Added thread-block support in async_logger, to wait for logs to finish

include/spdlog/async_logger-inl.h

@@ -23,11 +23,63 @@ SPDLOG_INLINE spdlog::async_logger::async_logger(
     : async_logger(std::move(logger_name), {std::move(single_sink)}, std::move(tp), overflow_policy)
 {}
 
+SPDLOG_INLINE spdlog::async_logger::async_logger(const async_logger& other) : logger(other)
+{
+    thread_pool_ = other.thread_pool_;
+    overflow_policy_ = other.overflow_policy_;
+    pending_log_count_ = other.pending_log_count_.load();
+}
+
+SPDLOG_INLINE size_t spdlog::async_logger::pending_log_count() const noexcept
+{
+    return pending_log_count_;
+}
+
+SPDLOG_INLINE void spdlog::async_logger::wait()
+{
+    if (pending_log_count_ > 0)
+    {
+        std::unique_lock<std::mutex> lock(wait_mutex_);
+        wait_condition_.wait(lock);
+    }
+}
+
+template< class Rep, class Period >
+SPDLOG_INLINE std::cv_status spdlog::async_logger::wait_for(const std::chrono::duration<Rep, Period>& rel_time)
+{
+    if (pending_log_count_ > 0)
+    {
+        std::unique_lock<std::mutex> lock(wait_mutex_);
+        return wait_condition_.wait_for(rel_time);
+    }
+}
+
+template< class Clock, class Duration>
+SPDLOG_INLINE std::cv_status spdlog::async_logger::wait_until(const std::chrono::time_point<Clock, Duration>& timeout_time)
+{
+    if (pending_log_count_ > 0)
+    {
+        std::unique_lock<std::mutex> lock(wait_mutex_);
+        return wait_condition_.wait_until(timeout_time);
+    }
+}
+
+SPDLOG_INLINE bool spdlog::async_logger::block_on_flush() const noexcept
+{
+    return block_on_flush_;
+}
+
+SPDLOG_INLINE void spdlog::async_logger::block_on_flush(bool value) noexcept
+{
+    block_on_flush_ = value;
+}
+
 // send the log message to the thread pool
 SPDLOG_INLINE void spdlog::async_logger::sink_it_(const details::log_msg &msg)
 {
     if (auto pool_ptr = thread_pool_.lock())
     {
+        on_log_dispatched_();
         pool_ptr->post_log(shared_from_this(), msg, overflow_policy_);
     }
     else
@@ -41,7 +93,14 @@ SPDLOG_INLINE void spdlog::async_logger::flush_()
 {
     if (auto pool_ptr = thread_pool_.lock())
     {
+        on_log_dispatched_();
         pool_ptr->post_flush(shared_from_this(), overflow_policy_);
+
+        /// this is to provide blocking functionality through logger(not async_logger) interface 
+        if (block_on_flush_)
+        {
+            wait();
+        }
     }
     else
     {
@@ -54,7 +113,9 @@ SPDLOG_INLINE void spdlog::async_logger::flush_()
 //
 SPDLOG_INLINE void spdlog::async_logger::backend_sink_it_(const details::log_msg &msg)
 {
-    for (auto &sink : sinks_)
+    on_logged_();
+
+    for (auto& sink : sinks_)
     {
         if (sink->should_log(msg.level))
         {
@@ -74,7 +135,9 @@ SPDLOG_INLINE void spdlog::async_logger::backend_sink_it_(const details::log_msg
 
 SPDLOG_INLINE void spdlog::async_logger::backend_flush_()
 {
-    for (auto &sink : sinks_)
+    on_logged_();
+
+    for (auto& sink : sinks_)
     {
         SPDLOG_TRY
         {
@@ -84,6 +147,27 @@ SPDLOG_INLINE void spdlog::async_logger::backend_flush_()
     }
 }
 
+SPDLOG_INLINE void spdlog::async_logger::on_log_dispatched_()
+{
+    ++pending_log_count_;
+}
+
+SPDLOG_INLINE void spdlog::async_logger::on_logged_()
+{
+    if (pending_log_count_ == 0)
+    {
+        throw_spdlog_ex("all dispatched messages by logger "
+            + name_ + " have already been logged, but on_message_logged() was invoked");
+    }
+
+    pending_log_count_--;
+
+    if (pending_log_count_ == 0)
+    {
+        wait_condition_.notify_all();
+    }
+}
+
 SPDLOG_INLINE std::shared_ptr<spdlog::logger> spdlog::async_logger::clone(std::string new_name)
 {
     auto cloned = std::make_shared<spdlog::async_logger>(*this);

include/spdlog/async_logger.h

@@ -14,7 +14,9 @@
 // Upon destruction, logs all remaining messages in the queue before
 // destructing..
 
+#include <condition_variable>
 #include <spdlog/logger.h>
+#include <iostream>
 
 namespace spdlog {
 
@@ -41,6 +43,8 @@ public:
         : logger(std::move(logger_name), begin, end)
         , thread_pool_(std::move(tp))
         , overflow_policy_(overflow_policy)
+        , pending_log_count_(0)
+        , block_on_flush_(false)
     {}
 
     async_logger(std::string logger_name, sinks_init_list sinks_list, std::weak_ptr<details::thread_pool> tp,
@@ -49,17 +53,42 @@ public:
     async_logger(std::string logger_name, sink_ptr single_sink, std::weak_ptr<details::thread_pool> tp,
         async_overflow_policy overflow_policy = async_overflow_policy::block);
 
+    // explicit copy constructor to manage mutex and cv
+    async_logger(const async_logger& other);
+
     std::shared_ptr<logger> clone(std::string new_name) override;
 
+public:
+    size_t pending_log_count() const noexcept;
+
+    bool block_on_flush() const noexcept;
+    void block_on_flush(bool value) noexcept;
+
+    void wait();
+
+    template< class Rep, class Period >
+    std::cv_status wait_for(const std::chrono::duration<Rep, Period>& rel_time);
+
+    template< class Clock, class Duration>
+    std::cv_status wait_until(const std::chrono::time_point<Clock, Duration>& timeout_time);
+
 protected:
     void sink_it_(const details::log_msg &msg) override;
     void flush_() override;
     void backend_sink_it_(const details::log_msg &incoming_log_msg);
     void backend_flush_();
 
+    void on_log_dispatched_();
+    void on_logged_();
+
 private:
     std::weak_ptr<details::thread_pool> thread_pool_;
     async_overflow_policy overflow_policy_;
+
+    std::mutex wait_mutex_;
+    std::condition_variable wait_condition_;
+    std::atomic<size_t> pending_log_count_;
+    bool block_on_flush_;
 };
 } // namespace spdlog
 

tests/test_async.cpp

@@ -84,7 +84,6 @@ TEST_CASE("flush", "[async]")
 
 TEST_CASE("async periodic flush", "[async]")
 {
-
     auto logger = spdlog::create_async<spdlog::sinks::test_sink_mt>("as");
     auto test_sink = std::static_pointer_cast<spdlog::sinks::test_sink_mt>(logger->sinks()[0]);