Merge pull request #1642 from gevent/issue1641

Make selectors2 truly optional on Py2 with dnspython

.travis.yml

@@ -13,7 +13,10 @@ os:
   - linux
   - osx
 osx_image: xcode11.4
-
+addons:
+  homebrew:
+    packages:
+      - ccache
 
 env:
     global:
@@ -95,7 +98,6 @@ before_install:
   - echo Running in stage $TRAVIS_BUILD_STAGE_NAME
   - |
     if [[ "$TRAVIS_OS_NAME" == "osx" && "$TRAVIS_BUILD_STAGE_NAME" != "test" ]]; then
-      brew install ccache
       export PATH="/usr/local/opt/ccache/libexec:$PATH"
       export CFLAGS="$CFLAGS -Wno-parentheses-equality"
     fi
@@ -313,7 +315,8 @@ jobs:
     # Run dnspython with coverage enabled, it's implemented in python whereas ares is C.
     # PyPy is supported.
     - &test-dnspython-jobs
-      script: GEVENT_RESOLVER=dnspython python -mgevent.tests --coverage --ignore tests_that_dont_use_resolver.txt
+      script:
+        - GEVENT_RESOLVER=dnspython python -mgevent.tests --coverage --ignore tests_that_dont_use_resolver.txt
       name: dnspython resolver (Python 2.7)
     # Now test the alternate backends, starting with libuv-cffi, which should be present everywhere
     - &test-libuv-jobs

docs/changes/issue1641.bugfix

+On Python 2, the dnspython resolver can be used without having
+selectors2 installed. Previously, an ImportError would be raised.

scripts/releases/make-manylinux

@@ -40,9 +40,15 @@ if [ -d /gevent -a -d /opt/python ]; then
     # Running inside docker
 
     # Set a cache directory for pip. This was
-    # mounted to be the same as it is outside docker
+    # mounted to be the same as it is outside docker so it
+    # can be persisted.
+    # XXX: This works for macOS, where everything bind-mounted
+    # is seen as owned by root in the container. But when the host is Linux
+    # the actual UIDs come through to the container, triggering
+    # pip to disable the cache when it detects that the owner doesn't match.
     export XDG_CACHE_HOME="/cache"
     ls -ld /cache
+    ls -ld /cache/pip
     yum -y install libffi-devel ccache
     # On Fedora Rawhide (F33)
     # yum install python39 python3-devel gcc kernel-devel kernel-headers make diffutils file

src/gevent/_patcher.py

@@ -38,8 +38,31 @@ MAPPING = {
     'gevent.contextvars': 'contextvars',
 }
 
+OPTIONAL_STDLIB_MODULES = frozenset() if PY3 else frozenset([
+    'selectors2',
+])
+
 _PATCH_PREFIX = '__g_patched_module_'
 
+def _collect_stdlib_gevent_modules():
+    """
+    Return a map from standard library name to
+    imported gevent module that provides the same API.
+
+    Optional modules are skipped if they cannot be imported.
+    """
+    result = {}
+
+    for gevent_name, stdlib_name in iteritems(MAPPING):
+        try:
+            result[stdlib_name] = importlib.import_module(gevent_name)
+        except ImportError:
+            if stdlib_name in OPTIONAL_STDLIB_MODULES:
+                continue
+            raise
+    return result
+
+
 class _SysModulesPatcher(object):
 
     def __init__(self, importing, extra_all=lambda mod_name: ()):
@@ -49,11 +72,7 @@ class _SysModulesPatcher(object):
         # green modules, replacing regularly imported modules.
         # This begins as the gevent list of modules, and
         # then gets extended with green things from the tree we import.
-        self._green_modules = {
-            stdlib_name: importlib.import_module(gevent_name)
-            for gevent_name, stdlib_name
-            in iteritems(MAPPING)
-        }
+        self._green_modules = _collect_stdlib_gevent_modules()
 
         ## Transient, reset each time we're called.
         # The set of things imported before we began.