better handling of thread::force_yield(), not to impact other threads

panda/src/pipeline/threadSimpleManager.cxx

@@ -98,9 +98,17 @@ void ThreadSimpleManager::
 enqueue_ready(ThreadSimpleImpl *thread, bool volunteer) {
   // We actually add it to _next_ready, so that we can tell when we
   // have processed every thread in a given epoch.
-  _next_ready.push_back(thread);
-  if (volunteer) {
-    ++_num_next_ready_volunteers;
+  if (!volunteer) {
+    _next_ready.push_back(thread);
+
+  } else {
+    // Unless it's a volunteer, in which case we actually put it to
+    // sleep for the duration of the timeslice, so it won't interfere
+    // with timeslice accounting for the remaining ready threads.
+    double now = get_current_time();
+    thread->_wake_time = now + _simple_thread_epoch_timeslice;
+    _volunteers.push_back(thread);
+    push_heap(_volunteers.begin(), _volunteers.end(), CompareStartTime());
   }
 }
 
@@ -314,6 +322,7 @@ prepare_for_exit() {
   }
 
   kill_non_joinable(_sleeping);
+  kill_non_joinable(_volunteers);
 
   next_context();
 
@@ -393,20 +402,24 @@ write_status(ostream &out) const {
 
   out << "Ready:";
   FifoThreads::const_iterator ti;
+  Sleeping::const_iterator si;
   for (ti = _ready.begin(); ti != _ready.end(); ++ti) {
     out << " " << *(*ti)->_parent_obj;
   }
   for (ti = _next_ready.begin(); ti != _next_ready.end(); ++ti) {
     out << " " << *(*ti)->_parent_obj;
   }
+  for (si = _volunteers.begin(); si != _volunteers.end(); ++si) {
+    out << " " << *(*si)->_parent_obj;
+  }
   out << "\n";
 
   double now = get_current_time();
+
   out << "Sleeping:";
   // Copy and sort for convenience.
   Sleeping s2 = _sleeping;
   sort(s2.begin(), s2.end(), CompareStartTime());
-  Sleeping::const_iterator si;
   for (si = s2.begin(); si != s2.end(); ++si) {
     out << " " << *(*si)->_parent_obj << "(" << (*si)->_wake_time - now
         << "s)";
@@ -497,8 +510,21 @@ choose_next_context() {
   do_timeslice_accounting(_current_thread, now);
   _current_thread = NULL;
 
-  if (!_sleeping.empty()) {
-    wake_sleepers(now);
+  if (!_sleeping.empty() || !_volunteers.empty()) {
+    if (_ready.empty() && _next_ready.empty()) {
+      // All of our threads are currently sleeping.  Therefore, wake
+      // the volunteer(s) immediately.
+      if (!_volunteers.empty()) {
+        wake_all_sleepers(_volunteers);
+
+      } else {
+        // No volunteers.  Sleep the whole process.
+        system_yield();
+        now = get_current_time();
+      }
+    }
+    wake_sleepers(_sleeping, now);
+    wake_sleepers(_volunteers, now);
   }
 
   bool new_epoch = !_ready.empty() && _next_ready.empty();
@@ -509,9 +535,7 @@ choose_next_context() {
     while (_ready.empty()) {
       if (!_next_ready.empty()) {
         // We've finished an epoch.
-        bool all_volunteers = (_num_next_ready_volunteers == (int)_next_ready.size());
         _ready.swap(_next_ready);
-        _num_next_ready_volunteers = 0;
 
         if (new_epoch && !_tick_records.empty()) {
           // Pop the oldest timeslice record off when we finish an
@@ -526,18 +550,19 @@ choose_next_context() {
           nassertv(record._thread->_run_ticks >= record._tick_count);
           record._thread->_run_ticks -= record._tick_count;
           _tick_records.pop_front();
-
-        } else {
-          // Otherwise, we're legitimately at the end of an epoch.
-          if (all_volunteers) {
-            // All of our non-blocked, non-sleeping threads have
-            // voluntarily yielded.  Therefore, yield the whole
-            // process.
-            system_yield();
-          }
         }
         new_epoch = true;
         
+      } else if (!_volunteers.empty()) {
+        // There are some volunteers.  Wake them.  Also wake any
+        // sleepers that need it.
+        if (thread_cat->is_debug()) {
+          thread_cat.debug()
+            << "Waking volunteers.\n";
+        }
+        wake_all_sleepers(_volunteers);
+        wake_sleepers(_sleeping, now);
+
       } else if (!_sleeping.empty()) {
         // All threads are sleeping.
         double wait = _sleeping.front()->_wake_time - now;
@@ -549,7 +574,8 @@ choose_next_context() {
           system_sleep(wait);
         }
         now = get_current_time();
-        wake_sleepers(now);
+        wake_sleepers(_sleeping, now);
+        wake_sleepers(_volunteers, now);
         
       } else {
         // No threads are ready!
@@ -609,7 +635,8 @@ choose_next_context() {
     thread_cat.debug()
       << "Switching to " << *_current_thread->_parent_obj
       << " for " << timeslice << " s ("
-      << _ready.size() + _next_ready.size()
+      << _ready.size() << " + " << _next_ready.size()
+      << " + " << _volunteers.size()
       << " other threads ready, " << blocked_count
       << " blocked, " << _sleeping.size() << " sleeping)\n";
   }
@@ -667,11 +694,27 @@ do_timeslice_accounting(ThreadSimpleImpl *thread, double now) {
 //               queue to the ready queue.
 ////////////////////////////////////////////////////////////////////
 void ThreadSimpleManager::
-wake_sleepers(double now) {
-  while (!_sleeping.empty() && _sleeping.front()->_wake_time <= now) {
-    ThreadSimpleImpl *thread = _sleeping.front();
-    pop_heap(_sleeping.begin(), _sleeping.end(), CompareStartTime());
-    _sleeping.pop_back();
+wake_sleepers(ThreadSimpleManager::Sleeping &sleepers, double now) {
+  while (!sleepers.empty() && sleepers.front()->_wake_time <= now) {
+    ThreadSimpleImpl *thread = sleepers.front();
+    pop_heap(sleepers.begin(), sleepers.end(), CompareStartTime());
+    sleepers.pop_back();
+    _ready.push_back(thread);
+  }
+}
+
+////////////////////////////////////////////////////////////////////
+//     Function: ThreadSimpleManager::wake_all_sleepers
+//       Access: Private
+//  Description: Moves all threads from the indicated sleeping queue
+//               to the ready queue, regardless of wake time.
+////////////////////////////////////////////////////////////////////
+void ThreadSimpleManager::
+wake_all_sleepers(ThreadSimpleManager::Sleeping &sleepers) {
+  while (!sleepers.empty()) {
+    ThreadSimpleImpl *thread = sleepers.front();
+    pop_heap(sleepers.begin(), sleepers.end(), CompareStartTime());
+    sleepers.pop_back();
     _ready.push_back(thread);
   }
 }

panda/src/pipeline/threadSimpleManager.h

@@ -84,12 +84,18 @@ public:
 private:
   static void init_pointers();
 
+  typedef pdeque<ThreadSimpleImpl *> FifoThreads;
+  typedef pvector<ThreadSimpleImpl *> Sleeping;
+
   static void st_choose_next_context(void *data);
   void choose_next_context();
   void do_timeslice_accounting(ThreadSimpleImpl *thread, double now);
-  void wake_sleepers(double now);
+  void wake_sleepers(Sleeping &sleepers, double now);
+  void wake_all_sleepers(Sleeping &sleepers);
   void report_deadlock();
   double determine_timeslice(ThreadSimpleImpl *chosen_thread);
+  void kill_non_joinable(FifoThreads &threads);
+  void kill_non_joinable(Sleeping &threads);
 
   // STL function object to sort the priority queue of sleeping threads.
   class CompareStartTime {
@@ -97,12 +103,6 @@ private:
     INLINE bool operator ()(ThreadSimpleImpl *a, ThreadSimpleImpl *b) const;
   };
 
-  typedef pdeque<ThreadSimpleImpl *> FifoThreads;
-  typedef pvector<ThreadSimpleImpl *> Sleeping;
-
-  void kill_non_joinable(FifoThreads &threads);
-  void kill_non_joinable(Sleeping &threads);
-
 public:
   // Defined within the class to avoid static-init ordering problems.
   ConfigVariableDouble _simple_thread_epoch_timeslice;
@@ -115,17 +115,31 @@ public:
 private:
   ThreadSimpleImpl *volatile _current_thread;
 
-  // FIFO list of ready threads.
+  // The list of ready threads: threads that are ready to execute
+  // right now.
   FifoThreads _ready;
+
+  // The list of threads that are ready, but will not be executed
+  // until next epoch (for instance, because they exceeded their
+  // timeslice budget this epoch).
   FifoThreads _next_ready;
-  int _num_next_ready_volunteers;
 
+  // The list of threads that are blocked on some ConditionVar or
+  // Mutex.
   typedef pmap<BlockerSimple *, FifoThreads> Blocked;
   Blocked _blocked;
 
-  // Priority queue (partially-ordered heap) based on wakeup time.
+  // Priority queue (partially-ordered heap) of sleeping threads,
+  // based on wakeup time.
   Sleeping _sleeping;
 
+  // Priority queue (partially-ordered heap) of volunteer threads,
+  // based on wakeup time.  This are threads that have voluntarily
+  // yielded a timeslice.  They are treated the same as sleeping
+  // threads, unless all threads are sleeping.
+  Sleeping _volunteers;
+
+  // Threads which have finished execution and are awaiting cleanup.
   FifoThreads _finished;
 
   ThreadSimpleImpl *_waiting_for_exit;