feat(logging): add dedicated executor controls

.github/workflows/ci.yml

@@ -276,11 +276,12 @@ jobs:
             -DLOGIT_CPP_BUILD_TESTS=ON \
             -DLOGIT_EMSCRIPTEN=ON -DLOGIT_FORCE_ASYNC_OFF=ON
       - name: Build
-        run: cmake --build build-ems --target ems_console ems_async_flush -j
+        run: cmake --build build-ems --target ems_console ems_async_flush ems_single_thread_executor -j
       - name: Run smoke tests
         run: |
           node --no-experimental-fetch build-ems/tests/ems_console.js
           node --no-experimental-fetch build-ems/tests/ems_async_flush.js
+          node --no-experimental-fetch build-ems/tests/ems_single_thread_executor.js
       - name: Upload logs
         if: failure()
         uses: actions/upload-artifact@v4

README.md

@@ -212,6 +212,40 @@ your workload needs a different baseline. See
 [`docs/TaskExecutor.md`](docs/TaskExecutor.md) for a full breakdown and tuning
 tips.
 
+Logger backend `Config` structs can opt into `use_dedicated_executor=true` when
+one slow sink must not delay other async loggers. On native builds this creates
+one worker thread per configured logger, so use it deliberately for expensive or
+isolated backends. Single-threaded Emscripten builds keep the same per-instance
+queue semantics but drain cooperatively on the browser event loop.
+
+You can always pass a configured backend through the generic macro:
+
+```cpp
+logit::ConsoleLogger::Config cfg;
+cfg.async = true;
+cfg.use_dedicated_executor = true;
+cfg.queue_capacity = 1024;
+cfg.queue_policy = logit::detail::QueuePolicy::Block;
+
+LOGIT_ADD_LOGGER(
+    logit::ConsoleLogger,
+    (cfg),
+    logit::SimpleLogFormatter,
+    (LOGIT_CONSOLE_PATTERN)
+);
+```
+
+Built-in helpers also expose config-first and short dedicated forms:
+
+```cpp
+LOGIT_ADD_CONSOLE_CONFIG(cfg, LOGIT_CONSOLE_PATTERN);
+LOGIT_ADD_CONSOLE_DEDICATED(
+    LOGIT_CONSOLE_PATTERN,
+    1024,
+    logit::detail::QueuePolicy::DropNewest
+);
+```
+
 ## Features
 
 - **Flexible Log Formatting**: 

docs/TaskExecutor.md

@@ -108,6 +108,13 @@ outlive static destructors inside logger components. Applications may call
 `shutdown()` explicitly (for example during test teardown), but the singleton
 remains valid until the process terminates.
 
+Logger backends with `Config::use_dedicated_executor=true` own a
+`SingleThreadExecutor` instead of using this singleton. Native builds create one
+worker thread per configured logger, while single-threaded Emscripten builds use
+a cooperative per-instance queue. `Logger::shutdown()` calls each backend's
+`ILogger::shutdown()` hook before stopping the global executor so these
+logger-owned workers drain and stop cleanly.
+
 ## 6. Emscripten (no pthreads)
 
 When targeting Emscripten without pthread support:
@@ -118,6 +125,8 @@ When targeting Emscripten without pthread support:
 * Tasks are executed by `emscripten_async_call`, which schedules a drain on the
   browser event loop. This keeps logging compatible with the cooperative
   execution model used in WebAssembly UI scenarios.
+* Dedicated logger executors use the same cooperative scheduling model in this
+  build; no OS thread is created.
 * Typical use cases: browser-hosted tools or demos that need asynchronous-style
   logging without pulling in pthread support.
 

docs/mainpage.dox

@@ -225,6 +225,33 @@ LOGIT_SET_QUEUE_POLICY(LOGIT_QUEUE_BLOCK); // Block when full
 \endcode
 Available policies: `LOGIT_QUEUE_DROP_NEWEST`, `LOGIT_QUEUE_DROP_OLDEST`, `LOGIT_QUEUE_BLOCK`.
 
+Backend `Config` structs can set `use_dedicated_executor=true` to isolate a slow
+async sink from the global task executor. Native builds create one worker thread
+per configured logger; single-threaded Emscripten builds use a cooperative
+per-instance queue instead.
+
+\code{.cpp}
+logit::ConsoleLogger::Config cfg;
+cfg.async = true;
+cfg.use_dedicated_executor = true;
+cfg.queue_capacity = 1024;
+cfg.queue_policy = logit::detail::QueuePolicy::Block;
+
+LOGIT_ADD_LOGGER(
+    logit::ConsoleLogger,
+    (cfg),
+    logit::SimpleLogFormatter,
+    (LOGIT_CONSOLE_PATTERN)
+);
+
+LOGIT_ADD_CONSOLE_CONFIG(cfg, LOGIT_CONSOLE_PATTERN);
+LOGIT_ADD_CONSOLE_DEDICATED(
+    LOGIT_CONSOLE_PATTERN,
+    1024,
+    logit::detail::QueuePolicy::DropNewest
+);
+\endcode
+
 \subsection stream_logging Stream-Based Logging
 
 Use stream operators for complex messages.

include/logit_cpp/logit/Logger.hpp

@@ -388,8 +388,8 @@ namespace logit {
         ///
         /// Ensures that all log messages are fully processed before continuing.
         void wait() {
-            LoggerReadLock lock(m_loggers_mx);
-            for (const auto& strategy : m_loggers) {
+            const auto snapshot = get_all_strategy_snapshots();
+            for (const auto& strategy : snapshot) {
                 if (!strategy) continue;
                 strategy->logger->wait();
             }
@@ -400,9 +400,14 @@ namespace logit {
         /// Disables further logging, waits for asynchronous tasks to complete,
         /// and shuts down TaskExecutor.
         void shutdown() {
-            if (m_shutdown) return;
-            m_shutdown = true;
-            wait();
+            if (m_shutdown.exchange(true)) return;
+
+            const auto snapshot = get_all_strategy_snapshots();
+            for (const auto& strategy : snapshot) {
+                if (!strategy) continue;
+                std::lock_guard<std::mutex> exec_lock(strategy->exec_mx);
+                strategy->logger->shutdown();
+            }
             detail::TaskExecutor::get_instance().shutdown();
         }
 
@@ -441,6 +446,11 @@ namespace logit {
             return std::shared_ptr<LoggerStrategy>();
         }
 
+        std::vector<std::shared_ptr<LoggerStrategy>> get_all_strategy_snapshots() const {
+            LoggerReadLock lock(m_loggers_mx);
+            return m_loggers;
+        }
+
         std::vector<std::shared_ptr<LoggerStrategy>> m_loggers;        ///< Container for logger-formatter pairs.
         mutable LoggerMutex m_loggers_mx;                        ///< Protects access to logger strategies.
         std::atomic<bool> m_shutdown = ATOMIC_VAR_INIT(false); ///< Flag indicating if shutdown was requested.

include/logit_cpp/logit/detail/QueuePolicy.hpp

@@ -0,0 +1,16 @@
+#pragma once
+#ifndef _LOGIT_DETAIL_QUEUE_POLICY_HPP_INCLUDED
+#define _LOGIT_DETAIL_QUEUE_POLICY_HPP_INCLUDED
+
+namespace logit { namespace detail {
+
+/// \brief Queue overflow handling policy used by TaskExecutor and SingleThreadExecutor.
+enum class QueuePolicy {
+    DropNewest, ///< Reject the incoming task when the queue is full.
+    DropOldest, ///< Drop the oldest queued task.
+    Block       ///< Producers wait until capacity is available.
+};
+
+}} // namespace logit::detail
+
+#endif // _LOGIT_DETAIL_QUEUE_POLICY_HPP_INCLUDED