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boost/interprocess/detail/intermodule_singleton.hpp

//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2009-2009. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/interprocess for documentation.
//
//////////////////////////////////////////////////////////////////////////////

#ifndef BOOST_INTERPROCESS_INTERMODULE_SINGLETON_HPP
#define BOOST_INTERPROCESS_INTERMODULE_SINGLETON_HPP

#if defined(_MSC_VER)&&(_MSC_VER>=1200)
#pragma once
#endif

#include <boost/interprocess/detail/config_begin.hpp>
#include <boost/interprocess/detail/workaround.hpp>

#include <boost/interprocess/managed_shared_memory.hpp>
#ifdef BOOST_INTERPROCESS_WINDOWS
#include <boost/interprocess/managed_windows_shared_memory.hpp>
#endif
#include <boost/interprocess/detail/atomic.hpp>
#include <boost/interprocess/detail/os_thread_functions.hpp>
#include <boost/interprocess/detail/tmp_dir_helpers.hpp>
#include <boost/interprocess/detail/os_file_functions.hpp>
#include <boost/interprocess/detail/mpl.hpp>
#include <boost/assert.hpp>
#include <cstddef>
#include <cstdio>
#include <cstring>
#include <string>

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>

#if defined (BOOST_INTERPROCESS_WINDOWS)
#include <fcntl.h>
#include <io.h>

#include <sys/locking.h>
#else
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#endif

namespace boost{
namespace interprocess{
namespace detail{

namespace file_locking_helpers {

inline void get_pid_creation_time_str(std::string &s)
{
   std::stringstream stream;
   stream << get_current_process_id() << '_';
   stream.precision(6);
   stream << std::fixed << get_current_process_creation_time();
   s = stream.str();
}

inline void create_tmp_subdir_and_get_pid_based_filepath(const char *subdir_name, const char *file_prefix, OS_process_id_t pid, std::string &s, bool creation_time = false)
{
   //Let's create a lock file for each process gmem that will mark if
   //the process is alive or not
   create_tmp_and_clean_old(s);
   s += "/";
   s += subdir_name;
   if(!open_or_create_directory(s.c_str())){
      throw interprocess_exception(error_info(system_error_code()));
   }
   s += "/";
   s += file_prefix;
   if(creation_time){
      std::string sstamp;   
      get_pid_creation_time_str(sstamp);
      s += sstamp;
   }
   else{
      pid_str_t pid_str;
      get_pid_str(pid_str, pid);
      s += pid_str;
   }
}

inline bool check_if_filename_complies_with_pid
   (const char *filename, const char *prefix, OS_process_id_t pid, std::string &file_suffix, bool creation_time = false)
{
   //Check if filename complies with lock file name pattern
   std::string fname(filename);
   std::string fprefix(prefix);
   if(fname.size() <= fprefix.size()){
      return false;
   }
   fname.resize(fprefix.size());
   if(fname != fprefix){
      return false;
   }

   //If not our lock file, delete it if we can lock it
   fname = filename;
   fname.erase(0, fprefix.size());
   pid_str_t pid_str;
   get_pid_str(pid_str, pid);
   file_suffix = pid_str;
   if(creation_time){
      std::size_t p = fname.find('_');
      if (p == std::string::npos){
         return false;
      }
      std::string save_suffix(fname);
      fname.erase(p);
      fname.swap(file_suffix);
      bool ret = (file_suffix == fname);
      file_suffix.swap(save_suffix);
      return ret;
   }
   else{
      fname.swap(file_suffix);
      return (file_suffix == fname);
   }
}

}  //file_locking_helpers

namespace intermodule_singleton_helpers {

const int GMemMarkToBeRemoved = -1;
const int GMemNotPresent      = -2;

inline const char *get_lock_file_subdir_name()
{  return "gmem";  }

inline const char *get_lock_file_base_name()
{  return "lck";  }

inline void create_and_get_singleton_lock_file_path(std::string &s)
{
   file_locking_helpers::create_tmp_subdir_and_get_pid_based_filepath
      (get_lock_file_subdir_name(), get_lock_file_base_name(), get_current_process_id(), s, true);
}

inline const char *get_shm_base_name()
{  return "bip.gmem.shm.";  }

inline void get_shm_name(std::string &shm_name)
{
   file_locking_helpers::get_pid_creation_time_str(shm_name);
   shm_name.insert(0, get_shm_base_name());
}

inline std::size_t get_shm_size()
{  return 65536;  }

template<class ManagedShMem>
struct managed_sh_dependant
{
   static void apply_gmem_erase_logic(const char *filepath, const char *filename);

   static bool remove_old_gmem()
   {
      std::string refcstrRootDirectory;
      tmp_folder(refcstrRootDirectory);
      refcstrRootDirectory += "/";
      refcstrRootDirectory += get_lock_file_subdir_name();
      return for_each_file_in_dir(refcstrRootDirectory.c_str(), apply_gmem_erase_logic);
   }
};

#if (defined BOOST_INTERPROCESS_WINDOWS)

template<>
struct managed_sh_dependant<managed_windows_shared_memory>
{
   static void apply_gmem_erase_logic(const char *, const char *){}

   static bool remove_old_gmem()
   { return true; }
};


struct locking_file_serial_id
{
   int fd;
   unsigned long dwVolumeSerialNumber;
   unsigned long nFileIndexHigh;
   unsigned long nFileIndexLow;
   //This reference count counts the number of modules attached
   //to the shared memory and lock file. This serves to unlink
   //the locking file and shared memory when all modules are
   //done with the global memory (shared memory)
   volatile boost::uint32_t modules_attached_to_gmem_count;
};

inline bool lock_locking_file(int fd)
{
   int ret = 0;
   while(ret != 0 && errno == EDEADLK){
      ret = _locking(fd, _LK_LOCK, 1/*lock_file_contents_length()*/);
   }
   return 0 == ret;
}

inline bool try_lock_locking_file(int fd)
{
   return 0 == _locking(fd, _LK_NBLCK , 1);
}

inline int open_or_create_and_lock_file(const char *name)
{
   permissions p;
   p.set_unrestricted();
   while(1){
      file_handle_t handle = create_or_open_file(name, read_write, p);
      int fd = _open_osfhandle((intptr_t)handle, _O_TEXT);
      if(fd < 0){
         close_file(handle);
         return fd;
      }
      if(!try_lock_locking_file(fd)){
         _close(fd);
         return -1;
      }
      struct _stat s;
      if(0 == _stat(name, &s)){
         return fd;
      }
      else{
         _close(fd);
      }
   }
}

inline int try_open_and_lock_file(const char *name)
{
   file_handle_t handle = open_existing_file(name, read_write);
   int fd = _open_osfhandle((intptr_t)handle, _O_TEXT);
   if(fd < 0){
      close_file(handle);
      return fd;
   }
   if(!try_lock_locking_file(fd)){
      _close(fd);
      return -1;
   }
   return fd;
}

inline void close_lock_file(int fd)
{  _close(fd); }

inline bool is_valid_fd(int fd)
{
   struct _stat s;
   return EBADF != _fstat(fd, &s);
}

inline bool is_normal_file(int fd)
{
   if(_isatty(fd))
      return false;
   struct _stat s;
   if(0 != _fstat(fd, &s))
      return false;
   return 0 != (s.st_mode & _S_IFREG);
}

inline std::size_t get_size(int fd)
{
   struct _stat s;
   if(0 != _fstat(fd, &s))
      return 0u;
   return (std::size_t)s.st_size;
}

inline bool fill_file_serial_id(int fd, locking_file_serial_id &id)
{
   winapi::interprocess_by_handle_file_information info;
   if(!winapi::get_file_information_by_handle((void*)_get_osfhandle(fd), &info))
      return false;
   id.fd = fd;
   id.dwVolumeSerialNumber = info.dwVolumeSerialNumber;
   id.nFileIndexHigh = info.nFileIndexHigh;
   id.nFileIndexLow = info.nFileIndexLow;
   id.modules_attached_to_gmem_count = 1; //Initialize attached count
   return true;
}

inline bool compare_file_serial(int fd, const locking_file_serial_id &id)
{
   winapi::interprocess_by_handle_file_information info;
   if(!winapi::get_file_information_by_handle((void*)_get_osfhandle(fd), &info))
      return false;

   return   id.dwVolumeSerialNumber == info.dwVolumeSerialNumber  &&
            id.nFileIndexHigh       == info.nFileIndexHigh        &&
            id.nFileIndexLow        == info.nFileIndexLow;
}

#else //UNIX

struct locking_file_serial_id
{
   int fd;
   dev_t st_dev;
   ino_t st_ino;
   //This reference count counts the number of modules attached
   //to the shared memory and lock file. This serves to unlink
   //the locking file and shared memory when all modules are
   //done with the global memory (shared memory)
   volatile boost::uint32_t modules_attached_to_gmem_count;
};

inline bool lock_locking_file(int fd)
{
   int ret = 0;
   while(ret != 0 && errno != EINTR){
      struct flock lock;
      lock.l_type = F_WRLCK;
      lock.l_whence = SEEK_SET;
      lock.l_start = 0;
      lock.l_len = 1;
      ret = fcntl (fd, F_SETLKW, &lock);
   }
   return 0 == ret;
}

inline bool try_lock_locking_file(int fd)
{
   struct flock lock;
   lock.l_type = F_WRLCK;
   lock.l_whence = SEEK_SET;
   lock.l_start = 0;
   lock.l_len = 1;
   return 0 == fcntl (fd, F_SETLK, &lock);
}

inline int open_or_create_and_lock_file(const char *name)
{
   permissions p;
   p.set_unrestricted();
   while(1){
      int fd = create_or_open_file(name, read_write, p);
      if(fd < 0){
         return fd;
      }
      if(!try_lock_locking_file(fd)){
         close(fd);
         return -1;
      }
      struct stat s;
      if(0 == stat(name, &s)){
         return fd;
      }
      else{
         close(fd);
      }
   }
}

inline int try_open_and_lock_file(const char *name)
{
   int fd = open_existing_file(name, read_write);
   if(fd < 0){
      return fd;
   }
   if(!try_lock_locking_file(fd)){
      close(fd);
      return -1;
   }
   return fd;
}

inline void close_lock_file(int fd)
{  close(fd); }

inline bool is_valid_fd(int fd)
{
   struct stat s;
   return EBADF != fstat(fd, &s);
}

inline bool is_normal_file(int fd)
{
   struct stat s;
   if(0 != fstat(fd, &s))
      return false;
   return 0 != (s.st_mode & S_IFREG);
}

inline std::size_t get_size(int fd)
{
   struct stat s;
   if(0 != fstat(fd, &s))
      return 0u;
   return (std::size_t)s.st_size;
}

inline bool fill_file_serial_id(int fd, locking_file_serial_id &id)
{
   struct stat s;
   if(0 != fstat(fd, &s))
      return false;
   id.fd = fd;
   id.st_dev = s.st_dev;
   id.st_ino = s.st_ino;
   id.modules_attached_to_gmem_count = 1; //Initialize attached count
   return true;
}

inline bool compare_file_serial(int fd, const locking_file_serial_id &id)
{
   struct stat info;
   if(0 != fstat(fd, &info))
      return false;

   return   id.st_dev == info.st_dev  &&
            id.st_ino == info.st_ino;
}

#endif

template<class ManagedShMem>
struct gmem_erase_func
{
   gmem_erase_func(const char *shm_name, const char *singleton_lock_file_path, ManagedShMem & shm)
      :shm_name_(shm_name), singleton_lock_file_path_(singleton_lock_file_path), shm_(shm)
   {}

   void operator()()
   {
      locking_file_serial_id *pserial_id = shm_.template find<locking_file_serial_id>("lock_file_fd").first;
      if(pserial_id){
         pserial_id->fd = GMemMarkToBeRemoved;
      }
      delete_file(singleton_lock_file_path_);
      shared_memory_object::remove(shm_name_);
   }
   
   const char * const shm_name_;
   const char * const singleton_lock_file_path_;
   ManagedShMem & shm_;
};

//This function applies shared memory erasure logic based on the passed lock file.
template<class ManagedShMem>
void managed_sh_dependant<ManagedShMem>::
   apply_gmem_erase_logic(const char *filepath, const char *filename)
{
   int fd = GMemMarkToBeRemoved;
   try{
      std::string str;
      //If the filename is current process lock file, then avoid it
      if(file_locking_helpers::check_if_filename_complies_with_pid
         (filename, get_lock_file_base_name(), get_current_process_id(), str, true)){
         return;
      }
      //Open and lock the other process' lock file
      fd = try_open_and_lock_file(filepath);
      if(fd < 0){
         return;
      }
      //If done, then the process is dead so take global shared memory name
      //(the name is based on the lock file name) and try to apply erasure logic
      str.insert(0, get_shm_base_name());
      try{
         ManagedShMem shm(open_only, str.c_str());
         gmem_erase_func<ManagedShMem> func(str.c_str(), filepath, shm);
         shm.try_atomic_func(func);
      }
      catch(interprocess_exception &e){
         //If shared memory is not found erase the lock file
         if(e.get_error_code() == not_found_error){
            delete_file(filepath);
         }
      }
   }
   catch(...){

   }
   if(fd >= 0){
      close_lock_file(fd);
   }
}

}  //namespace intermodule_singleton_helpers {



namespace intermodule_singleton_helpers {

//The lock file logic creates uses a unique instance to a file
template <class ManagedShMem>
struct lock_file_logic
{
   lock_file_logic(ManagedShMem &shm)
      : mshm(shm)
   {  shm.atomic_func(*this); }

   void operator()(void)
   {
      retry_with_new_shm = false;

      //First find the file locking descriptor id
      locking_file_serial_id *pserial_id =
         mshm.template find<locking_file_serial_id>("lock_file_fd").first;

      int fd;
      //If not found schedule a creation
      if(!pserial_id){
         fd = GMemNotPresent;
      }
      //Else get it
      else{
         fd = pserial_id->fd;
      }
      //If we need to create a new one, do it
      if(fd == GMemNotPresent){
         std::string lck_str;
         //Create a unique current pid based lock file path
         create_and_get_singleton_lock_file_path(lck_str);
         //Open or create and lock file
         int fd = intermodule_singleton_helpers::open_or_create_and_lock_file(lck_str.c_str());
         //If failed, write a bad file descriptor to notify other modules that
         //something was wrong and unlink shared memory. Mark the function object
         //to tell caller to retry with another shared memory
         if(fd < 0){
            this->register_lock_file(GMemMarkToBeRemoved);
            std::string s;
            get_shm_name(s);
            shared_memory_object::remove(s.c_str());
            retry_with_new_shm = true;
         }
         //If successful, register the file descriptor
         else{
            this->register_lock_file(fd);
         }
      }
      //If the fd was invalid (maybe a previous try failed) notify caller that
      //should retry creation logic, since this shm might have been already
      //unlinked since the shm was removed
      else if (fd == GMemMarkToBeRemoved){
         retry_with_new_shm = true;
      }
      //If the stored fd is not valid (a open fd, a normal file with the
      //expected size, or does not have the same file id number,
      //then it's an old shm from an old process with the same pid.
      //If that's the case, mark it as invalid
      else if(!is_valid_fd(fd) ||
            !is_normal_file(fd) ||
            0 != get_size(fd) ||
            !compare_file_serial(fd, *pserial_id)){
         pserial_id->fd = GMemMarkToBeRemoved;
         std::string s;
         get_shm_name(s);
         shared_memory_object::remove(s.c_str());
         retry_with_new_shm = true;
      }
      else{
         //If the lock file is ok, increment reference count of
         //attached modules to shared memory
         atomic_inc32(&pserial_id->modules_attached_to_gmem_count);
      }
   }

   private:
   locking_file_serial_id * register_lock_file(int fd)
   {
      locking_file_serial_id *pinfo = mshm.template construct<locking_file_serial_id>("lock_file_fd")();
      fill_file_serial_id(fd, *pinfo);
      return pinfo;
   }

   public:
   ManagedShMem &mshm;
   bool retry_with_new_shm;
};

#if defined (BOOST_INTERPROCESS_WINDOWS)

template<>
struct lock_file_logic<managed_windows_shared_memory>
{
   lock_file_logic(managed_windows_shared_memory &)
      : retry_with_new_shm(false)
   {}

   void operator()(void){}
   const bool retry_with_new_shm;
};

#endif

}  //namespace intermodule_singleton_helpers {

//This class contains common code for all singleton types, so that we instantiate this
//code just once per module. This class also holds a reference counted shared memory
//to be used by all instances

template<class ManagedShMem>
class intermodule_singleton_common
{
   public:
   typedef void*(singleton_constructor_t)(ManagedShMem &);
   typedef void (singleton_destructor_t)(void *, ManagedShMem &);

   static const ::boost::uint32_t Uninitialized       = 0u;
   static const ::boost::uint32_t Initializing        = 1u;
   static const ::boost::uint32_t Initialized         = 2u;
   static const ::boost::uint32_t Broken              = 3u;

   static void finalize_singleton_logic(void *ptr, singleton_destructor_t destructor)
   {
      if(ptr)
         destructor(ptr, get_shm());
      //If this is the last singleton of this module
      //apply shm destruction.
      //Note: singletons are destroyed when the module is unloaded
      //so no threads should be executing or holding references
      //to this module
      if(1 == atomic_dec32(&this_module_singleton_count)){
         destroy_shm();
      }
   }

   static void initialize_singleton_logic
      (void *&ptr, volatile boost::uint32_t &this_module_singleton_initialized, singleton_constructor_t ini_func);

   private:
   static ManagedShMem &get_shm()
   {
      return *static_cast<ManagedShMem *>(static_cast<void *>(&shm_mem));
   }

   enum { MemSize = ((sizeof(ManagedShMem)-1)/sizeof(max_align))+1u };

   static void initialize_shm();
   static void destroy_shm();
   //Static data, zero-initalized without any dependencies
   //this_module_singleton_count is the number of singletons used by this module
   static volatile boost::uint32_t this_module_singleton_count;
   //this_module_shm_initialized is the state of this module's shm class object
   static volatile boost::uint32_t this_module_shm_initialized;
   static max_align shm_mem[MemSize];
};

template<class ManagedShMem>
volatile boost::uint32_t intermodule_singleton_common<ManagedShMem>::this_module_singleton_count;

template<class ManagedShMem>
volatile boost::uint32_t intermodule_singleton_common<ManagedShMem>::this_module_shm_initialized;

template<class ManagedShMem>
max_align intermodule_singleton_common<ManagedShMem>::shm_mem[intermodule_singleton_common<ManagedShMem>::MemSize];

template<class ManagedShMem>
void intermodule_singleton_common<ManagedShMem>::initialize_shm()
{
   //Obtain unique shm name and size
   std::string s;
   intermodule_singleton_helpers::get_shm_name(s);
   const char *ShmName = s.c_str();
   const std::size_t ShmSize = intermodule_singleton_helpers::get_shm_size();;
   while(1){
      //Try to pass shm state to initializing
      ::boost::uint32_t tmp = atomic_cas32(&this_module_shm_initialized, Initializing, Uninitialized);
      if(tmp >= Initialized){
         break;
      }
      //If some other thread is doing the work wait
      else if(tmp == Initializing){
         thread_yield();
      }
      else{ //(tmp == Uninitialized)
         //If not initialized try it again?
         try{
            //Remove old shared memory from the system
            intermodule_singleton_helpers::managed_sh_dependant<ManagedShMem>::remove_old_gmem();
            //in-place construction of the shared memory class
            ::new (&get_shm())ManagedShMem(open_or_create, ShmName, ShmSize);
            //Use shared memory internal lock to initialize the lock file
            //that will mark this gmem as "in use".
            intermodule_singleton_helpers::lock_file_logic<ManagedShMem> f(get_shm());
            //If function failed (maybe a competing process has erased the shared
            //memory between creation and file locking), retry with a new instance.
            if(f.retry_with_new_shm){
               get_shm().~ManagedShMem();
               atomic_write32(&this_module_shm_initialized, Uninitialized);
            }
            else{
               //Locking succeeded, so this shared memory module-instance is ready
               atomic_write32(&this_module_shm_initialized, Initialized);
               break;
            }
         }
         catch(...){
            //
            throw;
         }
      }
   }
}

template<class ManagedShMem>
struct unlink_shmlogic
{
   unlink_shmlogic(ManagedShMem &mshm)
      : mshm_(mshm)
   {  mshm.atomic_func(*this);  }
   void operator()()
   {
      intermodule_singleton_helpers::locking_file_serial_id *pserial_id =
         mshm_.template find<intermodule_singleton_helpers::locking_file_serial_id>
            ("lock_file_fd").first;
      BOOST_ASSERT(0 != pserial_id);
      if(1 == atomic_dec32(&pserial_id->modules_attached_to_gmem_count)){
         int fd = pserial_id->fd;
         if(fd > 0){
            pserial_id->fd = intermodule_singleton_helpers::GMemMarkToBeRemoved;
            std::string s;
            intermodule_singleton_helpers::create_and_get_singleton_lock_file_path(s);
            delete_file(s.c_str());
            intermodule_singleton_helpers::close_lock_file(fd);
            intermodule_singleton_helpers::get_shm_name(s);
            shared_memory_object::remove(s.c_str());
         }
      }
   }
   ManagedShMem &mshm_;
};

#if defined (BOOST_INTERPROCESS_WINDOWS)

template<>
struct unlink_shmlogic<managed_windows_shared_memory>
{
   unlink_shmlogic(managed_windows_shared_memory &)
   {}
   void operator()(){}
};

#endif


template<class ManagedShMem>
void intermodule_singleton_common<ManagedShMem>::destroy_shm()
{
   if(!atomic_read32(&this_module_singleton_count)){
      //This module is being unloaded, so destroy
      //the shared memory object of this module
      //and unlink the shared memory if it's the last
      unlink_shmlogic<ManagedShMem> f(get_shm());
      (get_shm()).~ManagedShMem();
      atomic_write32(&this_module_shm_initialized, Uninitialized);
      //Do some cleanup for other processes old gmem instances
      intermodule_singleton_helpers::managed_sh_dependant<ManagedShMem>::remove_old_gmem();
   }
}

//Initialize this_module_singleton_ptr, creates the shared memory if needed and also creates an unique
//opaque type in shared memory through a singleton_constructor_t function call,
//initializing the passed pointer to that unique instance.
//
//We have two concurrency types here. a)the shared memory/singleton creation must
//be safe between threads of this process but in different modules/dlls. b)
//the pointer to the singleton is per-module, so we have to protect this
//initization between threads of the same module.
//
//All static variables declared here are shared between inside a module
//so atomic operations will synchronize only threads of the same module.
template<class ManagedShMem>
void intermodule_singleton_common<ManagedShMem>::initialize_singleton_logic
   (void *&ptr, volatile boost::uint32_t &this_module_singleton_initialized, singleton_constructor_t constructor)
{
   //If current module is not initialized enter to lock free logic
   if(atomic_read32(&this_module_singleton_initialized) != Initialized){
      //Now a single thread of the module will succeed in this CAS.
      //trying to pass from Uninitialized to Initializing
      ::boost::uint32_t previous_module_singleton_initialized = atomic_cas32
         (&this_module_singleton_initialized, Initializing, Uninitialized);
      //If the thread succeeded the CAS (winner) it will compete with other 
      //winner threads from other modules to create the shared memory
      if(previous_module_singleton_initialized == Uninitialized){
         try{
            //Now initialize shm, this function solves concurrency issues
            //between threads of several modules
            initialize_shm();
            //Increment the module reference count that reflects how many
            //singletons this module holds, so that we can safely destroy
            //module shared memory object when no singleton is left
            atomic_inc32(&this_module_singleton_count);
            //Now try to create the singleton in shared memory.
            //This function solves concurrency issues
            //between threads of several modules
            void *tmp = constructor(get_shm());
            //Insert a barrier before assigning the pointer to
            //make sure this assignment comes after the initialization
            atomic_write32(&this_module_singleton_initialized, Initializing);
            //Assign the singleton address to the module-local pointer
            ptr = tmp;
            //Memory barrier inserted, all previous operations should complete
            //before this one. Now marked as initialized
            atomic_inc32(&this_module_singleton_initialized);
         }
         catch(...){
            //Mark singleton failed to initialize
            atomic_write32(&this_module_singleton_initialized, Broken);
            throw;
         }
      }
      //If previous state was initializing, this means that another winner thread is
      //trying to initialize the singleton. Just wait until completes its work.
      else if(previous_module_singleton_initialized == Initializing){
         while(1){
            previous_module_singleton_initialized = atomic_read32(&this_module_singleton_initialized);
            if(previous_module_singleton_initialized >= Initialized){
               //Already initialized, or exception thrown by initializer thread
               break;
            }
            else if(previous_module_singleton_initialized == Initializing){
               detail::thread_yield();
            }
            else{
               //This can't be happening!
               BOOST_ASSERT(0);
            }
         }
      }
      else if(previous_module_singleton_initialized == Initialized){
         //Nothing to do here, the singleton is ready
      }
      //If previous state was greater than initialized, then memory is broken
      //trying to initialize the singleton.
      else{//(previous_module_singleton_initialized > Initialized)
         throw interprocess_exception("boost::interprocess::intermodule_singleton initialization failed");
      }
   }
   BOOST_ASSERT(ptr != 0);
}

//Now this class is a singleton, initializing the singleton in
//the first get() function call if LazyInit is false. If true
//then the singleton will be initialized when loading the module.
template<typename C, bool LazyInit, class ManagedShMem>
class intermodule_singleton_impl
{
   public:
   static C& get()   //Let's make inlining easy
   {
      if(!this_module_singleton_ptr){
         if(lifetime.dummy_function())  //This forces lifetime instantiation, for reference counted destruction
            intermodule_singleton_common<ManagedShMem>::initialize_singleton_logic
               (this_module_singleton_ptr, this_module_singleton_initialized, singleton_constructor);
      }
      return *static_cast<C*>(this_module_singleton_ptr);
   }

   private:

   struct ref_count_ptr
   {
      ref_count_ptr(C *p, boost::uint32_t count)
         : ptr(p), singleton_ref_count(count)
      {}
      C *ptr;
      //This reference count serves to count the number of attached
      //modules to this singleton
      volatile boost::uint32_t singleton_ref_count;
   };

   //These statics will be zero-initialized without any constructor call dependency
   //this_module_singleton_ptr will be a module-local pointer to the singleton
   static void*                      this_module_singleton_ptr;
   //this_module_singleton_count will be used to synchronize threads of the same module
   //for access to a singleton instance, and to flag the state of the
   //singleton.
   static volatile boost::uint32_t   this_module_singleton_initialized;

   //This class destructor will trigger singleton destruction
   struct lifetime_type_lazy
   {
      bool dummy_function()
      {  return m_dummy == 0; }

      ~lifetime_type_lazy()
      {
         intermodule_singleton_common<ManagedShMem>::finalize_singleton_logic
            (this_module_singleton_ptr, singleton_destructor);
      }
      //Dummy volatile so that the compiler can't resolve its value at compile-time
      //and can't avoid lifetime_type instantiation if dummy_function() is called.
      static volatile int m_dummy;
   };

   struct lifetime_type_static
      : public lifetime_type_lazy
   {
      lifetime_type_static()
      {
         intermodule_singleton_common<ManagedShMem>::initialize_singleton_logic
            (this_module_singleton_ptr, this_module_singleton_initialized, singleton_constructor);
      }
   };

   typedef typename if_c
      <LazyInit, lifetime_type_lazy, lifetime_type_static>::type lifetime_type;

   static lifetime_type lifetime;

   //A functor to be executed inside shared memory lock that just
   //searches for the singleton in shm and if not present creates a new one.
   //If singleton constructor throws, the exception is propagated
   struct init_atomic_func
   {
      init_atomic_func(ManagedShMem &m)
         : mshm(m)
      {}

      void operator()()
      {
         ref_count_ptr *rcount = mshm.template find<ref_count_ptr>(unique_instance).first;
         if(!rcount){
            C *p = new C();
            try{
               rcount = mshm.template construct<ref_count_ptr>(unique_instance)(p, 0u);
            }
            catch(...){
               delete p;
               throw;
            }
         }
         atomic_inc32(&rcount->singleton_ref_count);
         ret_ptr = rcount->ptr;
      }
      ManagedShMem &mshm;
      void *ret_ptr;
   };

   //A functor to be executed inside shared memory lock that just
   //deletes the singleton in shm if the attached count reaches to zero
   struct fini_atomic_func
   {
      fini_atomic_func(ManagedShMem &m)
         : mshm(m)
      {}

      void operator()()
      {
         ref_count_ptr *rcount = mshm.template find<ref_count_ptr>(unique_instance).first;
            //The object must exist
         BOOST_ASSERT(rcount);
         //Check if last reference
         if(atomic_dec32(&rcount->singleton_ref_count) == 1){
            //If last, destroy the object
            BOOST_ASSERT(rcount->ptr != 0);
            delete rcount->ptr;
            //Now destroy shm entry
            bool destroyed = mshm.template destroy<ref_count_ptr>(unique_instance);
            (void)destroyed;  BOOST_ASSERT(destroyed == true);
         }
      }
      ManagedShMem &mshm;
      void *ret_ptr;
   };

   //A wrapper to execute init_atomic_func
   static void *singleton_constructor(ManagedShMem &mshm)
   {
      init_atomic_func f(mshm);
      mshm.atomic_func(f);
      return f.ret_ptr;
   }

   //A wrapper to execute fini_atomic_func
   static void singleton_destructor(void *p, ManagedShMem &mshm)
   {  (void)p;
      fini_atomic_func f(mshm);
      mshm.atomic_func(f);
   }
};

template <typename C, bool L, class ManagedShMem>
volatile int intermodule_singleton_impl<C, L, ManagedShMem>::lifetime_type_lazy::m_dummy;

//These will be zero-initialized by the loader
template <typename C, bool L, class ManagedShMem>
void *intermodule_singleton_impl<C, L, ManagedShMem>::this_module_singleton_ptr;

template <typename C, bool L, class ManagedShMem>
volatile boost::uint32_t intermodule_singleton_impl<C, L, ManagedShMem>::this_module_singleton_initialized;

template <typename C, bool L, class ManagedShMem>
typename intermodule_singleton_impl<C, L, ManagedShMem>::lifetime_type
   intermodule_singleton_impl<C, L, ManagedShMem>::lifetime;

template<typename C, bool LazyInit = false>
class portable_intermodule_singleton
   : public intermodule_singleton_impl<C, LazyInit, managed_shared_memory>
{};

#ifdef BOOST_INTERPROCESS_WINDOWS

template<typename C, bool LazyInit = false>
class windows_intermodule_singleton
   : public intermodule_singleton_impl<C, LazyInit, managed_windows_shared_memory>
{};

#endif

//Now this class is a singleton, initializing the singleton in
//the first get() function call if LazyInit is false. If true
//then the singleton will be initialized when loading the module.
template<typename C, bool LazyInit = false>
class intermodule_singleton
   #ifdef BOOST_INTERPROCESS_WINDOWS
   : public windows_intermodule_singleton<C, LazyInit>
//   : public portable_intermodule_singleton<C, LazyInit>
   #else
   : public portable_intermodule_singleton<C, LazyInit>
   #endif
{};


}  //namespace detail{
}  //namespace interprocess{
}  //namespace boost{

#include <boost/interprocess/detail/config_end.hpp>

#endif