doc_managed_allocation_command.cpp

来自「Boost provides free peer-reviewed portab」· C++ 代码 · 共 90 行

//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2006-2007. 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.
//
//////////////////////////////////////////////////////////////////////////////
#include <boost/interprocess/detail/config_begin.hpp>
//[doc_managed_allocation_command
#include <boost/interprocess/managed_shared_memory.hpp>
#include <cassert>

int main()
{
   using namespace boost::interprocess;

   //Managed memory segment that allocates portions of a shared memory
   //segment with the default management algorithm
   shared_memory_object::remove("MyManagedShm");

   try{
      managed_shared_memory managed_shm(create_only, "MyManagedShm", 10000*sizeof(std::size_t));

      //Allocate at least 100 bytes, 1000 bytes if possible
      std::size_t received_size, min_size = 100, preferred_size = 1000;
      std::size_t *ptr = managed_shm.allocation_command<std::size_t>
         (allocate_new, min_size, preferred_size, received_size).first;

      //Received size must be bigger than min_size
      assert(received_size >= min_size);

      //Get free memory
      std::size_t free_memory_after_allocation = managed_shm.get_free_memory();

      //Now write the data
      for(std::size_t i = 0; i < received_size; ++i) ptr[i] = i;

      //Now try to triplicate the buffer. We won't admit an expansion
      //lower to the double of the original buffer.
      //This "should" be successful since no other class is allocating
      //memory from the segment
      std::size_t expanded_size;
      std::pair<std::size_t *, bool> ret = managed_shm.allocation_command
         (expand_fwd, received_size*2, received_size*3, expanded_size, ptr);

      //Check invariants
      assert(ret.second == true);
      assert(ret.first == ptr);
      assert(expanded_size >= received_size*2);

      //Get free memory and compare
      std::size_t free_memory_after_expansion = managed_shm.get_free_memory();
      assert(free_memory_after_expansion < free_memory_after_allocation);

      //Write new values
      for(std::size_t i = received_size; i < expanded_size; ++i)  ptr[i] = i;

      //Try to shrink approximately to min_size, but the new size
      //should be smaller than min_size*2.
      //This "should" be successful since no other class is allocating
      //memory from the segment
      std::size_t shrunk_size;
      ret = managed_shm.allocation_command
         (shrink_in_place, min_size*2, min_size, shrunk_size, ptr);

      //Check invariants
      assert(ret.second == true);
      assert(ret.first == ptr);
      assert(shrunk_size <= min_size*2);
      assert(shrunk_size >= min_size);

      //Get free memory and compare
      std::size_t free_memory_after_shrinking = managed_shm.get_free_memory();
      assert(free_memory_after_shrinking > free_memory_after_expansion);

      //Deallocate the buffer
      managed_shm.deallocate(ptr);
   }
   catch(...){
      shared_memory_object::remove("MyManagedShm");
      throw;
   }
   shared_memory_object::remove("MyManagedShm");
   return 0;
}
//]
#include <boost/interprocess/detail/config_end.hpp>