Common: Introduce a OneShotEvent class. Unlike Common::Event, OneShotEvent is safe in situations when being immediately destructed.

3 files changed, 57 insertions, 0 deletions

diff --git a/Source/Core/Common/CMakeLists.txt b/Source/Core/Common/CMakeLists.txt
index e833893a9d..2447d1ed40 100644
--- a/Source/Core/Common/CMakeLists.txt
+++ b/Source/Core/Common/CMakeLists.txt
@@ -118,6 +118,7 @@ add_library(common
   NandPaths.h
   Network.cpp
   Network.h
+  OneShotEvent.h
   PcapFile.cpp
   PcapFile.h
   Profiler.cpp
diff --git a/Source/Core/Common/OneShotEvent.h b/Source/Core/Common/OneShotEvent.h
new file mode 100644
index 0000000000..312848ed91
--- /dev/null
+++ b/Source/Core/Common/OneShotEvent.h
@@ -0,0 +1,55 @@
+// Copyright 2025 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <chrono>
+#include <memory>
+#include <semaphore>
+
+#include "Common/Functional.h"
+
+namespace Common
+{
+
+// A one-time-use single-producer single-consumer thread synchronization class.
+// Safe when `Set` will cause a `Wait`ing thread to immediately destruct the event itself.
+class OneShotEvent
+{
+public:
+  // One thread should call Set() exactly once.
+  void Set() { m_semaphore.release(1); }
+
+  // One thread may call Wait() once or WaitFor() until it returns true.
+
+  void Wait() { m_semaphore.acquire(); }
+
+  template <typename Rep, typename Period>
+  bool WaitFor(const std::chrono::duration<Rep, Period>& rel_time)
+  {
+    return m_semaphore.try_acquire_for(rel_time);
+  }
+
+private:
+  std::binary_semaphore m_semaphore{0};
+};
+
+// Invokes Set() on the given object upon destruction.
+template <typename EventType>
+class ScopedSetter
+{
+public:
+  ScopedSetter() = default;
+  explicit ScopedSetter(EventType* ptr) : m_ptr{ptr} {}
+
+  // Forgets the object without invoking Set().
+  void Dismiss() { m_ptr.release(); }
+
+private:
+  // Leveraging unique_ptr conveniently makes this class move-only.
+  // It does no actual deletion, just calls Set().
+  using NonOwningSetOnDeletePtr = std::unique_ptr<EventType, InvokerOf<&EventType::Set>>;
+  NonOwningSetOnDeletePtr m_ptr;
+};
+
+}  // namespace Common
diff --git a/Source/Core/DolphinLib.props b/Source/Core/DolphinLib.props
index 3cfac5838c..f4a9c04a92 100644
--- a/Source/Core/DolphinLib.props
+++ b/Source/Core/DolphinLib.props
@@ -149,6 +149,7 @@
     <ClInclude Include="Common\Mutex.h" />
     <ClInclude Include="Common\NandPaths.h" />
     <ClInclude Include="Common\Network.h" />
+    <ClInclude Include="Common\OneShotEvent.h" />
     <ClInclude Include="Common\PcapFile.h" />
     <ClInclude Include="Common\Profiler.h" />
     <ClInclude Include="Common\Projection.h" />