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// Copyright (C) 2002, 2004, 2006, 2008, 2009, 2010, 2011, 2012

// 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) \

  && (ATOMIC_INT_LOCK_FREE > 1) && defined(_GLIBCXX_HAVE_LINUX_FUTEX)

# include <climits>

# include <syscall.h>

# include <unistd.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 condition 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 */

//

// Here are C++ run-time routines for guarded initialization 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

// initialization 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 acquire 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. However,

// we need to use the POSIX thread condition 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 condition variables. For platforms that do not support condition

// variables, we need to fall back to the old code.

// If _GLIBCXX_USE_FUTEX, no global mutex or condition 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

  }

  // acquire() 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 __atomic_* and futex syscall are supported, don't use any global

    // mutex.

    if (__gthread_active_p ())

      {

        int *gi = (int *) (void *) g;

        int expected(0);

        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)

          {

            if (__atomic_compare_exchange_n(gi, &expected, pending_bit, false,

                                            __ATOMIC_ACQ_REL,

                                            __ATOMIC_RELAXED))

              {

                // This thread should do the initialization.

                return 1;

              }

            if (expected == guard_bit)

              {

                // Already initialized.

                return 0;

              }

             if (expected == pending_bit)

               {

                 int newv = expected | waiting_bit;

                 if (!__atomic_compare_exchange_n(gi, &expected, newv, false,

                                                  __ATOMIC_ACQ_REL,

                                                  __ATOMIC_RELAXED))

                   continue;

                 expected = newv;

               }

            syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAIT, expected, 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

                // condition 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 condition 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) throw ()

  {

#ifdef _GLIBCXX_USE_FUTEX

    // If __atomic_* 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 = __atomic_exchange_n (gi, 0, __ATOMIC_ACQ_REL);

        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 condition 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

    // condition variables.

    if (__gthread_active_p ())

      static_mutex->unlock();

#endif

  }

  extern "C"

  void __cxa_guard_release (__guard *g) throw ()

  {

#ifdef _GLIBCXX_USE_FUTEX

    // If __atomic_* 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 = __atomic_exchange_n (gi, guard_bit, __ATOMIC_ACQ_REL);

        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

    // condition variables.

    if (__gthread_active_p())

      static_mutex->unlock();

#endif

  }

}