MXS-1754 Add delayed calling to Worker

It's now possible to provide Worker with a function to call
at a later time. It's possible to provide a function or a
member function (with the object), taking zero or one argument
of any kind. The argument must be copyable.

There's currently no way to cancel a call, which must be added
as typically the delayed calling is associated with a session
and if the session is closed before the delayed call is made,
bad things are likely to happen.

server/core/test/CMakeLists.txt

@@ -27,6 +27,7 @@ add_executable(test_trxtracking test_trxtracking.cc)
 add_executable(test_users test_users.cc)
 add_executable(test_utils test_utils.cc)
 add_executable(test_session_track test_session_track.cc)
+add_executable(test_worker test_worker.cc)
 
 target_link_libraries(profile_trxboundaryparser maxscale-common)
 target_link_libraries(test_adminusers maxscale-common)
@@ -57,6 +58,7 @@ target_link_libraries(test_trxtracking maxscale-common)
 target_link_libraries(test_users maxscale-common)
 target_link_libraries(test_utils maxscale-common)
 target_link_libraries(test_session_track mysqlcommon)
+target_link_libraries(test_worker maxscale-common)
 
 add_test(test_adminusers test_adminusers)
 add_test(test_atomic test_atomic)
@@ -93,6 +95,7 @@ add_test(test_trxtracking test_trxtracking)
 add_test(test_users test_users)
 add_test(test_utils test_utils)
 add_test(test_session_track test_session_track)
+add_test(test_worker test_worker)
 
 add_subdirectory(rest-api)
 add_subdirectory(canonical_tests)

server/core/test/test_worker.cc

@@ -0,0 +1,159 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <iostream>
+#include "../internal/worker.hh"
+
+using namespace std;
+
+namespace
+{
+
+// TODO: Put this in some common place.
+int64_t get_monotonic_time_ms()
+{
+    struct timespec ts;
+    ss_debug(int rv =) clock_gettime(CLOCK_MONOTONIC, &ts);
+    ss_dassert(rv == 0);
+
+    return ts.tv_sec * 1000 + ts.tv_nsec / 1000000;
+}
+
+class TestWorker : public maxscale::Worker
+{
+    TestWorker(const TestWorker&);
+    TestWorker& operator = (const TestWorker&);
+
+public:
+    TestWorker()
+    {
+    }
+
+    ~TestWorker()
+    {
+    }
+
+private:
+    // TODO: Perhaps these could have default implementations, so that
+    // TODO: Worker could be used as such.
+    bool pre_run() // override
+    {
+        return true;
+    }
+
+    void post_run() // override
+    {
+    }
+
+    void epoll_tick() // override
+    {
+    }
+};
+
+class TimerTest
+{
+public:
+    static int s_ticks;
+
+    TimerTest(int* pRv, int32_t delay)
+        : m_id(s_id++)
+        , m_delay(delay)
+        , m_at(get_monotonic_time_ms() + delay)
+        , m_rv(*pRv)
+    {
+    }
+
+    int32_t delay() const
+    {
+        return m_delay;
+    }
+
+    bool tick()
+    {
+        int64_t now = get_monotonic_time_ms();
+        int64_t diff = abs(now - m_at);
+
+        cout << m_id << ": " << diff << endl;
+
+        if (diff > 50)
+        {
+            cout << "Error: Difference between expected and happened > 50: " << diff << endl;
+            m_rv = EXIT_FAILURE;
+        }
+
+        m_at += m_delay;
+
+        if (--s_ticks < 0)
+        {
+            maxscale::Worker::shutdown_all();
+        }
+
+        return true;
+    }
+
+private:
+    static int s_id;
+
+    int     m_id;
+    int32_t m_delay;
+    int64_t m_at;
+    int&    m_rv;
+};
+
+int TimerTest::s_id = 1;
+int TimerTest::s_ticks;
+
+int run()
+{
+    int rv = EXIT_SUCCESS;
+
+    TimerTest::s_ticks = 100;
+
+    TestWorker w;
+
+    TimerTest t1(&rv, 200);
+    TimerTest t2(&rv, 300);
+    TimerTest t3(&rv, 400);
+    TimerTest t4(&rv, 500);
+    TimerTest t5(&rv, 600);
+
+    w.delayed_call(t1.delay(), &t1, &TimerTest::tick);
+    w.delayed_call(t2.delay(), &t2, &TimerTest::tick);
+    w.delayed_call(t3.delay(), &t3, &TimerTest::tick);
+    w.delayed_call(t4.delay(), &t4, &TimerTest::tick);
+    w.delayed_call(t5.delay(), &t5, &TimerTest::tick);
+
+    w.run();
+
+    return EXIT_SUCCESS;
+}
+
+}
+
+int main()
+{
+    int rv = EXIT_FAILURE;
+
+    if (mxs_log_init(NULL, NULL, MXS_LOG_TARGET_STDOUT))
+    {
+        poll_init();
+        maxscale::MessageQueue::init();
+        maxscale::Worker::init();
+
+        rv = run();
+
+        mxs_log_finish();
+    }
+
+    return rv;
+}