ceph/src/boost/libs/interprocess/example/doc_managed_aligned_allocation.cpp

   1 //////////////////////////////////////////////////////////////////////////////
   2 //
   3 // (C) Copyright Ion Gaztanaga 2006-2012. Distributed under the Boost
   4 // Software License, Version 1.0. (See accompanying file
   5 // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 //
   7 // See http://www.boost.org/libs/interprocess for documentation.
   8 //
   9 //////////////////////////////////////////////////////////////////////////////
  10 //[doc_managed_aligned_allocation
  11 #include <boost/interprocess/managed_shared_memory.hpp>
  12 #include <cassert>
  13 //<-
  14 #include "../test/get_process_id_name.hpp"
  15 //->
  16
  17 int main()
  18 {
  19    using namespace boost::interprocess;
  20
  21    //Remove shared memory on construction and destruction
  22    struct shm_remove
  23    {
  24    //<-
  25    #if 1
  26       shm_remove() { shared_memory_object::remove(test::get_process_id_name()); }
  27       ~shm_remove(){ shared_memory_object::remove(test::get_process_id_name()); }
  28    #else
  29    //->
  30       shm_remove() { shared_memory_object::remove("MySharedMemory"); }
  31       ~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }
  32    //<-
  33    #endif
  34    //->
  35    } remover;
  36    //<-
  37    (void)remover;
  38    //->
  39
  40    //Managed memory segment that allocates portions of a shared memory
  41    //segment with the default management algorithm
  42    //<-
  43    #if 1
  44    managed_shared_memory managed_shm(create_only, test::get_process_id_name(), 65536);
  45    #else
  46    //->
  47    managed_shared_memory managed_shm(create_only, "MySharedMemory", 65536);
  48    //<-
  49    #endif
  50    //->
  51
  52    const std::size_t Alignment = 128;
  53
  54    //Allocate 100 bytes aligned to Alignment from segment, throwing version
  55    void *ptr = managed_shm.allocate_aligned(100, Alignment);
  56
  57    //Check alignment
  58    assert(std::size_t(static_cast<char*>(ptr)-static_cast<char*>(0)) % Alignment == 0);
  59
  60    //Deallocate it
  61    managed_shm.deallocate(ptr);
  62
  63    //Non throwing version
  64    ptr = managed_shm.allocate_aligned(100, Alignment, std::nothrow);
  65
  66    //Check alignment
  67    assert(std::size_t(static_cast<char*>(ptr)-static_cast<char*>(0)) % Alignment == 0);
  68
  69    //Deallocate it
  70    managed_shm.deallocate(ptr);
  71
  72    //If we want to efficiently allocate aligned blocks of memory
  73    //use managed_shared_memory::PayloadPerAllocation value
  74    assert(Alignment > managed_shared_memory::PayloadPerAllocation);
  75
  76    //This allocation will maximize the size of the aligned memory
  77    //and will increase the possibility of finding more aligned memory
  78    ptr = managed_shm.allocate_aligned
  79       (3u*Alignment - managed_shared_memory::PayloadPerAllocation, Alignment);
  80
  81    //Check alignment
  82    assert(std::size_t(static_cast<char*>(ptr)-static_cast<char*>(0)) % Alignment == 0);
  83
  84    //Deallocate it
  85    managed_shm.deallocate(ptr);
  86
  87    return 0;
  88 }
  89 //]
  90