sched: add a new thread state, prestarted

It may be that a thread that is initialized early is also started early. We need to
somehow mark that thread as already started, so we can start it for real later when
the scheduler is ready to go. We will do this by adding an extra state, prestarted.

Later on, we will take action to start those threads properly.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Reviewed-by: Pekka Enberg <penberg@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

core/sched.cc

@@ -486,10 +486,16 @@ thread::~thread()
 
 void thread::start()
 {
+    assert(_status == status::unstarted);
+
+    if (!sched::s_current) {
+        _status.store(status::prestarted);
+        return;
+    }
+
     _cpu = _attr.pinned_cpu ? _attr.pinned_cpu : current()->tcpu();
     remote_thread_local_var(percpu_base) = _cpu->percpu_base;
     remote_thread_local_var(current_cpu) = _cpu;
-    assert(_status == status::unstarted);
     _status.store(status::waiting);
     wake();
 }

include/sched.hh

@@ -245,6 +245,7 @@ private:
     thread_control_block* _tcb;
     enum class status {
         invalid,
+        prestarted,
         unstarted,
         waiting,
         running,