llfio_v2_xxx::byte_socket_handle Class Reference

A handle to a byte-orientated socket-like entity. More...

#include "byte_socket_handle.hpp"

Inheritance diagram for llfio_v2_xxx::byte_socket_handle:

Public Types
enum	shutdown_kind { shutdown_read , shutdown_write , shutdown_both }
	The channels which can be shut down. More...
using	path_type = byte_io_handle::path_type
using	extent_type = byte_io_handle::extent_type
using	size_type = byte_io_handle::size_type
using	mode = byte_io_handle::mode
using	creation = byte_io_handle::creation
using	caching = byte_io_handle::caching
using	flag = byte_io_handle::flag
using	buffer_type = byte_io_handle::buffer_type
using	const_buffer_type = byte_io_handle::const_buffer_type
using	buffers_type = byte_io_handle::buffers_type
using	const_buffers_type = byte_io_handle::const_buffers_type
template<class T >
using	io_request = byte_io_handle::io_request< T >
template<class T >
using	io_result = byte_io_handle::io_result< T >
using	barrier_kind = byte_io_multiplexer::barrier_kind
using	registered_buffer_type = byte_io_multiplexer::registered_buffer_type
template<class T >
using	awaitable = byte_io_multiplexer::awaitable< T >

Public Member Functions
virtual void	_deleter ()
constexpr	byte_socket_handle ()
	Default constructor.
constexpr	byte_socket_handle (native_handle_type h, flag flags, byte_io_multiplexer *ctx)
	Construct a handle from a supplied native handle.
	byte_socket_handle (const byte_socket_handle &)=delete
	No copy construction (use clone())
byte_socket_handle &	operator= (const byte_socket_handle &)=delete
	No copy assignment.
constexpr	byte_socket_handle (byte_socket_handle &&o) noexcept
	Implicit move construction of byte_socket_handle permitted.
constexpr	byte_socket_handle (handle &&o, byte_io_multiplexer *ctx) noexcept
	Explicit conversion from handle permitted.
constexpr	byte_socket_handle (byte_io_handle &&o) noexcept
	Explicit conversion from byte_io_handle permitted.
byte_socket_handle &	operator= (byte_socket_handle &&o) noexcept
	Move assignment of byte_socket_handle permitted.
void	swap (byte_socket_handle &o) noexcept
	Swap with another instance.
ip::family	family () const noexcept
	Returns the IP family of this socket instance.
virtual result< ip::address >	local_endpoint () const noexcept
	Returns the local endpoint of this socket instance.
virtual result< ip::address >	remote_endpoint () const noexcept
	Returns the remote endpoint of this socket instance.
virtual result< void >	shutdown (shutdown_kind=shutdown_write) noexcept
	Initiates shutting down further communication on the socket. More...
result< void >	connect (const ip::address &addr, deadline d={}) noexcept
	Connects to an address. More...
awaitable< io_result< void > >	co_connect (const ip::address &addr, deadline d={}) noexcept
	A coroutinised equivalent to .connect() which suspends the coroutine until a connection occurs. Blocks execution i.e is equivalent to .connect() if no i/o multiplexer has been set on this handle! More...
virtual result< void >	close () noexcept override
	Immediately close the native handle type managed by this handle.
result< void >	shutdown_and_close (deadline d={}) noexcept
	Convenience function to shut down the outbound connection and wait for the other side to shut down our inbound connection by throwing away any bytes read, then closing the socket. Note that if the deadline passes and we are still reading data, the socket is forced closed.
io_result< size_type >	read (std::initializer_list< buffer_type > lst, deadline d=deadline()) noexcept
io_result< size_type >	write (std::initializer_list< const_buffer_type > lst, deadline d=deadline()) noexcept
awaitable< io_result< buffers_type > >	co_read (io_request< buffers_type > reqs, deadline d=deadline()) noexcept
	A coroutinised equivalent to .read() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .read() if no i/o multiplexer has been set on this handle! More...
awaitable< io_result< buffers_type > >	co_read (registered_buffer_type base, io_request< buffers_type > reqs, deadline d=deadline()) noexcept
awaitable< io_result< const_buffers_type > >	co_write (io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
	A coroutinised equivalent to .write() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .write() if no i/o multiplexer has been set on this handle! More...
awaitable< io_result< const_buffers_type > >	co_write (registered_buffer_type base, io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
io_result< buffers_type >	read (io_request< buffers_type > reqs, deadline d=deadline()) noexcept
	Read data from the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation. More...
io_result< buffers_type >	read (registered_buffer_type base, io_request< buffers_type > reqs, deadline d=deadline()) noexcept
io_result< size_type >	read (extent_type offset, std::initializer_list< buffer_type > lst, deadline d=deadline()) noexcept
io_result< const_buffers_type >	write (io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
	Write data to the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation. More...
io_result< const_buffers_type >	write (registered_buffer_type base, io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
io_result< size_type >	write (extent_type offset, std::initializer_list< const_buffer_type > lst, deadline d=deadline()) noexcept
byte_io_multiplexer *	multiplexer () const noexcept
	The i/o multiplexer this handle will use to multiplex i/o. If this returns null, then this handle has not been registered with an i/o multiplexer yet.
virtual result< void >	set_multiplexer (byte_io_multiplexer *c=this_thread::multiplexer()) noexcept
	Sets the i/o multiplexer this handle will use to implement read(), write() and barrier(). More...
size_t	max_buffers () const noexcept
	The maximum number of buffers which a single read or write syscall can (atomically) process at a time for this specific open handle. On POSIX, this is known as IOV_MAX. Preferentially uses any i/o multiplexer set over the virtually overridable per-class implementation. More...
result< registered_buffer_type >	allocate_registered_buffer (size_t &bytes) noexcept
	Request the allocation of a new registered i/o buffer with the system suitable for maximum performance i/o, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation. More...
io_result< buffers_type >	read (io_request< buffers_type > reqs, deadline d=deadline()) noexcept
	Read data from the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation. More...
io_result< buffers_type >	read (registered_buffer_type base, io_request< buffers_type > reqs, deadline d=deadline()) noexcept
io_result< size_type >	read (extent_type offset, std::initializer_list< buffer_type > lst, deadline d=deadline()) noexcept
template<class... Args>
bool	try_read (Args &&... args) noexcept
template<class... Args, class Rep , class Period >
bool	try_read_for (Args &&... args, const std::chrono::duration< Rep, Period > &duration) noexcept
template<class... Args, class Clock , class Duration >
bool	try_read_until (Args &&... args, const std::chrono::time_point< Clock, Duration > &timeout) noexcept
io_result< const_buffers_type >	write (io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
	Write data to the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation. More...
io_result< const_buffers_type >	write (registered_buffer_type base, io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
io_result< size_type >	write (extent_type offset, std::initializer_list< const_buffer_type > lst, deadline d=deadline()) noexcept
template<class... Args>
bool	try_write (Args &&... args) noexcept
template<class... Args, class Rep , class Period >
bool	try_write_for (Args &&... args, const std::chrono::duration< Rep, Period > &duration) noexcept
template<class... Args, class Clock , class Duration >
bool	try_write_until (Args &&... args, const std::chrono::time_point< Clock, Duration > &timeout) noexcept
virtual io_result< const_buffers_type >	barrier (io_request< const_buffers_type > reqs=io_request< const_buffers_type >(), barrier_kind kind=barrier_kind::nowait_data_only, deadline d=deadline()) noexcept
	Issue a write reordering barrier such that writes preceding the barrier will reach storage before writes after this barrier, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation. More...
io_result< const_buffers_type >	barrier (barrier_kind kind, deadline d=deadline()) noexcept
template<class... Args>
bool	try_barrier (Args &&... args) noexcept
template<class... Args, class Rep , class Period >
bool	try_barrier_for (Args &&... args, const std::chrono::duration< Rep, Period > &duration) noexcept
template<class... Args, class Clock , class Duration >
bool	try_barrier_until (Args &&... args, const std::chrono::time_point< Clock, Duration > &timeout) noexcept
awaitable< io_result< buffers_type > >	co_read (io_request< buffers_type > reqs, deadline d=deadline()) noexcept
	A coroutinised equivalent to .read() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .read() if no i/o multiplexer has been set on this handle! More...
awaitable< io_result< buffers_type > >	co_read (registered_buffer_type base, io_request< buffers_type > reqs, deadline d=deadline()) noexcept
awaitable< io_result< const_buffers_type > >	co_write (io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
	A coroutinised equivalent to .write() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .write() if no i/o multiplexer has been set on this handle! More...
awaitable< io_result< const_buffers_type > >	co_write (registered_buffer_type base, io_request< const_buffers_type > reqs, deadline d=deadline()) noexcept
awaitable< io_result< const_buffers_type > >	co_barrier (io_request< const_buffers_type > reqs=io_request< const_buffers_type >(), barrier_kind kind=barrier_kind::nowait_data_only, deadline d=deadline()) noexcept
	A coroutinised equivalent to .barrier() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .barrier() if no i/o multiplexer has been set on this handle! More...
flag	flags () const noexcept
	The flags this handle was opened with.
	QUICKCPPLIB_BITFIELD_BEGIN_T (flag, uint16_t)
	Bitwise flags which can be specified. More...
void	swap (handle &o) noexcept
	Swap with another instance.
virtual result< path_type >	current_path () const noexcept
result< handle >	clone () const noexcept
virtual native_handle_type	release () noexcept
	Release the native handle type managed by this handle.
bool	is_valid () const noexcept
	True if the handle is valid (and usually open)
bool	is_readable () const noexcept
	True if the handle is readable.
bool	is_writable () const noexcept
	True if the handle is writable.
bool	is_append_only () const noexcept
	True if the handle is append only.
virtual result< void >	set_append_only (bool enable) noexcept
	EXTENSION: Changes whether this handle is append only or not. More...
bool	is_multiplexable () const noexcept
	True if multiplexable.
bool	is_nonblocking () const noexcept
	True if nonblocking.
bool	is_seekable () const noexcept
	True if seekable.
bool	requires_aligned_io () const noexcept
	True if requires aligned i/o.
bool	is_kernel_handle () const noexcept
	True if native_handle() is a valid kernel handle.
bool	is_regular () const noexcept
	True if a regular file or device.
bool	is_directory () const noexcept
	True if a directory.
bool	is_symlink () const noexcept
	True if a symlink.
bool	is_pipe () const noexcept
	True if a pipe.
bool	is_socket () const noexcept
	True if a socket.
bool	is_multiplexer () const noexcept
	True if a multiplexer like BSD kqueues, Linux epoll or Windows IOCP.
bool	is_process () const noexcept
	True if a process.
bool	is_section () const noexcept
	True if a memory section.
bool	is_allocation () const noexcept
	True if a memory allocation.
bool	is_path () const noexcept
	True if a path or a directory.
bool	is_tls_socket () const noexcept
	True if a TLS socket.
bool	is_http_socket () const noexcept
	True if a HTTP socket.
caching	kernel_caching () const noexcept
	Kernel cache strategy used by this handle.
bool	are_reads_from_cache () const noexcept
	True if the handle uses the kernel page cache for reads.
bool	are_writes_durable () const noexcept
	True if writes are safely on storage on completion.
bool	are_safety_barriers_issued () const noexcept
	True if issuing safety fsyncs is on.
native_handle_type	native_handle () const noexcept
	The native handle used by this handle.

Static Public Member Functions
static result< byte_socket_handle >	byte_socket (ip::family family, mode _mode=mode::write, caching _caching=caching::all, flag flags=flag::none) noexcept
static result< byte_socket_handle >	multiplexable_byte_socket (ip::family family, mode _mode=mode::write, caching _caching=caching::all, flag flags=flag::multiplexable) noexcept
	Convenience function defaulting flag::multiplexable set.

Protected Member Functions
virtual result< void >	_do_connect (const ip::address &addr, deadline d) noexcept
result< void >	_do_multiplexer_connect (const ip::address &addr, deadline d) noexcept
virtual size_t	_do_max_buffers () const noexcept
	The virtualised implementation of max_buffers() used if no multiplexer has been set.
virtual result< registered_buffer_type >	_do_allocate_registered_buffer (size_t &bytes) noexcept
	The virtualised implementation of allocate_registered_buffer() used if no multiplexer has been set.
virtual io_result< buffers_type >	_do_read (io_request< buffers_type > reqs, deadline d) noexcept
	The virtualised implementation of read() used if no multiplexer has been set.
virtual io_result< buffers_type >	_do_read (registered_buffer_type base, io_request< buffers_type > reqs, deadline d) noexcept
	The virtualised implementation of read() used if no multiplexer has been set.
virtual io_result< const_buffers_type >	_do_write (io_request< const_buffers_type > reqs, deadline d) noexcept
	The virtualised implementation of write() used if no multiplexer has been set.
virtual io_result< const_buffers_type >	_do_write (registered_buffer_type base, io_request< const_buffers_type > reqs, deadline d) noexcept
	The virtualised implementation of write() used if no multiplexer has been set.
virtual io_result< const_buffers_type >	_do_barrier (io_request< const_buffers_type > reqs, barrier_kind kind, deadline d) noexcept
	The virtualised implementation of barrier() used if no multiplexer has been set.
io_result< buffers_type >	_do_multiplexer_read (registered_buffer_type &&base, io_request< buffers_type > reqs, deadline d) noexcept
io_result< const_buffers_type >	_do_multiplexer_write (registered_buffer_type &&base, io_request< const_buffers_type > reqs, deadline d) noexcept
io_result< const_buffers_type >	_do_multiplexer_barrier (registered_buffer_type &&base, io_request< const_buffers_type > reqs, barrier_kind kind, deadline d) noexcept

Protected Attributes
byte_io_multiplexer *	_ctx {nullptr}
union {
native_handle_type   _v
struct {
intptr_t   _padding0_
uint32_t   _padding1_
flag   flags
uint16_t   _padding2_
}   _
};

Detailed Description

A handle to a byte-orientated socket-like entity.

Warning

This is deprecated and scheduled for removal in 2025.

This handle, or subclasses thereof, may refer to:

• a BSD socket in the kernel configured for TCP.
• a TLS socket in a userspace library.
• a userspace socket for certain types of high end network card.
• or indeed, anything which quacks like a SOCK_STREAM socket.

If you construct it directly and assign it a socket that you created, then it refers to a kernel BSD socket, as the default implementation is for a kernel BSD socket. If you get an instance from elsewhere, it may have a very different implementation.

The default is blocking sockets, on which timed out i/o is not possible. In this use case, byte_socket() will block until a successful connection is established with the remote address. Thereafter read() and write() block based on i/o from the other side, returning immediately if at least one byte is transferred.

If flag::multiplexable is specified which causes the handle to be created as native_handle_type::disposition::nonblocking, byte_socket() no longer blocks. However it will then block in read() or write(), unless its deadline is zero.

If you want to create a socket which awaits connections, you need to instance a listening_byte_socket_handle. Reads from that handle yield new byte_socket_handle instances.

<tt>caching::safety_barriers</tt>

TCP connections need to be closed by both parties in a specific way to not cause the tail of data sent to get truncated:

1. Local side calls shutdown(SHUT_WR) to send the FIN packet.
2. Remote side calls shutdown(SHUT_WR) to send the FIN packet.
3. Local side read() returns no bytes read as remote side has closed down. Local side can now call close().
4. Remote side read() returns no bytes read as local side has closed down. Remote side can now call close().

This is obviously inefficient and prone to issues if the remote side is not a good faith actor, so most TCP based protocols such as HTTP send the length of the data to be transferred, and one loops reading until that length of data is read, whereupon the TCP connection is immediately forced closed without the TCP shutdown ceremony.

The default caching is when close() is called it immediately closes the socket handle, causing an abort in the connection if any data remains in buffers. If you wish close() to instead issue a shutdown and to then block on read() until it returns no bytes before closing, set caching::safety_barriers.

This should avoid the need for SO_LINGER for remote sides acting in good faith. If you don't control remote side code quality, you may still need to set SO_LINGER, though be aware that that socket option is full of gotchas.

If you don't wish to have this operation occur during close, you can call shutdown_and_close() manually instead.

Member Enumeration Documentation

shutdown_kind

enum llfio_v2_xxx::byte_socket_handle::shutdown_kind

The channels which can be shut down.

Enumerator
shutdown_read	Shutdown further reads.
shutdown_write	Shutdown further writes.
shutdown_both	Shutdown both further reads and writes.

  {
    shutdown_read,   //!< Shutdown further reads.
    shutdown_write,  //!< Shutdown further writes.
    shutdown_both    //!< Shutdown both further reads and writes.
  };

Member Function Documentation

allocate_registered_buffer()

result<registered_buffer_type> llfio_v2_xxx::byte_io_handle::allocate_registered_buffer ( size_t &  bytes )

inlinenoexceptinherited

Request the allocation of a new registered i/o buffer with the system suitable for maximum performance i/o, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation.

Returns

A shared pointer to the i/o buffer. Note that the pointer returned is not the resource under management, using shared ptr's aliasing feature.

Parameters

bytes

The size of the i/o buffer requested. This may be rounded (considerably) upwards, you should always use the value returned.

Some i/o multiplexer implementations have the ability to allocate i/o buffers in special memory shared between the i/o hardware and user space processes. Using registered i/o buffers can entirely eliminate all kernel transitions and memory copying during i/o, and can saturate very high end hardware from a single kernel thread.

If no multiplexer is set, the default implementation uses map_handle to allocate raw memory pages from the OS kernel. If the requested buffer size is a multiple of one of the larger page sizes from utils::page_sizes(), an attempt to satisfy the request using the larger page size will be attempted first.

  {
    if(_ctx == nullptr)
    {
      return _do_allocate_registered_buffer(bytes);
    }
    return _ctx->do_byte_io_handle_allocate_registered_buffer(this, bytes);
  }

barrier()

virtual io_result<const_buffers_type> llfio_v2_xxx::byte_io_handle::barrier ( io_request< const_buffers_type >  reqs = io_request<const_buffers_type>(), barrier_kind  kind = barrier_kind::nowait_data_only, deadline  d = deadline()  )

inlinevirtualnoexceptinherited

Issue a write reordering barrier such that writes preceding the barrier will reach storage before writes after this barrier, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation.

Warning

Assume that this call is a no-op. It is not reliably implemented in many common use cases, for example if your code is running inside a LXC container, or if the user has mounted the filing system with non-default options. Instead open the handle with caching::reads which means that all writes form a strict sequential order not completing until acknowledged by the storage device. Filing system can and do use different algorithms to give much better performance with caching::reads, some (e.g. ZFS) spectacularly better.

Let me repeat again: consider this call to be a hint to poke the kernel with a stick to go start to do some work sooner rather than later. It may be ignored entirely.

For portability, you can only assume that barriers write order for a single handle instance. You cannot assume that barriers write order across multiple handles to the same inode, or across processes.

Returns

The buffers barriered, which may not be the buffers input. The size of each scatter-gather buffer is updated with the number of bytes of that buffer barriered.

Parameters

reqs	A scatter-gather and offset request for what range to barrier. May be ignored on some platforms which always write barrier the entire file. Supplying a default initialised reqs write barriers the entire file.
kind	Which kind of write reordering barrier to perform.
d	An optional deadline by which the i/o must complete, else it is cancelled. Note function may return significantly after this deadline if the i/o takes long to cancel.

Errors returnable\n Any of the values POSIX fdatasync() or Windows NtFlushBuffersFileEx() can return.

Memory Allocations\n None.

  {
    return (_ctx == nullptr) ? _do_barrier(reqs, kind, d) : _do_multiplexer_barrier({}, std::move(reqs), kind, d);
  }

byte_socket()

static result<byte_socket_handle> llfio_v2_xxx::byte_socket_handle::byte_socket ( ip::family  family, mode  _mode = mode::write, caching  _caching = caching::all, flag  flags = flag::none  )

inlinestaticnoexcept

Create a socket handle.

Parameters

family	Which IP family to create the socket in.
_mode	How to open the socket. If this is mode::append, the read side of the socket is shutdown; if this is mode::read, the write side of the socket is shutdown.
_caching	How to ask the kernel to cache the socket. If writes are not cached, SO_SNDBUF to the minimum possible value and TCP_NODELAY is set, this should cause writes to hit the network as quickly as possible.
flags	Any additional custom behaviours.

Errors returnable\n Any of the values POSIX socket() or WSASocket() can return.

clone()

result<handle> llfio_v2_xxx::handle::clone ( ) const

inlinenoexceptinherited

Clone this handle (copy constructor is disabled to avoid accidental copying)

Errors returnable\n Any of the values POSIX dup() or DuplicateHandle() can return.

co_barrier()

awaitable<io_result<const_buffers_type> > llfio_v2_xxx::byte_io_handle::co_barrier ( io_request< const_buffers_type >  reqs = io_request<const_buffers_type>(), barrier_kind  kind = barrier_kind::nowait_data_only, deadline  d = deadline()  )

inlinenoexceptinherited

A coroutinised equivalent to .barrier() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .barrier() if no i/o multiplexer has been set on this handle!

The awaitable returned is eager i.e. it immediately begins the i/o. If the i/o completes and finishes immediately, no coroutine suspension occurs.

  {
    if(_ctx == nullptr)
    {
      return awaitable<io_result<const_buffers_type>>(barrier(std::move(reqs), kind, d));
    }
    awaitable<io_result<const_buffers_type>> ret;
    ret.set_state(_ctx->construct(ret._state_storage, this, nullptr, {}, d, std::move(reqs), kind));
    return ret;
  }

co_connect()

awaitable<io_result<void> > llfio_v2_xxx::byte_socket_handle::co_connect ( const ip::address &  addr, deadline  d = {}  )

noexcept

A coroutinised equivalent to .connect() which suspends the coroutine until a connection occurs. Blocks execution i.e is equivalent to .connect() if no i/o multiplexer has been set on this handle!

The awaitable returned is eager i.e. it immediately begins the i/o. If the i/o completes and finishes immediately, no coroutine suspension occurs.

co_read() [1/2]

awaitable<io_result<buffers_type> > llfio_v2_xxx::byte_io_handle::co_read ( io_request< buffers_type >  reqs, deadline  d = deadline()  )

inlinenoexceptinherited

A coroutinised equivalent to .read() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .read() if no i/o multiplexer has been set on this handle!

The awaitable returned is eager i.e. it immediately begins the i/o. If the i/o completes and finishes immediately, no coroutine suspension occurs.

  {
    if(_ctx == nullptr)
    {
      return awaitable<io_result<buffers_type>>(read(std::move(reqs), d));
    }
    awaitable<io_result<buffers_type>> ret;
    ret.set_state(_ctx->construct(ret._state_storage, this, nullptr, {}, d, std::move(reqs)));
    return ret;
  }

co_read() [2/2]

awaitable<io_result<buffers_type> > llfio_v2_xxx::byte_io_handle::co_read

inlinenoexcept

A coroutinised equivalent to .read() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .read() if no i/o multiplexer has been set on this handle!

The awaitable returned is eager i.e. it immediately begins the i/o. If the i/o completes and finishes immediately, no coroutine suspension occurs.

  {
    if(_ctx == nullptr)
    {
      return awaitable<io_result<buffers_type>>(read(std::move(reqs), d));
    }
    awaitable<io_result<buffers_type>> ret;
    ret.set_state(_ctx->construct(ret._state_storage, this, nullptr, {}, d, std::move(reqs)));
    return ret;
  }

co_write() [1/2]

awaitable<io_result<const_buffers_type> > llfio_v2_xxx::byte_io_handle::co_write ( io_request< const_buffers_type >  reqs, deadline  d = deadline()  )

inlinenoexceptinherited

A coroutinised equivalent to .write() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .write() if no i/o multiplexer has been set on this handle!

The awaitable returned is eager i.e. it immediately begins the i/o. If the i/o completes and finishes immediately, no coroutine suspension occurs.

  {
    if(_ctx == nullptr)
    {
      return awaitable<io_result<const_buffers_type>>(write(std::move(reqs), d));
    }
    awaitable<io_result<const_buffers_type>> ret;
    ret.set_state(_ctx->construct(ret._state_storage, this, nullptr, {}, d, std::move(reqs)));
    return ret;
  }

co_write() [2/2]

awaitable<io_result<const_buffers_type> > llfio_v2_xxx::byte_io_handle::co_write

inlinenoexcept

A coroutinised equivalent to .write() which suspends the coroutine until the i/o finishes. Blocks execution i.e is equivalent to .write() if no i/o multiplexer has been set on this handle!

The awaitable returned is eager i.e. it immediately begins the i/o. If the i/o completes and finishes immediately, no coroutine suspension occurs.

  {
    if(_ctx == nullptr)
    {
      return awaitable<io_result<const_buffers_type>>(write(std::move(reqs), d));
    }
    awaitable<io_result<const_buffers_type>> ret;
    ret.set_state(_ctx->construct(ret._state_storage, this, nullptr, {}, d, std::move(reqs)));
    return ret;
  }

connect()

result<void> llfio_v2_xxx::byte_socket_handle::connect ( const ip::address &  addr, deadline  d = {}  )

inlinenoexcept

Connects to an address.

Parameters

addr	The address to connect to.
d	How long to wait for a connection.

The connection begins upon first call, if it times out then you can call this function again with a new timeout to poll the socket for when it connects. Eventually this function will either succeed, or fail with an error if the connection failed.

Errors returnable\n Any of the values connect() can return;

                                                           {}) noexcept
  {
    return (_ctx == nullptr) ? _do_connect(addr, d) : _do_multiplexer_connect(addr, d);
  }

current_path()

virtual result<path_type> llfio_v2_xxx::handle::current_path ( ) const

inlinevirtualnoexceptinherited

Returns the current path of the open handle as said by the operating system. Note that you are NOT guaranteed that any path refreshed bears any resemblance to the original, some operating systems will return some different path which still reaches the same inode via some other route e.g. hardlinks, dereferenced symbolic links, etc. Windows and Linux correctly track changes to the specific path the handle was opened with, not getting confused by other hard links. MacOS nearly gets it right, but under some circumstances e.g. renaming may switch to a different hard link's path which is almost certainly a bug.

If LLFIO was not able to determine the current path for this open handle e.g. the inode has been unlinked, it returns an empty path. Be aware that FreeBSD can return an empty (deleted) path for file inodes no longer cached by the kernel path cache, LLFIO cannot detect the difference. FreeBSD will also return any path leading to the inode if it is hard linked. FreeBSD does implement path retrieval for directory inodes correctly however, and see algorithm::cached_parent_handle_adapter<T> for a handle adapter which makes use of that.

On Linux if /proc is not mounted, this call fails with an error. All APIs in LLFIO which require the use of current_path() can be told to not use it e.g. flag::disable_safety_unlinks. It is up to you to detect if current_path() is not working, and to change how you call LLFIO appropriately.

On Windows, you will almost certainly get back a path of the form \!!\Device\HarddiskVolume10\Users\ned\.... See path_view for what all the path prefix sequences mean, but to summarise the \!!\ prefix is LLFIO-only and will not be accepted by other Windows APIs. Pass LLFIO derived paths through the function to_win32_path() to Win32-ise them. This function is also available on Linux where it does nothing, so you can use it in portable code.

Warning

This call is expensive, it always asks the kernel for the current path, and no checking is done to ensure what the kernel returns is accurate or even sensible. Be aware that despite these precautions, paths are unstable and can change randomly at any moment. Most code written to use absolute file systems paths is racy, so don't do it, use path_handle to fix a base location on the file system and work from that anchor instead!

Memory Allocations\n At least one malloc for the path_type, likely several more.

See also

algorithm::cached_parent_handle_adapter<T> which overrides this with an implementation based on retrieving the current path of a cached handle to the parent directory. On platforms with instability or failure to retrieve the correct current path for regular files, the cached parent handle adapter works around the problem by taking advantage of directory inodes not having the same instability problems on any platform.

Reimplemented in llfio_v2_xxx::symlink_handle, and llfio_v2_xxx::process_handle.

max_buffers()

size_t llfio_v2_xxx::byte_io_handle::max_buffers ( ) const

inlinenoexceptinherited

The maximum number of buffers which a single read or write syscall can (atomically) process at a time for this specific open handle. On POSIX, this is known as IOV_MAX. Preferentially uses any i/o multiplexer set over the virtually overridable per-class implementation.

Note that the actual number of buffers accepted for a read or a write may be significantly lower than this system-defined limit, depending on available resources. The read() or write() call will return the buffers accepted at the time of invoking the syscall.

Note also that some OSs will error out if you supply more than this limit to read() or write(), but other OSs do not. Some OSs guarantee that each i/o syscall has effects atomically visible or not to other i/o, other OSs do not.

OS X does not implement scatter-gather file i/o syscalls. Thus this function will always return 1 in that situation.

Microsoft Windows may implement scatter-gather i/o under certain handle configurations. Most of the time for non-socket handles this function will return 1.

For handles which implement i/o entirely in user space, and thus syscalls are not involved, this function will return 0.

  {
    if(_ctx == nullptr)
    {
      return _do_max_buffers();
    }
    return _ctx->do_byte_io_handle_max_buffers(this);
  }

QUICKCPPLIB_BITFIELD_BEGIN_T()

llfio_v2_xxx::handle::QUICKCPPLIB_BITFIELD_BEGIN_T ( flag  , uint16_t    )

inlineinherited

Bitwise flags which can be specified.

< No flags

Unlinks the file on handle close. On POSIX, this simply unlinks whatever is pointed to by path() upon the call of close() if and only if the inode matches. On Windows, if you are on Windows 10 1709 or later, exactly the same thing occurs. If on previous editions of Windows, the file entry does not disappears but becomes unavailable for anyone else to open with an errc::resource_unavailable_try_again error return. Because this is confusing, unless the win_disable_unlink_emulation flag is also specified, this POSIX behaviour is somewhat emulated by LLFIO on older Windows by renaming the file to a random name on close() causing it to appear to have been unlinked immediately.

Some kernel caching modes have unhelpfully inconsistent behaviours in getting your data onto storage, so by default unless this flag is specified LLFIO adds extra fsyncs to the following operations for the caching modes specified below: truncation of file length either explicitly or during file open. closing of the handle either explicitly or in the destructor.

Additionally on Linux only to prevent loss of file metadata: On the parent directory whenever a file might have been created. On the parent directory on file close.

This only occurs for these kernel caching modes: caching::none caching::reads caching::reads_and_metadata caching::safety_barriers

file_handle::unlink() could accidentally delete the wrong file if someone has renamed the open file handle since the time it was opened. To prevent this occuring, where the OS doesn't provide race free unlink-by-open-handle we compare the inode of the path we are about to unlink with that of the open handle before unlinking.

Warning

This does not prevent races where in between the time of checking the inode and executing the unlink a third party changes the item about to be unlinked. Only operating systems with a true race-free unlink syscall are race free.

Ask the OS to disable prefetching of data. This can improve random i/o performance.

Ask the OS to maximise prefetching of data, possibly prefetching the entire file into kernel cache. This can improve sequential i/o performance.

< See the documentation for unlink_on_first_close

Microsoft Windows NTFS, having been created in the late 1980s, did not originally implement extents-based storage and thus could only represent sparse files via efficient compression of intermediate zeros. With NTFS v3.0 (Microsoft Windows 2000), a proper extents-based on-storage representation was added, thus allowing only 64Kb extent chunks written to be stored irrespective of whatever the maximum file extent was set to.

For various historical reasons, extents-based storage is disabled by default in newly created files on NTFS, unlike in almost every other major filing system. You have to explicitly "opt in" to extents-based storage.

As extents-based storage is nearly cost free on NTFS, LLFIO by default opts in to extents-based storage for any empty file it creates. If you don't want this, you can specify this flag to prevent that happening.

Filesystems tend to be embarrassingly parallel for operations performed to different inodes. Where LLFIO performs i/o to multiple inodes at a time, it will use OpenMP or the Parallelism or Concurrency standard library extensions to usually complete the operation in constant rather than linear time. If you don't want this default, you can disable default using this flag.

Microsoft Windows NTFS has the option, when creating a directory, to set whether leafname lookup will be case sensitive. This is the only way of getting exact POSIX semantics on Windows without resorting to editing the system registry, however it also affects all code doing lookups within that directory, so we must default it to off.

Create the handle in a way where i/o upon it can be multiplexed with other i/o on the same initiating thread of execution i.e. you can perform more than one read concurrently, without using threads. The blocking operations .read() and .write() may have to use a less efficient, but cancellable, blocking implementation for handles created in this way. On Microsoft Windows, this creates handles with OVERLAPPED semantics. On POSIX, this creates handles with nonblocking semantics for non-file handles such as pipes and sockets, however for file, directory and symlink handles it does not set nonblocking, as it is non-portable.

< Using insane POSIX byte range locks

< This is an inode created with no representation on the filing system

                                              {
  none = uint16_t(0),  //!< No flags
  /*! Unlinks the file on handle close. On POSIX, this simply unlinks whatever is pointed
  to by `path()` upon the call of `close()` if and only if the inode matches. On Windows,
  if you are on Windows 10 1709 or later, exactly the same thing occurs. If on previous
  editions of Windows, the file entry does not disappears but becomes unavailable for
  anyone else to open with an `errc::resource_unavailable_try_again` error return. Because this is confusing, unless the
  `win_disable_unlink_emulation` flag is also specified, this POSIX behaviour is
  somewhat emulated by LLFIO on older Windows by renaming the file to a random name on `close()`
  causing it to appear to have been unlinked immediately.
  */
  unlink_on_first_close = uint16_t(1U << 0U),
 
  /*! Some kernel caching modes have unhelpfully inconsistent behaviours
  in getting your data onto storage, so by default unless this flag is
  specified LLFIO adds extra fsyncs to the following operations for the
  caching modes specified below:
  * truncation of file length either explicitly or during file open.
  * closing of the handle either explicitly or in the destructor.
 
  Additionally on Linux only to prevent loss of file metadata:
  * On the parent directory whenever a file might have been created.
  * On the parent directory on file close.
 
  This only occurs for these kernel caching modes:
  * caching::none
  * caching::reads
  * caching::reads_and_metadata
  * caching::safety_barriers
  */
  disable_safety_barriers = uint16_t(1U << 2U),
  /*! `file_handle::unlink()` could accidentally delete the wrong file if someone has
  renamed the open file handle since the time it was opened. To prevent this occuring,
  where the OS doesn't provide race free unlink-by-open-handle we compare the inode of
  the path we are about to unlink with that of the open handle before unlinking.
  \warning This does not prevent races where in between the time of checking the inode
  and executing the unlink a third party changes the item about to be unlinked. Only
  operating systems with a true race-free unlink syscall are race free.
  */
  disable_safety_unlinks = uint16_t(1U << 3U),
  /*! Ask the OS to disable prefetching of data. This can improve random
  i/o performance.
  */
  disable_prefetching = uint16_t(1U << 4U),
  /*! Ask the OS to maximise prefetching of data, possibly prefetching the entire file
  into kernel cache. This can improve sequential i/o performance.
  */
  maximum_prefetching = uint16_t(1U << 5U),
 
  win_disable_unlink_emulation = uint16_t(1U << 9U),  //!< See the documentation for `unlink_on_first_close`
  /*! Microsoft Windows NTFS, having been created in the late 1980s, did not originally
  implement extents-based storage and thus could only represent sparse files via
  efficient compression of intermediate zeros. With NTFS v3.0 (Microsoft Windows 2000),
  a proper extents-based on-storage representation was added, thus allowing only 64Kb
  extent chunks written to be stored irrespective of whatever the maximum file extent
  was set to.
 
  For various historical reasons, extents-based storage is disabled by default in newly
  created files on NTFS, unlike in almost every other major filing system. You have to
  explicitly "opt in" to extents-based storage.
 
  As extents-based storage is nearly cost free on NTFS, LLFIO by default opts in to
  extents-based storage for any empty file it creates. If you don't want this, you
  can specify this flag to prevent that happening.
  */
  win_disable_sparse_file_creation = uint16_t(1U << 10U),
  /*! Filesystems tend to be embarrassingly parallel for operations performed to different
  inodes. Where LLFIO performs i/o to multiple inodes at a time, it will use OpenMP or
  the Parallelism or Concurrency standard library extensions to usually complete the
  operation in constant rather than linear time. If you don't want this default, you can
  disable default using this flag.
  */
  disable_parallelism = uint16_t(1U << 11U),
  /*! Microsoft Windows NTFS has the option, when creating a directory, to set whether
  leafname lookup will be case sensitive. This is the only way of getting exact POSIX
  semantics on Windows without resorting to editing the system registry, however it also
  affects all code doing lookups within that directory, so we must default it to off.
  */
  win_create_case_sensitive_directory = uint16_t(1U << 12U),
 
  /*! Create the handle in a way where i/o upon it can be multiplexed with other i/o
  on the same initiating thread of execution i.e. you can perform more than one read
  concurrently, without using threads. The blocking operations `.read()` and `.write()`
  may have to use a less efficient, but cancellable, blocking implementation for handles created
  in this way. On Microsoft Windows, this creates handles with `OVERLAPPED` semantics.
  On POSIX, this creates handles with nonblocking semantics for non-file handles such
  as pipes and sockets, however for file, directory and symlink handles it does not set
  nonblocking, as it is non-portable.
  */
  multiplexable = uint16_t(1U << 13U),
 
  // NOTE: IF UPDATING THIS UPDATE THE std::ostream PRINTER BELOW!!!
 
  byte_lock_insanity = uint16_t(1U << 14U),  //!< Using insane POSIX byte range locks
  anonymous_inode = uint16_t(1U << 15U)      //!< This is an inode created with no representation on the filing system
  } QUICKCPPLIB_BITFIELD_END(flag)

read() [1/3]

io_result<buffers_type> llfio_v2_xxx::byte_io_handle::read ( io_request< buffers_type >  reqs, deadline  d = deadline()  )

inlinenoexceptinherited

Read data from the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation.

Warning

Depending on the implementation backend, very different buffers may be returned than you supplied. You should always use the buffers returned and assume that they point to different memory and that each buffer's size will have changed.

Returns

The buffers read, which may not be the buffers input. The size of each scatter-gather buffer returned is updated with the number of bytes of that buffer transferred, and the pointer to the data may be completely different to what was submitted (e.g. it may point into a memory map).

Parameters

reqs	A scatter-gather and offset request.
d	An optional deadline by which the i/o must complete, else it is cancelled. Note function may return significantly after this deadline if the i/o takes long to cancel.

Errors returnable\n Any of the values POSIX read() can return, errc::timed_out, errc::operation_canceled. errc::not_supported may be

returned if deadline i/o is not possible with this particular handle configuration (e.g. reading from regular files on POSIX or reading from a non-overlapped HANDLE on Windows).

Memory Allocations\n The default synchronous implementation in file_handle performs no memory allocation.

  {
    return (_ctx == nullptr) ? _do_read(reqs, d) : _do_multiplexer_read({}, reqs, d);
  }

read() [2/3]

io_result<buffers_type> llfio_v2_xxx::byte_io_handle::read

inlinenoexcept

Read data from the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation.

Warning

Depending on the implementation backend, very different buffers may be returned than you supplied. You should always use the buffers returned and assume that they point to different memory and that each buffer's size will have changed.

Returns

The buffers read, which may not be the buffers input. The size of each scatter-gather buffer returned is updated with the number of bytes of that buffer transferred, and the pointer to the data may be completely different to what was submitted (e.g. it may point into a memory map).

Parameters

reqs	A scatter-gather and offset request.
d	An optional deadline by which the i/o must complete, else it is cancelled. Note function may return significantly after this deadline if the i/o takes long to cancel.

Errors returnable\n Any of the values POSIX read() can return, errc::timed_out, errc::operation_canceled. errc::not_supported may be

returned if deadline i/o is not possible with this particular handle configuration (e.g. reading from regular files on POSIX or reading from a non-overlapped HANDLE on Windows).

Memory Allocations\n The default synchronous implementation in file_handle performs no memory allocation.

  {
    return (_ctx == nullptr) ? _do_read(reqs, d) : _do_multiplexer_read({}, reqs, d);
  }

read() [3/3]

Convenience initialiser list based overload for< tt > llfio_v2_xxx::byte_socket_handle::read ( std::initializer_list< buffer_type >  lst, deadline  d = deadline()  )

inlinenoexcept

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

  {
    buffer_type *_reqs = reinterpret_cast<buffer_type *>(alloca(sizeof(buffer_type) * lst.size()));
    memcpy(_reqs, lst.begin(), sizeof(buffer_type) * lst.size());
    io_request<buffers_type> reqs(buffers_type(_reqs, lst.size()));
    auto ret = read(reqs, d);
    if(ret)
    {
      return ret.bytes_transferred();
    }
    return std::move(ret).error();
  }

set_append_only()

virtual result<void> llfio_v2_xxx::handle::set_append_only ( bool  enable )

inlinevirtualnoexceptinherited

EXTENSION: Changes whether this handle is append only or not.

Warning

On Windows this is implemented as a bit of a hack to make it fast like on POSIX, so make sure you open the handle for read/write originally. Note unlike on POSIX the append_only disposition will be the only one toggled, seekable and readable will remain turned on.

Errors returnable\n Whatever POSIX fcntl() returns. On Windows nothing is changed on the handle.

Memory Allocations\n No memory allocation.

Reimplemented in llfio_v2_xxx::process_handle.

set_multiplexer()

result< void > llfio_v2_xxx::byte_io_handle::set_multiplexer ( byte_io_multiplexer *  c = this_thread::multiplexer() )

inlinevirtualnoexceptinherited

Sets the i/o multiplexer this handle will use to implement read(), write() and barrier().

Note that this call deregisters this handle from any existing i/o multiplexer, and registers it with the new i/o multiplexer. You must therefore not call it if any i/o is currently outstanding on this handle. You should also be aware that multiple dynamic memory allocations and deallocations may occur, as well as multiple syscalls (i.e. this is an expensive call, try to do it from cold code).

If the handle was not created as multiplexable, this call always fails.

Memory Allocations\n Multiple dynamic memory allocations and deallocations.

Reimplemented in llfio_v2_xxx::mapped_file_handle.

{
  if(!is_multiplexable())
  {
    return errc::operation_not_supported;
  }
  if(c == _ctx)
  {
    return success();
  }
  if(_ctx != nullptr)
  {
    OUTCOME_TRY(_ctx->do_byte_io_handle_deregister(this));
    _ctx = nullptr;
  }
  if(c != nullptr)
  {
    OUTCOME_TRY(auto &&state, c->do_byte_io_handle_register(this));
    _v.behaviour = (_v.behaviour & ~(native_handle_type::disposition::_multiplexer_state_bit0 | native_handle_type::disposition::_multiplexer_state_bit1));
    if((state & 1) != 0)
    {
      _v.behaviour |= native_handle_type::disposition::_multiplexer_state_bit0;
    }
    if((state & 2) != 0)
    {
      _v.behaviour |= native_handle_type::disposition::_multiplexer_state_bit1;
    }
  }
  _ctx = c;
  return success();
}

shutdown()

virtual result<void> llfio_v2_xxx::byte_socket_handle::shutdown ( shutdown_kind  = shutdown_write )

inlinevirtualnoexcept

Initiates shutting down further communication on the socket.

The default is shutdown_write, as generally if shutting down you want send a FIN packet to remote and loop polling reads until you receive a FIN from remote.

write() [1/3]

io_result<const_buffers_type> llfio_v2_xxx::byte_io_handle::write ( io_request< const_buffers_type >  reqs, deadline  d = deadline()  )

inlinenoexceptinherited

Write data to the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation.

Warning

Depending on the implementation backend, not all of the buffers input may be written. For example, with a zeroed deadline, some backends may only consume as many buffers as the system has available write slots for, thus for those backends this call is "non-blocking" in the sense that it will return immediately even if it could not schedule a single buffer write. Another example is that some implementations will not auto-extend the length of a file when a write exceeds the maximum extent, you will need to issue a truncate(newsize) first.

Returns

The buffers written, which may not be the buffers input. The size of each scatter-gather buffer returned is updated with the number of bytes of that buffer transferred.

Parameters

reqs	A scatter-gather and offset request.
d	An optional deadline by which the i/o must complete, else it is cancelled. Note function may return significantly after this deadline if the i/o takes long to cancel.

Errors returnable\n Any of the values POSIX write() can return, errc::timed_out, errc::operation_canceled. errc::not_supported may be

returned if deadline i/o is not possible with this particular handle configuration (e.g. writing to regular files on POSIX or writing to a non-overlapped HANDLE on Windows).

Memory Allocations\n The default synchronous implementation in file_handle performs no memory allocation.

  {
    return (_ctx == nullptr) ? _do_write(reqs, d) : _do_multiplexer_write({}, std::move(reqs), d);
  }

write() [2/3]

io_result<const_buffers_type> llfio_v2_xxx::byte_io_handle::write

inlinenoexcept

Write data to the open handle, preferentially using any i/o multiplexer set over the virtually overridable per-class implementation.

Warning

Depending on the implementation backend, not all of the buffers input may be written. For example, with a zeroed deadline, some backends may only consume as many buffers as the system has available write slots for, thus for those backends this call is "non-blocking" in the sense that it will return immediately even if it could not schedule a single buffer write. Another example is that some implementations will not auto-extend the length of a file when a write exceeds the maximum extent, you will need to issue a truncate(newsize) first.

Returns

The buffers written, which may not be the buffers input. The size of each scatter-gather buffer returned is updated with the number of bytes of that buffer transferred.

Parameters

reqs	A scatter-gather and offset request.
d	An optional deadline by which the i/o must complete, else it is cancelled. Note function may return significantly after this deadline if the i/o takes long to cancel.

Errors returnable\n Any of the values POSIX write() can return, errc::timed_out, errc::operation_canceled. errc::not_supported may be

returned if deadline i/o is not possible with this particular handle configuration (e.g. writing to regular files on POSIX or writing to a non-overlapped HANDLE on Windows).

Memory Allocations\n The default synchronous implementation in file_handle performs no memory allocation.

  {
    return (_ctx == nullptr) ? _do_write(reqs, d) : _do_multiplexer_write({}, std::move(reqs), d);
  }

write() [3/3]

Convenience initialiser list based overload for< tt > llfio_v2_xxx::byte_socket_handle::write ( std::initializer_list< const_buffer_type >  lst, deadline  d = deadline()  )

inlinenoexcept

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

  {
    const_buffer_type *_reqs = reinterpret_cast<const_buffer_type *>(alloca(sizeof(const_buffer_type) * lst.size()));
    memcpy(_reqs, lst.begin(), sizeof(const_buffer_type) * lst.size());
    io_request<const_buffers_type> reqs(const_buffers_type(_reqs, lst.size()));
    auto ret = write(reqs, d);
    if(ret)
    {
      return ret.bytes_transferred();
    }
    return std::move(ret).error();
  }

---

The documentation for this class was generated from the following file:

• include/llfio/v2.0/byte_socket_handle.hpp