support nccl2 dist train in trainer

python/paddle/fluid/trainer.py

@@ -131,7 +131,40 @@ class Trainer(object):
             # load params from param_path into scope
             io.load_persistables(exe, dirname=param_path)
 
+    def _transpile_nccl2_dist(self):
+        # PADDLE_TRAINER_IPS
+        if "PADDLE_TRAINER_IPS" not in os.environ:
+            self.nccl_id_var = None
+        else:
+            self.trainer_id = int(os.getenv("PADDLE_TRAINER_ID"))
+            port = os.getenv("PADDLE_PSERVER_PORT")
+            worker_ips = os.getenv("PADDLE_TRAINER_IPS")
+            worker_endpoints = []
+            for ip in worker_ips.split(","):
+                worker_endpoints.append(':'.join([ip, port]))
+            self.num_trainers = len(worker_endpoints)
+            current_endpoint = os.getenv("POD_IP") + ":" + port
+            worker_endpoints.remove(current_endpoint)
+            # TODO(wuyi): use self.nccl_id_var, self.num_trainers and self.trainer_id
+            # in ParallelExecutor to start
+            # distributed training using NCCL2
+            self.nccl_id_var = self.startup_program.global_block().create_var(
+                name="NCCLID", persistable=True, type=core.VarDesc.VarType.RAW)
+            self.startup_program.global_block().append_op(
+                type="gen_nccl_id",
+                inputs={},
+                outputs={"NCCLID": self.nccl_id_var},
+                attrs={
+                    "endpoint": current_endpoint,
+                    "endpoint_list": worker_endpoints,
+                    "trainer_id": self.trainer_id
+                })
+
     def _dist_transpile_if_necessary(self, optimize_ops, params_grads):
+        self._transpile_nccl2_dist()
+        if self.nccl_id_var != None:
+            return
+
         if "PADDLE_TRAINING_ROLE" not in os.environ:
             return