[llvm] [lit] Explicitly unset timer to free thread stack (PR #188717)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-testing-tools

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

Currently the virtual address space usage of lit fluctuates wildly, with peak usage exceeding 4GB, which results in subsequent thread spawning errors on 32-bit systems.

The cause of this is a circular reference in threading._timer (via the callback), which causes the 8MB thread stack to not be immediately reclaimed when the timer is cancelled.

We can avoid this by explicitly unsetting the timer.

---
Full diff: https://github.com/llvm/llvm-project/pull/188717.diff


1 Files Affected:

- (modified) llvm/utils/lit/lit/TestRunner.py (+2) 


``````````diff
diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
index d856642e3f447..8bd44a8c30707 100644
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -126,6 +126,8 @@ def cancel(self):
         if not self.active():
             return
         self._timer.cancel()
+        # Break reference cycle so that thread stack is freed immediately.
+        self._timer = None
 
     def active(self):
         return self.timeout > 0

``````````

</details>


https://github.com/llvm/llvm-project/pull/188717