wip async sink

include/spdlog/details/async_log_msg.h

@@ -15,10 +15,10 @@ namespace details {
 
 class SPDLOG_API async_log_msg : public log_msg {
 public:
-    enum class msg_type:std::uint8_t { log, flush, terminate };
+    enum class type:std::uint8_t { log, flush, terminate };
     async_log_msg() = default;
-    explicit async_log_msg(msg_type type);
-    async_log_msg(msg_type type, const log_msg &orig_msg);
+    explicit async_log_msg(type type);
+    async_log_msg(type type, const log_msg &orig_msg);
 
     ~async_log_msg() = default;
     async_log_msg(const async_log_msg &other);
@@ -26,9 +26,9 @@ public:
     async_log_msg &operator=(const async_log_msg &other);
     async_log_msg &operator=(async_log_msg &&other) noexcept;
 
-    msg_type message_type() const {return msg_type_;}
+    type message_type() const {return msg_type_;}
 private:
-    msg_type msg_type_{msg_type::log};
+    type msg_type_{type::log};
     memory_buf_t buffer_;
     void update_string_views();
 };

include/spdlog/sinks/async_sink.h

@@ -1,10 +1,17 @@
 #pragma once
 
+#include <cstdint>
 #include <thread>
+#include <atomic>
+#include <cassert>
 
 #include "../details/async_log_msg.h"
 #include "../details/mpmc_blocking_q.h"
-#include "./dist_sink.h"
+#include "dist_sink.h"
+
+// async_sink is a sink that sends log messages to a dist_sink in a separate thread using a queue.
+// The worker thread dequeues the messages and sends them to the dist_sink to perform the actual logging.
+// The worker thread is terminated when the async_sink is destroyed.
 
 namespace spdlog {
 namespace sinks {
@@ -13,14 +20,31 @@ template <typename Mutex>
 class async_sink final : public dist_sink<Mutex> {
 public:
     using base_t = dist_sink<Mutex>;
-  using queue_t = details::mpmc_blocking_queue<details::async_log_msg>;
-  async_sink() {
-    q_ = std::make_unique<queue_t>(8192);
+    using async_message_t = details::async_log_msg;
+    using queue_t = details::mpmc_blocking_queue<async_message_t>;
+    enum { max_queue_size = 1024 * 1024 * 10 };
+
+    // Async overflow policy - block by default.
+    enum class overflow_policy : std::uint8_t {
+        block,           // Block until message can be enqueued (default
+        overrun_oldest,  // Discard oldest message in the queue if full when trying to
+                         // add new item.
+        discard_new      // Discard new message if the queue is full when trying to add new item.
+    };
+
+    explicit async_sink(size_t queue_size) {
+        if (queue_size == 0 || queue_size > max_queue_size) {
+            throw spdlog_ex("async_sink: invalid queue size");
+        }
+        // printf("........... Allocating queue: slot: %zu X %zu bytes ====> %lld KB ..............\n",
+        //   queue_size, sizeof(details::async_log_msg), (sizeof(details::async_log_msg) * queue_size)/1024);
+        q_ = std::make_unique<queue_t>(queue_size);
+
         worker_thread_ = std::thread([this] {
             details::async_log_msg incoming_msg;
             for (;;) {
                 q_->dequeue(incoming_msg);
-        if (incoming_msg.message_type() == details::async_log_msg::msg_type::terminate) {
+                if (incoming_msg.message_type() == async_message_t::type::terminate) {
                     break;
                 }
                 base_t::sink_it_(incoming_msg);
@@ -29,9 +53,10 @@ public:
     }
     ~async_sink() override {
         try {
-      q_->enqueue(details::async_log_msg(details::async_log_msg::msg_type::terminate));
+            q_->enqueue(async_message_t(async_message_t::type::terminate));
             worker_thread_.join();
-    } catch (...) {}
+        } catch (...) {
+        }
     };
 
     async_sink(const async_sink &) = delete;
@@ -39,21 +64,47 @@ public:
     async_sink(async_sink &&) = default;
     async_sink &operator=(async_sink &&) = default;
 
+    void set_overflow_policy(overflow_policy policy) { overflow_policy_ = policy; }
+    [[nodiscard]] overflow_policy get_overflow_policy() const { return overflow_policy_; }
 
+    [[nodiscard]] size_t get_overrun_counter() const { return q_->overrun_counter(); }
+    void reset_overrun_counter() { q_->reset_overrun_counter(); }
 
+    [[nodiscard]] size_t get_discard_counter() const { return q_->discard_counter(); }
+    void reset_discard_counter() { q_->reset_discard_counter(); }
 
 private:
     void sink_it_(const details::log_msg &msg) override {
-    // Asynchronously send the log message to the base sink
-    q_->enqueue(details::async_log_msg(details::async_log_msg::msg_type::log, msg));
-  }
-  void flush_() override {
-    // Asynchronously flush the base sink
-    q_->enqueue(details::async_log_msg(details::async_log_msg::msg_type::flush));
+        send_message_(async_message_t::type::log, msg);
     }
 
-  std::thread worker_thread_;
+    void flush_() override {
+        send_message_(async_message_t::type::flush, details::log_msg());
+    }
+
+    // asynchronously send the log message to the worker thread using the queue.
+    // take into account the configured overflow policy.
+    void send_message_(const async_message_t::type msg_type, const details::log_msg &msg) {
+        switch (overflow_policy_) {
+            case overflow_policy::block:
+                q_->enqueue(async_message_t(msg_type, msg));
+                break;
+            case overflow_policy::overrun_oldest:
+                q_->enqueue_nowait(async_message_t(msg_type, msg));
+                break;
+            case overflow_policy::discard_new:
+                q_->enqueue_if_have_room(async_message_t(msg_type, msg));
+                break;
+            default:
+                assert(false);
+                throw spdlog_ex("async_sink: invalid overflow policy");
+        }
+
+    }
+
+    std::atomic<overflow_policy> overflow_policy_ = overflow_policy::block;
     std::unique_ptr<queue_t> q_;
+    std::thread worker_thread_;
 };
 
 using async_sink_mt = async_sink<std::mutex>;

src/details/async_log_msg.cpp

@@ -7,14 +7,14 @@ namespace spdlog {
 namespace details {
 
 
-async_log_msg::async_log_msg(const msg_type type)
+async_log_msg::async_log_msg(const type type)
     : msg_type_{type} {}
 
 // copy logger name and payload to buffer so can be used asynchronously
 // note: source location pointers are copied without allocation since they
 // are compiler generated const chars* (__FILE__, __LINE__, __FUNCTION__)
 // if you pass custom strings to source location, make sure they outlive the async_log_msg
-async_log_msg::async_log_msg(const msg_type type, const log_msg &orig_msg)
+async_log_msg::async_log_msg(const type type, const log_msg &orig_msg)
     : log_msg{orig_msg}, msg_type_(type) {
     buffer_.append(logger_name);
     buffer_.append(payload);
@@ -23,7 +23,6 @@ async_log_msg::async_log_msg(const msg_type type, const log_msg &orig_msg)
 
 async_log_msg::async_log_msg(const async_log_msg &other)
     : log_msg{other}, msg_type_{other.msg_type_} {
-
     buffer_.append(logger_name);
     buffer_.append(payload);
     update_string_views();