[libcxx-commits] [libcxx] [libc++] Don't try to wait on a thread that hasn't started in std::async (PR #125433)

[via libcxx-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

<details>
<summary>Changes</summary>

If the creation of a thread fails, this causes an idle loop that will never end because the thread wasn't started in the first place.

Fixes #<!-- -->125428


---
Full diff: https://github.com/llvm/llvm-project/pull/125433.diff


2 Files Affected:

- (modified) libcxx/include/future (+4-2) 
- (added) libcxx/test/std/thread/futures/futures.async/thread_create_failure.pass.cpp (+46) 


``````````diff
diff --git a/libcxx/include/future b/libcxx/include/future
index db1f624244b8f77..514d4c3d633d6cf 100644
--- a/libcxx/include/future
+++ b/libcxx/include/future
@@ -865,7 +865,8 @@ void __async_assoc_state<_Rp, _Fp>::__execute() {
 
 template <class _Rp, class _Fp>
 void __async_assoc_state<_Rp, _Fp>::__on_zero_shared() _NOEXCEPT {
-  this->wait();
+  if (base::__state_ & base::__constructed)
+    this->wait();
   base::__on_zero_shared();
 }
 
@@ -902,7 +903,8 @@ void __async_assoc_state<void, _Fp>::__execute() {
 
 template <class _Fp>
 void __async_assoc_state<void, _Fp>::__on_zero_shared() _NOEXCEPT {
-  this->wait();
+  if (base::__state_ & base::__constructed)
+    this->wait();
   base::__on_zero_shared();
 }
 
diff --git a/libcxx/test/std/thread/futures/futures.async/thread_create_failure.pass.cpp b/libcxx/test/std/thread/futures/futures.async/thread_create_failure.pass.cpp
new file mode 100644
index 000000000000000..ac5db590dbd8d1d
--- /dev/null
+++ b/libcxx/test/std/thread/futures/futures.async/thread_create_failure.pass.cpp
@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: no-threads
+
+// There is no way to limit the number of threads on windows
+// UNSUPPORTED: msvc
+
+#include <cassert>
+#include <future>
+#include <system_error>
+
+#if __has_include(<sys/resource.h>)
+#  include <sys/resource.h>
+#  ifdef RLIMIT_NPROC
+void force_thread_creation_failure() {
+  rlimit lim = {1, 1};
+  setrlimit(RLIMIT_NPROC, &lim);
+}
+#  else
+#    error "No known way to force only one thread being available"
+#  endif
+#else
+#  error "No known way to force only one thread being available"
+#endif
+
+int main() {
+  force_thread_creation_failure();
+
+  try {
+    auto fut = std::async(std::launch::async, [] { return 1; });
+    assert(false);
+  } catch (const std::system_error&) {
+  }
+
+  try {
+    auto fut = std::async(std::launch::async, [] { return; });
+    assert(false);
+  } catch (const std::system_error&) {
+  }
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/125433