2 * Copyright 2013 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_IO_ASYNCIO_H_
18 #define FOLLY_IO_ASYNCIO_H_
20 #include <sys/types.h>
33 #include <boost/noncopyable.hpp>
35 #include "folly/Portability.h"
36 #include "folly/Range.h"
41 * An AsyncIOOp represents a pending operation. You may set a notification
42 * callback or you may use this class's methods directly.
44 * The op must remain allocated until completion.
46 class AsyncIOOp : private boost::noncopyable {
48 friend std::ostream& operator<<(std::ostream& stream, const AsyncIOOp& o);
50 typedef std::function<void(AsyncIOOp*)> NotificationCallback;
52 explicit AsyncIOOp(NotificationCallback cb = NotificationCallback());
55 // There would be a cancel() method here if Linux AIO actually implemented
56 // it. But let's not get your hopes up.
66 * Initiate a read request.
68 void pread(int fd, void* buf, size_t size, off_t start);
69 void pread(int fd, Range<unsigned char*> range, off_t start);
70 void preadv(int fd, const iovec* iov, int iovcnt, off_t start);
73 * Initiate a write request.
75 void pwrite(int fd, const void* buf, size_t size, off_t start);
76 void pwrite(int fd, Range<const unsigned char*> range, off_t start);
77 void pwritev(int fd, const iovec* iov, int iovcnt, off_t start);
80 * Return the current operation state.
82 State state() const { return state_; }
85 * Reset the operation for reuse. It is an error to call reset() on
86 * an Op that is still pending.
88 void reset(NotificationCallback cb = NotificationCallback());
90 void setNotificationCallback(NotificationCallback cb) { cb_ = std::move(cb); }
91 const NotificationCallback& notificationCallback() const { return cb_; }
94 * Retrieve the result of this operation. Returns >=0 on success,
95 * -errno on failure (that is, using the Linux kernel error reporting
96 * conventions). Use checkKernelError (folly/Exception.h) on the result to
97 * throw a std::system_error in case of error instead.
99 * It is an error to call this if the Op hasn't yet started or is still
102 ssize_t result() const;
107 void complete(ssize_t result);
109 NotificationCallback cb_;
115 std::ostream& operator<<(std::ostream& stream, const AsyncIOOp& o);
116 std::ostream& operator<<(std::ostream& stream, AsyncIOOp::State state);
119 * C++ interface around Linux Async IO.
121 class AsyncIO : private boost::noncopyable {
123 typedef AsyncIOOp Op;
131 * Create an AsyncIO context capable of holding at most 'capacity' pending
132 * requests at the same time. As requests complete, others can be scheduled,
133 * as long as this limit is not exceeded.
135 * Note: the maximum number of allowed concurrent requests is controlled
136 * by the fs.aio-max-nr sysctl, the default value is usually 64K.
138 * If pollMode is POLLABLE, pollFd() will return a file descriptor that
139 * can be passed to poll / epoll / select and will become readable when
140 * any IOs on this AsyncIO have completed. If you do this, you must use
141 * pollCompleted() instead of wait() -- do not read from the pollFd()
142 * file descriptor directly.
144 * You may use the same AsyncIO object from multiple threads, as long as
145 * there is only one concurrent caller of wait() / pollCompleted() (perhaps
146 * by always calling it from the same thread, or by providing appropriate
147 * mutual exclusion) In this case, pending() returns a snapshot
148 * of the current number of pending requests.
150 explicit AsyncIO(size_t capacity, PollMode pollMode=NOT_POLLABLE);
154 * Wait for at least minRequests to complete. Returns the requests that
155 * have completed; the returned range is valid until the next call to
156 * wait(). minRequests may be 0 to not block.
158 Range<Op**> wait(size_t minRequests);
161 * Return the number of pending requests.
163 size_t pending() const { return pending_; }
166 * Return the maximum number of requests that can be kept outstanding
169 size_t capacity() const { return capacity_; }
172 * If POLLABLE, return a file descriptor that can be passed to poll / epoll
173 * and will become readable when any async IO operations have completed.
174 * If NOT_POLLABLE, return -1.
176 int pollFd() const { return pollFd_; }
179 * If POLLABLE, call instead of wait after the file descriptor returned
180 * by pollFd() became readable. The returned range is valid until the next
181 * call to pollCompleted().
183 Range<Op**> pollCompleted();
186 * Submit an op for execution.
191 void decrementPending();
192 void initializeContext();
194 Range<Op**> doWait(size_t minRequests, size_t maxRequests);
197 std::atomic<bool> ctxSet_;
198 std::mutex initMutex_;
200 std::atomic<ssize_t> pending_;
201 const ssize_t capacity_;
203 std::vector<Op*> completed_;
207 * Wrapper around AsyncIO that allows you to schedule more requests than
208 * the AsyncIO's object capacity. Other requests are queued and processed
214 * Create a queue, using the given AsyncIO object.
215 * The AsyncIO object may not be used by anything else until the
216 * queue is destroyed.
218 explicit AsyncIOQueue(AsyncIO* asyncIO);
221 size_t queued() const { return queue_.size(); }
224 * Submit an op to the AsyncIO queue. The op will be queued until
225 * the AsyncIO object has room.
227 void submit(AsyncIOOp* op);
230 * Submit a delayed op to the AsyncIO queue; this allows you to postpone
231 * creation of the Op (which may require allocating memory, etc) until
232 * the AsyncIO object has room.
234 typedef std::function<AsyncIOOp*()> OpFactory;
235 void submit(OpFactory op);
237 void onCompleted(AsyncIOOp* op);
242 std::deque<OpFactory> queue_;
247 #endif /* FOLLY_IO_ASYNCIO_H_ */