From a3701093f6cd1d37bca79db67dc8840b2f304a33 Mon Sep 17 00:00:00 2001
From: Xottab-DUTY <xottab-duty@yandex.ru>
Date: Sat, 18 Jan 2025 14:27:49 +0300
Subject: [PATCH] xrCore/Threading/TaskManager.cpp: replace
 std::condition_variable with Event

std::condition_variable serves different purpose and event exactly fits
our use case.
1. We had used std::condition_variable::wait wrongly as all threads must
lock the same mutex and this requirement wasn't satisfied.
2. Previous implementation (before std::condition_variable) was using an
event per each worker thread. I only now figured out that we can just
use one event.

Fixes #1731.
---
 src/xrCore/Threading/TaskManager.cpp | 10 ++++------
 src/xrCore/Threading/TaskManager.hpp |  4 ++--
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/src/xrCore/Threading/TaskManager.cpp b/src/xrCore/Threading/TaskManager.cpp
index b1a6e1d50b4..88ba116c5aa 100644
--- a/src/xrCore/Threading/TaskManager.cpp
+++ b/src/xrCore/Threading/TaskManager.cpp
@@ -140,7 +140,6 @@ struct TaskWorkerStats
 class TaskWorker : public TaskQueue, public TaskWorkerStats
 {
 public:
-    std::mutex       mutex;
     fast_lc16        random{ this };
     size_t           id    { size_t(-1) };
 } static thread_local s_tl_worker;
@@ -179,7 +178,7 @@ TaskManager::~TaskManager()
     UnregisterThisThreadAsWorker();
     while (!workers.empty())
     {
-        newWorkArrived.notify_all();
+        newWorkArrived.Set();
         SDL_PumpEvents();
         Sleep(0);
     }
@@ -242,10 +241,9 @@ void TaskManager::TaskWorkerStart()
 
         SetThreadStatus(false);
         {
-            std::unique_lock lck(s_tl_worker.mutex);
             do
             {
-                newWorkArrived.wait(lck); // spurious wakeups allowed
+                newWorkArrived.Wait();
             } while (shouldPause.load(std::memory_order_consume));
         }
         SetThreadStatus(true);
@@ -277,7 +275,7 @@ Task* TaskManager::TryToSteal() const
         if (auto* task = other->steal())
         {
             if (!other->empty())
-                newWorkArrived.notify_all();
+                newWorkArrived.Set();
             return task;
         }
         --steal_attempts;
@@ -294,7 +292,7 @@ Task* TaskManager::AllocateTask() noexcept
 void TaskManager::PushTask(Task& task) noexcept
 {
     s_tl_worker.push(&task);
-    newWorkArrived.notify_one();
+    newWorkArrived.Set();
     ++s_tl_worker.pushedTasks;
 }
 
diff --git a/src/xrCore/Threading/TaskManager.hpp b/src/xrCore/Threading/TaskManager.hpp
index 60780220ed0..fa87dfb393b 100644
--- a/src/xrCore/Threading/TaskManager.hpp
+++ b/src/xrCore/Threading/TaskManager.hpp
@@ -16,9 +16,9 @@
 #pragma once
 
 #include "Task.hpp"
+#include "Event.hpp"
 
 #include <atomic>
-#include <condition_variable>
 #include <mutex>
 
 class TaskWorker;
@@ -30,7 +30,7 @@ class XRCORE_API TaskManager final
     xr_vector<std::thread> workerThreads;
     std::mutex workersLock;
 
-    inline static std::condition_variable newWorkArrived;
+    inline static Event newWorkArrived;
     std::atomic_size_t activeWorkersCount{};
 
     std::atomic_bool shouldPause{};