Re: std::jthread::operator=(std::jthread&&) calls std::terminate if *this has an associated running thread.

[Jonathan Wakely via Gcc-patches]

On 08/11/20 14:51 +0100, Paul Scharnofske via Libstdc++ wrote:

I think this would work:

  jthread& operator=(jthread&& __x) noexcept
  {
    std::jthread(std::move(__x)).swap(*this);
    return *this;
  }

That looks a lot better than what I did, it's also consistent with other
places like std::stop_token::operator=(std::stop_token&&).

I updated my patch and also created a test that checks the post
conditions described in the standard.

Thanks, I've committed the patch and will also backport it to the
gcc-10 branch.

This patch is small enough to not require a copyright assignment, but
if you would like to make further contritbutions please contact me
off-list to discuss the legal prerequisites as described at
https://gcc.gnu.org/contribute.html

Thanks again for contributing to GCC!

---
libstdc++-v3/include/std/thread               |  6 +++++-
.../testsuite/30_threads/jthread/jthread.cc   | 20 +++++++++++++++++++
2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/thread b/libstdc++-v3/include/std/thread
index 887ee579962..080036e2609 100644
--- a/libstdc++-v3/include/std/thread
+++ b/libstdc++-v3/include/std/thread
@@ -456,7 +456,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    operator=(const jthread&) = delete;

    jthread&
-    operator=(jthread&&) noexcept = default;
+    operator=(jthread&& __other) noexcept
+    {
+      std::jthread(std::move(__other)).swap(*this);
+      return *this;
+    }

    void
    swap(jthread& __other) noexcept
diff --git a/libstdc++-v3/testsuite/30_threads/jthread/jthread.cc 
b/libstdc++-v3/testsuite/30_threads/jthread/jthread.cc
index 746ff437c1d..b8ba62f6df2 100644
--- a/libstdc++-v3/testsuite/30_threads/jthread/jthread.cc
+++ b/libstdc++-v3/testsuite/30_threads/jthread/jthread.cc
@@ -187,6 +187,25 @@ void test_detach()
  VERIFY(t1FinallyInterrupted.load());
}

+//------------------------------------------------------
+
+void test_move_assignment()
+{
+    std::jthread thread1([]{});
+    std::jthread thread2([]{});
+
+    const auto id2 = thread2.get_id();
+    const auto ssource2 = thread2.get_stop_source();
+
+    thread1 = std::move(thread2);
+
+    VERIFY(thread1.get_id() == id2);
+    VERIFY(thread2.get_id() == std::jthread::id());
+
+    VERIFY(thread1.get_stop_source() == ssource2);
+    VERIFY(!thread2.get_stop_source().stop_possible());
+}
+
int main()
{
  std::set_terminate([](){
@@ -197,4 +216,5 @@ int main()
  test_stop_token();
  test_join();
  test_detach();
+  test_move_assignment();
}
--
2.29.2