throw future_error in future.get()

[Ekkorus101]

fix segfault when we call future.get() twice, it's future_error in libstdc++ and recommended throw future_error in cppref

https://en.cppreference.com/w/cpp/thread/future/get.html

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[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Ekkoruse (Ekkorus101)

Changes

fix segfault when we call future.get() twice, it's future_error in libstdc++ and recommended throw future_error in cppref

https://en.cppreference.com/w/cpp/thread/future/get.html

<img width="815" height="90" alt="image" src="https://github.com/user-attachments/assets/c201bb60-e3b4-4080-bba2-ffda8bab514d" />

---

Full diff: https://github.com/llvm/llvm-project/pull/179409.diff

1 Files Affected:

• (modified) libcxx/include/future (+3)

diff --git a/libcxx/include/future b/libcxx/include/future
index 4084148e52af6..e25153eded4a9 100644
--- a/libcxx/include/future
+++ b/libcxx/include/future
@@ -985,6 +985,9 @@ future<_Rp>::~future() {
 
 template <class _Rp>
 _Rp future<_Rp>::get() {
+  if (__state_ == nullptr) [[unlikely]] {
+    throw future_error(make_error_code(future_errc::no_state));
+  }
   unique_ptr<__shared_count, __release_shared_count> __guard(__state_);
   __assoc_state<_Rp>* __s = __state_;
   __state_                = nullptr;