427 lines
12 KiB
C++
427 lines
12 KiB
C++
// Copyright (C) 2002-2017 Free Software Foundation, Inc.
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//
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// This file is part of GCC.
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//
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// GCC is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// GCC is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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// Written by Mark Mitchell, CodeSourcery LLC, <mark@codesourcery.com>
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// Thread support written by Jason Merrill, Red Hat Inc. <jason@redhat.com>
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#include <bits/c++config.h>
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#include <cxxabi.h>
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#include <exception>
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#include <new>
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#include <ext/atomicity.h>
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#include <ext/concurrence.h>
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#if defined(__GTHREADS) && defined(__GTHREAD_HAS_COND) \
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&& (ATOMIC_INT_LOCK_FREE > 1) && defined(_GLIBCXX_HAVE_LINUX_FUTEX)
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# include <climits>
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# include <syscall.h>
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# include <unistd.h>
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# define _GLIBCXX_USE_FUTEX
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# define _GLIBCXX_FUTEX_WAIT 0
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# define _GLIBCXX_FUTEX_WAKE 1
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#endif
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// The IA64/generic ABI uses the first byte of the guard variable.
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// The ARM EABI uses the least significant bit.
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// Thread-safe static local initialization support.
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#ifdef __GTHREADS
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# ifndef _GLIBCXX_USE_FUTEX
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namespace
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{
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// A single mutex controlling all static initializations.
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static __gnu_cxx::__recursive_mutex* static_mutex;
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typedef char fake_recursive_mutex[sizeof(__gnu_cxx::__recursive_mutex)]
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__attribute__ ((aligned(__alignof__(__gnu_cxx::__recursive_mutex))));
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fake_recursive_mutex fake_mutex;
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static void init()
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{ static_mutex = new (&fake_mutex) __gnu_cxx::__recursive_mutex(); }
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__gnu_cxx::__recursive_mutex&
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get_static_mutex()
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{
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static __gthread_once_t once = __GTHREAD_ONCE_INIT;
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__gthread_once(&once, init);
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return *static_mutex;
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}
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// Simple wrapper for exception safety.
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struct mutex_wrapper
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{
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bool unlock;
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mutex_wrapper() : unlock(true)
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{ get_static_mutex().lock(); }
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~mutex_wrapper()
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{
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if (unlock)
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static_mutex->unlock();
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}
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};
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}
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# endif
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# if defined(__GTHREAD_HAS_COND) && !defined(_GLIBCXX_USE_FUTEX)
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namespace
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{
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// A single condition variable controlling all static initializations.
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static __gnu_cxx::__cond* static_cond;
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// using a fake type to avoid initializing a static class.
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typedef char fake_cond_t[sizeof(__gnu_cxx::__cond)]
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__attribute__ ((aligned(__alignof__(__gnu_cxx::__cond))));
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fake_cond_t fake_cond;
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static void init_static_cond()
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{ static_cond = new (&fake_cond) __gnu_cxx::__cond(); }
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__gnu_cxx::__cond&
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get_static_cond()
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{
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static __gthread_once_t once = __GTHREAD_ONCE_INIT;
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__gthread_once(&once, init_static_cond);
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return *static_cond;
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}
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}
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# endif
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# ifndef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
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// Test the guard variable with a memory load with
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// acquire semantics.
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inline bool
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__test_and_acquire (__cxxabiv1::__guard *g)
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{
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unsigned char __c;
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unsigned char *__p = reinterpret_cast<unsigned char *>(g);
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__atomic_load (__p, &__c, __ATOMIC_ACQUIRE);
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(void) __p;
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return _GLIBCXX_GUARD_TEST(&__c);
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}
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# define _GLIBCXX_GUARD_TEST_AND_ACQUIRE(G) __test_and_acquire (G)
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# endif
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# ifndef _GLIBCXX_GUARD_SET_AND_RELEASE
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// Set the guard variable to 1 with memory order release semantics.
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inline void
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__set_and_release (__cxxabiv1::__guard *g)
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{
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unsigned char *__p = reinterpret_cast<unsigned char *>(g);
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unsigned char val = 1;
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__atomic_store (__p, &val, __ATOMIC_RELEASE);
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(void) __p;
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}
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# define _GLIBCXX_GUARD_SET_AND_RELEASE(G) __set_and_release (G)
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# endif
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#else /* !__GTHREADS */
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# undef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
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# undef _GLIBCXX_GUARD_SET_AND_RELEASE
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# define _GLIBCXX_GUARD_SET_AND_RELEASE(G) _GLIBCXX_GUARD_SET (G)
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#endif /* __GTHREADS */
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//
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// Here are C++ run-time routines for guarded initialization of static
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// variables. There are 4 scenarios under which these routines are called:
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//
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// 1. Threads not supported (__GTHREADS not defined)
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// 2. Threads are supported but not enabled at run-time.
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// 3. Threads enabled at run-time but __gthreads_* are not fully POSIX.
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// 4. Threads enabled at run-time and __gthreads_* support all POSIX threads
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// primitives we need here.
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//
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// The old code supported scenarios 1-3 but was broken since it used a global
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// mutex for all threads and had the mutex locked during the whole duration of
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// initialization of a guarded static variable. The following created a
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// dead-lock with the old code.
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//
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// Thread 1 acquires the global mutex.
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// Thread 1 starts initializing static variable.
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// Thread 1 creates thread 2 during initialization.
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// Thread 2 attempts to acquire mutex to initialize another variable.
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// Thread 2 blocks since thread 1 is locking the mutex.
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// Thread 1 waits for result from thread 2 and also blocks. A deadlock.
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//
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// The new code here can handle this situation and thus is more robust. However,
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// we need to use the POSIX thread condition variable, which is not supported
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// in all platforms, notably older versions of Microsoft Windows. The gthr*.h
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// headers define a symbol __GTHREAD_HAS_COND for platforms that support POSIX
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// like condition variables. For platforms that do not support condition
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// variables, we need to fall back to the old code.
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// If _GLIBCXX_USE_FUTEX, no global mutex or condition variable is used,
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// only atomic operations are used together with futex syscall.
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// Valid values of the first integer in guard are:
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// 0 No thread encountered the guarded init
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// yet or it has been aborted.
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// _GLIBCXX_GUARD_BIT The guarded static var has been successfully
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// initialized.
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// _GLIBCXX_GUARD_PENDING_BIT The guarded static var is being initialized
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// and no other thread is waiting for its
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// initialization.
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// (_GLIBCXX_GUARD_PENDING_BIT The guarded static var is being initialized
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// | _GLIBCXX_GUARD_WAITING_BIT) and some other threads are waiting until
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// it is initialized.
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namespace __cxxabiv1
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{
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#ifdef _GLIBCXX_USE_FUTEX
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namespace
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{
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static inline int __guard_test_bit (const int __byte, const int __val)
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{
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union { int __i; char __c[sizeof (int)]; } __u = { 0 };
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__u.__c[__byte] = __val;
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return __u.__i;
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}
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}
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#endif
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static inline int
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init_in_progress_flag(__guard* g)
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{ return ((char *)g)[1]; }
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static inline void
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set_init_in_progress_flag(__guard* g, int v)
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{ ((char *)g)[1] = v; }
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static inline void
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throw_recursive_init_exception()
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{
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#if __cpp_exceptions
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throw __gnu_cxx::recursive_init_error();
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#else
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// Use __builtin_trap so we don't require abort().
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__builtin_trap();
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#endif
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}
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// acquire() is a helper function used to acquire guard if thread support is
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// not compiled in or is compiled in but not enabled at run-time.
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static int
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acquire(__guard *g)
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{
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// Quit if the object is already initialized.
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if (_GLIBCXX_GUARD_TEST(g))
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return 0;
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if (init_in_progress_flag(g))
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throw_recursive_init_exception();
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set_init_in_progress_flag(g, 1);
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return 1;
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}
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extern "C"
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int __cxa_guard_acquire (__guard *g)
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{
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#ifdef __GTHREADS
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// If the target can reorder loads, we need to insert a read memory
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// barrier so that accesses to the guarded variable happen after the
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// guard test.
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if (_GLIBCXX_GUARD_TEST_AND_ACQUIRE (g))
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return 0;
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# ifdef _GLIBCXX_USE_FUTEX
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// If __atomic_* and futex syscall are supported, don't use any global
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// mutex.
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if (__gthread_active_p ())
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{
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int *gi = (int *) (void *) g;
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const int guard_bit = _GLIBCXX_GUARD_BIT;
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const int pending_bit = _GLIBCXX_GUARD_PENDING_BIT;
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const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
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while (1)
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{
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int expected(0);
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if (__atomic_compare_exchange_n(gi, &expected, pending_bit, false,
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__ATOMIC_ACQ_REL,
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__ATOMIC_ACQUIRE))
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{
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// This thread should do the initialization.
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return 1;
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}
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if (expected == guard_bit)
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{
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// Already initialized.
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return 0;
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}
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if (expected == pending_bit)
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{
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// Use acquire here.
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int newv = expected | waiting_bit;
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if (!__atomic_compare_exchange_n(gi, &expected, newv, false,
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__ATOMIC_ACQ_REL,
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__ATOMIC_ACQUIRE))
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{
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if (expected == guard_bit)
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{
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// Make a thread that failed to set the
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// waiting bit exit the function earlier,
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// if it detects that another thread has
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// successfully finished initialising.
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return 0;
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}
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if (expected == 0)
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continue;
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}
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expected = newv;
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}
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syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAIT, expected, 0);
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}
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}
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# else
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if (__gthread_active_p ())
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{
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mutex_wrapper mw;
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while (1) // When this loop is executing, mutex is locked.
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{
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# ifdef __GTHREAD_HAS_COND
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// The static is already initialized.
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if (_GLIBCXX_GUARD_TEST(g))
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return 0; // The mutex will be unlocked via wrapper
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if (init_in_progress_flag(g))
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{
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// The guarded static is currently being initialized by
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// another thread, so we release mutex and wait for the
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// condition variable. We will lock the mutex again after
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// this.
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get_static_cond().wait_recursive(&get_static_mutex());
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}
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else
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{
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set_init_in_progress_flag(g, 1);
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return 1; // The mutex will be unlocked via wrapper.
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}
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# else
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// This provides compatibility with older systems not supporting
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// POSIX like condition variables.
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if (acquire(g))
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{
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mw.unlock = false;
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return 1; // The mutex still locked.
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}
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return 0; // The mutex will be unlocked via wrapper.
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# endif
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}
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}
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# endif
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#endif
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return acquire (g);
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}
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extern "C"
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void __cxa_guard_abort (__guard *g) throw ()
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{
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#ifdef _GLIBCXX_USE_FUTEX
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// If __atomic_* and futex syscall are supported, don't use any global
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// mutex.
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if (__gthread_active_p ())
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{
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int *gi = (int *) (void *) g;
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const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
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int old = __atomic_exchange_n (gi, 0, __ATOMIC_ACQ_REL);
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if ((old & waiting_bit) != 0)
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syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAKE, INT_MAX);
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return;
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}
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#elif defined(__GTHREAD_HAS_COND)
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if (__gthread_active_p())
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{
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mutex_wrapper mw;
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set_init_in_progress_flag(g, 0);
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// If we abort, we still need to wake up all other threads waiting for
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// the condition variable.
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get_static_cond().broadcast();
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return;
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}
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#endif
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set_init_in_progress_flag(g, 0);
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#if defined(__GTHREADS) && !defined(__GTHREAD_HAS_COND)
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// This provides compatibility with older systems not supporting POSIX like
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// condition variables.
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if (__gthread_active_p ())
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static_mutex->unlock();
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#endif
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}
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extern "C"
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void __cxa_guard_release (__guard *g) throw ()
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{
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#ifdef _GLIBCXX_USE_FUTEX
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// If __atomic_* and futex syscall are supported, don't use any global
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// mutex.
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if (__gthread_active_p ())
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{
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int *gi = (int *) (void *) g;
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const int guard_bit = _GLIBCXX_GUARD_BIT;
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const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
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int old = __atomic_exchange_n (gi, guard_bit, __ATOMIC_ACQ_REL);
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if ((old & waiting_bit) != 0)
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syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAKE, INT_MAX);
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return;
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}
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#elif defined(__GTHREAD_HAS_COND)
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if (__gthread_active_p())
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{
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mutex_wrapper mw;
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set_init_in_progress_flag(g, 0);
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_GLIBCXX_GUARD_SET_AND_RELEASE(g);
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get_static_cond().broadcast();
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return;
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}
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#endif
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set_init_in_progress_flag(g, 0);
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_GLIBCXX_GUARD_SET_AND_RELEASE (g);
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#if defined(__GTHREADS) && !defined(__GTHREAD_HAS_COND)
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// This provides compatibility with older systems not supporting POSIX like
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// condition variables.
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if (__gthread_active_p())
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static_mutex->unlock();
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#endif
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}
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}
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