[committed] libstdc++: Fix exception thrown by std::shared_lock::unlock() [PR112089]

[Jonathan Wakely]

Tested x86_64-linux. Pushed to trunk. Worth backporting to all active
branches, I think.

-- >8 --

The incorrect errc constant here looks like a copy&paste error.

libstdc++-v3/ChangeLog:

        PR libstdc++/112089
        * include/std/shared_mutex (shared_lock::unlock): Change errc
        constant to operation_not_permitted.
        * testsuite/30_threads/shared_lock/locking/112089.cc: New test.
---
 libstdc++-v3/include/std/shared_mutex         |  2 +-
 .../30_threads/shared_lock/locking/112089.cc  | 23 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 
libstdc++-v3/testsuite/30_threads/shared_lock/locking/112089.cc

diff --git a/libstdc++-v3/include/std/shared_mutex 
b/libstdc++-v3/include/std/shared_mutex
index 4f236a19806..f205c36533b 100644
--- a/libstdc++-v3/include/std/shared_mutex
+++ b/libstdc++-v3/include/std/shared_mutex
@@ -820,7 +820,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       unlock()
       {
        if (!_M_owns)
-         __throw_system_error(int(errc::resource_deadlock_would_occur));
+         __throw_system_error(int(errc::operation_not_permitted));
        _M_pm->unlock_shared();
        _M_owns = false;
       }
diff --git a/libstdc++-v3/testsuite/30_threads/shared_lock/locking/112089.cc 
b/libstdc++-v3/testsuite/30_threads/shared_lock/locking/112089.cc
new file mode 100644
index 00000000000..432c17591a1
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/shared_lock/locking/112089.cc
@@ -0,0 +1,23 @@
+// { dg-do run { target c++14 } }
+// { dg-require-gthreads "" }
+// { dg-additional-options "-pthread" { target pthread } }
+
+#include <shared_mutex>
+#include <system_error>
+#include <testsuite_hooks.h>
+
+// PR libstdc++/112089 shared_lock::unlock should throw operation_not_permitted
+
+int main()
+{
+  std::shared_lock<std::shared_timed_mutex> l;
+  try
+  {
+    l.unlock();
+    VERIFY( false );
+  }
+  catch (const std::system_error& e)
+  {
+    VERIFY( e.code() == std::errc::operation_not_permitted );
+  }
+}
-- 
2.41.0