This patch adds the new thread model `mcf`, which implements mutexes
and condition variables with the mcfgthread library.
Source code for mcfgthread is available at <https://github.com/lhmouse/mcfgthread>.
config/ChangeLog:
* gthr.m4 (GCC_AC_THREAD_HEADER): Add new case for `mcf` thread
model
gcc/ChangeLog:
* config/i386/mingw-mcfgthread.h: New file
* config/i386/mingw32.h: Add builtin macro and default libraries
for mcfgthread when thread model is `mcf`
* config.gcc: Include 'i386/mingw-mcfgthread.h' when thread model
is `mcf`
* configure.ac: Recognize `mcf` as a valid thread model
* config.in: Regenerate
* configure: Regenerate
libatomic/ChangeLog:
* configure.tgt: Add new case for `mcf` thread model
libgcc/ChangeLog:
* config.host: Add new cases for `mcf` thread model
* config/i386/gthr-mcf.h: New file
* config/i386/t-mingw-mcfgthread: New file
* config/i386/t-slibgcc-cygming: Add mcfgthread for libgcc DLL
* configure: Regenerate
libstdc++-v3/ChangeLog:
* libsupc++/atexit_thread.cc (__cxa_thread_atexit): Use
implementation from mcfgthread if available
* libsupc++/guard.cc (__cxa_guard_acquire, __cxa_guard_release,
__cxa_guard_abort): Use implementations from mcfgthread if
available
* configure: Regenerate
Glibc 2.32 adds a global variable that says whether the process is
single-threaded. We can use this to decide whether to elide atomic
operations, as a more precise and reliable indicator than
__gthread_active_p.
This means that guard variables for statics and reference counting in
shared_ptr can use less expensive, non-atomic ops even in processes that
are linked to libpthread, as long as no threads have been created yet.
It also means that we switch to using atomics if libpthread gets loaded
later via dlopen (this still isn't supported in general, for other
reasons).
We can't use __libc_single_threaded to replace __gthread_active_p
everywhere. If we replaced the uses of __gthread_active_p in std::mutex
then we would elide the pthread_mutex_lock in the code below, but not
the pthread_mutex_unlock:
std::mutex m;
m.lock(); // pthread_mutex_lock
std::thread t([]{}); // __libc_single_threaded = false
t.join();
m.unlock(); // pthread_mutex_unlock
We need the lock and unlock to use the same "is threading enabled"
predicate, and similarly for init/destroy pairs for mutexes and
condition variables, so that we don't try to release resources that were
never acquired.
There are other places that could use __libc_single_threaded, such as
_Sp_locker in src/c++11/shared_ptr.cc and locale init functions, but
they can be changed later.
libstdc++-v3/ChangeLog:
PR libstdc++/96817
* include/ext/atomicity.h (__gnu_cxx::__is_single_threaded()):
New function wrapping __libc_single_threaded if available.
(__exchange_and_add_dispatch, __atomic_add_dispatch): Use it.
* libsupc++/guard.cc (__cxa_guard_acquire, __cxa_guard_abort)
(__cxa_guard_release): Likewise.
* testsuite/18_support/96817.cc: New test.
2015-07-02 Uros Bizjak <ubizjak@gmail.com>
* libsupc++/guard.cc (__test_and_acquire): Use __p after __atomic_load
to avoid unused variable warning.
(__set_and_release): Use __p after __atomic_store to avoid unused
variable warning.
From-SVN: r234331
* libsupc++/guard.cc (__test_and_acquire): Use __p after __atomic_load
to avoid unused variable warning.
(__set_and_release): Use __p after __atomic_store to avoid unused
variable warning.
From-SVN: r225298
2012-09-06 Thiago Macieira <thiago.macieira@intel.com>
PR libstdc++/54172
* libsupc++/guard.cc (__cxa_guard_acquire): Exit the loop earlier if
we detect that another thread has had success. Don't compare_exchange
from a finished state back to a waiting state. Comment.
From-SVN: r191042
/gcc
2011-07-15 Paolo Carlini <paolo.carlini@oracle.com>
Jakub Jelinek <jakub@redhat.com>
Jonathan Wakely <jwakely.gcc@gmail.com>
PR libstdc++/49745
* gthr-posix.h: Do not include <unistd.h> unconditionally; use
_GTHREADS_USE_MUTEX_TIMEDLOCK instead of _POSIX_TIMEOUTS.
/libstdc++-v3
2011-07-15 Paolo Carlini <paolo.carlini@oracle.com>
Jakub Jelinek <jakub@redhat.com>
PR libstdc++/49745
* acinclude.m4 ([GLIBCXX_CHECK_GTHREADS]): Check separately for
_POSIX_TIMEOUTS and define _GTHREADS_USE_MUTEX_TIMEDLOCK.
* libstdc++-v3/libsupc++/guard.cc: Include <unistd.h>.
* testsuite/17_intro/headers/c++1998/49745.cc: New.
* configure: Regenerate.
* config.h.in: Likewise.
Co-Authored-By: Jakub Jelinek <jakub@redhat.com>
Co-Authored-By: Jonathan Wakely <jwakely.gcc@gmail.com>
From-SVN: r176335
* unwind-cxx.h (__cxa_get_globals, __cxa_get_globals_fast): Mark const.
(__cxa_get_exception_ptr): Mark pure.
(__cxa_bad_cast, __cxa_bad_typeid): Mark noreturn
(__terminate): Makr throw ().
* exception (terminate): Mark throw().
(uncaught_exception): Mark pure.
* eh_ptr.cc (_M_safe_bool_dummy): Mark throw().
* guard.cc (__cxa_guard_abort, __cxa_guard_release): Mark throw().
* eh_terminate.cc (__terminate, terminate): Mark throw().
* vec.cc (__cxa_vec_cleanup): Mark throw().
* cxxabi.h (__cxa_vec_cleanup, __cxa_guard_release, __cxa_guard_abort): Mark throw ().
(__cxa_pure_virtual): Mark noreturn.
(__cxa_current_exception_type): Mark throw and pure.
* exception_ptr.h (operator ==, !=, _M_get, !, ==,
__cxa_exception_type): Mark pure.
(_M_safe_bool_dummy): Mark pure and const.
From-SVN: r146331
2008-04-24 Benjamin Kosnik <bkoz@redhat.com>
* acinclude.m4 (GLIBCXX_ENABLE_ATOMIC_BUILTINS): Check for set of
all used __sync builtins, in two sizes.
* config.h.in: Regenerate.
* configure: Regenerate.
* src/atomic.cc: Use _GLIBCXX_ATOMIC_BUILTINS_1.
* include/ext/atomicity.h: Use _GLIBCXX_ATOMIC_BUILTINS_4.
* libsupc++/guard.cc: Use _GLIBCXX_ATOMIC_BUILTINS_4.
* doc/xml/manual/concurrency.xm: Update docs.
From-SVN: r134629
2007-09-13 Doug Kwan <dougkwan@google.com>
* gcc/gthr-posix.h (__gthread_cond_broadcast, __gthread_cond_wait,
__gthread_cond_wait_recursive): Add to extend interface for POSIX
conditional variables. (__GTHREAD_HAS_COND): Macro defined to signify
support of conditional variables.
* gcc/gthr-posix95.h (__gthread_cond_broadcast, __gthread_cond_wait,
__gthread_cond_wait_recursive): Add to extend interface for POSIX
conditional variables. (__GTHREAD_HAS_COND): Macro defined to signify
support of conditional variables.
* gcc/gthr-single.h (__gthread_cond_broadcast, __gthread_cond_wait,
__gthread_cond_wait_recursive): Add to extend interface for POSIX
conditional variables.
* gcc/gthr.h: Update comments to document new interface.
* libstdc++-v3/include/ext/concurrent.h (class __mutex,
class __recursive_mutex): Add new method gthread_mutex to access
inner gthread mutex.
[__GTHREAD_HAS_COND] (class __concurrence_broadcast_error,
class __concurrence_wait_error, class __cond): Add.
* guard.cc (recursive_push, recursive_pop): Delete.
(init_in_progress_flag, set_init_in_progress_flag): Add to
replace recursive_push and recursive_pop.
(throw_recursive_init_exception): Add.
(acquire, __cxa_guard_acquire, __cxa_guard_abort and
__cxa_guard_release): [__GTHREAD_HAS_COND] Use a conditional
for synchronization of static variable initialization.
The global mutex is only held briefly when guards are
accessed. [!__GTHREAD_HAS_COND] Fall back to the old code,
which deadlocks.
* testsuite/thread/guard.cc: Add new test. It deadlocks with the
old locking code in libstdc++-v3/libsup++/guard.cc.
From-SVN: r129030
2006-10-11 Benjamin Kosnik <bkoz@redhat.com>
PR libstdc++/29426
* libsupc++/guard.cc (get_static_mutex): New.
(mutex_wrapper::mutex_wrapper): Use it to get properly initialized
recursive mutex without ordering issues.
* src/locale_init.cc (__get_locale_mutex): No need to
uglify. Change to get_locale_mutex.
From-SVN: r117643
PR c++/13684
* cp/decl.c (expand_static_init): Use thread-safety API.
(register_dtor_fn): Return the call, don't expand it.
* cp/tree.c (add_stmt_to_compound): New fn.
(stabilize_call): Use it.
* gimplify.c (gimplify_cleanup_point_expr): Handle CLEANUP_EH_ONLY.
(gimple_push_cleanup): Add eh_only parm.
(gimplify_target_expr): Pass it.
* c.opt (-fno-threadsafe-statics): New option.
* c-opts.c (c_common_handle_option): Handle it.
* c-common.h (flag_threadsafe_statics): Declare it.
* c-common.c (flag_threadsafe_statics): Record it.
* doc/invoke.texi: Document it.
* tsystem.h (_GNU_SOURCE): Define.
* gthr-posix.h (__gthread_recursive_mutex_t): New typedef.
(__GTHREAD_RECURSIVE_MUTEX_INIT): New macro.
(__GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION): New macro.
(__gthread_recursive_mutex_init_function): New fn.
(__gthread_recursive_mutex_lock): New fn.
(__gthread_recursive_mutex_trylock): New fn.
(__gthread_recursive_mutex_unlock): New fn.
* gthr-solaris.h, gthr-single.h, gthr-dce.h: Likewise.
* gthr-win32.h, gthr-vxworks.h: Likewise.
* gthr.h: Document.
* libsupc++/guard.cc (static_mutex): Internal class implementing a
recursive mutex which controls initialization of local statics.
(__gnu_cxx::recursive_init): New exception class.
(__cxa_guard_acquire): Deal with locking and recursion detection.
(acquire_1, __cxa_guard_abort, __cxa_guard_release): Likewise.
From-SVN: r86687
* configure.ac: Set ABI_TWEAKS_SRCDIR.
* configure.host: Set abi_tweaks_dir. Check for atomicity.h when
setting atomicity_dir. Override type_cpu for arm based targets.
* include/Makefile.am (host_headers): Add cxxabi_tweaks.h.
* libsupc++/cxxabi.h: Include bits/cxxabi.h. Don't declare __guard.
* libsupc++/guard.cc: Use definitions from cxxabi_tweaks.h.
* libsupc++/vec.cc: Ditto.
* config/cpu/arm/cxxabi_tweaks.h: New file.
* config/cpu/generic/cxxabi_tweaks.h: New file.
* */Makefile.in: Regenerate.
* configure: Regenerate.
From-SVN: r84032
