try different apprach to backtracer object

include/spdlog/details/backtracer.h

@@ -16,20 +16,60 @@ namespace spdlog {
     namespace details {
         class backtracer
         {
-    std::mutex mutex_;    
+            mutable std::mutex mutex_;
-    size_t n_messages_;
+            std::atomic<bool> enabled_ {false};      
             circular_q<log_msg_buffer> messages_;
 
         public:
-    explicit backtracer(size_t n_messages) : n_messages_{n_messages}, messages_{n_messages}
+            backtracer() = default;            
-    {}
+            backtracer(const backtracer& other)
-    
-    size_t n_messages() const
             {
-        return n_messages_;
+                std::lock_guard<std::mutex> lock(other.mutex_);
+                enabled_ = other.enabled();
+                messages_ = other.messages_;
             }
 
-    void add(const log_msg &msg)
+            backtracer(backtracer&& other) SPDLOG_NOEXCEPT             
+            {
+                std::lock_guard<std::mutex> lock(other.mutex_);
+                enabled_ = other.enabled();
+                messages_ = std::move(other.messages_);
+            }
+
+            backtracer& operator=(backtracer other)
+            {
+                std::lock_guard<std::mutex> lock(mutex_);
+                enabled_ = other.enabled();
+                messages_ = other.messages_;
+                return *this;
+            }
+
+            void enable(size_t size)
+            {
+                std::lock_guard<std::mutex> lock{ mutex_ };
+                enabled_.store(true, std::memory_order_relaxed);
+                messages_ = circular_q<log_msg_buffer>{ size };
+            }
+
+
+            void disable()
+            {
+                std::lock_guard<std::mutex> lock{ mutex_ };
+                enabled_.store(false, std::memory_order_relaxed);
+            }
+
+
+            bool enabled() const
+            {
+                return enabled_.load(std::memory_order_relaxed);
+            }
+
+            operator bool() const
+            {
+                return enabled();
+            }
+
+            void push_back(const log_msg &msg)
             {
                 std::lock_guard<std::mutex> lock{ mutex_ };
                 messages_.push_back(log_msg_buffer{ msg });
@@ -47,5 +87,6 @@ public:
                 }
             }
         };
+
     } // namespace details
 } // namespace spdlog

include/spdlog/details/circular_q.h

@@ -14,13 +14,37 @@ class circular_q
         public:
             using item_type = T;
 
+            // empty cir
+            circular_q() = default;
+
             explicit circular_q(size_t max_items)
                 : max_items_(max_items + 1) // one item is reserved as marker for full q
                 , v_(max_items_)
             {}
 
+
+
+            circular_q(const circular_q&) = default;
+            circular_q& operator=(const circular_q&) = default;
+
+            // move cannot be default,
+            // since we need to reset head_, tail_, etc to zero in the moved object
+            circular_q(circular_q&& other) SPDLOG_NOEXCEPT:
+            {
+                copy_moveable(std::move(other));
+            }
+
+            circular_q& operator=(circular_q&& other) SPDLOG_NOEXCEPT
+            {
+                copy_moveable(std::move(other));
+                return *this;
+            }
+
+
             // push back, overrun (oldest) item if no room left
             void push_back(T &&item)
+            {               
+                if(max_items_ > 0)
                 {
                     v_[tail_] = std::move(item);
                     tail_ = (tail_ + 1) % max_items_;
@@ -31,14 +55,18 @@ public:
                         ++overrun_counter_;
                     }
                 }
+            }
 
             // Pop item from front.
             // If there are no elements in the container, the behavior is undefined.
             void pop_front(T &popped_item)
+            {
+                if(max_items_ > 0)
                 {
                     popped_item = std::move(v_[head_]);
                     head_ = (head_ + 1) % max_items_;
                 }
+            }
 
             bool empty()
             {
@@ -57,12 +85,23 @@ public:
             }
 
         private:
-    size_t max_items_;
+            size_t max_items_ = 0;
             typename std::vector<T>::size_type head_ = 0;
             typename std::vector<T>::size_type tail_ = 0;
             size_t overrun_counter_ = 0;
             std::vector<T> v_;
 
+
+            void copy_moveable(circular_q&& other) SPDLOG_NOEXCEPT
+            {
+                max_items_ = other.max_items_;
+                head_ = other.head_;
+                tail_ = other.tail_;
+                overrun_counter_ = other.overrun_counter_,
+                v_ = std::move(other.v_);                
+                other.max_items_ = 0; // disable other                                
+            }
+
         };
     } // namespace details
 } // namespace spdlog

include/spdlog/details/log_msg_buffer.h

@@ -47,6 +47,14 @@ public:
         update_string_views();
     }
 
+    log_msg_buffer &operator=(log_msg_buffer &other)
+    {
+        log_msg::operator=(other);
+        buffer.append(other.buffer.begin(), other.buffer.end());
+        update_string_views();
+        return *this;
+    }
+
     log_msg_buffer &operator=(log_msg_buffer &&other)
     {
         log_msg::operator=(std::move(other));

include/spdlog/logger-inl.h

@@ -24,10 +24,6 @@ SPDLOG_INLINE logger::logger(const logger &other)
     , custom_err_handler_(other.custom_err_handler_)
     , tracer_(other.tracer_)
 {    
-    if (tracer_)
-    {
-        enable_backtrace(tracer_->n_messages());
-    }
 }
 
 SPDLOG_INLINE logger::logger(logger &&other) SPDLOG_NOEXCEPT : name_(std::move(other.name_)),
@@ -61,7 +57,7 @@ SPDLOG_INLINE void logger::swap(spdlog::logger &other) SPDLOG_NOEXCEPT
     other.flush_level_.store(tmp);
 
     custom_err_handler_.swap(other.custom_err_handler_);
-    tracer_.swap(other.tracer_);
+    std::swap(tracer_, other.tracer_);    
 }
 
 SPDLOG_INLINE void swap(logger &a, logger &b)
@@ -116,13 +112,13 @@ SPDLOG_INLINE void logger::set_pattern(std::string pattern, pattern_time_type ti
 // create new backtrace sink and move to it all our child sinks
 SPDLOG_INLINE void logger::enable_backtrace(size_t n_messages)
 {
-    tracer_ = std::make_shared<details::backtracer>(n_messages);
+    tracer_.enable(n_messages);
 }
 
 // restore orig sinks and level and delete the backtrace sink
 SPDLOG_INLINE void logger::disable_backtrace()
 {
-    tracer_.reset();
+    tracer_.disable();
 }
 
 SPDLOG_INLINE void logger::dump_backtrace()
@@ -206,7 +202,7 @@ SPDLOG_INLINE void logger::flush_()
 
 SPDLOG_INLINE void logger::backtrace_add_(const details::log_msg &msg)
 {
-    tracer_->add(msg);
+    tracer_.push_back(msg);
 }
 
 SPDLOG_INLINE void logger::dump_backtrace_()
@@ -215,7 +211,7 @@ SPDLOG_INLINE void logger::dump_backtrace_()
     if (tracer_)
     {
         sink_it_(log_msg{name(), level::info, "****************** Backtrace Start ******************"});
-        tracer_->foreach_pop([this](const details::log_msg &msg) { this->sink_it_(msg); });
+        tracer_.foreach_pop([this](const details::log_msg &msg) { this->sink_it_(msg); });
         sink_it_(log_msg{name(), level::info, "****************** Backtrace End ********************"});
     }
 }

include/spdlog/logger.h

@@ -17,6 +17,7 @@
 
 #include "spdlog/common.h"
 #include "spdlog/details/log_msg.h"
+#include "spdlog/details/backtracer.h"
 
 #ifdef SPDLOG_WCHAR_TO_UTF8_SUPPORT
 #include "spdlog/details/os.h"
@@ -39,10 +40,6 @@
 
 namespace spdlog {
 
-namespace details {
-class backtracer;
-}
-
 class logger
 {
 public:
@@ -365,7 +362,7 @@ protected:
     spdlog::level_t level_{level::info};
     spdlog::level_t flush_level_{level::off};
     err_handler custom_err_handler_{nullptr};
-    std::shared_ptr<details::backtracer> tracer_;
+    details::backtracer tracer_;
 
     virtual void sink_it_(const details::log_msg &msg);
     virtual void flush_();