MXS-1754 Reintroduce maxscale::Worker

Worker is now the base class of all workers. It has a message
queue and can be run in a thread of its own, or in the calling
thread. Worker can not be used as such, but a concrete worker
class must be derived from it. Currently there is only one
concrete class RoutingWorker.

There is some overlapping in functionality between Worker and
RoutingWorker, as there is e.g. a need for broadcasting a
message to all routing workers, but not to other workers.

Currently other workers can not be created as the array for
holding the pointers to the workers is exactly as large as
there will be RoutingWorkers. That will be changed so that
the maximum number of threads is hardwired to some ridiculous
value such as 128. That's the first step in the path towards
a situation where the number of worker threads can be changed
at runtime.

server/core/gateway.cc

@@ -1399,8 +1399,6 @@ bool set_dirs(const char *basedir)
 int main(int argc, char **argv)
 {
     int      rc = MAXSCALE_SHUTDOWN;
-    int      n_threads; /*< number of epoll listener threads */
-    size_t   thread_stack_size;
     int      n_services;
     int      eno = 0;   /*< local variable for errno */
     int      opt;
@@ -2129,6 +2127,13 @@ int main(int argc, char **argv)
         goto return_main;
     }
 
+    if (!RoutingWorker::init())
+    {
+        MXS_ERROR("Failed to initialize routing workers.");
+        rc = MAXSCALE_INTERNALERROR;
+        goto return_main;
+    }
+
     /* Init MaxScale modules */
     if (!modules_process_init())
     {
@@ -2183,27 +2188,14 @@ int main(int argc, char **argv)
     }
 
     /*<
-     * Start the polling threads, note this is one less than is
-     * configured as the main thread will also poll.
+     * Start the routing workers running in their own thread.
      */
-    n_threads = config_threadcount();
-
-    /*<
-     * Start workers. We start from 1, worker 0 will be running in the main thread.
-     */
-    thread_stack_size = config_thread_stack_size();
-    for (int i = 1; i < n_threads; i++)
+    if (!RoutingWorker::start_threaded_workers())
     {
-        worker = Worker::get(i);
-        ss_dassert(worker);
-
-        if (!worker->start(thread_stack_size))
-        {
-            const char* logerr = "Failed to start worker thread.";
-            print_log_n_stderr(true, true, logerr, logerr, 0);
-            rc = MAXSCALE_INTERNALERROR;
-            goto return_main;
-        }
+        const char* logerr = "Failed to start routing workers.";
+        print_log_n_stderr(true, true, logerr, logerr, 0);
+        rc = MAXSCALE_INTERNALERROR;
+        goto return_main;
     }
 
     if (cnf->admin_enabled)
@@ -2232,7 +2224,7 @@ int main(int argc, char **argv)
     }
 
     MXS_NOTICE("MaxScale started with %d worker threads, each with a stack size of %lu bytes.",
-               n_threads, thread_stack_size);
+               config_threadcount(), config_thread_stack_size());
 
     /**
      * Successful start, notify the parent process that it can exit.
@@ -2246,7 +2238,7 @@ int main(int argc, char **argv)
     /*<
      * Run worker 0 in the main thread.
      */
-    worker = Worker::get(0);
+    worker = RoutingWorker::get(RoutingWorker::MAIN);
     ss_dassert(worker);
     worker->run();
 
@@ -2267,13 +2259,7 @@ int main(int argc, char **argv)
     /*<
      * Wait for worker threads to exit.
      */
-    for (int i = 1; i < n_threads; i++)
-    {
-        worker = Worker::get(i);
-        ss_dassert(worker);
-
-        worker->join();
-    }
+    RoutingWorker::join_threaded_workers();
 
     MXS_NOTICE("All workers have shut down.");
 
@@ -2282,6 +2268,7 @@ int main(int argc, char **argv)
      */
     service_destroy_instances();
 
+    RoutingWorker::finish();
     Worker::finish();
     MessageQueue::finish();