added tp getter to async api

bench/spdlog-null-async.cpp

@@ -63,17 +63,16 @@ int main(int argc, char *argv[])
         cout << "*******************************************************************************\n";
 
         size_t total_rate = 0;
-		spdlog::init_thread_pool(tp_queue_size, tp_threads);		
+        spdlog::init_thread_pool(tp_queue_size, tp_threads);
         for (int i = 0; i < iters; ++i)
         {
             auto as = spdlog::create_async_logger<null_sink_mt>("async(null-sink)");
             total_rate += bench_as(howmany, as, client_threads);
             spdlog::drop("async(null-sink)");
-			spdlog::details::registry::instance().get_thread_pool()->wait_empty ();
+            spdlog::thread_pool()->wait_empty();
         }
         std::cout << endl;
         std::cout << "Avg rate: " << format(total_rate / iters) << "/sec" << std::endl;
-		
     }
     catch (std::exception &ex)
     {

example/bench.cpp

@@ -74,12 +74,13 @@ int main(int argc, char *argv[])
         cout << "async logging.. " << threads << " threads sharing same logger, " << format(howmany) << " iterations " << endl;
         cout << "*******************************************************************************\n";
 
+        spdlog::init_thread_pool(queue_size, 1);
         for (int i = 0; i < 3; ++i)
         {
-            spdlog::init_thread_pool(queue_size, 1);
             auto as = spdlog::basic_logger_mt<spdlog::create_async>("as", "logs/basic_async.log", true);
             bench_mt(howmany, as, threads);
             spdlog::drop("as");
+            spdlog::thread_pool()->wait_empty();
         }
     }
     catch (std::exception &ex)

include/spdlog/async.h

@@ -59,4 +59,10 @@ inline void init_thread_pool(size_t q_size, size_t thread_count)
     auto tp = std::make_shared<thread_pool>(q_size, thread_count);
     registry::instance().set_thread_pool(std::move(tp));
 }
+
+// get the global thread pool.
+inline std::shared_ptr<spdlog::details::thread_pool> thread_pool()
+{
+    return details::registry::instance().get_thread_pool();
+}
 } // namespace spdlog

tests/test_async.cpp

@@ -101,14 +101,13 @@ TEST_CASE("multi threads", "[async]")
                     logger->info("Hello message #{}", j);
                 }
             });
-			logger->flush();
+            logger->flush();
         }
 
         for (auto &t : threads)
         {
             t.join();
         }
-        
     }
 
     REQUIRE(test_sink->msg_counter() == messages * n_threads);