Fix failing distributed ci

tests/ignite/conftest.py

@@ -90,14 +90,54 @@ def _destroy_dist_context():
     _set_model(_SerialModel())
 
 
+def _find_free_port():
+    # Taken from https://github.com/facebookresearch/detectron2/blob/master/detectron2/engine/launch.py
+    import socket
+
+    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    sock.bind(("", 0))
+    port = sock.getsockname()[1]
+    sock.close()
+    return port
+
+
+def _setup_free_port(local_rank):
+    import time
+    import os
+
+    port_file = "/tmp/free_port"
+
+    if local_rank == 0:
+        port = _find_free_port()
+        with open(port_file, "w") as h:
+            h.write(str(port))
+        return port
+    else:
+        counter = 10
+        while counter > 0:
+            counter -= 1
+            time.sleep(1)
+            if not os.path.exists(port_file):
+                continue
+            with open(port_file, "r") as h:
+                port = h.readline()
+                return int(port)
+
+        raise RuntimeError("Failed to fetch free port on local rank {}".format(local_rank))
+
+
 @pytest.fixture()
 def distributed_context_single_node_nccl(local_rank, world_size):
 
+    free_port = _setup_free_port(local_rank)
+
+    print(local_rank, "Port:", free_port)
+
     dist_info = {
         "backend": "nccl",
         "world_size": world_size,
         "rank": local_rank,
-        "init_method": "tcp://localhost:2223",
+        "init_method": "tcp://localhost:{}".format(free_port),
     }
     yield _create_dist_context(dist_info, local_rank)
     _destroy_dist_context()
@@ -108,11 +148,14 @@ def distributed_context_single_node_gloo(local_rank, world_size):
 
     from datetime import timedelta
 
-    init_method = "tcp://localhost:2223"
-    temp_file = None
     if sys.platform.startswith("win"):
         temp_file = tempfile.NamedTemporaryFile(delete=False)
         init_method = "file:///{}".format(temp_file.name.replace("\\", "/"))
+    else:
+        free_port = _setup_free_port(local_rank)
+        print(local_rank, "Port:", free_port)
+        init_method = "tcp://localhost:{}".format(free_port)
+        temp_file = None
 
     dist_info = {
         "backend": "gloo",