ceph/src/boost/libs/asio/doc/requirements/AsyncRandomAccessReadDevice.qbk

   1 [/
   2  / Copyright (c) 2003-2016 Christopher M. Kohlhoff (chris at kohlhoff dot com)
   3  /
   4  / Distributed under the Boost Software License, Version 1.0. (See accompanying
   5  / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6  /]
   7
   8 [section:AsyncRandomAccessReadDevice Buffer-oriented asynchronous random-access
   9 read device requirements]
  10
  11 In the table below, `a` denotes an asynchronous random access read device
  12 object, `o` denotes an offset of type `boost::uint64_t`, `mb` denotes an object
  13 satisfying [link boost_asio.reference.MutableBufferSequence mutable buffer sequence]
  14 requirements, and `h` denotes an object satisfying [link
  15 boost_asio.reference.ReadHandler read handler] requirements.
  16
  17 [table Buffer-oriented asynchronous random-access read device requirements
  18   [[operation] [type] [semantics, pre/post-conditions]]
  19   [
  20     [`a.get_io_service();`]
  21     [`io_service&`]
  22     [Returns the `io_service` object through which the `async_read_some_at`
  23     handler `h` will be invoked.]
  24   ]
  25   [
  26     [`a.async_read_some_at(o, mb, h);`]
  27     [`void`]
  28     [
  29       Initiates an asynchronous operation to read one or more bytes of data
  30       from the device `a` at the offset `o`. The operation is performed via the
  31       `io_service` object `a.get_io_service()` and behaves according to [link
  32       boost_asio.reference.asynchronous_operations asynchronous operation]
  33       requirements.\n
  34       \n
  35       The mutable buffer sequence `mb` specifies memory where the data should
  36       be placed. The `async_read_some_at` operation shall always fill a buffer
  37       in the sequence completely before proceeding to the next.\n
  38       \n
  39       The implementation shall maintain one or more copies of `mb` until such
  40       time as the read operation no longer requires access to the memory
  41       specified by the buffers in the sequence. The program must ensure the
  42       memory is valid until:\n
  43       \n
  44       [mdash] the last copy of `mb` is destroyed, or\n
  45       \n
  46       [mdash] the handler for the asynchronous read operation is invoked,\n
  47       \n
  48       whichever comes first.\n
  49       \n
  50       If the total size of all buffers in the sequence `mb` is `0`, the
  51       asynchronous read operation shall complete immediately and pass `0` as
  52       the argument to the handler that specifies the number of bytes read.
  53     ]
  54   ]
  55 ]
  56
  57 [endsect]