TAO/tao/MMAP_Allocator.cpp

   1 #include "tao/MMAP_Allocator.h"
   2
   3 #if TAO_HAS_SENDFILE == 1
   4
   5 #include "ace/Mem_Map.h"
   6 #include "ace/Default_Constants.h"
   7
   8
   9 TAO_BEGIN_VERSIONED_NAMESPACE_DECL
  10
  11 namespace
  12 {
  13   // Default size mmap()ed memory pool will be the sum of the control
  14   // block size and the default CDR buffer chosen by the user.  The
  15   // final size may be rounded up by the allocator to be aligned on
  16   // the appropriate boundary/page.
  17   //
  18   // @@ This type really should be ACE_LOFF_T but ACE's mmap()-based
  19   //    classes currently do not handle large file offsets.
  20   //        -Ossama
  21   off_t const the_default_buf_size =
  22     sizeof (ACE_Control_Block) + ACE_DEFAULT_CDR_BUFSIZE;
  23
  24   ACE_MMAP_Memory_Pool_Options const the_pool_options (
  25     ACE_DEFAULT_BASE_ADDR,
  26     ACE_MMAP_Memory_Pool_Options::ALWAYS_FIXED,
  27     0, // No need to sync
  28     the_default_buf_size,
  29     MAP_SHARED, // Written data must be reflected in the backing store
  30                 // file in order for sendfile() to be able to read it.
  31     1,
  32     0,
  33     /* 0 */ ACE_DEFAULT_FILE_PERMS,
  34     true); // Generate for each mmap an unqiue pool
  35 }
  36
  37
  38 // Ideally we should open the backing store with shm_open() so that we
  39 // can avoid creating an on-disk backing store.  An on-disk backing
  40 // store could potentially cause sendfile() to block on disk I/O,
  41 // which is undesirable.  Unfortunately, ACE_Mem_Map currently
  42 // provides no way to configure which "open" function to use,
  43 // i.e. open(2) or shm_open(3).  Alternatively we could shm_open() the
  44 // backing store file beforehand.  Unfortunately,
  45 // ACE_{Lite_}MMAP_Memory_Pool currently doesn't provide a means to
  46 // pass the file descriptor for the desired backing store to the
  47 // underlying ACE_Mem_Map object.
  48 //
  49 // It may be tempting to mmap() /dev/zero.  That would certainly
  50 // provide the desired transient "scratch space" memory that we can
  51 // write and read to and from, respectively.  Unfortunately, the data
  52 // in /dev/zero-based memory mapped buffer can only be read through
  53 // the buffer itself, not through the file descriptor (e.g. using
  54 // read(2)) for the open()ed /dev/zero device.  Reading through the
  55 // /dev/zero file descriptor simply returns zero, as /dev/zero was
  56 // designed to do.  So unfortunate. :)
  57 TAO_MMAP_Allocator::TAO_MMAP_Allocator ()
  58   : TAO_MMAP_Allocator_Base ((char const *) nullptr /* pool name */,
  59                              nullptr,  // No need to explicitly name the lock.
  60                              &the_pool_options)
  61 {
  62 }
  63
  64 TAO_MMAP_Allocator::~TAO_MMAP_Allocator ()
  65 {
  66 }
  67
  68 // @@ Should be const but underlying allocator methods are not!
  69 ACE_HANDLE
  70 TAO_MMAP_Allocator::handle ()
  71 {
  72   return this->alloc ().memory_pool ().mmap ().handle ();
  73 }
  74
  75 // @@ Should be const but underlying allocator methods are not!
  76 off_t
  77 TAO_MMAP_Allocator::offset (void * p)
  78 {
  79   ACE_Mem_Map const & m = this->alloc ().memory_pool ().mmap ();
  80
  81   ptrdiff_t const off  = reinterpret_cast<ptrdiff_t> (p);
  82   ptrdiff_t const base = reinterpret_cast<ptrdiff_t> (m.addr ());
  83   ptrdiff_t const end  = base + m.size ();
  84
  85   // Check if p is in the range of the mmap pool, if not we return -1
  86   if (off < base || off > end)
  87     return -1;
  88
  89   off_t const the_offset = static_cast<off_t> (off - base);
  90
  91   return (the_offset < 0 ? static_cast<off_t> (-1) : the_offset);
  92 }
  93
  94 TAO_END_VERSIONED_NAMESPACE_DECL
  95
  96 #endif  /* TAO_HAS_SENDFILE==1 */