[llvm] Support: don't block signals around close if it can be avoided (PR #73009)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-support

Author: Mateusz Guzik (mjguzik)

<details>
<summary>Changes</summary>

Signal blocking originally showed up in 51c2afc4b65b2782 ("Support: Don't call close again if we get EINTR"), but it was overzealous -- there are systems where the error is known to be fine.

This commit elides signal blocking for said systems (the list is incomplete though).

Note close() can still fail for other reasons (like ENOSPC), in which case an error will be returned while the fd slot is cleared up.

---
Full diff: https://github.com/llvm/llvm-project/pull/73009.diff


1 Files Affected:

- (modified) llvm/lib/Support/Unix/Process.inc (+20) 


``````````diff
diff --git a/llvm/lib/Support/Unix/Process.inc b/llvm/lib/Support/Unix/Process.inc
index d3d9fb7d71878e1..bc638439754c71e 100644
--- a/llvm/lib/Support/Unix/Process.inc
+++ b/llvm/lib/Support/Unix/Process.inc
@@ -234,6 +234,25 @@ std::error_code Process::FixupStandardFileDescriptors() {
   return std::error_code();
 }
 
+// Close a file descriptor while being mindful of EINTR.
+//
+// On Unix systems closing a file descriptor usually starts with removing it
+// from the fd table (or an equivalent structure). This means any error
+// generated past that point will still result in the entry being cleared.
+//
+// Make sure to not bubble up EINTR as there is nothing to do in that case.
+// XXX what about other errors?
+#if defined(__linux__) || defined(__DragonFly__) || defined(__FreeBSD__) || \
+    defined(__NetBSD__) || defined(__OpenBSD__)
+std::error_code Process::SafelyCloseFileDescriptor(int FD) {
+  int EC = 0;
+  if (::close(FD) < 0) {
+    if (errno != EINTR)
+      EC = errno;
+  }
+  return std::error_code(EC, std::generic_category());
+}
+#else
 std::error_code Process::SafelyCloseFileDescriptor(int FD) {
   // Create a signal set filled with *all* signals.
   sigset_t FullSet, SavedSet;
@@ -268,6 +287,7 @@ std::error_code Process::SafelyCloseFileDescriptor(int FD) {
     return std::error_code(ErrnoFromClose, std::generic_category());
   return std::error_code(EC, std::generic_category());
 }
+#endif
 
 bool Process::StandardInIsUserInput() {
   return FileDescriptorIsDisplayed(STDIN_FILENO);

``````````

</details>


https://github.com/llvm/llvm-project/pull/73009