Use "nodes * 4" as default for --max-worker-restart

Fix #226

changelog/226.feature.rst

@@ -0,0 +1,2 @@
+``--max-worker-restart`` now assumes a more reasonable value (4 times the number of
+nodes) when not given explicitly. This prevents test suites from running forever when the suite crashes during collection.

src/xdist/dsession.py

@@ -46,9 +46,8 @@ class DSession(object):
         self._failed_collection_errors = {}
         self._active_nodes = set()
         self._failed_nodes_count = 0
-        self._max_worker_restart = self.config.option.maxworkerrestart
-        if self._max_worker_restart is not None:
-            self._max_worker_restart = int(self._max_worker_restart)
+        self._max_worker_restart = get_default_max_worker_restart(self.config)
+
         try:
             self.terminal = config.pluginmanager.getplugin("terminalreporter")
         except KeyError:
@@ -390,10 +389,16 @@ class TerminalDistReporter(object):
             return
         self.write_line("[%s] node down: %s" % (node.gateway.id, error))
 
-    # def pytest_xdist_rsyncstart(self, source, gateways):
-    #    targets = ",".join([gw.id for gw in gateways])
-    #    msg = "[%s] rsyncing: %s" %(targets, source)
-    #    self.write_line(msg)
-    # def pytest_xdist_rsyncfinish(self, source, gateways):
-    #    targets = ", ".join(["[%s]" % gw.id for gw in gateways])
-    #    self.write_line("rsyncfinish: %s -> %s" %(source, targets))
+
+def get_default_max_worker_restart(config):
+    """gets the default value of --max-worker-restart option if it is not provided.
+
+    Use a reasonable default to avoid workers from restarting endlessly due to crashing collections (#226).
+    """
+    result = config.option.maxworkerrestart
+    if result is not None:
+        result = int(result)
+    elif config.option.numprocesses:
+        # if --max-worker-restart was not provided, use a reasonable default (#226)
+        result = config.option.numprocesses * 4
+    return result

testing/test_dsession.py

@@ -1,4 +1,4 @@
-from xdist.dsession import DSession
+from xdist.dsession import DSession, get_default_max_worker_restart
 from xdist.report import report_collection_diff
 from xdist.scheduler import EachScheduling, LoadScheduling
 
@@ -268,6 +268,24 @@ def test_report_collection_diff_equal():
     assert report_collection_diff(from_collection, to_collection, 1, 2) is None
 
 
+def test_default_max_worker_restart():
+    class config:
+        class option:
+            maxworkerrestart = None
+            numprocesses = 0
+
+    assert get_default_max_worker_restart(config) is None
+
+    config.option.numprocesses = 2
+    assert get_default_max_worker_restart(config) == 8
+
+    config.option.maxworkerrestart = "1"
+    assert get_default_max_worker_restart(config) == 1
+
+    config.option.maxworkerrestart = "0"
+    assert get_default_max_worker_restart(config) == 0
+
+
 def test_report_collection_diff_different():
     """Test reporting of different collections."""
     from_collection = ["aaa", "bbb", "ccc", "YYY"]