[libc-commits] [libc] [libc] EAGAIN and EWOULDBLOCK should be treated as success in futex wait (PR #203407)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

<details>
<summary>Changes</summary>

The `futex` wait function means waiting until a real change has been detected. We should not reject valid EAGAIN/EWOULDBLOCK kernel detection as failures.

Pure human code.

---
Full diff: https://github.com/llvm/llvm-project/pull/203407.diff


1 Files Affected:

- (modified) libc/src/__support/threads/linux/futex_utils.h (+5) 


``````````diff
diff --git a/libc/src/__support/threads/linux/futex_utils.h b/libc/src/__support/threads/linux/futex_utils.h
index ff6b5d526a3c1..61c1b7353e05b 100644
--- a/libc/src/__support/threads/linux/futex_utils.h
+++ b/libc/src/__support/threads/linux/futex_utils.h
@@ -66,6 +66,11 @@ class Futex : public cpp::Atomic<FutexWordType> {
       if (ret == -EINTR)
         continue;
 
+      // the value pointed to by uaddr was not equal to the expected
+      // value val at the time of the call (EAGAIN or EWOULDBLOCK).
+      if (ret == -EAGAIN || ret == -EWOULDBLOCK)
+        return 0;
+
       if (ret < 0)
         return cpp::unexpected(-ret);
       return ret;

``````````

</details>


https://github.com/llvm/llvm-project/pull/203407