[libcxxabi] r283988 - Provide a fallback __cxa_thread_atexit() implementation. Patch from Tavian Barnes
Eric Fiselier via cfe-commits
cfe-commits at lists.llvm.org
Wed Oct 12 01:54:10 PDT 2016
Author: ericwf
Date: Wed Oct 12 03:54:10 2016
New Revision: 283988
URL: http://llvm.org/viewvc/llvm-project?rev=283988&view=rev
Log:
Provide a fallback __cxa_thread_atexit() implementation. Patch from Tavian Barnes
Added:
libcxxabi/trunk/test/thread_local_destruction_order.pass.cpp
Modified:
libcxxabi/trunk/src/cxa_thread_atexit.cpp
libcxxabi/trunk/test/CMakeLists.txt
libcxxabi/trunk/test/cxa_thread_atexit_test.pass.cpp
libcxxabi/trunk/test/libcxxabi/test/config.py
libcxxabi/trunk/test/lit.site.cfg.in
Modified: libcxxabi/trunk/src/cxa_thread_atexit.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/src/cxa_thread_atexit.cpp?rev=283988&r1=283987&r2=283988&view=diff
==============================================================================
--- libcxxabi/trunk/src/cxa_thread_atexit.cpp (original)
+++ libcxxabi/trunk/src/cxa_thread_atexit.cpp Wed Oct 12 03:54:10 2016
@@ -7,20 +7,133 @@
//
//===----------------------------------------------------------------------===//
+#include "abort_message.h"
#include "cxxabi.h"
+#include <cstdlib>
+#include <pthread.h>
namespace __cxxabiv1 {
-extern "C" {
-#ifdef HAVE___CXA_THREAD_ATEXIT_IMPL
+ using Dtor = void(*)(void*);
-_LIBCXXABI_FUNC_VIS int __cxa_thread_atexit(void (*dtor)(void *), void *obj,
- void *dso_symbol) throw() {
- extern int __cxa_thread_atexit_impl(void (*)(void *), void *, void *);
- return __cxa_thread_atexit_impl(dtor, obj, dso_symbol);
-}
+ 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
+ __attribute__((__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 pthread_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 {
+ Dtor dtor;
+ void* obj;
+ DtorList* next;
+ };
+
+ // The linked list of thread-local destructors to run
+ __thread DtorList* dtors = nullptr;
+ // True if the destructors are currently scheduled to run on this thread
+ __thread bool dtors_alive = false;
+ // Used to trigger destructors on thread exit; value is ignored
+ pthread_key_t dtors_key;
+
+ void run_dtors(void*) {
+ while (auto head = dtors) {
+ dtors = head->next;
+ head->dtor(head->obj);
+ std::free(head);
+ }
+
+ dtors_alive = false;
+ }
+
+ struct DtorsManager {
+ DtorsManager() {
+ // There is intentionally no matching pthread_key_delete call, as
+ // __cxa_thread_atexit() may be called arbitrarily late (for example, from
+ // global destructors or atexit() handlers).
+ if (pthread_key_create(&dtors_key, run_dtors) != 0) {
+ abort_message("pthread_key_create() failed in __cxa_thread_atexit()");
+ }
+ }
+
+ ~DtorsManager() {
+ // pthread_key destructors do not run on threads that call exit()
+ // (including when the main thread returns from main()), so we explicitly
+ // call the destructor here. This runs at exit time (potentially earlier
+ // if libc++abi is dlclose()'d). Any thread_locals initialized after this
+ // point will not be destroyed.
+ run_dtors(nullptr);
+ }
+ };
+} // namespace
#endif // HAVE__CXA_THREAD_ATEXIT_IMPL
+extern "C" {
+
+ _LIBCXXABI_FUNC_VIS int __cxa_thread_atexit(Dtor dtor, void* obj, void* dso_symbol) throw() {
+#ifdef HAVE___CXA_THREAD_ATEXIT_IMPL
+ return __cxa_thread_atexit_impl(dtor, obj, dso_symbol);
+#else
+ if (__cxa_thread_atexit_impl) {
+ return __cxa_thread_atexit_impl(dtor, obj, dso_symbol);
+ } else {
+ // Initialize the dtors pthread_key (uses __cxa_guard_*() for one-time
+ // initialization and __cxa_atexit() for destruction)
+ static DtorsManager manager;
+
+ if (!dtors_alive) {
+ if (pthread_setspecific(dtors_key, &dtors_key) != 0) {
+ return -1;
+ }
+ dtors_alive = true;
+ }
+
+ auto head = static_cast<DtorList*>(std::malloc(sizeof(DtorList)));
+ if (!head) {
+ return -1;
+ }
+
+ head->dtor = dtor;
+ head->obj = obj;
+ head->next = dtors;
+ dtors = head;
+
+ return 0;
+ }
+#endif // HAVE___CXA_THREAD_ATEXIT_IMPL
+ }
+
} // extern "C"
} // namespace __cxxabiv1
Modified: libcxxabi/trunk/test/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/CMakeLists.txt?rev=283988&r1=283987&r2=283988&view=diff
==============================================================================
--- libcxxabi/trunk/test/CMakeLists.txt (original)
+++ libcxxabi/trunk/test/CMakeLists.txt Wed Oct 12 03:54:10 2016
@@ -17,7 +17,6 @@ pythonize_bool(LIBCXXABI_ENABLE_SHARED)
pythonize_bool(LIBCXXABI_ENABLE_THREADS)
pythonize_bool(LIBCXXABI_ENABLE_EXCEPTIONS)
pythonize_bool(LIBCXXABI_USE_LLVM_UNWINDER)
-pythonize_bool(LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL)
set(LIBCXXABI_TARGET_INFO "libcxx.test.target_info.LocalTI" CACHE STRING
"TargetInfo to use when setting up test environment.")
set(LIBCXXABI_EXECUTOR "None" CACHE STRING
Modified: libcxxabi/trunk/test/cxa_thread_atexit_test.pass.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/cxa_thread_atexit_test.pass.cpp?rev=283988&r1=283987&r2=283988&view=diff
==============================================================================
--- libcxxabi/trunk/test/cxa_thread_atexit_test.pass.cpp (original)
+++ libcxxabi/trunk/test/cxa_thread_atexit_test.pass.cpp Wed Oct 12 03:54:10 2016
@@ -8,7 +8,6 @@
//===----------------------------------------------------------------------===//
// REQUIRES: linux
-// REQUIRES: thread_atexit
#include <assert.h>
#include <cxxabi.h>
Modified: libcxxabi/trunk/test/libcxxabi/test/config.py
URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/libcxxabi/test/config.py?rev=283988&r1=283987&r2=283988&view=diff
==============================================================================
--- libcxxabi/trunk/test/libcxxabi/test/config.py (original)
+++ libcxxabi/trunk/test/libcxxabi/test/config.py Wed Oct 12 03:54:10 2016
@@ -37,8 +37,6 @@ class Configuration(LibcxxConfiguration)
super(Configuration, self).configure_features()
if not self.get_lit_bool('enable_exceptions', True):
self.config.available_features.add('libcxxabi-no-exceptions')
- if self.get_lit_bool('thread_atexit', True):
- self.config.available_features.add('thread_atexit')
def configure_compile_flags(self):
self.cxx.compile_flags += ['-DLIBCXXABI_NO_TIMER']
Modified: libcxxabi/trunk/test/lit.site.cfg.in
URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/lit.site.cfg.in?rev=283988&r1=283987&r2=283988&view=diff
==============================================================================
--- libcxxabi/trunk/test/lit.site.cfg.in (original)
+++ libcxxabi/trunk/test/lit.site.cfg.in Wed Oct 12 03:54:10 2016
@@ -13,7 +13,6 @@ config.use_sanitizer = "@LLVM
config.enable_32bit = "@LIBCXXABI_BUILD_32_BITS@"
config.target_info = "@LIBCXXABI_TARGET_INFO@"
config.executor = "@LIBCXXABI_EXECUTOR@"
-config.thread_atexit = "@LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL@"
config.libcxxabi_shared = "@LIBCXXABI_ENABLE_SHARED@"
config.enable_shared = "@LIBCXX_ENABLE_SHARED@"
config.enable_exceptions = "@LIBCXXABI_ENABLE_EXCEPTIONS@"
Added: libcxxabi/trunk/test/thread_local_destruction_order.pass.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/thread_local_destruction_order.pass.cpp?rev=283988&view=auto
==============================================================================
--- libcxxabi/trunk/test/thread_local_destruction_order.pass.cpp (added)
+++ libcxxabi/trunk/test/thread_local_destruction_order.pass.cpp Wed Oct 12 03:54:10 2016
@@ -0,0 +1,56 @@
+//===-------------- thread_local_destruction_order.pass.cpp ---------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+#include <cassert>
+#include <thread>
+
+int seq = 0;
+
+class OrderChecker {
+public:
+ explicit OrderChecker(int n) : n_{n} { }
+
+ ~OrderChecker() {
+ assert(seq++ == n_);
+ }
+
+private:
+ int n_;
+};
+
+template <int ID>
+class CreatesThreadLocalInDestructor {
+public:
+ ~CreatesThreadLocalInDestructor() {
+ thread_local OrderChecker checker{ID};
+ }
+};
+
+OrderChecker global{7};
+
+void thread_fn() {
+ static OrderChecker fn_static{5};
+ thread_local CreatesThreadLocalInDestructor<2> creates_tl2;
+ thread_local OrderChecker fn_thread_local{1};
+ thread_local CreatesThreadLocalInDestructor<0> creates_tl0;
+}
+
+int main() {
+ static OrderChecker fn_static{6};
+
+ std::thread{thread_fn}.join();
+ assert(seq == 3);
+
+ thread_local OrderChecker fn_thread_local{4};
+ thread_local CreatesThreadLocalInDestructor<3> creates_tl;
+
+ return 0;
+}
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