event: Update AsyncFuture to use new atomics implementation

With explicit barriers, and the non-timeout version of wait() is now significantly more efficient by using the new futexes if available

panda/src/audio/audioLoadRequest.I

@@ -59,7 +59,7 @@ get_positional() const {
  */
 INLINE bool AudioLoadRequest::
 is_ready() const {
-  return (FutureState)AtomicAdjust::get(_future_state) == FS_finished;
+  return (FutureState)_future_state.load(std::memory_order_relaxed) == FS_finished;
 }
 
 /**
@@ -70,6 +70,5 @@ is_ready() const {
  */
 INLINE AudioSound *AudioLoadRequest::
 get_sound() const {
-  nassertr_always(done(), nullptr);
-  return (AudioSound *)_result;
+  return (AudioSound *)get_result();
 }

panda/src/event/asyncFuture.I

@@ -27,7 +27,9 @@ AsyncFuture() :
  */
 INLINE bool AsyncFuture::
 done() const {
-  return (FutureState)AtomicAdjust::get(_future_state) >= FS_finished;
+  // Not an acquire barrier because the caller may not even care about the
+  // result.  Instead, a fence is put in get_result().
+  return _future_state.load(std::memory_order_relaxed) >= FS_finished;
 }
 
 /**
@@ -35,7 +37,7 @@ done() const {
  */
 INLINE bool AsyncFuture::
 cancelled() const {
-  return (FutureState)AtomicAdjust::get(_future_state) == FS_cancelled;
+  return _future_state.load(std::memory_order_relaxed) == FS_cancelled;
 }
 
 /**
@@ -65,7 +67,7 @@ INLINE TypedObject *AsyncFuture::
 get_result() const {
   // This is thread safe, since _result may no longer be modified after the
   // state is changed to "done".
-  nassertr_always(done(), nullptr);
+  nassertr_always(_future_state.load(std::memory_order_acquire) >= FS_finished, nullptr);
   return _result;
 }
 
@@ -77,10 +79,14 @@ INLINE void AsyncFuture::
 get_result(TypedObject *&ptr, ReferenceCount *&ref_ptr) const {
   // This is thread safe, since _result may no longer be modified after the
   // state is changed to "done".
-  nassertd(done()) {
+#ifdef NDEBUG
+  patomic_thread_fence(std::memory_order_acquire);
+#else
+  nassertd(_future_state.load(std::memory_order_acquire) >= FS_finished) {
     ptr = nullptr;
     ref_ptr = nullptr;
   }
+#endif
   ptr = _result;
   ref_ptr = _result_ref.p();
 }
@@ -124,7 +130,7 @@ INLINE AsyncFuture *AsyncFuture::
 gather(Futures futures) {
   if (futures.empty()) {
     AsyncFuture *fut = new AsyncFuture;
-    fut->_future_state = (AtomicAdjust::Integer)FS_finished;
+    fut->_future_state.store(FS_finished, std::memory_order_relaxed);
     return fut;
   } else if (futures.size() == 1) {
     return futures[0].p();
@@ -167,10 +173,18 @@ try_lock_pending() {
 INLINE void AsyncFuture::
 unlock(FutureState new_state) {
   nassertv(new_state != FS_locked_pending);
-  FutureState orig_state = (FutureState)AtomicAdjust::set(_future_state, (AtomicAdjust::Integer)new_state);
+  FutureState orig_state = (FutureState)_future_state.exchange(new_state, std::memory_order_release);
   nassertv(orig_state == FS_locked_pending);
 }
 
+/**
+ * Atomically returns the current state.
+ */
+INLINE AsyncFuture::FutureState AsyncFuture::
+get_future_state() const {
+  return (FutureState)_future_state.load(std::memory_order_relaxed);
+}
+
 /**
  * Atomically changes the future state from pending to another state.  Returns
  * true if successful, false if the future was already done.
@@ -179,19 +193,18 @@ unlock(FutureState new_state) {
  */
 INLINE bool AsyncFuture::
 set_future_state(FutureState state) {
-  FutureState orig_state = (FutureState)
-    AtomicAdjust::compare_and_exchange(
-      _future_state,
-      (AtomicAdjust::Integer)FS_pending,
-      (AtomicAdjust::Integer)state);
+  patomic_unsigned_lock_free::value_type orig_state = FS_pending;
+  if (_future_state.compare_exchange_strong(orig_state, state,
+                                            std::memory_order_relaxed)) {
+    return true;
+  }
 
 #if defined(HAVE_THREADS) && !defined(SIMPLE_THREADS)
   while (orig_state == FS_locked_pending) {
-    Thread::force_yield();
-    orig_state = (FutureState)AtomicAdjust::compare_and_exchange(
-      _future_state,
-      (AtomicAdjust::Integer)FS_pending,
-      (AtomicAdjust::Integer)state);
+    Thread::relax();
+    orig_state = FS_pending;
+    _future_state.compare_exchange_weak(orig_state, state,
+                                        std::memory_order_relaxed);
   }
 #else
   nassertr(orig_state != FS_locked_pending, false);

panda/src/event/asyncFuture.cxx

@@ -17,6 +17,7 @@
 #include "config_event.h"
 #include "pStatTimer.h"
 #include "throw_event.h"
+#include "trueClock.h"
 
 TypeHandle AsyncFuture::_type_handle;
 TypeHandle AsyncGatheringFuture::_type_handle;
@@ -51,6 +52,11 @@ AsyncFuture::
  * future was already done.  Either way, done() will return true after this
  * call returns.
  *
+ * Please note that calling this is not a guarantee that the operation
+ * corresponding this future does not run.  It could already be in the process
+ * of running, or perhaps not respond to a cancel signal.  All this guarantees
+ * is that the future is marked as done when this call returns.
+ *
  * In the case of a task, this is equivalent to remove().
  */
 bool AsyncFuture::
@@ -71,8 +77,7 @@ cancel() {
 void AsyncFuture::
 output(std::ostream &out) const {
   out << get_type();
-  FutureState state = (FutureState)AtomicAdjust::get(_future_state);
-  switch (state) {
+  switch (get_future_state()) {
   case FS_pending:
   case FS_locked_pending:
     out << " (pending)";
@@ -94,47 +99,66 @@ output(std::ostream &out) const {
  */
 void AsyncFuture::
 wait() {
-  if (done()) {
-    return;
+  if (!done()) {
+    PStatTimer timer(AsyncTaskChain::_wait_pcollector);
+    if (task_cat.is_debug()) {
+      task_cat.debug()
+        << "Waiting for future " << *this << "\n";
+    }
+
+    FutureState state = get_future_state();
+    while (state < FS_finished) {
+      if (state == FS_locked_pending) {
+        // If it's locked, someone is probably about to finish it, so don't
+        // go to sleep.
+        do {
+          Thread::relax();
+          state = get_future_state();
+        }
+        while (state == FS_locked_pending);
+
+        if (state >= FS_finished) {
+          return;
+        }
+      }
+
+      // Go to sleep.
+      _future_state.wait(state, std::memory_order_relaxed);
+      state = get_future_state();
+    }
   }
 
-  PStatTimer timer(AsyncTaskChain::_wait_pcollector);
-  if (task_cat.is_debug()) {
-    task_cat.debug()
-      << "Waiting for future " << *this << "\n";
-  }
-
-  // Continue to yield while the future isn't done.  It may be more efficient
-  // to use a condition variable, but let's not add the extra complexity
-  // unless we're sure that we need it.
-  do {
-    Thread::force_yield();
-  } while (!done());
+  // Let's make wait() an acquire op, so that people can use a future for
+  // synchronization.
+  patomic_thread_fence(std::memory_order_acquire);
 }
 
 /**
- * Waits until the future is done, or until the timeout is reached.
+ * Waits until the future is done, or until the timeout is reached.  Note that
+ * this can be considerably less efficient than wait() without a timeout, so
+ * it's generally not a good idea to use this unless you really need to.
  */
 void AsyncFuture::
 wait(double timeout) {
-  if (done()) {
-    return;
-  }
+  if (!done()) {
+    PStatTimer timer(AsyncTaskChain::_wait_pcollector);
+    if (task_cat.is_debug()) {
+      task_cat.debug()
+        << "Waiting up to " << timeout << " seconds for future " << *this << "\n";
+    }
 
-  PStatTimer timer(AsyncTaskChain::_wait_pcollector);
-  if (task_cat.is_debug()) {
-    task_cat.debug()
-      << "Waiting up to " << timeout << " seconds for future " << *this << "\n";
-  }
+    // Continue to yield while the future isn't done.  It may be more efficient
+    // to use a condition variable, but let's not add the extra complexity
+    // unless we're sure that we need it.
+    TrueClock *clock = TrueClock::get_global_ptr();
+    double end = clock->get_short_time() + timeout;
+    do {
+      Thread::relax();
+    }
+    while (!done() && clock->get_short_time() < end);
 
-  // Continue to yield while the future isn't done.  It may be more efficient
-  // to use a condition variable, but let's not add the extra complexity
-  // unless we're sure that we need it.
-  ClockObject *clock = ClockObject::get_global_clock();
-  double end = clock->get_real_time() + timeout;
-  do {
-    Thread::force_yield();
-  } while (!done() && clock->get_real_time() < end);
+    patomic_thread_fence(std::memory_order_acquire);
+  }
 }
 
 /**
@@ -144,8 +168,12 @@ wait(double timeout) {
  */
 void AsyncFuture::
 notify_done(bool clean_exit) {
+  patomic_thread_fence(std::memory_order_acquire);
   nassertv(done());
 
+  // Let any calls to wait() know that we're done.
+  _future_state.notify_all();
+
   // This will only be called by the thread that managed to set the
   // _future_state away from the "pending" state, so this is thread safe.
 
@@ -159,7 +187,7 @@ notify_done(bool clean_exit) {
       // It's a gathering future.  Decrease the pending count on it, and if
       // we're the last one, call notify_done() on it.
       AsyncGatheringFuture *gather = (AsyncGatheringFuture *)fut;
-      if (!AtomicAdjust::dec(gather->_num_pending)) {
+      if (gather->_num_pending.fetch_sub(1, std::memory_order_relaxed) == 1) {
         if (gather->set_future_state(FS_finished)) {
           gather->notify_done(true);
         }
@@ -223,22 +251,22 @@ void AsyncFuture::
 set_result(TypedObject *ptr, ReferenceCount *ref_ptr) {
   // We don't strictly need to lock the future since only one thread is
   // allowed to call set_result(), but we might as well.
-  FutureState orig_state = (FutureState)AtomicAdjust::
-    compare_and_exchange(_future_state, (AtomicAdjust::Integer)FS_pending,
-                                        (AtomicAdjust::Integer)FS_locked_pending);
-
+  patomic_unsigned_lock_free::value_type orig_state = FS_pending;
+  if (!_future_state.compare_exchange_strong(orig_state, FS_locked_pending,
+                                             std::memory_order_relaxed)) {
 #if defined(HAVE_THREADS) && !defined(SIMPLE_THREADS)
-  while (orig_state == FS_locked_pending) {
-    Thread::force_yield();
-    orig_state = (FutureState)AtomicAdjust::
-      compare_and_exchange(_future_state, (AtomicAdjust::Integer)FS_pending,
-                                          (AtomicAdjust::Integer)FS_locked_pending);
-  }
+    while (orig_state == FS_locked_pending) {
+      Thread::relax();
+      orig_state = FS_pending;
+      _future_state.compare_exchange_weak(orig_state, FS_locked_pending,
+                                          std::memory_order_relaxed);
+    }
 #else
-  // We can't lose control between now and calling unlock() if we're using a
-  // cooperative threading model.
-  nassertv(orig_state != FS_locked_pending);
+    // We can't lose control between now and calling unlock() if we're using a
+    // cooperative threading model.
+    nassertv(false);
 #endif
+  }
 
   if (orig_state == FS_pending) {
     _result = ptr;
@@ -247,15 +275,15 @@ set_result(TypedObject *ptr, ReferenceCount *ref_ptr) {
 
     // OK, now our thread owns the _waiting vector et al.
     notify_done(true);
-
-  } else if (orig_state == FS_cancelled) {
+  }
+  else if (orig_state == FS_cancelled) {
     // This was originally illegal, but there is a chance that the future was
     // cancelled while another thread was setting the result.  So, we drop
     // this, but we can issue a warning.
     task_cat.warning()
       << "Ignoring set_result() called on cancelled " << *this << "\n";
-
-  } else {
+  }
+  else {
     task_cat.error()
       << "set_result() was called on finished " << *this << "\n";
   }
@@ -371,9 +399,7 @@ AsyncGatheringFuture(AsyncFuture::Futures futures) :
 
   bool any_pending = false;
 
-  AsyncFuture::Futures::const_iterator it;
-  for (it = _futures.begin(); it != _futures.end(); ++it) {
-    AsyncFuture *fut = *it;
+  for (AsyncFuture *fut : _futures) {
     // If this returns true, the future is not yet done and we need to
     // register ourselves with it.  This creates a circular reference, but it
     // is resolved when the future is completed or cancelled.
@@ -382,7 +408,7 @@ AsyncGatheringFuture(AsyncFuture::Futures futures) :
         _manager = fut->_manager;
       }
       fut->_waiting.push_back((AsyncFuture *)this);
-      AtomicAdjust::inc(_num_pending);
+      _num_pending.fetch_add(1, std::memory_order_relaxed);
       fut->unlock();
       any_pending = true;
     }
@@ -391,7 +417,7 @@ AsyncGatheringFuture(AsyncFuture::Futures futures) :
     // Start in the done state if all the futures we were passed are done.
     // Note that it is only safe to set this member in this manner if indeed
     // no other future holds a reference to us.
-    _future_state = (AtomicAdjust::Integer)FS_finished;
+    _future_state.store(FS_finished, std::memory_order_relaxed);
   }
 }
 
@@ -411,7 +437,7 @@ cancel() {
 
     // Temporarily increase the pending count so that the notify_done()
     // callbacks won't end up causing it to be set to "finished".
-    AtomicAdjust::inc(_num_pending);
+    _num_pending.fetch_add(1, std::memory_order_relaxed);
 
     bool any_cancelled = false;
     for (AsyncFuture *fut : _futures) {
@@ -422,7 +448,7 @@ cancel() {
 
     // If all the futures were cancelled, change state of this future to
     // "cancelled" and call the notify_done() callbacks.
-    if (!AtomicAdjust::dec(_num_pending)) {
+    if (_num_pending.fetch_sub(1, std::memory_order_relaxed) == 1) {
       if (set_future_state(FS_cancelled)) {
         notify_done(false);
       }

panda/src/event/asyncFuture.h

@@ -18,7 +18,7 @@
 #include "typedReferenceCount.h"
 #include "typedWritableReferenceCount.h"
 #include "eventParameter.h"
-#include "atomicAdjust.h"
+#include "patomic.h"
 
 class AsyncTaskManager;
 class AsyncTask;
@@ -110,7 +110,7 @@ private:
   void wake_task(AsyncTask *task);
 
 protected:
-  enum FutureState {
+  enum FutureState : patomic_unsigned_lock_free::value_type {
     // Pending states
     FS_pending,
     FS_locked_pending,
@@ -121,12 +121,13 @@ protected:
   };
   INLINE bool try_lock_pending();
   INLINE void unlock(FutureState new_state = FS_pending);
+  INLINE FutureState get_future_state() const;
   INLINE bool set_future_state(FutureState state);
 
   AsyncTaskManager *_manager;
   TypedObject *_result;
   PT(ReferenceCount) _result_ref;
-  AtomicAdjust::Integer _future_state;
+  patomic_unsigned_lock_free _future_state;
 
   std::string _done_event;
 
@@ -176,7 +177,7 @@ public:
 
 private:
   const Futures _futures;
-  AtomicAdjust::Integer _num_pending;
+  patomic<size_t> _num_pending;
 
   friend class AsyncFuture;
 

panda/src/gobj/animateVerticesRequest.I

@@ -27,5 +27,5 @@ AnimateVerticesRequest(GeomVertexData *geom_vertex_data) :
  */
 INLINE bool AnimateVerticesRequest::
 is_ready() const {
-  return (FutureState)AtomicAdjust::get(_future_state) == FS_finished;
+  return (FutureState)_future_state.load(std::memory_order_relaxed) == FS_finished;
 }

panda/src/gobj/textureReloadRequest.I

@@ -62,5 +62,5 @@ get_allow_compressed() const {
  */
 INLINE bool TextureReloadRequest::
 is_ready() const {
-  return (FutureState)AtomicAdjust::get(_future_state) == FS_finished;
+  return (FutureState)_future_state.load(std::memory_order_relaxed) == FS_finished;
 }

panda/src/pgraph/modelFlattenRequest.I

@@ -39,7 +39,7 @@ get_orig() const {
  */
 INLINE bool ModelFlattenRequest::
 is_ready() const {
-  return (FutureState)AtomicAdjust::get(_future_state) == FS_finished;
+  return (FutureState)_future_state.load(std::memory_order_relaxed) == FS_finished;
 }
 
 /**

panda/src/pgraph/modelLoadRequest.I

@@ -46,7 +46,7 @@ get_loader() const {
  */
 INLINE bool ModelLoadRequest::
 is_ready() const {
-  return (FutureState)AtomicAdjust::get(_future_state) == FS_finished;
+  return (FutureState)_future_state.load(std::memory_order_relaxed) == FS_finished;
 }
 
 /**

panda/src/pgraph/modelSaveRequest.I

@@ -54,7 +54,7 @@ get_loader() const {
  */
 INLINE bool ModelSaveRequest::
 is_ready() const {
-  return (FutureState)AtomicAdjust::get(_future_state) == FS_finished;
+  return (FutureState)_future_state.load(std::memory_order_relaxed) == FS_finished;
 }
 
 /**