[rllib] Fix KeyError: 'kl' in multiagent ppo training

python/ray/rllib/optimizers/multi_gpu_optimizer.py

@@ -131,7 +131,11 @@ class LocalMultiGPUOptimizer(PolicyOptimizer):
                         "This may be because you have many workers or "
                         "long episodes in 'complete_episodes' batch mode.")
             else:
-                samples = self.local_evaluator.sample()
+                samples = []
+                while sum(s.count for s in samples) < self.train_batch_size:
+                    samples.append(self.local_evaluator.sample())
+                samples = SampleBatch.concat_samples(samples)
+
             # Handle everything as if multiagent
             if isinstance(samples, SampleBatch):
                 samples = MultiAgentBatch({
@@ -174,7 +178,8 @@ class LocalMultiGPUOptimizer(PolicyOptimizer):
         with self.grad_timer:
             for policy_id, tuples_per_device in num_loaded_tuples.items():
                 optimizer = self.optimizers[policy_id]
-                num_batches = (
+                num_batches = max(
+                    1,
                     int(tuples_per_device) // int(self.per_device_batch_size))
                 logger.debug("== sgd epochs for {} ==".format(policy_id))
                 for i in range(self.num_sgd_iter):