Fix CPU hog on async methods: Clear the event descriptor by reading from it (#16)

test/integrationtests/AdaptorAndProxy_test.cpp

@@ -225,6 +225,37 @@ TEST_F(SdbusTestObject, DoesServerSideAsynchoronousMethodInParallel)
     ASSERT_THAT(results, ElementsAre(500, 1000, 1500));
 }
 
+TEST_F(SdbusTestObject, HandlesCorrectlyABulkOfParallelServerSideAsyncMethods)
+{
+    std::mutex mtx;
+    std::atomic<size_t> resultCount{};
+    std::atomic<bool> invoke{};
+    std::atomic<int> startedCount{};
+    auto call = [&]()
+    {
+        TestingProxy proxy{INTERFACE_NAME, OBJECT_PATH};
+        ++startedCount;
+        while (!invoke) ;
+
+        size_t localResultCount{};
+        for (size_t i = 0; i < 500; ++i)
+        {
+            auto result = proxy.doOperationAsync(i % 2);
+            if (result == (i % 2)) // Correct return value?
+                localResultCount++;
+        }
+
+        resultCount += localResultCount;
+    };
+
+    std::thread invocations[]{std::thread{call}, std::thread{call}, std::thread{call}};
+    while (startedCount != 3) ;
+    invoke = true;
+    std::for_each(std::begin(invocations), std::end(invocations), [](auto& t){ t.join(); });
+
+    ASSERT_THAT(resultCount, Eq(1500));
+}
+
 TEST_F(SdbusTestObject, FailsCallingNonexistentMethod)
 {
     ASSERT_THROW(m_proxy->callNonexistentMethod(), sdbus::Error);

test/integrationtests/TestingAdaptor.h

@@ -107,12 +107,20 @@ protected:
 
     void doOperationAsync(uint32_t param, sdbus::Result<uint32_t> result)
     {
-        // The same as doOperationSync, just written as an asynchronous method callback
-        std::thread([param, result = std::move(result)]()
+        if (param == 0)
         {
-            std::this_thread::sleep_for(std::chrono::milliseconds(param));
+            // Don't sleep and return the result from this thread
             result.returnResults(param);
-        }).detach();
+        }
+        else
+        {
+            // Process asynchronously in another thread and return the result from there
+            std::thread([param, result = std::move(result)]()
+            {
+                std::this_thread::sleep_for(std::chrono::milliseconds(param));
+                result.returnResults(param);
+            }).detach();
+        }
     }
 
     sdbus::Signature getSignature() const { return SIGNATURE_VALUE; }