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This section lists platform-specific implementation details, such as the default demultiplexing mechanism, the number of threads created internally, and when threads are created.
Demultiplexing mechanism:
select for demultiplexing. This means that the number
of file descriptors in the process cannot be permitted to exceed FD_SETSIZE.
Threads:
select is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
epoll for demultiplexing.
Threads:
epoll is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
/dev/poll for demultiplexing.
Threads:
/dev/poll is performed in one
of the threads that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
select for demultiplexing. This means that the number
of file descriptors in the process cannot be permitted to exceed FD_SETSIZE.
Threads:
select is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
kqueue for demultiplexing.
Threads:
kqueue is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
kqueue for demultiplexing.
Threads:
kqueue is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
select for demultiplexing. This means that the number
of file descriptors in the process cannot be permitted to exceed FD_SETSIZE.
Threads:
select is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
select for demultiplexing. This means that the number
of file descriptors in the process cannot be permitted to exceed FD_SETSIZE.
Threads:
select is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
select for demultiplexing. This means that the number
of file descriptors in the process cannot be permitted to exceed FD_SETSIZE.
Threads:
select is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
min(64,IOV_MAX) buffers may be transferred in a
single operation.
Demultiplexing mechanism:
select for demultiplexing.
Threads:
select is performed in one of the threads
that calls io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
Demultiplexing mechanism:
select for emulating asynchronous connect.
Threads:
io_context::run(), io_context::run_one(),
io_context::poll() or io_context::poll_one().
io_context is used to trigger timers.
This thread is created on construction of the first basic_deadline_timer
or basic_waitable_timer objects.
io_context may be used for select
demultiplexing. This thread is created on the first call to:
async_wait() function, except when using
wait_read on a stream-oriented socket. (For wait_read
on a stream-oriented socket, the overlapped I/O operation WSARecv
is used and no additional thread is required.)
async_connect() operation, if the overlapped
I/O operation ConnectEx is unavailable. (On recent
versions of Windows, ConnectEx is used and no additional
thread is required.)
io_context is used to emulate asynchronous
host resolution. This thread is created on the first call to either
ip::tcp::resolver::async_resolve() or ip::udp::resolver::async_resolve().
Scatter-Gather:
Asio provides limited support for the Windows Runtime. It requires that the language extensions be enabled. Due to the restricted facilities exposed by the Windows Runtime API, the support comes with the following caveats:
io_context, strand,
buffers, composed operations, timers, etc., should all work as normal.
cancel() function is not supported for sockets. Asynchronous
operations may only be cancelled by closing the socket.
null_buffers are not supported.
tcp::no_delay and socket_base::keep_alive
options are supported.
Demultiplexing mechanism:
Windows::Networking::Sockets::StreamSocket class
to implement asynchronous TCP socket operations.
Threads:
io_context for the handler to be executed.
io_context is used to trigger timers.
This thread is created on construction of the first timer objects.
Scatter-Gather: