From 5a69801877eb72899dd9867c39a1b88b7114fe5b Mon Sep 17 00:00:00 2001
From: Taloth Saldono <Taloth@users.noreply.github.com>
Date: Fri, 19 Mar 2021 02:48:09 +0100
Subject: [PATCH] Fixed: Unnecessary idle cpu usage

ref #4386
---
 .../Messaging/Commands/CommandQueue.cs        | 39 +++++++++++++++++--
 .../Messaging/Commands/CommandQueueManager.cs |  4 ++
 2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/src/NzbDrone.Core/Messaging/Commands/CommandQueue.cs b/src/NzbDrone.Core/Messaging/Commands/CommandQueue.cs
index e566fcee8..67fa437b7 100644
--- a/src/NzbDrone.Core/Messaging/Commands/CommandQueue.cs
+++ b/src/NzbDrone.Core/Messaging/Commands/CommandQueue.cs
@@ -23,6 +23,8 @@ public void Add(CommandModel item)
             lock (_mutex)
             {
                 _items.Add(item);
+
+                Monitor.PulseAll(_mutex);
             }
         }
 
@@ -68,6 +70,8 @@ public void RemoveMany(IEnumerable<CommandModel> commands)
                 {
                     _items.Remove(command);
                 }
+
+                Monitor.PulseAll(_mutex);
             }
         }
         public bool RemoveIfQueued(int id)
@@ -82,6 +86,8 @@ public bool RemoveIfQueued(int id)
                 {
                     _items.Remove(command);
                     rval = true;
+
+                    Monitor.PulseAll(_mutex);
                 }
             }
 
@@ -101,18 +107,43 @@ public IEnumerable<CommandModel> GetConsumingEnumerable()
 
         public IEnumerable<CommandModel> GetConsumingEnumerable(CancellationToken cancellationToken)
         {
+            cancellationToken.Register(PulseAllConsumers);
+
             while (!cancellationToken.IsCancellationRequested)
             {
-                if (TryGet(out var command))
+                CommandModel command = null;
+
+                lock (_mutex)
+                {
+                    if (cancellationToken.IsCancellationRequested)
+                    {
+                        break;
+                    }
+
+                    if (!TryGet(out command))
+                    {
+                        Monitor.Wait(_mutex);
+                        continue;
+                    }
+                }
+
+                if (command != null)
                 {
                     yield return command;
                 }
-
-                Thread.Sleep(10);
             }
         }
 
-        public bool TryGet(out CommandModel item)
+        public void PulseAllConsumers()
+        {
+            // Signal all consumers to reevaluate cancellation token
+            lock (_mutex)
+            {
+                Monitor.PulseAll(_mutex);
+            }
+        }
+
+        private bool TryGet(out CommandModel item)
         {
             var rval = true;
             item = default(CommandModel);
diff --git a/src/NzbDrone.Core/Messaging/Commands/CommandQueueManager.cs b/src/NzbDrone.Core/Messaging/Commands/CommandQueueManager.cs
index c1e8631d1..9156e0844 100644
--- a/src/NzbDrone.Core/Messaging/Commands/CommandQueueManager.cs
+++ b/src/NzbDrone.Core/Messaging/Commands/CommandQueueManager.cs
@@ -183,6 +183,8 @@ public void Start(CommandModel command)
         public void Complete(CommandModel command, string message)
         {
             Update(command, CommandStatus.Completed, message);
+
+            _commandQueue.PulseAllConsumers();
         }
 
         public void Fail(CommandModel command, string message, Exception e)
@@ -190,6 +192,8 @@ public void Fail(CommandModel command, string message, Exception e)
             command.Exception = e.ToString();
             
             Update(command, CommandStatus.Failed, message);
+
+            _commandQueue.PulseAllConsumers();
         }
 
         public void Requeue()