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// Copyright (C) 2002-2015 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

// .

// Written by Mark Mitchell, CodeSourcery LLC, 

// Thread support written by Jason Merrill, Red Hat Inc. 

#include 

#include 

#include 

#include 

#include 

#include 

#if defined(__GTHREADS) && defined(__GTHREAD_HAS_COND) \

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

# include 

# include 

# include 

# 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()

  {

#if __cpp_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;

	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 expected(0);

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

					    __ATOMIC_ACQ_REL,

					    __ATOMIC_ACQUIRE))

	      {

		// This thread should do the initialization.

		return 1;

	      }

	    if (expected == guard_bit)

	      {

		// Already initialized.

		return 0;

	      }

	     if (expected == pending_bit)

	       {

		 // Use acquire here.

		 int newv = expected | waiting_bit;

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

						  __ATOMIC_ACQ_REL,

						  __ATOMIC_ACQUIRE))

		   {

		     if (expected == guard_bit)

		       {

			 // Make a thread that failed to set the

			 // waiting bit exit the function earlier,

			 // if it detects that another thread has

			 // successfully finished initialising.

			 return 0;

		       }

		     if (expected == 0)

		       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

  }

}