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/continuation_op.hpp>
24		#include <boost/corosio/detail/thread_pool.hpp>
25		#include <boost/corosio/detail/scheduler.hpp>
26		#include <boost/corosio/detail/buffer_param.hpp>
27		#include <boost/corosio/native/detail/make_err.hpp>
28		#include <boost/capy/ex/executor_ref.hpp>
29		#include <boost/capy/error.hpp>
30		#include <boost/capy/buffers.hpp>
31
32		#include <atomic>
33		#include <coroutine>
34		#include <cstddef>
35		#include <cstdint>
36		#include <filesystem>
37		#include <limits>
38		#include <memory>
39		#include <optional>
40		#include <stop_token>
41		#include <system_error>
42
43		#include <errno.h>
44		#include <fcntl.h>
45		#include <sys/stat.h>
46		#include <sys/uio.h>
47		#include <unistd.h>
48
49		/*
50		POSIX Stream File Implementation
51		=================================
52
53		Regular files cannot be monitored by epoll/kqueue/select — the kernel
54		always reports them as ready. Blocking I/O (pread/pwrite) is dispatched
55		to a shared thread pool, with completion posted back to the scheduler.
56
57		This follows the same pattern as posix_resolver: pool_work_item for
58		dispatch, scheduler_op for completion, shared_from_this for lifetime.
59
60		Completion Flow
61		---------------
62		1. read_some() sets up file_read_op, posts to thread pool
63		2. Pool thread runs preadv() (blocking)
64		3. Pool thread stores results, posts scheduler_op to scheduler
65		4. Scheduler invokes op() which resumes the coroutine
66
67		Single-Inflight Constraint
68		--------------------------
69		Only one asynchronous operation may be in flight at a time on a
70		given file object. Concurrent read and write is not supported
71		because both share offset_ without synchronization.
72		*/
73
74		namespace boost::corosio::detail {
75
76		struct scheduler;
77		class posix_stream_file_service;
78
79		/** Stream file implementation for POSIX backends.
80
81		Each instance contains embedded operation objects (read_op_, write_op_)
82		that are reused across calls. This avoids per-operation heap allocation.
83		*/
84		class posix_stream_file final
85		: public stream_file::implementation
86		, public std::enable_shared_from_this<posix_stream_file>
87		, public intrusive_list<posix_stream_file>::node
88		{
89		friend class posix_stream_file_service;
90
91		public:
92		static constexpr std::size_t max_buffers = 16;
93
94		/** Operation state for a single file read or write. */
95		struct file_op : scheduler_op
96		{
97		struct canceller
98		{
99		file_op* op;
100	1x	void operator()() const noexcept
101		{
102	1x	op->request_cancel();
103	1x	}
104		};
105
106		// Coroutine state
107		std::coroutine_handle<> h;
108		detail::continuation_op cont_op;
109		capy::executor_ref ex;
110
111		// Output pointers
112		std::error_code* ec_out = nullptr;
113		std::size_t* bytes_out = nullptr;
114
115		// Buffer data (copied from buffer_param at submission time)
116		iovec iovecs[max_buffers];
117		int iovec_count = 0;
118
119		// Result storage (populated by worker thread)
120		int errn = 0;
121		std::size_t bytes_transferred = 0;
122		bool is_read = false;
123
124		// Thread coordination
125		std::atomic<bool> cancelled{false};
126		std::optional<std::stop_callback<canceller>> stop_cb;
127
128		/// Prevents use-after-free when file is closed with pending ops.
129		std::shared_ptr<void> impl_ref;
130
131	52x	file_op() = default;
132
133	12x	void reset() noexcept
134		{
135	12x	iovec_count = 0;
136	12x	errn = 0;
137	12x	bytes_transferred = 0;
138	12x	is_read = false;
139	12x	cancelled.store(false, std::memory_order_relaxed);
140	12x	stop_cb.reset();
141	12x	impl_ref.reset();
142	12x	ec_out = nullptr;
143	12x	bytes_out = nullptr;
144	12x	}
145
146		void operator()() override;
147		void destroy() override;
148
149	141x	void request_cancel() noexcept
150		{
151	141x	cancelled.store(true, std::memory_order_release);
152	141x	}
153
154	12x	void start(std::stop_token const& token)
155		{
156	12x	cancelled.store(false, std::memory_order_release);
157	12x	stop_cb.reset();
158	12x	if (token.stop_possible())
159	1x	stop_cb.emplace(token, canceller{this});
160	12x	}
161		};
162
163		/** Pool work item for thread pool dispatch. */
164		struct pool_op : pool_work_item
165		{
166		posix_stream_file* file_ = nullptr;
167		std::shared_ptr<posix_stream_file> ref_;
168		};
169
170		explicit posix_stream_file(posix_stream_file_service& svc) noexcept;
171
172		// -- io_stream::implementation --
173
174		std::coroutine_handle<> read_some(
175		std::coroutine_handle<>,
176		capy::executor_ref,
177		buffer_param,
178		std::stop_token,
179		std::error_code*,
180		std::size_t*) override;
181
182		std::coroutine_handle<> write_some(
183		std::coroutine_handle<>,
184		capy::executor_ref,
185		buffer_param,
186		std::stop_token,
187		std::error_code*,
188		std::size_t*) override;
189
190		// -- stream_file::implementation --
191
192	81x	native_handle_type native_handle() const noexcept override
193		{
194	81x	return fd_;
195		}
196
197	70x	void cancel() noexcept override
198		{
199	70x	read_op_.request_cancel();
200	70x	write_op_.request_cancel();
201	70x	}
202
203		std::uint64_t size() const override;
204		void resize(std::uint64_t new_size) override;
205		void sync_data() override;
206		void sync_all() override;
207		native_handle_type release() override;
208		void assign(native_handle_type handle) override;
209		std::uint64_t seek(std::int64_t offset, file_base::seek_basis origin) override;
210
211		// -- Internal --
212
213		/** Open the file and store the fd. */
214		std::error_code open_file(
215		std::filesystem::path const& path, file_base::flags mode);
216
217		/** Close the file descriptor. */
218		void close_file() noexcept;
219
220		private:
221		posix_stream_file_service& svc_;
222		int fd_ = -1;
223		std::uint64_t offset_ = 0;
224
225		file_op read_op_;
226		file_op write_op_;
227		pool_op read_pool_op_;
228		pool_op write_pool_op_;
229
230		static void do_read_work(pool_work_item*) noexcept;
231		static void do_write_work(pool_work_item*) noexcept;
232		};
233
234		// ---------------------------------------------------------------------------
235		// Inline implementation
236		// ---------------------------------------------------------------------------
237
238		inline
239	26x	posix_stream_file::posix_stream_file(posix_stream_file_service& svc) noexcept
240	26x	: svc_(svc)
241		{
242	26x	}
243
244		inline std::error_code
245	19x	posix_stream_file::open_file(
246		std::filesystem::path const& path, file_base::flags mode)
247		{
248	19x	close_file();
249
250	19x	int oflags = 0;
251
252		// Access mode
253	19x	unsigned access = static_cast<unsigned>(mode) & 3u;
254	19x	if (access == static_cast<unsigned>(file_base::read_write))
255	2x	oflags \|= O_RDWR;
256	17x	else if (access == static_cast<unsigned>(file_base::write_only))
257	7x	oflags \|= O_WRONLY;
258		else
259	10x	oflags \|= O_RDONLY;
260
261		// Creation flags
262	19x	if ((mode & file_base::create) != file_base::flags(0))
263	6x	oflags \|= O_CREAT;
264	19x	if ((mode & file_base::exclusive) != file_base::flags(0))
265	1x	oflags \|= O_EXCL;
266	19x	if ((mode & file_base::truncate) != file_base::flags(0))
267	5x	oflags \|= O_TRUNC;
268	19x	if ((mode & file_base::append) != file_base::flags(0))
269	1x	oflags \|= O_APPEND;
270	19x	if ((mode & file_base::sync_all_on_write) != file_base::flags(0))
271	✗	oflags \|= O_SYNC;
272
273	19x	int fd = ::open(path.c_str(), oflags, 0666);
274	19x	if (fd < 0)
275	2x	return make_err(errno);
276
277	17x	fd_ = fd;
278	17x	offset_ = 0;
279
280		// Append mode: position at end-of-file (preadv/pwritev use
281		// explicit offsets, so O_APPEND alone is not sufficient).
282	17x	if ((mode & file_base::append) != file_base::flags(0))
283		{
284		struct stat st;
285	1x	if (::fstat(fd, &st) < 0)
286		{
287	✗	int err = errno;
288	✗	::close(fd);
289	✗	fd_ = -1;
290	✗	return make_err(err);
291		}
292	1x	offset_ = static_cast<std::uint64_t>(st.st_size);
293		}
294
295		#ifdef POSIX_FADV_SEQUENTIAL
296	17x	::posix_fadvise(fd_, 0, 0, POSIX_FADV_SEQUENTIAL);
297		#endif
298
299	17x	return {};
300		}
301
302		inline void
303	89x	posix_stream_file::close_file() noexcept
304		{
305	89x	if (fd_ >= 0)
306		{
307	17x	::close(fd_);
308	17x	fd_ = -1;
309		}
310	89x	}
311
312		inline std::uint64_t
313	3x	posix_stream_file::size() const
314		{
315		struct stat st;
316	3x	if (::fstat(fd_, &st) < 0)
317	✗	throw_system_error(make_err(errno), "stream_file::size");
318	3x	return static_cast<std::uint64_t>(st.st_size);
319		}
320
321		inline void
322	1x	posix_stream_file::resize(std::uint64_t new_size)
323		{
324	1x	if (new_size > static_cast<std::uint64_t>(std::numeric_limits<off_t>::max()))
325	✗	throw_system_error(make_err(EOVERFLOW), "stream_file::resize");
326	1x	if (::ftruncate(fd_, static_cast<off_t>(new_size)) < 0)
327	✗	throw_system_error(make_err(errno), "stream_file::resize");
328	1x	}
329
330		inline void
331	1x	posix_stream_file::sync_data()
332		{
333		#if BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
334	1x	if (::fdatasync(fd_) < 0)
335		#else // BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
336		if (::fsync(fd_) < 0)
337		#endif // BOOST_COROSIO_HAS_POSIX_SYNCHRONIZED_IO
338	✗	throw_system_error(make_err(errno), "stream_file::sync_data");
339	1x	}
340
341		inline void
342	1x	posix_stream_file::sync_all()
343		{
344	1x	if (::fsync(fd_) < 0)
345	✗	throw_system_error(make_err(errno), "stream_file::sync_all");
346	1x	}
347
348		inline native_handle_type
349	1x	posix_stream_file::release()
350		{
351	1x	int fd = fd_;
352	1x	fd_ = -1;
353	1x	offset_ = 0;
354	1x	return fd;
355		}
356
357		inline void
358	1x	posix_stream_file::assign(native_handle_type handle)
359		{
360	1x	close_file();
361	1x	fd_ = handle;
362	1x	offset_ = 0;
363	1x	}
364
365		inline std::uint64_t
366	7x	posix_stream_file::seek(std::int64_t offset, file_base::seek_basis origin)
367		{
368		// We track offset_ ourselves (not the kernel fd offset)
369		// because preadv/pwritev use explicit offsets.
370		std::int64_t new_pos;
371
372	7x	if (origin == file_base::seek_set)
373		{
374	3x	new_pos = offset;
375		}
376	4x	else if (origin == file_base::seek_cur)
377		{
378	2x	new_pos = static_cast<std::int64_t>(offset_) + offset;
379		}
380		else
381		{
382		struct stat st;
383	2x	if (::fstat(fd_, &st) < 0)
384	✗	throw_system_error(make_err(errno), "stream_file::seek");
385	2x	new_pos = st.st_size + offset;
386		}
387
388	7x	if (new_pos < 0)
389	3x	throw_system_error(make_err(EINVAL), "stream_file::seek");
390	4x	if (new_pos > static_cast<std::int64_t>(std::numeric_limits<off_t>::max()))
391	✗	throw_system_error(make_err(EOVERFLOW), "stream_file::seek");
392
393	4x	offset_ = static_cast<std::uint64_t>(new_pos);
394
395	4x	return offset_;
396		}
397
398		// -- file_op completion handler --
399		// (read_some, write_some, do_read_work, do_write_work are
400		// defined in posix_stream_file_service.hpp after the service)
401
402		inline void
403	12x	posix_stream_file::file_op::operator()()
404		{
405	12x	stop_cb.reset();
406
407	12x	bool const was_cancelled = cancelled.load(std::memory_order_acquire);
408
409	12x	if (ec_out)
410		{
411	12x	if (was_cancelled)
412	1x	*ec_out = capy::error::canceled;
413	11x	else if (errn != 0)
414	✗	*ec_out = make_err(errn);
415	11x	else if (is_read && bytes_transferred == 0)
416	1x	*ec_out = capy::error::eof;
417		else
418	10x	*ec_out = {};
419		}
420
421	12x	if (bytes_out)
422	12x	*bytes_out = was_cancelled ? 0 : bytes_transferred;
423
424		// Move impl_ref to a local so members remain valid through
425		// dispatch — impl_ref may be the last shared_ptr keeping
426		// the parent posix_stream_file (which embeds this file_op) alive.
427	12x	auto prevent_destroy = std::move(impl_ref);
428	12x	ex.on_work_finished();
429	12x	cont_op.cont.h = h;
430	12x	dispatch_coro(ex, cont_op.cont).resume();
431	12x	}
432
433		inline void
434	✗	posix_stream_file::file_op::destroy()
435		{
436	✗	stop_cb.reset();
437	✗	auto local_ex = ex;
438	✗	impl_ref.reset();
439	✗	local_ex.on_work_finished();
440	✗	}
441
442		} // namespace boost::corosio::detail
443
444		#endif // BOOST_COROSIO_POSIX
445
446		#endif // BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_STREAM_FILE_HPP
447