From 5ce8a6ec1aa36cf68478808d5199c07ba00df50c Mon Sep 17 00:00:00 2001
From: Pavel Pristupa <pristupa@gmail.com>
Date: Wed, 17 Oct 2018 16:37:13 +0700
Subject: [PATCH] Add maxprocesses option to limit the maximum number of
 workers when using numprocesses=auto

Fix #337
---
 changelog/337.feature  |  3 +++
 testing/test_plugin.py |  4 ++++
 xdist/plugin.py        | 13 ++++++++++++-
 xdist/remote.py        |  1 +
 4 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 changelog/337.feature

diff --git a/changelog/337.feature b/changelog/337.feature
new file mode 100644
index 00000000..7425db9d
--- /dev/null
+++ b/changelog/337.feature
@@ -0,0 +1,3 @@
+```
+Add --maxprocesses command-line option to limit the maximum number of workers when using --numprocesses=auto
+```
diff --git a/testing/test_plugin.py b/testing/test_plugin.py
index 182a3e5b..0ea5b747 100644
--- a/testing/test_plugin.py
+++ b/testing/test_plugin.py
@@ -25,6 +25,10 @@ def test_dist_options(testdir):
     check_options(config)
     assert config.option.dist == "load"
     assert config.option.tx == ["popen"] * 2
+    config = testdir.parseconfigure("--numprocesses", "3", "--maxprocesses", "2")
+    check_options(config)
+    assert config.option.dist == "load"
+    assert config.option.tx == ["popen"] * 2
     config = testdir.parseconfigure("-d")
     check_options(config)
     assert config.option.dist == "load"
diff --git a/xdist/plugin.py b/xdist/plugin.py
index 9c7324cd..336c93a6 100644
--- a/xdist/plugin.py
+++ b/xdist/plugin.py
@@ -47,6 +47,14 @@ def pytest_addoption(parser):
         "you can use 'auto' here for auto detection CPUs number on "
         "host system",
     )
+    group._addoption(
+        "--maxprocesses",
+        dest="maxprocesses",
+        metavar="maxprocesses",
+        action="store",
+        type=int,
+        help="limit the maximum number of workers to process the tests when using --numprocesses=auto",
+    )
     group.addoption(
         "--max-worker-restart",
         "--max-slave-restart",
@@ -172,7 +180,10 @@ def pytest_cmdline_main(config):
     if config.option.numprocesses:
         if config.option.dist == "no":
             config.option.dist = "load"
-        config.option.tx = ["popen"] * config.option.numprocesses
+        numprocesses = config.option.numprocesses
+        if config.option.maxprocesses:
+            numprocesses = min(numprocesses, config.option.maxprocesses)
+        config.option.tx = ["popen"] * numprocesses
     if config.option.distload:
         config.option.dist = "load"
     val = config.getvalue
diff --git a/xdist/remote.py b/xdist/remote.py
index bee34711..0c5aa300 100644
--- a/xdist/remote.py
+++ b/xdist/remote.py
@@ -234,6 +234,7 @@ def remote_initconfig(option_dict, args):
     config.option.dist = "no"
     config.option.distload = False
     config.option.numprocesses = None
+    config.option.maxprocesses = None
     config.args = args
     return config