();
+
+    /// Update the scheduler with a difftime in ms.
+    TaskScheduler& Update(size_t const milliseconds);
+
+    /// Update the scheduler with a difftime.
+    template<class _Rep, class _Period>
+    TaskScheduler& Update(std::chrono::duration<_Rep, _Period> const& difftime)
+    {
+        _now += difftime;
+        Dispatch();
+        return *this;
+    }
+
+    /// Schedule an callable function that is executed at the next update tick.
+    /// Its safe to modify the TaskScheduler from within the callable.
+    TaskScheduler& Async(std::function<void()> const& callable);
+
+    /// Schedule an event with a fixed rate.
+    /// Never call this from within a task context! Use TaskContext::Schedule instead!
+    template<class _Rep, class _Period>
+    TaskScheduler& Schedule(std::chrono::duration<_Rep, _Period> const& time,
+        task_handler_t const& task)
+    {
+        return ScheduleAt(_now, time, task);
+    }
+
+    /// Schedule an event with a fixed rate.
+    /// Never call this from within a task context! Use TaskContext::Schedule instead!
+    template<class _Rep, class _Period>
+    TaskScheduler& Schedule(std::chrono::duration<_Rep, _Period> const& time,
+        group_t const group, task_handler_t const& task)
+    {
+        return ScheduleAt(_now, time, group, task);
+    }
+
+    /// Schedule an event with a randomized rate between min and max rate.
+    /// Never call this from within a task context! Use TaskContext::Schedule instead!
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskScheduler& Schedule(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max, task_handler_t const& task)
+    {
+        return Schedule(RandomDurationBetween(min, max), task);
+    }
+
+    /// Schedule an event with a fixed rate.
+    /// Never call this from within a task context! Use TaskContext::Schedule instead!
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskScheduler& Schedule(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max, group_t const group,
+        task_handler_t const& task)
+    {
+        return Schedule(RandomDurationBetween(min, max), group, task);
+    }
+
+    /// Cancels all tasks.
+    /// Never call this from within a task context! Use TaskContext::CancelAll instead!
+    TaskScheduler& CancelAll();
+
+    /// Cancel all tasks of a single group.
+    /// Never call this from within a task context! Use TaskContext::CancelGroup instead!
+    TaskScheduler& CancelGroup(group_t const group);
+
+    /// Cancels all groups in the given std::vector.
+    /// Hint: Use std::initializer_list for this: "{1, 2, 3, 4}"
+    TaskScheduler& CancelGroupsOf(std::vector<group_t> const& groups);
+
+    /// Delays all tasks with the given duration.
+    template<class _Rep, class _Period>
+    TaskScheduler& DelayAll(std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        _task_holder.ModifyIf([&duration](TaskContainer const& task) -> bool
+        {
+            task->_end += duration;
+            return true;
+        });
+        return *this;
+    }
+
+    /// Delays all tasks with a random duration between min and max.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskScheduler& DelayAll(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return DelayAll(RandomDurationBetween(min, max));
+    }
+
+    /// Delays all tasks of a group with the given duration.
+    template<class _Rep, class _Period>
+    TaskScheduler& DelayGroup(group_t const group, std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        _task_holder.ModifyIf([&duration, group](TaskContainer const& task) -> bool
+        {
+            if (task->IsInGroup(group))
+            {
+                task->_end += duration;
+                return true;
+            }
+            else
+                return false;
+        });
+        return *this;
+    }
+
+    /// Delays all tasks of a group with a random duration between min and max.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskScheduler& DelayGroup(group_t const group,
+        std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return DelayGroup(group, RandomDurationBetween(min, max));
+    }
+
+    /// Reschedule all tasks with a given duration.
+    template<class _Rep, class _Period>
+    TaskScheduler& RescheduleAll(std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        auto const end = _now + duration;
+        _task_holder.ModifyIf([end](TaskContainer const& task) -> bool
+        {
+            task->_end = end;
+            return true;
+        });
+        return *this;
+    }
+
+    /// Reschedule all tasks with a random duration between min and max.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskScheduler& RescheduleAll(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return RescheduleAll(RandomDurationBetween(min, max));
+    }
+
+    /// Reschedule all tasks of a group with the given duration.
+    template<class _Rep, class _Period>
+    TaskScheduler& RescheduleGroup(group_t const group, std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        auto const end = _now + duration;
+       _task_holder.ModifyIf([end, group](TaskContainer const& task) -> bool
+        {
+            if (task->IsInGroup(group))
+            {
+                task->_end = end;
+                return true;
+            }
+            else
+                return false;
+        });
+        return *this;
+    }
+
+    /// Reschedule all tasks of a group with a random duration between min and max.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskScheduler& RescheduleGroup(group_t const group,
+        std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return RescheduleGroup(group, RandomDurationBetween(min, max));
+    }
+
+private:
+    /// Insert a new task to the enqueued tasks.
+    TaskScheduler& InsertTask(TaskContainer task);
+
+    template<class _Rep, class _Period>
+    TaskScheduler& ScheduleAt(timepoint_t const& end,
+        std::chrono::duration<_Rep, _Period> const& time, task_handler_t const& task)
+    {
+        return InsertTask(TaskContainer(new Task(end + time, time, task)));
+    }
+
+    /// Schedule an event with a fixed rate.
+    /// Never call this from within a task context! Use TaskContext::schedule instead!
+    template<class _Rep, class _Period>
+    TaskScheduler& ScheduleAt(timepoint_t const& end,
+        std::chrono::duration<_Rep, _Period> const& time,
+        group_t const group, task_handler_t const& task)
+    {
+        static repeated_t const DEFAULT_REPEATED = 0;
+        return InsertTask(TaskContainer(new Task(end + time, time, group, DEFAULT_REPEATED, task)));
+    }
+
+    // Returns a random duration between min and max
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    std::chrono::milliseconds
+    static RandomDurationBetween(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+            std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        auto const milli_min = std::chrono::duration_cast<std::chrono::milliseconds>(min);
+        auto const milli_max = std::chrono::duration_cast<std::chrono::milliseconds>(max);
+
+        // TC specific: use SFMT URandom
+        return std::chrono::milliseconds(urand(milli_min.count(), milli_max.count()));
+    }
+
+    /// Dispatch remaining tasks
+    void Dispatch();
+};
+
+class TaskContextInstance
+    : public std::enable_shared_from_this<TaskContextInstance>
+{
+    friend class TaskScheduler;
+
+    /// Associated task
+    TaskScheduler::TaskContainer _task;
+
+    /// Owner
+    std::weak_ptr<TaskScheduler> const _owner;
+
+    /// Dispatches an action safe on the TaskScheduler
+    TaskContextInstance& Dispatch(std::function<TaskScheduler&(TaskScheduler&)> const& apply);
+
+public:
+    explicit TaskContextInstance(TaskScheduler::TaskContainer task, std::weak_ptr<TaskScheduler>&& owner)
+        : _task(task), _owner(owner) { }
+
+    /// Returns true if the event is in the given group
+    bool IsInGroup(TaskScheduler::group_t const group) const;
+
+    /// Sets the event in the given group
+    TaskContextInstance& SetGroup(TaskScheduler::group_t const group);
+
+    /// Removes the group from the event
+    TaskContextInstance& ClearGroup();
+
+    /// Returns the repeat counter which increases every time the task is repeated.
+    TaskScheduler::repeated_t GetRepeatCounter() const;
+
+    /// Repeats the event and sets a new duration.
+    /// std::chrono::seconds(5) for example.
+    /// This will consume the task context, its not possible to repeat the task again
+    /// from the same task context!
+    template<class _Rep, class _Period>
+    TaskContextInstance& Repeat(std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        AssertOnConsumed();
+
+        // Set new duration, in-context timing and increment repeat counter
+        _task->_duration = duration;
+        _task->_end += duration;
+        _task->_repeated += 1;
+        return Dispatch(std::bind(&TaskScheduler::InsertTask, std::placeholders::_1, _task));
+    }
+
+    /// Repeats the event with the same duration.
+    /// This will consume the task context, its not possible to repeat the task again
+    /// from the same task context!
+    TaskContextInstance& Repeat()
+    {
+        return Repeat(_task->_duration);
+    }
+
+    /// Repeats the event and set a new duration that is randomized between min and max.
+    /// std::chrono::seconds(5) for example.
+    /// This will consume the task context, its not possible to repeat the task again
+    /// from the same task context!
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskContextInstance& Repeat(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return Repeat(TaskScheduler::RandomDurationBetween(min, max));
+    }
+
+    /// Schedule a callable function that is executed at the next update tick from within the context.
+    /// Its safe to modify the TaskScheduler from within the callable.
+    TaskContextInstance& Async(std::function<void()> const& callable);
+
+    /// Schedule an event with a fixed rate from within the context.
+    /// Its possible that the new event is executed immediately!
+    /// Use TaskScheduler::Async to create a task
+    /// which will be called at the next update tick.
+    template<class _Rep, class _Period>
+    TaskContextInstance& Schedule(std::chrono::duration<_Rep, _Period> const& time,
+        TaskScheduler::task_handler_t const& task)
+    {
+        auto const end = _task->_end;
+        return Dispatch([end, time, task](TaskScheduler& scheduler) -> TaskScheduler&
+        {
+            return scheduler.ScheduleAt<_Rep, _Period>(end, time, task);
+        });
+    }
+
+    /// Schedule an event with a fixed rate from within the context.
+    /// Its possible that the new event is executed immediately!
+    /// Use TaskScheduler::Async to create a task
+    /// which will be called at the next update tick.
+    template<class _Rep, class _Period>
+    TaskContextInstance& Schedule(std::chrono::duration<_Rep, _Period> const& time,
+        TaskScheduler::group_t const group, TaskScheduler::task_handler_t const& task)
+    {
+        auto const end = _task->_end;
+        return Dispatch([end, time, group, task](TaskScheduler& scheduler) -> TaskScheduler&
+        {
+            return scheduler.ScheduleAt<_Rep, _Period>(end, time, group, task);
+        });
+    }
+
+    /// Schedule an event with a randomized rate between min and max rate from within the context.
+    /// Its possible that the new event is executed immediately!
+    /// Use TaskScheduler::Async to create a task
+    /// which will be called at the next update tick.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskContextInstance& Schedule(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max, TaskScheduler::task_handler_t const& task)
+    {
+        return Schedule(TaskScheduler::RandomDurationBetween(min, max), task);
+    }
+
+    /// Schedule an event with a randomized rate between min and max rate from within the context.
+    /// Its possible that the new event is executed immediately!
+    /// Use TaskScheduler::Async to create a task
+    /// which will be called at the next update tick.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskContextInstance& Schedule(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max, TaskScheduler::group_t const group,
+        TaskScheduler::task_handler_t const& task)
+    {
+        return Schedule(TaskScheduler::RandomDurationBetween(min, max), group, task);
+    }
+
+    /// Cancels all tasks from within the context.
+    TaskContextInstance& CancelAll();
+
+    /// Cancel all tasks of a single group from within the context.
+    TaskContextInstance& CancelGroup(TaskScheduler::group_t const group);
+
+    /// Cancels all groups in the given std::vector from within the context.
+    /// Hint: Use std::initializer_list for this: "{1, 2, 3, 4}"
+    TaskContextInstance& CancelGroupsOf(std::vector<TaskScheduler::group_t> const& groups);
+
+    /// Delays all tasks with the given duration from within the context.
+    template<class _Rep, class _Period>
+    TaskContextInstance& DelayAll(std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        return Dispatch(std::bind(&TaskScheduler::DelayAll<_Rep, _Period>, std::placeholders::_1, duration));
+    }
+
+    /// Delays all tasks with a random duration between min and max from within the context.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskContextInstance& DelayAll(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return DelayAll(TaskScheduler::RandomDurationBetween(min, max));
+    }
+
+    /// Delays all tasks of a group with the given duration from within the context.
+    template<class _Rep, class _Period>
+    TaskContextInstance& DelayGroup(TaskScheduler::group_t const group, std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        return Dispatch(std::bind(&TaskScheduler::DelayGroup<_Rep, _Period>, std::placeholders::_1, group, duration));
+    }
+
+    /// Delays all tasks of a group with a random duration between min and max from within the context.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskContextInstance& DelayGroup(TaskScheduler::group_t const group,
+        std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return DelayGroup(group, TaskScheduler::RandomDurationBetween(min, max));
+    }
+
+    /// Reschedule all tasks with the given duration.
+    template<class _Rep, class _Period>
+    TaskContextInstance& RescheduleAll(std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        return Dispatch(std::bind(&TaskScheduler::RescheduleAll, std::placeholders::_1, duration));
+    }
+
+    /// Reschedule all tasks with a random duration between min and max.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskContextInstance& RescheduleAll(std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return RescheduleAll(TaskScheduler::RandomDurationBetween(min, max));
+    }
+
+    /// Reschedule all tasks of a group with the given duration.
+    template<class _Rep, class _Period>
+    TaskContextInstance& RescheduleGroup(TaskScheduler::group_t const group, std::chrono::duration<_Rep, _Period> const& duration)
+    {
+        return Dispatch(std::bind(&TaskScheduler::RescheduleGroup<_Rep, _Period>, std::placeholders::_1, group, duration));
+    }
+
+    /// Reschedule all tasks of a group with a random duration between min and max.
+    template<class _RepLeft, class _PeriodLeft, class _RepRight, class _PeriodRight>
+    TaskContextInstance& RescheduleGroup(TaskScheduler::group_t const group,
+        std::chrono::duration<_RepLeft, _PeriodLeft> const& min,
+        std::chrono::duration<_RepRight, _PeriodRight> const& max)
+    {
+        return RescheduleGroup(group, TaskScheduler::RandomDurationBetween(min, max));
+    }
+
+private:
+    void AssertOnConsumed();
+
+    /// Invokes the associated hook of the task.
+    void Invoke();
+};
+
+/// Milliseconds shorthand typedef.
+typedef std::chrono::milliseconds Milliseconds;
+
+/// Seconds shorthand typedef.
+typedef std::chrono::seconds Seconds;
+
+/// Minutes shorthand typedef.
+typedef std::chrono::minutes Minutes;
+
+/// Hours shorthand typedef.
+typedef std::chrono::hours Hours;
+
+#endif /// _TASK_SCHEDULER_H_