306 lines
9.3 KiB
Plaintext
306 lines
9.3 KiB
Plaintext
[/
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/ Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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/
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/ Distributed under the Boost Software License, Version 1.0. (See accompanying
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/ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:implementation Platform-Specific Implementation Notes]
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This section lists platform-specific implementation details, such as the
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default demultiplexing mechanism, the number of threads created internally, and
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when threads are created.
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[heading Linux Kernel 2.4]
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Demultiplexing mechanism:
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* Uses `select` for demultiplexing. This means that the number of file
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descriptors in the process cannot be permitted to exceed `FD_SETSIZE`.
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Threads:
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* Demultiplexing using `select` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading Linux Kernel 2.6]
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Demultiplexing mechanism:
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* Uses `epoll` for demultiplexing.
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Threads:
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* Demultiplexing using `epoll` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading Solaris]
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Demultiplexing mechanism:
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* Uses [^/dev/poll] for demultiplexing.
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Threads:
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* Demultiplexing using [^/dev/poll] is performed in one of the threads that
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calls `io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading QNX Neutrino]
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Demultiplexing mechanism:
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* Uses `select` for demultiplexing. This means that the number of file
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descriptors in the process cannot be permitted to exceed `FD_SETSIZE`.
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Threads:
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* Demultiplexing using `select` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading Mac OS X]
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Demultiplexing mechanism:
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* Uses `kqueue` for demultiplexing.
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Threads:
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* Demultiplexing using `kqueue` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading FreeBSD]
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Demultiplexing mechanism:
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* Uses `kqueue` for demultiplexing.
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Threads:
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* Demultiplexing using `kqueue` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading AIX]
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Demultiplexing mechanism:
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* Uses `select` for demultiplexing. This means that the number of file
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descriptors in the process cannot be permitted to exceed `FD_SETSIZE`.
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Threads:
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* Demultiplexing using `select` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading HP-UX]
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Demultiplexing mechanism:
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* Uses `select` for demultiplexing. This means that the number of file
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descriptors in the process cannot be permitted to exceed `FD_SETSIZE`.
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Threads:
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* Demultiplexing using `select` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading Tru64]
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Demultiplexing mechanism:
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* Uses `select` for demultiplexing. This means that the number of file
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descriptors in the process cannot be permitted to exceed `FD_SETSIZE`.
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Threads:
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* Demultiplexing using `select` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* At most `min(64,IOV_MAX)` buffers may be transferred in a single operation.
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[heading Windows 95, 98 and Me]
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Demultiplexing mechanism:
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* Uses `select` for demultiplexing.
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Threads:
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* Demultiplexing using `select` is performed in one of the threads that calls
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* For sockets, at most 16 buffers may be transferred in a single operation.
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[heading Windows NT, 2000, XP, 2003, Vista, 7 and 8]
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Demultiplexing mechanism:
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* Uses overlapped I/O and I/O completion ports for all asynchronous socket
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operations except for asynchronous connect.
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* Uses `select` for emulating asynchronous connect.
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Threads:
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* Demultiplexing using I/O completion ports is performed in all threads that call
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`io_context::run()`, `io_context::run_one()`, `io_context::poll()` or
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`io_context::poll_one()`.
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* An additional thread per `io_context` is used to trigger timers. This thread
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is created on construction of the first `basic_deadline_timer` or
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`basic_waitable_timer` objects.
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* An additional thread per `io_context` is used for the `select`
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demultiplexing. This thread is created on the first call to `async_connect()`.
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* An additional thread per `io_context` is used to emulate asynchronous host
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resolution. This thread is created on the first call to either
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`ip::tcp::resolver::async_resolve()` or `ip::udp::resolver::async_resolve()`.
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Scatter-Gather:
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* For sockets, at most 64 buffers may be transferred in a single operation.
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* For stream-oriented handles, only one buffer may be transferred in a single
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operation.
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[heading Windows Runtime]
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Boost.Asio provides limited support for the Windows Runtime. It requires that the
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language extensions be enabled. Due to the restricted facilities exposed by the
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Windows Runtime API, the support comes with the following caveats:
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* The core facilities such as the `io_context`, `strand`, buffers, composed
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operations, timers, etc., should all work as normal.
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* For sockets, only client-side TCP is supported.
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* Explicit binding of a client-side TCP socket is not supported.
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* The `cancel()` function is not supported for sockets. Asynchronous
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operations may only be cancelled by closing the socket.
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* Operations that use `null_buffers` are not supported.
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* Only `tcp::no_delay` and `socket_base::keep_alive` options are supported.
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* Resolvers do not support service names, only numbers. I.e. you must
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use "80" rather than "http".
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* Most resolver query flags have no effect.
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Demultiplexing mechanism:
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* Uses the `Windows::Networking::Sockets::StreamSocket` class to implement
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asynchronous TCP socket operations.
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Threads:
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* Event completions are delivered to the Windows thread pool and posted to the
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`io_context` for the handler to be executed.
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* An additional thread per `io_context` is used to trigger timers. This thread
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is created on construction of the first timer objects.
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Scatter-Gather:
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* For sockets, at most one buffer may be transferred in a single operation.
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[endsect]
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