Fix ChatbotAMD to clear completed futures (#290)

Author: bernardnormier

cpp/Ice/greeter/ChatbotAMD.cpp

@@ -2,6 +2,7 @@
 
 #include "ChatbotAMD.h"
 
+#include <algorithm>
 #include <chrono>
 #include <future>
 #include <iostream>
@@ -33,6 +34,7 @@ ServerAMD::Chatbot::greetAsync(
 
     // Simulate a long-running background operation by using std::async.
     // Note that we're moving all arguments except current into the lambda expression.
+
     _tasks.push_back(std::async(
         std::launch::async,
         [name = std::move(name), response = std::move(response), exception = std::move(exception)]()
@@ -43,6 +45,15 @@ ServerAMD::Chatbot::greetAsync(
             response(os.str());
         }));
 
+    // We don't want the _tasks vector to grow forever so remove all completed tasks here, without waiting.
+    // TODO: switch to std::erase_if when we can use C++20.
+    _tasks.erase(
+        std::remove_if(
+            _tasks.begin(),
+            _tasks.end(),
+            [](const auto& task) { return task.wait_for(std::chrono::seconds(0)) == std::future_status::ready; }),
+        _tasks.end());
+
     // greetAsync completes immediately (releasing the Ice server thread pool thread) while the task runs in the
     // background.
 }

cpp/Ice/greeter/ChatbotAMD.h

@@ -11,7 +11,7 @@ namespace ServerAMD
     class Chatbot : public VisitorCenter::Greeter
     {
     public:
-        // Waits for all tasks to complete
+        // Waits for all outstanding tasks to complete.
         ~Chatbot() override;
 
         // Implements the pure virtual function in the base class (VisitorCenter::Greeter) generated by the Slice