[gcc(refs/users/aoliva/heads/testme)] [libstdc++] ensure mutex_pool survives _Safe_sequence_base

[Alexandre Oliva]

https://gcc.gnu.org/g:e298c760cab78f831cd25d398636f4b8befc88a7

commit e298c760cab78f831cd25d398636f4b8befc88a7
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Thu Feb 16 07:45:40 2023 -0300

    [libstdc++] ensure mutex_pool survives _Safe_sequence_base
    
    On vxworks, after destroying the semaphore used to implement a mutex,
    __gthread_mutex_lock fails and __gnu_cxx::__mutex::lock calls
    __throw_concurrence_lock_error.  Nothing ensures the mutex_pool
    mutexes survive init-once objects containing _Safe_sequence_base.  If
    such an object completes construction before mutex_pool
    initialization, it will be registered for atexit destruction after the
    mutex_pool mutexes, so the _M_detach_all() call in the
    _Safe_sequence_base dtor will use already-destructed mutexes, and
    basic_string/requirements/citerators_cc fails calling terminate.
    
    This patch fixes this problem by ensuring the mutex pool completes
    construction before any _Safe_sequence_base-containing object, so that
    the mutex pool survives them all.
    
    
    for  libstdc++-v3/ChangeLog
    
            * include/debug/safe_base.h (_Safe_sequence_base): Ensure
            the mutex pool survives *this.

Diff:
---
 libstdc++-v3/include/debug/safe_base.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/debug/safe_base.h b/libstdc++-v3/include/debug/safe_base.h
index 1dfa9f68b65..d4ba404cdac 100644
--- a/libstdc++-v3/include/debug/safe_base.h
+++ b/libstdc++-v3/include/debug/safe_base.h
@@ -203,7 +203,15 @@ namespace __gnu_debug
     // Initialize with a version number of 1 and no iterators
     _Safe_sequence_base() _GLIBCXX_NOEXCEPT
     : _M_iterators(0), _M_const_iterators(0), _M_version(1)
-    { }
+    {
+      // Make sure the mutex_pool machinery is initialized before any
+      // full object containing a _Safe_sequence_base completes
+      // construction, so that any local static mutexes in the mutex
+      // pool won't be destructed before our destructor runs;
+      // _M_detach_all could fail otherwise, on targets whose mutexes
+      // stop working after being destroyed.
+      (void)this->_M_get_mutex();
+    }
 
 #if __cplusplus >= 201103L
     _Safe_sequence_base(const _Safe_sequence_base&) noexcept