module: be less strange about extension key lifetimes

tych0 · tych0 · commit d7411f30fe11 · 2025-01-24T07:38:16.000-07:00
We just got a CI failure: 2025-01-12T16:37:45.5888665Z Fatal Python error: Segmentation fault 2025-01-12T16:37:45.5889018Z 2025-01-12T16:37:45.5889270Z Thread 0x00007f3e0ae006c0 (most recent call first): 2025-01-12T16:37:45.5890898Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 534 in read 2025-01-12T16:37:45.5893372Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 567 in from_io 2025-01-12T16:37:45.5895355Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 1160 in _thread_receiver 2025-01-12T16:37:45.5897310Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 341 in run 2025-01-12T16:37:45.5899179Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 411 in _perform_spawn 2025-01-12T16:37:45.5900143Z 2025-01-12T16:37:45.5900589Z Current thread 0x00007f3e0c3dfb80 (most recent call first): 2025-01-12T16:37:45.5901534Z File "/home/runner/work/xcffib/xcffib/xcffib/__init__.py", line 554 in _setup_extensions 2025-01-12T16:37:45.5902549Z File "/home/runner/work/xcffib/xcffib/xcffib/__init__.py", line 546 in _init_x 2025-01-12T16:37:45.5903523Z File "/home/runner/work/xcffib/xcffib/xcffib/__init__.py", line 533 in __init__ 2025-01-12T16:37:45.5904555Z File "/home/runner/work/xcffib/xcffib/xcffib/testing.py", line 133 in _connect_to_xvfb 2025-01-12T16:37:45.5905560Z File "/home/runner/work/xcffib/xcffib/xcffib/testing.py", line 83 in setUp 2025-01-12T16:37:45.5906470Z File "/home/runner/work/xcffib/xcffib/test/conftest.py", line 39 in setUp 2025-01-12T16:37:45.5907373Z File "/home/runner/work/xcffib/xcffib/xcffib/testing.py", line 116 in __enter__ 2025-01-12T16:37:45.5908315Z File "/home/runner/work/xcffib/xcffib/test/conftest.py", line 25 in xcffib_test 2025-01-12T16:37:45.5909756Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/fixtures.py", line 891 in call_fixture_func 2025-01-12T16:37:45.5911860Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/fixtures.py", line 1140 in pytest_fixture_setup 2025-01-12T16:37:45.5913712Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_callers.py", line 103 in _multicall 2025-01-12T16:37:45.5915445Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_manager.py", line 120 in _hookexec 2025-01-12T16:37:45.5916992Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_hooks.py", line 513 in __call__ 2025-01-12T16:37:45.5918405Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/fixtures.py", line 1091 in execute 2025-01-12T16:37:45.5919707Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/fixtures.py", line 617 in _get_active_fixturedef 2025-01-12T16:37:45.5921851Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/fixtures.py", line 532 in getfixturevalue 2025-01-12T16:37:45.5923730Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/fixtures.py", line 697 in _fillfixtures 2025-01-12T16:37:45.5925572Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/python.py", line 1630 in setup 2025-01-12T16:37:45.5927343Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/runner.py", line 514 in setup 2025-01-12T16:37:45.5929435Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/runner.py", line 160 in pytest_runtest_setup 2025-01-12T16:37:45.5931936Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_callers.py", line 103 in _multicall 2025-01-12T16:37:45.5933720Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_manager.py", line 120 in _hookexec 2025-01-12T16:37:45.5935753Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_hooks.py", line 513 in __call__ 2025-01-12T16:37:45.5937515Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/runner.py", line 242 in <lambda> 2025-01-12T16:37:45.5939298Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/runner.py", line 341 in from_call 2025-01-12T16:37:45.5941233Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/runner.py", line 241 in call_and_report 2025-01-12T16:37:45.5943079Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/runner.py", line 126 in runtestprotocol 2025-01-12T16:37:45.5944982Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/runner.py", line 113 in pytest_runtest_protocol 2025-01-12T16:37:45.5946847Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_callers.py", line 103 in _multicall 2025-01-12T16:37:45.5948594Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_manager.py", line 120 in _hookexec 2025-01-12T16:37:45.5950400Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_hooks.py", line 513 in __call__ 2025-01-12T16:37:45.5952062Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/xdist/remote.py", line 195 in run_one_test 2025-01-12T16:37:45.5953854Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/xdist/remote.py", line 174 in pytest_runtestloop 2025-01-12T16:37:45.5955648Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_callers.py", line 103 in _multicall 2025-01-12T16:37:45.5957196Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_manager.py", line 120 in _hookexec 2025-01-12T16:37:45.5958246Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_hooks.py", line 513 in __call__ 2025-01-12T16:37:45.5959947Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/main.py", line 337 in _main 2025-01-12T16:37:45.5961876Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/main.py", line 283 in wrap_session 2025-01-12T16:37:45.5963765Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/_pytest/main.py", line 330 in pytest_cmdline_main 2025-01-12T16:37:45.5965619Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_callers.py", line 103 in _multicall 2025-01-12T16:37:45.5967366Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_manager.py", line 120 in _hookexec 2025-01-12T16:37:45.5969132Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/pluggy/_hooks.py", line 513 in __call__ 2025-01-12T16:37:45.5971008Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/xdist/remote.py", line 393 in <module> 2025-01-12T16:37:45.5972833Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 1291 in executetask 2025-01-12T16:37:45.5974827Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 341 in run 2025-01-12T16:37:45.5976255Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 411 in _perform_spawn 2025-01-12T16:37:45.5977369Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 389 in integrate_as_primary_thread 2025-01-12T16:37:45.5978630Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 1273 in serve 2025-01-12T16:37:45.5979632Z File "/home/runner/work/xcffib/xcffib/xcffib-test-abi.teoYalBIO9/lib/python3.10/site-packages/execnet/gateway_base.py", line 1806 in serve 2025-01-12T16:37:45.5980450Z File "<string>", line 8 in <module> 2025-01-12T16:37:45.5980812Z File "<string>", line 1 in <module> https://github.com/tych0/xcffib/actions/runs/12735265435/job/35493822666 which represents *another* race that has probably been around forever that we are only now finding. I'm not exactly sure what is going on here, but it seems likely that some CFFI lifetime thing has gone awry, and the memory was re-used and caused some kind of seg fault. But we don't need all the fancy cffi lifetime gunk here: we have a 1:1 mapping for an owner of the xcb_extension_t: the xcffib.ExtensionKey object. So let's stash the key there as a one-time allocation when the extension object is created at module import. This way the object will be pinned, and we hopefully won't get any of these strange seg faults. Signed-off-by: Tycho Andersen <tycho@tycho.pizza>
diff --git a/module/__init__.py b/module/__init__.py
@@ -253,12 +253,12 @@ def _add_ext(key, value, events, errors):
 
 
 class ExtensionKey(object):
-    """This definitely isn't needed, but we keep it around for compatibility
-    with xpyb.
-    """
-
     def __init__(self, name):
         self.name = name
+        self.c_key = ffi.new("struct xcb_extension_t *")
+        self.c_name = ffi.new("char[]", self.name.encode())
+        self.c_key.name = self.c_name
+        self.c_key.global_id = 0
 
     def __hash__(self):
         return hash(self.name)
@@ -269,15 +269,6 @@ def __eq__(self, o):
     def __ne__(self, o):
         return self.name != o.name
 
-    def to_cffi(self):
-        c_key = ffi.new("struct xcb_extension_t *")
-        c_key.name = name = ffi.new("char[]", self.name.encode())
-        cffi_explicit_lifetimes[c_key] = name
-        # xpyb doesn't ever set global_id, which seems wrong, but whatever.
-        c_key.global_id = 0
-
-        return c_key
-
 
 class Protobj(object):
     """Note: Unlike xcb.Protobj, this does NOT implement the sequence
@@ -355,9 +346,7 @@ def __init__(self, conn, key=None):
         if key is None:
             self.c_key = ffi.NULL
         else:
-            c_key = key.to_cffi()
-            cffi_explicit_lifetimes[self] = c_key
-            self.c_key = c_key
+            self.c_key = key.c_key
 
     def send_request(
         self, opcode, data, cookie=VoidCookie, reply=None, is_checked=False
@@ -559,10 +548,7 @@ def _init_x(self):
 
     def _setup_extensions(self):
         for key, (_, events, errors) in extensions.items():
-            # We're explicitly not putting this as an argument to the next call
-            # as a hack for lifetime management.
-            c_ext = key.to_cffi()
-            reply = lib.xcb_get_extension_data(self._conn, c_ext)
+            reply = lib.xcb_get_extension_data(self._conn, key.c_key)
             self._event_offsets.add(reply.first_event, reply.major_opcode, events)
             self._error_offsets.add(reply.first_error, reply.major_opcode, errors)
 
