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

[Jonathan Wakely <jwakely@redhat.com>]

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
>