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cmake build test error on macOS #3058
Description
During build / test from source (version 3.3.6) with CMake on macOS, 1 of 33 tests failed. The error message was as below.
32/33 Test #34: test_event .......................Subprocess aborted***Exception: 0.01 sec
Assertion failed: (bind(fd, (struct sockaddr *)&address, sizeof(address)) == 0), function main, file test_event.c, line 56.
Start 35: test_resolv_async
97% tests passed, 1 tests failed out of 33
The following tests FAILED:
34 - test_event (Subprocess aborted) unit
Errors while running CTest
The command executed:
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --parallel
ctest --test-dir build -L 'unit|vendor' --output-on-failure
Testing environment:
cmake version 4.4.3
Darwin Kernel Version 25.6.0: arm64
Activity
madeye commentedon Sep 12, 2026
Thanks for the report. This is caused by macOS's default per-process file descriptor limit rather than a bug in the event loop.
test_eventdeliberately opens 256 UDP sockets (to exceed Winsock's 64-descriptorselect()limit) plus a sender socket and the loop's own kqueue descriptor. A stock macOS Terminal session starts with a soft limit of 256 (ulimit -nprints256), sosocket()starts returning -1 near the end of that loop and the unchecked descriptor trips thebind()assertion you saw. Running with a higher limit already makes the test pass on 3.3.6:#3060 fixes this properly: CTest now raises the soft limit to 1024 before launching each unit test,
test_eventraises its own limit when run directly, and asocket()failure is now reported as such instead of as abind()failure.Raise the file descriptor limit for descriptor-heavy tests