From c95cb8f8ec6ce256b75fd85c858c7b80f91e088e Mon Sep 17 00:00:00 2001
From: lizzie <lizzie@eden-emu.dev>
Date: Thu, 9 Apr 2026 23:46:38 +0200
Subject: [PATCH] [hle] improved flusher that uses jthread (#3837)

not happy with this impl, but I made this a bit quickly to demostrate it can be done better :)

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3837
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>
---
 src/core/hle/kernel/svc/svc_debug_string.cpp | 102 ++++++++-----------
 1 file changed, 43 insertions(+), 59 deletions(-)

diff --git a/src/core/hle/kernel/svc/svc_debug_string.cpp b/src/core/hle/kernel/svc/svc_debug_string.cpp
index 92cc334a81..c190fa7a3f 100644
--- a/src/core/hle/kernel/svc/svc_debug_string.cpp
+++ b/src/core/hle/kernel/svc/svc_debug_string.cpp
@@ -6,6 +6,8 @@
 
 #include <condition_variable>
 #include <mutex>
+#include <optional>
+#include <stop_token>
 #include <thread>
 
 #include "core/core.h"
@@ -18,59 +20,53 @@ namespace Kernel::Svc {
 constexpr auto MAX_MSG_TIME = std::chrono::milliseconds(250);
 const auto MAX_MSG_SIZE = 0x1000;
 
-static std::string msg_buffer;
-static std::mutex msg_mutex;
-static std::condition_variable msg_cv;
-static std::chrono::steady_clock::time_point last_msg_time;
-static bool worker_running = true;
-static std::unique_ptr<std::thread> flush_thread;
-static std::once_flag start_flag;
-
-static void FlushDbgLoop() {
-    while (true) {
-        std::unique_lock lock(msg_mutex);
-
-        msg_cv.wait(lock, [] { return !msg_buffer.empty() || !worker_running; });
-        if (!worker_running && msg_buffer.empty()) break;
-
-        auto timeout = last_msg_time + MAX_MSG_TIME;
-        bool woke_early = msg_cv.wait_until(lock, timeout, [] {
-            return msg_buffer.size() >= MAX_MSG_SIZE || !worker_running;
-        });
-
-        if (!woke_early || msg_buffer.size() >= MAX_MSG_SIZE || !worker_running) {
-            if (!msg_buffer.empty()) {
-                // Remove trailing newline as LOG_INFO adds that anyways
-                if (msg_buffer.back() == '\n')
-                    msg_buffer.pop_back();
-
-                LOG_INFO(Debug_Emulated, "\n{}", msg_buffer);
-                msg_buffer.clear();
-            }
-            if (!worker_running) break;
-        }
-    }
-}
-
 /// Used to output a message on a debug hardware unit - does nothing on a retail unit
 Result OutputDebugString(Core::System& system, u64 address, u64 len) {
+    static struct DebugFlusher {
+        std::string msg_buffer;
+        std::mutex msg_mutex;
+        std::condition_variable msg_cv;
+        std::chrono::steady_clock::time_point last_msg_time;
+        std::optional<std::jthread> thread;
+    } flusher_data;
     R_SUCCEED_IF(len == 0);
-
     // Only start the thread the very first time this function is called
-    std::call_once(start_flag, [] {
-        flush_thread = std::make_unique<std::thread>(FlushDbgLoop);
-    });
+    if (!flusher_data.thread) {
+        flusher_data.thread.emplace([](std::stop_token stop_token) {
+            while (!stop_token.stop_requested()) {
+                std::unique_lock lock(flusher_data.msg_mutex);
+                flusher_data.msg_cv.wait(lock, [&stop_token] {
+                    return !flusher_data.msg_buffer.empty() || stop_token.stop_requested();
+                });
+                if (stop_token.stop_requested() && flusher_data.msg_buffer.empty())
+                    break;
+                auto timeout = flusher_data.last_msg_time + MAX_MSG_TIME;
+                bool woke_early = flusher_data.msg_cv.wait_until(lock, timeout, [&stop_token] {
+                    return flusher_data.msg_buffer.size() >= MAX_MSG_SIZE || stop_token.stop_requested();
+                });
+                if (!woke_early || flusher_data.msg_buffer.size() >= MAX_MSG_SIZE || stop_token.stop_requested()) {
+                    if (!flusher_data.msg_buffer.empty()) {
+                        // Remove trailing newline as LOG_INFO adds that anyways
+                        if (flusher_data.msg_buffer.back() == '\n')
+                            flusher_data.msg_buffer.pop_back();
 
-    {
-        std::lock_guard lock(msg_mutex);
-        const auto old_size = msg_buffer.size();
-        msg_buffer.resize(old_size + len);
-        GetCurrentMemory(system.Kernel()).ReadBlock(address, msg_buffer.data() + old_size, len);
-
-        last_msg_time = std::chrono::steady_clock::now();
+                        LOG_INFO(Debug_Emulated, "\n{}", flusher_data.msg_buffer);
+                        flusher_data.msg_buffer.clear();
+                    }
+                    if (stop_token.stop_requested()) break;
+                }
+            }
+            flusher_data.msg_cv.notify_all();
+        });
     }
-
-    msg_cv.notify_one();
+    {
+        std::lock_guard lock(flusher_data.msg_mutex);
+        const auto old_size = flusher_data.msg_buffer.size();
+        flusher_data.msg_buffer.resize(old_size + len);
+        GetCurrentMemory(system.Kernel()).ReadBlock(address, flusher_data.msg_buffer.data() + old_size, len);
+        flusher_data.last_msg_time = std::chrono::steady_clock::now();
+    }
+    flusher_data.msg_cv.notify_one();
     R_SUCCEED();
 }
 
@@ -82,16 +78,4 @@ Result OutputDebugString64From32(Core::System& system, uint32_t debug_str, uint3
     R_RETURN(OutputDebugString(system, debug_str, len));
 }
 
-struct BufferAutoFlush {
-    ~BufferAutoFlush() {
-        {
-            std::lock_guard lock(msg_mutex);
-            worker_running = false;
-        }
-        msg_cv.notify_all();
-        if (flush_thread && flush_thread->joinable()) flush_thread->join();
-    }
-};
-static BufferAutoFlush auto_flusher;
-
 } // namespace Kernel::Svc