feat(timers): Adds timer pooling, fixes timer related bugs, and changes timer api (#667)

### Changes/Fixes:
* Adds timer pooling.
* Allows pool to be configurable in ModernUO.json
* Pool replenishes itself asynchronously if depleted.
* Fixes an issue with barkeeps and town criers
* Fixes an issue with incognito buff icons not being removed
* Fixes an issue with polymorph name mod not being removed
* Fixes several places where timers go on forever even after an object is deleted, keeping a reference (memory leak)
* Eliminates the timer for MiningCart altogether.
* Deletes `AcidSlime` since it is a duplicate of `PoolOfAcid`
* Fixes HonorableExecution and standardizes the code for other Bushido moves.

## Changes to the Timer API:
```cs
public class Timer
{
  // Creates a timer that will be returned to the pool once execution stops.
  public static void StartTimer(Action callback);
  public static void StartTimer(TimeSpan delay, Action callback);
  public static void StartTimer(TimeSpan delay, TimeSpan interval, Action callback);
  public static void StartTimer(TimeSpan interval, int count, Action callback);
  public static void StartTimer(TimeSpan delay, TimeSpan interval, int count, Action callback);

  // Creates a timer and returns a token for more control. Requires manual cancellation in order for the timer to be returned to the pool.
  // If the token is dereferenced, the timer will be dereferenced too. While not returning a timer to the pool is not considered hazardous, it does defeat the purpose of pooled timers.
  public static void StartTimer(Action callback, out TimerExecutionToken token);
  public static void StartTimer(TimeSpan delay, Action callback, out TimerExecutionToken token);
  public static void StartTimer(TimeSpan delay, TimeSpan interval, Action callback, out TimerExecutionToken token);
  public static void StartTimer(TimeSpan interval, int count, Action callback, out TimerExecutionToken token);
  public static void StartTimer(TimeSpan delay, TimeSpan interval, int count, Action callback, out TimerExecutionToken token);

  // If you aren't sure how to use the API above, or you don't care about performance, then you can use the old RunUO Timer.DelayCall
  public static DelayCallTimer DelayCall(Action callback);
  public static DelayCallTimer DelayCall(TimeSpan delay, Action callback);
  public static DelayCallTimer DelayCall(TimeSpan delay, TimeSpan interval, Action callback);
  public static DelayCallTimer DelayCall(TimeSpan interval, int count, Action callback);
  public static DelayCallTimer DelayCall(TimeSpan delay, TimeSpan interval, int count, Action callback);
}

public struct TimerExecutionToken
{
  public bool Running { get; }
  public int Index { get; }
  public int RemainingCount { get; }
  public DateTime Next { get; }
}
```

## When to use `TimerExecutionToken`?
Use tokens when you want to gain the performance benefit of using a pooled timer, but you need one of the following:
* Access to the next time the timer will tick:`token.Next`
* Access to which interval, how many intervals there are, or how many are remaining: `token.Index`, `token.Count`, and `token.RemainingCount`
* Stop a timer manually.
* Determine if the timer is running: `timer.Running`
* See notes below about requirements for using tokens!

## Notes about using the TimerExecutionToken:
When you opt-in to receive a token, you must call `Cancel()` to return the timer. This can be done inside of the callback, or outside of the callback at any time.
If this is not called and your timer is an infinite interval, then you will create a potential memory leak, or null pointer exception in your callback.
If the timer ends and is stopped, but cancel is not called, then the timer will never return to the pool and stay referenced until the token is deleted or cancel is called. (Memory leak)

## Is this thread safe?
No. The ModernUO timer system is not thread safe at all. If you require a thread safe timer system, contact me and I'll help adapt this system. Keep in mind that there is a massive performance hit to make this thread safe when there are literally no use cases for it.

If you need to synchronize execution, meaning you want to execute code from another thread on the core thread. Let's say you have a discord bot that is pushing commands to the game server. Then use `EventLoopContext.Post(SendOrPostCallback callback, object state);`.

Projects/Server/Mobiles/Mobile.cs

@@ -454,7 +454,7 @@ namespace Server
         private List<object> _actions;
         private AccessLevel m_AccessLevel;
 
-        private Timer m_AutoManifestTimer;
+        private TimerExecutionToken _autoManifestTimerToken;
 
         private Container m_Backpack;
 
@@ -465,7 +465,7 @@ namespace Server
 
         private int m_ChangingCombatant;
         private Mobile m_Combatant;
-        private Timer m_CombatTimer;
+        private TimerExecutionToken _combatTimerToken;
         private ContextMenu m_ContextMenu;
         private bool m_Criminal;
 
@@ -473,14 +473,15 @@ namespace Server
         private Direction m_Direction;
         private bool m_DisplayGuildTitle;
 
-        private Timer m_ExpireAggrTimer;
-        private Timer m_ExpireCombatant;
+        private TimerExecutionToken _expireAggrTimerToken;
+        private TimerExecutionToken _expireCombatantTimerToken;
+        private TimerExecutionToken _expireCriminalTimerToken;
         private FacialHairInfo m_FacialHair;
         private int m_Fame, m_Karma;
         private bool m_Female, m_Warmode, m_Hidden, m_Blessed, m_Flying;
         private int m_Followers, m_FollowersMax;
         private bool m_Frozen;
-        private Timer m_FrozenTimer;
+        private TimerExecutionToken _frozenTimerToken;
         private BaseGuild m_Guild;
         private string m_GuildTitle;
 
@@ -498,7 +499,7 @@ namespace Server
         private string m_Language;
         private int m_LightLevel;
         private Point3D m_Location;
-        private Timer m_LogoutTimer;
+        private TimerExecutionToken _logoutTimerToken;
         private Timer m_ManaTimer, m_HitsTimer, m_StamTimer;
 
         private Map m_Map;
@@ -525,7 +526,7 @@ namespace Server
         private NetState m_NetState;
         private DateTime m_NextWarmodeChange;
         private bool m_Paralyzed;
-        private Timer m_ParaTimer;
+        private TimerExecutionToken _paraTimerToken;
         private bool m_Player;
         private Poison m_Poison;
         private Prompt m_Prompt;
@@ -546,7 +547,7 @@ namespace Server
         private int m_VirtualArmor;
         private int m_VirtualArmorMod;
         private int m_WarmodeChanges;
-        private WarmodeTimer m_WarmodeTimer;
+        private bool _warmodeSpamValue;
         private IWeapon m_Weapon;
 
         private bool m_YellowHealthbar;
@@ -768,12 +769,7 @@ namespace Server
                     Delta(MobileDelta.Flags);
 
                     SendLocalizedMessage(m_Paralyzed ? 502381 : 502382);
-
-                    if (m_ParaTimer != null)
-                    {
-                        m_ParaTimer.Stop();
-                        m_ParaTimer = null;
-                    }
+                    _paraTimerToken.Cancel();
                 }
             }
         }
@@ -794,12 +790,7 @@ namespace Server
                 {
                     m_Frozen = value;
                     Delta(MobileDelta.Flags);
-
-                    if (m_FrozenTimer != null)
-                    {
-                        m_FrozenTimer.Stop();
-                        m_FrozenTimer = null;
-                    }
+                    _frozenTimerToken.Cancel();
                 }
             }
         }
@@ -880,7 +871,11 @@ namespace Server
 
         public bool ChangingCombatant => m_ChangingCombatant > 0;
 
-        private void ExpireCombatant() => Combatant = null;
+        private void ExpireCombatant()
+        {
+            Combatant = null;
+            _expireCombatantTimerToken.Cancel();
+        }
 
         /// <summary>
         ///     Overridable. Gets or sets which Mobile that this Mobile is currently engaged in combat with.
@@ -915,20 +910,14 @@ namespace Server
                     if (m_Combatant == null)
                     {
                         m_NetState.SendChangeCombatant(Serial.Zero);
-                        m_ExpireCombatant?.Stop();
-                        m_CombatTimer?.Stop();
-
-                        m_ExpireCombatant = null;
-                        m_CombatTimer = null;
+                        _expireCombatantTimerToken.Cancel();
+                        _combatTimerToken.Cancel();
                     }
                     else
                     {
                         m_NetState.SendChangeCombatant(m_Combatant.Serial);
-                        m_ExpireCombatant ??= Timer.DelayCall(ExpireCombatantDelay, ExpireCombatant);
-                        m_ExpireCombatant.Start();
-
-                        m_CombatTimer ??= new CombatTimer(this);
-                        m_CombatTimer.Start();
+                        Timer.StartTimer(ExpireCombatantDelay, ExpireCombatant, out _expireCombatantTimerToken);
+                        Timer.StartTimer(TimeSpan.FromSeconds(0.01), 0, CheckCombatTime, out _combatTimerToken);
 
                         if (CanBeHarmful(m_Combatant, false))
                         {
@@ -943,6 +932,40 @@ namespace Server
             }
         }
 
+        private void CheckCombatTime()
+        {
+            if (Core.TickCount - NextCombatTime < 0)
+            {
+                return;
+            }
+
+            var combatant = Combatant;
+
+            // If no combatant, wrong map, one of us is a ghost, or cannot see, or deleted, then stop combat
+            if (combatant?.Deleted != false || Deleted || combatant.m_Map != m_Map ||
+                !combatant.Alive || !Alive || !CanSee(combatant) || combatant.IsDeadBondedPet ||
+                IsDeadBondedPet)
+            {
+                Combatant = null;
+                return;
+            }
+
+            var weapon = Weapon;
+
+            if (!InRange(combatant, weapon.MaxRange))
+            {
+                return;
+            }
+
+            if (InLOS(combatant))
+            {
+                weapon.OnBeforeSwing(this, combatant);
+                RevealingAction();
+                NextCombatTime =
+                    Core.TickCount + (int)weapon.OnSwing(this, combatant).TotalMilliseconds;
+            }
+        }
+
         [CommandProperty(AccessLevel.GameMaster)]
         public int TotalGold => GetTotal(TotalType.Gold);
 
@@ -1347,11 +1370,7 @@ namespace Server
 
                 if (m_Warmode != value)
                 {
-                    if (m_AutoManifestTimer != null)
-                    {
-                        m_AutoManifestTimer.Stop();
-                        m_AutoManifestTimer = null;
-                    }
+                    _autoManifestTimerToken.Cancel();
 
                     m_Warmode = value;
                     Delta(MobileDelta.Flags);
@@ -1439,6 +1458,7 @@ namespace Server
                 }
 
                 m_NetState = value;
+                _logoutTimerToken.Cancel();
 
                 if (m_NetState == null)
                 {
@@ -1446,27 +1466,13 @@ namespace Server
                     EventSink.InvokeDisconnected(this);
 
                     // Disconnected, start the logout timer
-                    if (m_LogoutTimer == null)
-                    {
-                        m_LogoutTimer = Timer.DelayCall(GetLogoutDelay(), Logout);
-                    }
-                    else
-                    {
-                        m_LogoutTimer.Stop();
-                        m_LogoutTimer.Delay = GetLogoutDelay();
-                        m_LogoutTimer.Start();
-                    }
+                    Timer.StartTimer(GetLogoutDelay(), Logout, out _logoutTimerToken);
                 }
                 else
                 {
                     OnConnected();
                     EventSink.InvokeConnected(this);
 
-                    // Connected, stop the logout timer and if needed, move to the world
-                    m_LogoutTimer?.Stop();
-
-                    m_LogoutTimer = null;
-
                     if (m_Map == Map.Internal && LogoutMap != null)
                     {
                         Map = LogoutMap;
@@ -1494,7 +1500,7 @@ namespace Server
                             }
                         }
 
-                        Timer.DelayCall(item.Delete);
+                        Timer.StartTimer(item.Delete);
                     }
                 }
 
@@ -1852,8 +1858,6 @@ namespace Server
             }
         }
 
-        public Timer ExpireCriminalTimer { get; set; }
-
         [CommandProperty(AccessLevel.Counselor, AccessLevel.GameMaster)]
         public virtual bool Criminal
         {
@@ -1867,23 +1871,11 @@ namespace Server
                     InvalidateProperties();
                 }
 
+                _expireCriminalTimerToken.Cancel();
+
                 if (m_Criminal)
                 {
-                    if (ExpireCriminalTimer == null)
-                    {
-                        ExpireCriminalTimer = Timer.DelayCall(ExpireCriminalDelay, ExpireCriminal);
-                    }
-                    else
-                    {
-                        ExpireCriminalTimer.Stop();
-                    }
-
-                    ExpireCriminalTimer.Start();
-                }
-                else if (ExpireCriminalTimer != null)
-                {
-                    ExpireCriminalTimer.Stop();
-                    ExpireCriminalTimer = null;
+                    Timer.StartTimer(ExpireCriminalDelay, ExpireCriminal, out _expireCriminalTimerToken);
                 }
             }
         }
@@ -3545,10 +3537,9 @@ namespace Server
             {
                 StopAggrExpire();
             }
-            else if (m_ExpireAggrTimer == null)
+            else if (!_expireAggrTimerToken.Running)
             {
-                m_ExpireAggrTimer = Timer.DelayCall(ExpireAggressorsDelay, ExpireAggressorsDelay, ExpireAggr);
-                m_ExpireAggrTimer.Start();
+                Timer.StartTimer(ExpireAggressorsDelay, ExpireAggressorsDelay, ExpireAggr, out _expireAggrTimerToken);
             }
         }
 
@@ -3566,8 +3557,7 @@ namespace Server
 
         private void StopAggrExpire()
         {
-            m_ExpireAggrTimer?.Stop();
-            m_ExpireAggrTimer = null;
+            _expireAggrTimerToken.Cancel();
         }
 
         private void CheckAggrExpire()
@@ -3712,9 +3702,10 @@ namespace Server
 
         public void DelayChangeWarmode(bool value)
         {
-            if (m_WarmodeTimer != null)
+            if (m_WarmodeChanges > WarmodeCatchCount)
             {
-                m_WarmodeTimer.Value = value;
+                _warmodeSpamValue = value;
+                m_WarmodeChanges++;
                 return;
             }
 
@@ -3731,21 +3722,21 @@ namespace Server
                 m_WarmodeChanges = 1;
                 m_NextWarmodeChange = now + WarmodeSpamCatch;
             }
-            else if (m_WarmodeChanges == WarmodeCatchCount)
+            else if (m_WarmodeChanges++ == WarmodeCatchCount)
             {
-                m_WarmodeTimer = new WarmodeTimer(this, value);
-                m_WarmodeTimer.Start();
-
+                Timer.StartTimer(WarmodeSpamDelay, WarmodeSpamTimeout);
                 return;
             }
-            else
-            {
-                ++m_WarmodeChanges;
-            }
 
             Warmode = value;
         }
 
+        private void WarmodeSpamTimeout()
+        {
+            Warmode = _warmodeSpamValue;
+            m_WarmodeChanges = 0;
+        }
+
         public bool InLOS(Mobile target) =>
             !Deleted && m_Map != null &&
             (target == this || m_AccessLevel > AccessLevel.Player || m_Map.LineOfSight(this, target));
@@ -3808,9 +3799,7 @@ namespace Server
             if (!m_Paralyzed)
             {
                 Paralyzed = true;
-
-                m_ParaTimer = Timer.DelayCall(duration, ExpireParalyzed);
-                m_ParaTimer.Start();
+                Timer.StartTimer(duration, ExpireParalyzed, out _paraTimerToken);
             }
         }
 
@@ -3824,9 +3813,7 @@ namespace Server
             if (!m_Frozen)
             {
                 Frozen = true;
-
-                m_FrozenTimer = Timer.DelayCall(duration, ExpireFrozen);
-                m_FrozenTimer.Start();
+                Timer.StartTimer(duration, ExpireFrozen, out _frozenTimerToken);
             }
         }
 
@@ -3938,16 +3925,8 @@ namespace Server
 
             if (Combatant == aggressor)
             {
-                if (m_ExpireCombatant == null)
-                {
-                    m_ExpireCombatant = Timer.DelayCall(ExpireCombatantDelay, ExpireCombatant);
-                }
-                else
-                {
-                    m_ExpireCombatant.Stop();
-                }
-
-                m_ExpireCombatant.Start();
+                _expireCombatantTimerToken.Cancel();
+                Timer.StartTimer(ExpireCombatantDelay, ExpireCombatant, out _expireCombatantTimerToken);
             }
 
             var addAggressor = true;
@@ -4787,14 +4766,13 @@ namespace Server
             m_HitsTimer?.Stop();
             m_StamTimer?.Stop();
             m_ManaTimer?.Stop();
-            m_CombatTimer?.Stop();
-            m_ExpireCombatant?.Stop();
-            m_LogoutTimer?.Stop();
-            ExpireCriminalTimer?.Stop();
-            m_WarmodeTimer?.Stop();
-            m_ParaTimer?.Stop();
-            m_FrozenTimer?.Stop();
-            m_AutoManifestTimer?.Stop();
+            _combatTimerToken.Cancel();
+            _expireCombatantTimerToken.Cancel();
+            _logoutTimerToken.Cancel();
+            _expireCriminalTimerToken.Cancel();
+            _paraTimerToken.Cancel();
+            _frozenTimerToken.Cancel();
+            _autoManifestTimerToken.Cancel();
         }
 
         public virtual bool AllowSkillUse(SkillName name) => true;
@@ -4864,15 +4842,11 @@ namespace Server
             if (Paralyzed)
             {
                 Paralyzed = false;
-
-                m_ParaTimer?.Stop();
             }
 
             if (Frozen)
             {
                 Frozen = false;
-
-                m_FrozenTimer?.Stop();
             }
 
             var content = new List<Item>();
@@ -5570,17 +5544,8 @@ namespace Server
         public virtual void Manifest(TimeSpan delay)
         {
             Warmode = true;
-
-            if (m_AutoManifestTimer == null)
-            {
-                m_AutoManifestTimer = Timer.DelayCall(delay, AutoManifest);
-            }
-            else
-            {
-                m_AutoManifestTimer.Stop();
-            }
-
-            m_AutoManifestTimer.Start();
+            _autoManifestTimerToken.Cancel();
+            Timer.StartTimer(delay, AutoManifest, out _autoManifestTimerToken);
         }
 
         public virtual bool CheckSpeechManifest()
@@ -5592,7 +5557,7 @@ namespace Server
 
             var delay = AutoManifestTimeout;
 
-            if (delay > TimeSpan.Zero && (!Warmode || m_AutoManifestTimer != null))
+            if (delay > TimeSpan.Zero && (!Warmode || _autoManifestTimerToken.Running))
             {
                 Manifest(delay);
                 return true;
@@ -6548,8 +6513,7 @@ namespace Server
 
                         if (m_Criminal)
                         {
-                            ExpireCriminalTimer ??= Timer.DelayCall(ExpireCriminalDelay, ExpireCriminal);
-                            ExpireCriminalTimer.Start();
+                            Timer.StartTimer(ExpireCriminalDelay, ExpireCriminal, out _expireCriminalTimerToken);
                         }
 
                         if (ShouldCheckStatTimers)
@@ -8186,27 +8150,6 @@ namespace Server
         {
         }
 
-        private class WarmodeTimer : Timer
-        {
-            private Mobile m_Mobile;
-
-            public WarmodeTimer(Mobile m, bool value) : base(WarmodeSpamDelay)
-            {
-                m_Mobile = m;
-                Value = value;
-            }
-
-            public bool Value{ get; set; }
-
-            protected override void OnTick()
-            {
-                m_Mobile.Warmode = Value;
-                m_Mobile.m_WarmodeChanges = 0;
-
-                m_Mobile.m_WarmodeTimer = null;
-            }
-        }
-
         public static TimeSpan GetHitsRegenRate(Mobile m) => HitsRegenRateHandler?.Invoke(m) ?? DefaultHitsRate;
 
         public static TimeSpan GetStamRegenRate(Mobile m) => StamRegenRateHandler?.Invoke(m) ?? DefaultStamRate;
@@ -8588,16 +8531,8 @@ namespace Server
                 Combatant = target;
             }
 
-            if (m_ExpireCombatant == null)
-            {
-                m_ExpireCombatant = Timer.DelayCall(ExpireCombatantDelay, ExpireCombatant);
-            }
-            else
-            {
-                m_ExpireCombatant.Stop();
-            }
-
-            m_ExpireCombatant.Start();
+            _expireCombatantTimerToken.Cancel();
+            Timer.StartTimer(ExpireCombatantDelay, ExpireCombatant, out _expireCombatantTimerToken);
         }
 
         public virtual bool HarmfulCheck(Mobile target)
@@ -9446,48 +9381,6 @@ namespace Server
             }
         }
 
-        private class CombatTimer : Timer
-        {
-            private readonly Mobile m_Mobile;
-
-            public CombatTimer(Mobile m) : base(TimeSpan.FromSeconds(0.0), TimeSpan.FromSeconds(0.01)) =>
-                m_Mobile = m;
-
-            protected override void OnTick()
-            {
-                if (Core.TickCount - m_Mobile.NextCombatTime < 0)
-                {
-                    return;
-                }
-
-                var combatant = m_Mobile.Combatant;
-
-                // If no combatant, wrong map, one of us is a ghost, or cannot see, or deleted, then stop combat
-                if (combatant?.Deleted != false || m_Mobile.Deleted || combatant.m_Map != m_Mobile.m_Map ||
-                    !combatant.Alive || !m_Mobile.Alive || !m_Mobile.CanSee(combatant) || combatant.IsDeadBondedPet ||
-                    m_Mobile.IsDeadBondedPet)
-                {
-                    m_Mobile.Combatant = null;
-                    return;
-                }
-
-                var weapon = m_Mobile.Weapon;
-
-                if (!m_Mobile.InRange(combatant, weapon.MaxRange))
-                {
-                    return;
-                }
-
-                if (m_Mobile.InLOS(combatant))
-                {
-                    weapon.OnBeforeSwing(m_Mobile, combatant);
-                    m_Mobile.RevealingAction();
-                    m_Mobile.NextCombatTime =
-                        Core.TickCount + (int)weapon.OnSwing(m_Mobile, combatant).TotalMilliseconds;
-                }
-            }
-        }
-
         private void ExpireCriminal()
         {
             Criminal = false;