[Lldb-commits] [lldb] [lldb][Windows] Dump thread stacks before lit's timeout kills a test (PR #213239)

[Charles Zablit via lldb-commits]

https://github.com/charles-zablit created https://github.com/llvm/llvm-project/pull/213239

On Windows, when a test hits a timeout, we currently don't get a stacktrace. dotest solves this on POSIX: it registers a SIGTERM handler, so a killed test prints its stack. The handler does not run on Windows however because `faulthandler.register` doesn't exist there, and lit terminates the process instead of signalling it (no signals on Windows).

This patch adds `faulthandler.dump_traceback_later()` with a default timeout value of 300s. That's longer than the longest test in CI (~150s) and does not kill the test. It simply dumps the stacktrace at a point where the test is very likely stuck.

# Before

```
TIMEOUT: lldb-api :: types/TestFloatTypesExpr.py (2698 of 2698)
******************** TEST 'lldb-api :: types/TestFloatTypesExpr.py' FAILED ********************
Exit Code: 15
Timeout: Reached timeout of 900 seconds
```

There is no stacktrace.

# After

```
Timeout (0:00:20)!
Thread 0x00012fe8 (most recent call first):
  File ".../types/TestFloatTypesExpr.py", line 22 in test_float_type
  File ".../lldbsuite/test/lldbtest.py", line 2097 in test_method
  File ".../unittest/case.py", line 549 in _callTestMethod
  ...
  File ".../lldbsuite/test/dotest.py", line 1212 in run_suite
```

>From c9328894f9f598158357fee314aa89b06705f0eb Mon Sep 17 00:00:00 2001
From: Charles Zablit <c_zablit at apple.com>
Date: Fri, 31 Jul 2026 12:31:33 +0200
Subject: [PATCH] [lldb][Windows] Dump thread stacks before lit's timeout kills
 a test

---
 lldb/packages/Python/lldbsuite/test/dotest.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/lldb/packages/Python/lldbsuite/test/dotest.py b/lldb/packages/Python/lldbsuite/test/dotest.py
index 604fb98b1e2e5..3c966dceb96c7 100644
--- a/lldb/packages/Python/lldbsuite/test/dotest.py
+++ b/lldb/packages/Python/lldbsuite/test/dotest.py
@@ -504,6 +504,19 @@ def registerFaulthandler():
     if getattr(faulthandler, "register", None):
         faulthandler.register(signal.SIGTERM, chain=True)
 
+    if sys.platform != "win32":
+        return
+
+    # lit kills a hung test with TerminateProcess on Windows, so the SIGTERM
+    # handler above never runs and a timeout is reported with no indication of
+    # where it hung. Dump every thread's stack while the process is still alive.
+    try:
+        secs = float(os.environ.get("LLDB_TEST_STACK_DUMP_SECS", 300))
+    except ValueError:
+        secs = 300
+    if secs > 0:
+        faulthandler.dump_traceback_later(secs, exit=False)
+
 
 def setupSysPath():
     """