RequestServer: Manually destroy the thread pool before exit

The ThreadPool destructor joins all threads. Therefore, this
destructor should be called before the destructors of all static
variables that are used in those threads.

Userland/Services/RequestServer/ConnectionFromClient.cpp

@@ -47,12 +47,7 @@ struct ThreadPoolEntry {
 static HashMap<int, RefPtr<ConnectionFromClient>> s_connections;
 static IDAllocator s_client_ids;
 static ThreadPipeFds s_thread_pipe_fds {};
-static Threading::ThreadPool<ThreadPoolEntry, ConnectionFromClient::Looper> s_thread_pool {
-    [](ThreadPoolEntry entry) {
-        entry.client->worker_do_work(move(entry.work));
-    },
-    {}, s_thread_pipe_fds.fds[0]
-};
+static OwnPtr<Threading::ThreadPool<ThreadPoolEntry, ConnectionFromClient::Looper>> s_thread_pool;
 
 ConnectionFromClient::ConnectionFromClient(NonnullOwnPtr<Core::LocalSocket> socket)
     : IPC::ConnectionFromClient<RequestClientEndpoint, RequestServerEndpoint>(*this, move(socket), s_client_ids.allocate())
@@ -245,7 +240,14 @@ Messages::RequestServer::ConnectNewClientResponse ConnectionFromClient::connect_
 
 void ConnectionFromClient::enqueue(Work work)
 {
-    s_thread_pool.submit({ *this, move(work) });
+    if (!s_thread_pool) {
+        s_thread_pool = adopt_own(*new (nothrow) Threading::ThreadPool<ThreadPoolEntry, ConnectionFromClient::Looper>(
+            [](ThreadPoolEntry entry) {
+                entry.client->worker_do_work(move(entry.work));
+            },
+            {}, s_thread_pipe_fds.fds[0]));
+    }
+    s_thread_pool->submit({ *this, move(work) });
     auto nwritten = write(s_thread_pipe_fds[1], "x", 1); // notify the worker threads
     if (nwritten < 0) {
         VERIFY_NOT_REACHED();
@@ -429,4 +431,9 @@ void ConnectionFromClient::dump_connection_info()
     ConnectionCache::dump_jobs();
 }
 
+void ConnectionFromClient::destroy_thread_pool()
+{
+    s_thread_pool.clear();
+}
+
 }

Userland/Services/RequestServer/ConnectionFromClient.h

@@ -32,6 +32,8 @@ public:
     void did_progress_request(Badge<Request>, Request&);
     void did_request_certificates(Badge<Request>, Request&);
 
+    static void destroy_thread_pool();
+
     template<typename Pool>
     struct Looper : public Threading::ThreadPoolLooper<Pool> {
         Looper(int pipe_fd)

Userland/Services/RequestServer/main.cpp

@@ -50,6 +50,10 @@ ErrorOr<int> serenity_main(Main::Arguments)
     RequestServer::HttpProtocol::install();
     RequestServer::HttpsProtocol::install();
 
+    ScopeGuard destroy_thread_pool_on_exit = [] {
+        RequestServer::ConnectionFromClient::destroy_thread_pool();
+    };
+
     auto client = TRY(IPC::take_over_accepted_client_from_system_server<RequestServer::ConnectionFromClient>());
 
     return event_loop.exec();