--- /dev/null
+// Copyright (C) 2002, 2004, 2006, 2008, 2009 Free Software Foundation, Inc.
+//
+// This file is part of GCC.
+//
+// GCC is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// GCC is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+// Written by Mark Mitchell, CodeSourcery LLC, <mark@codesourcery.com>
+// Thread support written by Jason Merrill, Red Hat Inc. <jason@redhat.com>
+
+#include <bits/c++config.h>
+#include <cxxabi.h>
+#include <exception>
+#include <new>
+#include <ext/atomicity.h>
+#include <ext/concurrence.h>
+#if defined(__GTHREADS) && defined(__GTHREAD_HAS_COND) \
+ && defined(_GLIBCXX_ATOMIC_BUILTINS_4) && defined(_GLIBCXX_HAVE_LINUX_FUTEX)
+# include <climits>
+# include <syscall.h>
+# define _GLIBCXX_USE_FUTEX
+# define _GLIBCXX_FUTEX_WAIT 0
+# define _GLIBCXX_FUTEX_WAKE 1
+#endif
+
+// The IA64/generic ABI uses the first byte of the guard variable.
+// The ARM EABI uses the least significant bit.
+
+// Thread-safe static local initialization support.
+#ifdef __GTHREADS
+# ifndef _GLIBCXX_USE_FUTEX
+namespace
+{
+ // A single mutex controlling all static initializations.
+ static __gnu_cxx::__recursive_mutex* static_mutex;
+
+ typedef char fake_recursive_mutex[sizeof(__gnu_cxx::__recursive_mutex)]
+ __attribute__ ((aligned(__alignof__(__gnu_cxx::__recursive_mutex))));
+ fake_recursive_mutex fake_mutex;
+
+ static void init()
+ { static_mutex = new (&fake_mutex) __gnu_cxx::__recursive_mutex(); }
+
+ __gnu_cxx::__recursive_mutex&
+ get_static_mutex()
+ {
+ static __gthread_once_t once = __GTHREAD_ONCE_INIT;
+ __gthread_once(&once, init);
+ return *static_mutex;
+ }
+
+ // Simple wrapper for exception safety.
+ struct mutex_wrapper
+ {
+ bool unlock;
+ mutex_wrapper() : unlock(true)
+ { get_static_mutex().lock(); }
+
+ ~mutex_wrapper()
+ {
+ if (unlock)
+ static_mutex->unlock();
+ }
+ };
+}
+# endif
+
+# if defined(__GTHREAD_HAS_COND) && !defined(_GLIBCXX_USE_FUTEX)
+namespace
+{
+ // A single conditional variable controlling all static initializations.
+ static __gnu_cxx::__cond* static_cond;
+
+ // using a fake type to avoid initializing a static class.
+ typedef char fake_cond_t[sizeof(__gnu_cxx::__cond)]
+ __attribute__ ((aligned(__alignof__(__gnu_cxx::__cond))));
+ fake_cond_t fake_cond;
+
+ static void init_static_cond()
+ { static_cond = new (&fake_cond) __gnu_cxx::__cond(); }
+
+ __gnu_cxx::__cond&
+ get_static_cond()
+ {
+ static __gthread_once_t once = __GTHREAD_ONCE_INIT;
+ __gthread_once(&once, init_static_cond);
+ return *static_cond;
+ }
+}
+# endif
+
+# ifndef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
+inline bool
+__test_and_acquire (__cxxabiv1::__guard *g)
+{
+ bool b = _GLIBCXX_GUARD_TEST (g);
+ _GLIBCXX_READ_MEM_BARRIER;
+ return b;
+}
+# define _GLIBCXX_GUARD_TEST_AND_ACQUIRE(G) __test_and_acquire (G)
+# endif
+
+# ifndef _GLIBCXX_GUARD_SET_AND_RELEASE
+inline void
+__set_and_release (__cxxabiv1::__guard *g)
+{
+ _GLIBCXX_WRITE_MEM_BARRIER;
+ _GLIBCXX_GUARD_SET (g);
+}
+# define _GLIBCXX_GUARD_SET_AND_RELEASE(G) __set_and_release (G)
+# endif
+
+#else /* !__GTHREADS */
+
+# undef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
+# undef _GLIBCXX_GUARD_SET_AND_RELEASE
+# define _GLIBCXX_GUARD_SET_AND_RELEASE(G) _GLIBCXX_GUARD_SET (G)
+
+#endif /* __GTHREADS */
+
+namespace __gnu_cxx
+{
+ // 6.7[stmt.dcl]/4: If control re-enters the declaration (recursively)
+ // while the object is being initialized, the behavior is undefined.
+
+ // Since we already have a library function to handle locking, we might
+ // as well check for this situation and throw an exception.
+ // We use the second byte of the guard variable to remember that we're
+ // in the middle of an initialization.
+ class recursive_init_error: public std::exception
+ {
+ public:
+ recursive_init_error() throw() { }
+ virtual ~recursive_init_error() throw ();
+ };
+
+ recursive_init_error::~recursive_init_error() throw() { }
+}
+
+//
+// Here are C++ run-time routines for guarded initiailization of static
+// variables. There are 4 scenarios under which these routines are called:
+//
+// 1. Threads not supported (__GTHREADS not defined)
+// 2. Threads are supported but not enabled at run-time.
+// 3. Threads enabled at run-time but __gthreads_* are not fully POSIX.
+// 4. Threads enabled at run-time and __gthreads_* support all POSIX threads
+// primitives we need here.
+//
+// The old code supported scenarios 1-3 but was broken since it used a global
+// mutex for all threads and had the mutex locked during the whole duration of
+// initlization of a guarded static variable. The following created a dead-lock
+// with the old code.
+//
+// Thread 1 acquires the global mutex.
+// Thread 1 starts initializing static variable.
+// Thread 1 creates thread 2 during initialization.
+// Thread 2 attempts to acuqire mutex to initialize another variable.
+// Thread 2 blocks since thread 1 is locking the mutex.
+// Thread 1 waits for result from thread 2 and also blocks. A deadlock.
+//
+// The new code here can handle this situation and thus is more robust. Howere,
+// we need to use the POSIX thread conditional variable, which is not supported
+// in all platforms, notably older versions of Microsoft Windows. The gthr*.h
+// headers define a symbol __GTHREAD_HAS_COND for platforms that support POSIX
+// like conditional variables. For platforms that do not support conditional
+// variables, we need to fall back to the old code.
+
+// If _GLIBCXX_USE_FUTEX, no global mutex or conditional variable is used,
+// only atomic operations are used together with futex syscall.
+// Valid values of the first integer in guard are:
+// 0 No thread encountered the guarded init
+// yet or it has been aborted.
+// _GLIBCXX_GUARD_BIT The guarded static var has been successfully
+// initialized.
+// _GLIBCXX_GUARD_PENDING_BIT The guarded static var is being initialized
+// and no other thread is waiting for its
+// initialization.
+// (_GLIBCXX_GUARD_PENDING_BIT The guarded static var is being initialized
+// | _GLIBCXX_GUARD_WAITING_BIT) and some other threads are waiting until
+// it is initialized.
+
+namespace __cxxabiv1
+{
+#ifdef _GLIBCXX_USE_FUTEX
+ namespace
+ {
+ static inline int __guard_test_bit (const int __byte, const int __val)
+ {
+ union { int __i; char __c[sizeof (int)]; } __u = { 0 };
+ __u.__c[__byte] = __val;
+ return __u.__i;
+ }
+ }
+#endif
+
+ static inline int
+ init_in_progress_flag(__guard* g)
+ { return ((char *)g)[1]; }
+
+ static inline void
+ set_init_in_progress_flag(__guard* g, int v)
+ { ((char *)g)[1] = v; }
+
+ static inline void
+ throw_recursive_init_exception()
+ {
+#ifdef __EXCEPTIONS
+ throw __gnu_cxx::recursive_init_error();
+#else
+ // Use __builtin_trap so we don't require abort().
+ __builtin_trap();
+#endif
+ }
+
+ // acuire() is a helper function used to acquire guard if thread support is
+ // not compiled in or is compiled in but not enabled at run-time.
+ static int
+ acquire(__guard *g)
+ {
+ // Quit if the object is already initialized.
+ if (_GLIBCXX_GUARD_TEST(g))
+ return 0;
+
+ if (init_in_progress_flag(g))
+ throw_recursive_init_exception();
+
+ set_init_in_progress_flag(g, 1);
+ return 1;
+ }
+
+ extern "C"
+ int __cxa_guard_acquire (__guard *g)
+ {
+#ifdef __GTHREADS
+ // If the target can reorder loads, we need to insert a read memory
+ // barrier so that accesses to the guarded variable happen after the
+ // guard test.
+ if (_GLIBCXX_GUARD_TEST_AND_ACQUIRE (g))
+ return 0;
+
+# ifdef _GLIBCXX_USE_FUTEX
+ // If __sync_* and futex syscall are supported, don't use any global
+ // mutex.
+ if (__gthread_active_p ())
+ {
+ int *gi = (int *) (void *) g;
+ const int guard_bit = _GLIBCXX_GUARD_BIT;
+ const int pending_bit = _GLIBCXX_GUARD_PENDING_BIT;
+ const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
+
+ while (1)
+ {
+ int old = __sync_val_compare_and_swap (gi, 0, pending_bit);
+ if (old == 0)
+ return 1; // This thread should do the initialization.
+
+ if (old == guard_bit)
+ return 0; // Already initialized.
+
+ if (old == pending_bit)
+ {
+ int newv = old | waiting_bit;
+ if (__sync_val_compare_and_swap (gi, old, newv) != old)
+ continue;
+
+ old = newv;
+ }
+
+ syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAIT, old, 0);
+ }
+ }
+# else
+ if (__gthread_active_p ())
+ {
+ mutex_wrapper mw;
+
+ while (1) // When this loop is executing, mutex is locked.
+ {
+# ifdef __GTHREAD_HAS_COND
+ // The static is already initialized.
+ if (_GLIBCXX_GUARD_TEST(g))
+ return 0; // The mutex will be unlocked via wrapper
+
+ if (init_in_progress_flag(g))
+ {
+ // The guarded static is currently being initialized by
+ // another thread, so we release mutex and wait for the
+ // conditional variable. We will lock the mutex again after
+ // this.
+ get_static_cond().wait_recursive(&get_static_mutex());
+ }
+ else
+ {
+ set_init_in_progress_flag(g, 1);
+ return 1; // The mutex will be unlocked via wrapper.
+ }
+# else
+ // This provides compatibility with older systems not supporting
+ // POSIX like conditional variables.
+ if (acquire(g))
+ {
+ mw.unlock = false;
+ return 1; // The mutex still locked.
+ }
+ return 0; // The mutex will be unlocked via wrapper.
+# endif
+ }
+ }
+# endif
+#endif
+
+ return acquire (g);
+ }
+
+ extern "C"
+ void __cxa_guard_abort (__guard *g)
+ {
+#ifdef _GLIBCXX_USE_FUTEX
+ // If __sync_* and futex syscall are supported, don't use any global
+ // mutex.
+ if (__gthread_active_p ())
+ {
+ int *gi = (int *) (void *) g;
+ const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
+ int old = __sync_lock_test_and_set (gi, 0);
+
+ if ((old & waiting_bit) != 0)
+ syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAKE, INT_MAX);
+ return;
+ }
+#elif defined(__GTHREAD_HAS_COND)
+ if (__gthread_active_p())
+ {
+ mutex_wrapper mw;
+
+ set_init_in_progress_flag(g, 0);
+
+ // If we abort, we still need to wake up all other threads waiting for
+ // the conditional variable.
+ get_static_cond().broadcast();
+ return;
+ }
+#endif
+
+ set_init_in_progress_flag(g, 0);
+#if defined(__GTHREADS) && !defined(__GTHREAD_HAS_COND)
+ // This provides compatibility with older systems not supporting POSIX like
+ // conditional variables.
+ if (__gthread_active_p ())
+ static_mutex->unlock();
+#endif
+ }
+
+ extern "C"
+ void __cxa_guard_release (__guard *g)
+ {
+#ifdef _GLIBCXX_USE_FUTEX
+ // If __sync_* and futex syscall are supported, don't use any global
+ // mutex.
+ if (__gthread_active_p ())
+ {
+ int *gi = (int *) (void *) g;
+ const int guard_bit = _GLIBCXX_GUARD_BIT;
+ const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
+ int old = __sync_lock_test_and_set (gi, guard_bit);
+
+ if ((old & waiting_bit) != 0)
+ syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAKE, INT_MAX);
+ return;
+ }
+#elif defined(__GTHREAD_HAS_COND)
+ if (__gthread_active_p())
+ {
+ mutex_wrapper mw;
+
+ set_init_in_progress_flag(g, 0);
+ _GLIBCXX_GUARD_SET_AND_RELEASE(g);
+
+ get_static_cond().broadcast();
+ return;
+ }
+#endif
+
+ set_init_in_progress_flag(g, 0);
+ _GLIBCXX_GUARD_SET_AND_RELEASE (g);
+
+#if defined(__GTHREADS) && !defined(__GTHREAD_HAS_COND)
+ // This provides compatibility with older systems not supporting POSIX like
+ // conditional variables.
+ if (__gthread_active_p())
+ static_mutex->unlock();
+#endif
+ }
+}
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