include/boost/corosio/native/detail/posix/posix_stream_file.hpp

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posix_stream_file.hpp

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1		//
2		// Copyright (c) 2026 Michael Vandeberg
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		// Official repository: https://github.com/cppalliance/corosio
8		//
9
10		#ifndef BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_STREAM_FILE_HPP
11		#define BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_STREAM_FILE_HPP
12
13		#include <boost/corosio/detail/platform.hpp>
14
15		#if BOOST_COROSIO_POSIX
16
17		#include <boost/corosio/detail/config.hpp>
18		#include <boost/corosio/stream_file.hpp>
19		#include <boost/corosio/file_base.hpp>
20		#include <boost/corosio/detail/intrusive.hpp>
21		#include <boost/corosio/detail/dispatch_coro.hpp>
22		#include <boost/corosio/detail/scheduler_op.hpp>
23		#include <boost/corosio/detail/thread_pool.hpp>
24		#include <boost/corosio/detail/scheduler.hpp>
25		#include <boost/corosio/detail/buffer_param.hpp>
26		#include <boost/corosio/native/detail/coro_op.hpp>
27		#include <boost/corosio/native/detail/coro_op_complete.hpp>
28		#include <boost/corosio/native/detail/make_err.hpp>
29		#include <boost/capy/ex/executor_ref.hpp>
30		#include <boost/capy/error.hpp>
31		#include <boost/capy/buffers.hpp>
32
33		#include <atomic>
34		#include <coroutine>
35		#include <cstddef>
36		#include <cstdint>
37		#include <filesystem>
38		#include <limits>
39		#include <memory>
40		#include <optional>
41		#include <stop_token>
42		#include <system_error>
43
44		#include <errno.h>
45		#include <fcntl.h>
46		#include <sys/stat.h>
47		#include <sys/uio.h>
48		#include <unistd.h>
49
50		/*
51		POSIX Stream File Implementation
52		=================================
53
54		Regular files cannot be monitored by epoll/kqueue/select — the kernel
55		always reports them as ready. Blocking I/O (pread/pwrite) is dispatched
56		to a shared thread pool, with completion posted back to the scheduler.
57
58		This follows the same pattern as posix_resolver: pool_work_item for
59		dispatch, scheduler_op for completion, shared_from_this for lifetime.
60
61		Completion Flow
62		---------------
63		1. read_some() sets up file_read_op, posts to thread pool
64		2. Pool thread runs preadv() (blocking)
65		3. Pool thread stores results, posts scheduler_op to scheduler
66		4. Scheduler invokes op() which resumes the coroutine
67
68		Single-Inflight Constraint
69		--------------------------
70		Only one asynchronous operation may be in flight at a time on a
71		given file object. Concurrent read and write is not supported
72		because both share offset_ without synchronization.
73		*/
74
75		namespace boost::corosio::detail {
76
77		struct scheduler;
78		class posix_stream_file_service;
79
80		/** Stream file implementation for POSIX backends.
81
82		Each instance contains embedded operation objects (read_op_, write_op_)
83		that are reused across calls. This avoids per-operation heap allocation.
84		*/
85		class posix_stream_file final
86		: public stream_file::implementation
87		, public std::enable_shared_from_this<posix_stream_file>
88		, public intrusive_list<posix_stream_file>::node
89		{
90		friend class posix_stream_file_service;
91
92		public:
93		static constexpr std::size_t max_buffers = 16;
94
95		/** Operation state for a single file read or write.
96
97		The coroutine, cancellation and keepalive machinery is inherited
98		from `coro_op`; only the pool-path result state lives here.
99		*/
100		struct file_op : coro_op
101		{
102		// Buffer data (copied from buffer_param at submission time)
103		iovec iovecs[max_buffers];
104		int iovec_count = 0;
105
106		// Result storage (populated by worker thread)
107		int errn = 0;
108		std::size_t bytes_transferred = 0;
109
110	528x	file_op() = default;
111
112	267x	void reset() noexcept
113		{
114	267x	iovec_count = 0;
115	267x	errn = 0;
116	267x	bytes_transferred = 0;
117	267x	is_read = false;
118	267x	cancelled.store(false, std::memory_order_relaxed);
119	267x	stop_cb.reset();
120	267x	impl_ptr.reset();
121	267x	ec_out = nullptr;
122	267x	bytes_out = nullptr;
123	267x	}
124
125		void operator()() override;
126		void destroy() override;
127		};
128
129		/** Pool work item for thread pool dispatch. */
130		struct pool_op : pool_work_item
131		{
132		posix_stream_file* file_ = nullptr;
133		std::shared_ptr<posix_stream_file> ref_;
134		};
135
136		explicit posix_stream_file(posix_stream_file_service& svc) noexcept;
137
138		// -- io_stream::implementation --
139
140		std::coroutine_handle<> read_some(
141		std::coroutine_handle<>,
142		capy::executor_ref,
143		buffer_param,
144		std::stop_token,
145		std::error_code*,
146		std::size_t*) override;
147
148		std::coroutine_handle<> write_some(
149		std::coroutine_handle<>,
150		capy::executor_ref,
151		buffer_param,
152		std::stop_token,
153		std::error_code*,
154		std::size_t*) override;
155
156		// -- stream_file::implementation --
157
158	793x	native_handle_type native_handle() const noexcept override
159		{
160	793x	return fd_;
161		}
162
163	763x	void cancel() noexcept override
164		{
165	763x	read_op_.request_cancel();
166	763x	write_op_.request_cancel();
167	763x	}
168
169		std::uint64_t size() const override;
170		std::error_code resize(std::uint64_t new_size) noexcept override;
171		std::error_code sync_data() noexcept override;
172		std::error_code sync_all() noexcept override;
173		native_handle_type release() override;
174		std::error_code assign(native_handle_type handle) noexcept override;
175		capy::io_result<std::uint64_t>
176		seek(std::int64_t offset, file_base::seek_basis origin) noexcept override;
177
178		// -- Internal --
179
180		/** Open the file and store the fd. */
181		std::error_code
182		open_file(std::filesystem::path const& path, file_base::flags mode);
183
184		/** Close the file descriptor. */
185		void close_file() noexcept;
186
187		private:
188		posix_stream_file_service& svc_;
189		int fd_ = -1;
190		std::uint64_t offset_ = 0;
191
192		file_op read_op_;
193		file_op write_op_;
194		pool_op read_pool_op_;
195		pool_op write_pool_op_;
196
197		static void do_read_work(pool_work_item*) noexcept;
198		static void do_write_work(pool_work_item*) noexcept;
199		};
200
201		// ---------------------------------------------------------------------------
202		// Inline implementation
203		// ---------------------------------------------------------------------------
204
205	264x	inline posix_stream_file::posix_stream_file(
206	264x	posix_stream_file_service& svc) noexcept
207	264x	: svc_(svc)
208		{
209	264x	}
210
211		inline std::error_code
212	247x	posix_stream_file::open_file(
213		std::filesystem::path const& path, file_base::flags mode)
214		{
215	247x	close_file();
216
217	247x	int oflags = 0;
218
219		// Access mode
220	247x	unsigned access = static_cast<unsigned>(mode) & 3u;
221	247x	if (access == static_cast<unsigned>(file_base::read_write))
222	21x	oflags \|= O_RDWR;
223	226x	else if (access == static_cast<unsigned>(file_base::write_only))
224	81x	oflags \|= O_WRONLY;
225		else
226	145x	oflags \|= O_RDONLY;
227
228		// Creation flags
229	247x	if ((mode & file_base::create) != file_base::flags(0))
230	40x	oflags \|= O_CREAT;
231	247x	if ((mode & file_base::exclusive) != file_base::flags(0))
232	2x	oflags \|= O_EXCL;
233	247x	if ((mode & file_base::truncate) != file_base::flags(0))
234	17x	oflags \|= O_TRUNC;
235	247x	if ((mode & file_base::append) != file_base::flags(0))
236	8x	oflags \|= O_APPEND;
237	247x	if ((mode & file_base::sync_all_on_write) != file_base::flags(0))
238	2x	oflags \|= O_SYNC;
239
240	247x	int fd = ::open(path.c_str(), oflags, 0666);
241	247x	if (fd < 0)
242	9x	return make_err(errno);
243
244	238x	fd_ = fd;
245	238x	offset_ = 0;
246
247		// Append mode: position at end-of-file (preadv/pwritev use
248		// explicit offsets, so O_APPEND alone is not sufficient).
249	238x	if ((mode & file_base::append) != file_base::flags(0))
250		{
251		struct stat st;
252	8x	if (::fstat(fd, &st) < 0)
253		{
254	5x	int err = errno;
255	5x	::close(fd);
256	5x	fd_ = -1;
257	5x	return make_err(err);
258		}
259	3x	offset_ = static_cast<std::uint64_t>(st.st_size);
260		}
261
262		#ifdef POSIX_FADV_SEQUENTIAL
263	233x	::posix_fadvise(fd_, 0, 0, POSIX_FADV_SEQUENTIAL);
264		#endif
265
266	233x	return {};
267		}
268
269		inline void
270	1014x	posix_stream_file::close_file() noexcept
271		{
272	1014x	if (fd_ >= 0)
273		{
274	237x	::close(fd_);
275	237x	fd_ = -1;
276		}
277	1014x	}
278
279		inline std::uint64_t
280	17x	posix_stream_file::size() const
281		{
282		struct stat st;
283	17x	if (::fstat(fd_, &st) < 0)
284	5x	throw_system_error(make_err(errno), "stream_file::size");
285	12x	return static_cast<std::uint64_t>(st.st_size);
286		}
287
288		inline std::error_code
289	12x	posix_stream_file::resize(std::uint64_t new_size) noexcept
290		{
291	12x	if (new_size >
292	12x	static_cast<std::uint64_t>((std::numeric_limits<off_t>::max)()))
293	2x	return make_err(EOVERFLOW);
294	10x	if (::ftruncate(fd_, static_cast<off_t>(new_size)) < 0)
295	7x	return make_err(errno);
296	3x	return {};
297		}
298
299		inline std::error_code
300	10x	posix_stream_file::sync_data() noexcept
301		{
302		#if BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
303	10x	if (::fdatasync(fd_) < 0)
304		#else // BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
305		if (::fsync(fd_) < 0)
306		#endif // BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
307	7x	return make_err(errno);
308	3x	return {};
309		}
310
311		inline std::error_code
312	10x	posix_stream_file::sync_all() noexcept
313		{
314	10x	if (::fsync(fd_) < 0)
315	7x	return make_err(errno);
316	3x	return {};
317		}
318
319		inline native_handle_type
320	2x	posix_stream_file::release()
321		{
322	2x	int fd = fd_;
323	2x	fd_ = -1;
324	2x	offset_ = 0;
325	2x	return fd;
326		}
327
328		inline std::error_code
329	6x	posix_stream_file::assign(native_handle_type handle) noexcept
330		{
331	6x	close_file();
332	6x	fd_ = handle;
333	6x	offset_ = 0;
334	6x	return {};
335		}
336
337		inline capy::io_result<std::uint64_t>
338	30x	posix_stream_file::seek(
339		std::int64_t offset, file_base::seek_basis origin) noexcept
340		{
341		// We track offset_ ourselves (not the kernel fd offset)
342		// because preadv/pwritev use explicit offsets.
343		std::int64_t new_pos;
344
345	30x	if (origin == file_base::seek_set)
346		{
347	14x	new_pos = offset;
348		}
349	16x	else if (origin == file_base::seek_cur)
350		{
351	5x	new_pos = static_cast<std::int64_t>(offset_) + offset;
352		}
353		else
354		{
355		struct stat st;
356	11x	if (::fstat(fd_, &st) < 0)
357	5x	return {make_err(errno), 0};
358	6x	new_pos = st.st_size + offset;
359		}
360
361	25x	if (new_pos < 0)
362	6x	return {make_err(EINVAL), 0};
363	19x	if (new_pos >
364	19x	static_cast<std::int64_t>((std::numeric_limits<off_t>::max)()))
365	✗	return {make_err(EOVERFLOW), 0};
366
367	19x	offset_ = static_cast<std::uint64_t>(new_pos);
368
369	19x	return {std::error_code{}, offset_};
370		}
371
372		// -- file_op completion handler --
373		// (read_some, write_some, do_read_work, do_write_work are
374		// defined in posix_stream_file_service.hpp after the service)
375
376		inline void
377	241x	posix_stream_file::file_op::operator()()
378		{
379	241x	stop_cb.reset();
380
381		// Empty buffers never reach the pool (diverted at initiation), so
382		// empty_buffer stays false and a 0-byte read is a genuine EOF.
383	468x	decode_io_result(
384	241x	ec_out, bytes_out, cancelled.load(std::memory_order_acquire),
385	241x	errn != 0 ? make_err(errn) : std::error_code{}, is_read,
386		bytes_transferred, /empty_buffer=/false);
387
388		// Move impl_ptr to a local so members remain valid through
389		// dispatch — impl_ptr may be the last shared_ptr keeping
390		// the parent posix_stream_file (which embeds this file_op) alive.
391	241x	auto prevent_destroy = std::move(impl_ptr);
392	241x	ex.on_work_finished();
393	241x	cont.h = h;
394	241x	dispatch_coro(ex, cont).resume();
395	241x	}
396
397		inline void
398	2x	posix_stream_file::file_op::destroy()
399		{
400	2x	stop_cb.reset();
401	2x	auto local_ex = ex;
402	2x	impl_ptr.reset();
403	2x	local_ex.on_work_finished();
404	2x	}
405
406		} // namespace boost::corosio::detail
407
408		#endif // BOOST_COROSIO_POSIX
409
410		#endif // BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_STREAM_FILE_HPP
411