cxa_thread_atexit.cpp | Explore in Territory

//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "abort_message.h"
#include "cxxabi.h"
#include <__thread/support.h>
#ifndef _LIBCXXABI_HAS_NO_THREADS
#if defined(__ELF__) && defined(_LIBCXXABI_LINK_PTHREAD_LIB)
#pragma comment(lib, "pthread")
#endif
#endif

#include <stdlib.h>

namespace __cxxabiv1 {

  Dtor;

  extern "C"
#ifndef HAVE___CXA_THREAD_ATEXIT_IMPL
  // A weak symbol is used to detect this function's presence in the C library
  // at runtime, even if libc++ is built against an older libc
  _LIBCXXABI_WEAK
#endif
  int __cxa_thread_atexit_impl(Dtor, void*, void*);

#ifndef HAVE___CXA_THREAD_ATEXIT_IMPL

namespace {
  // This implementation is used if the C library does not provide
  // __cxa_thread_atexit_impl() for us.  It has a number of limitations that are
  // difficult to impossible to address without ..._impl():
  //
  // - dso_symbol is ignored.  This means that a shared library may be unloaded
  //   (via dlclose()) before its thread_local destructors have run.
  //
  // - thread_local destructors for the main thread are run by the destructor of
  //   a static object.  This is later than expected; they should run before the
  //   destructors of any objects with static storage duration.
  //
  // - thread_local destructors on non-main threads run on the first iteration
  //   through the __libccpp_tls_key destructors.
  //   std::notify_all_at_thread_exit() and similar functions must be careful to
  //   wait until the second iteration to provide their intended ordering
  //   guarantees.
  //
  // Another limitation, though one shared with ..._impl(), is that any
  // thread_locals that are first initialized after non-thread_local global
  // destructors begin to run will not be destroyed.  [basic.start.term] states
  // that all thread_local destructors are sequenced before the destruction of
  // objects with static storage duration, resulting in a contradiction if a
  // thread_local is constructed after that point.  Thus we consider such
  // programs ill-formed, and don't bother to run those destructors.  (If the
  // program terminates abnormally after such a thread_local is constructed,
  // the destructor is not expected to run and thus there is no contradiction.
  // So construction still has to work.)

  struct DtorList { … };

  // The linked list of thread-local destructors to run
  __thread DtorList* dtors = …;
  // True if the destructors are currently scheduled to run on this thread
  __thread bool dtors_alive = …;
  // Used to trigger destructors on thread exit; value is ignored
  std::__libcpp_tls_key dtors_key;

  void run_dtors(void*) { … }

  struct DtorsManager { … };
} // namespace

#endif // HAVE___CXA_THREAD_ATEXIT_IMPL

extern "C" {

  _LIBCXXABI_FUNC_VIS int __cxa_thread_atexit(Dtor dtor, void* obj, void* dso_symbol) throw() { … }

} // extern "C"
} // namespace __cxxabiv1
chromium/third_party/libc++abi/src/src/cxa_thread_atexit.cpp
