2 * Copyright 2016 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.
19 #include <sys/types.h>
32 #include <boost/noncopyable.hpp>
34 #include <folly/Portability.h>
35 #include <folly/Range.h>
40 * An AsyncIOOp represents a pending operation. You may set a notification
41 * callback or you may use this class's methods directly.
43 * The op must remain allocated until completion.
45 class AsyncIOOp : private boost::noncopyable {
47 friend std::ostream& operator<<(std::ostream& stream, const AsyncIOOp& o);
49 typedef std::function<void(AsyncIOOp*)> NotificationCallback;
51 explicit AsyncIOOp(NotificationCallback cb = NotificationCallback());
54 // There would be a cancel() method here if Linux AIO actually implemented
55 // it. But let's not get your hopes up.
65 * Initiate a read request.
67 void pread(int fd, void* buf, size_t size, off_t start);
68 void pread(int fd, Range<unsigned char*> range, off_t start);
69 void preadv(int fd, const iovec* iov, int iovcnt, off_t start);
72 * Initiate a write request.
74 void pwrite(int fd, const void* buf, size_t size, off_t start);
75 void pwrite(int fd, Range<const unsigned char*> range, off_t start);
76 void pwritev(int fd, const iovec* iov, int iovcnt, off_t start);
79 * Return the current operation state.
81 State state() const { return state_; }
84 * Reset the operation for reuse. It is an error to call reset() on
85 * an Op that is still pending.
87 void reset(NotificationCallback cb = NotificationCallback());
89 void setNotificationCallback(NotificationCallback cb) { cb_ = std::move(cb); }
90 const NotificationCallback& notificationCallback() const { return cb_; }
93 * Retrieve the result of this operation. Returns >=0 on success,
94 * -errno on failure (that is, using the Linux kernel error reporting
95 * conventions). Use checkKernelError (folly/Exception.h) on the result to
96 * throw a std::system_error in case of error instead.
98 * It is an error to call this if the Op hasn't yet started or is still
101 ssize_t result() const;
106 void complete(ssize_t result);
108 NotificationCallback cb_;
114 std::ostream& operator<<(std::ostream& stream, const AsyncIOOp& o);
115 std::ostream& operator<<(std::ostream& stream, AsyncIOOp::State state);
118 * C++ interface around Linux Async IO.
120 class AsyncIO : private boost::noncopyable {
122 typedef AsyncIOOp Op;
130 * Create an AsyncIO context capable of holding at most 'capacity' pending
131 * requests at the same time. As requests complete, others can be scheduled,
132 * as long as this limit is not exceeded.
134 * Note: the maximum number of allowed concurrent requests is controlled
135 * by the fs.aio-max-nr sysctl, the default value is usually 64K.
137 * If pollMode is POLLABLE, pollFd() will return a file descriptor that
138 * can be passed to poll / epoll / select and will become readable when
139 * any IOs on this AsyncIO have completed. If you do this, you must use
140 * pollCompleted() instead of wait() -- do not read from the pollFd()
141 * file descriptor directly.
143 * You may use the same AsyncIO object from multiple threads, as long as
144 * there is only one concurrent caller of wait() / pollCompleted() (perhaps
145 * by always calling it from the same thread, or by providing appropriate
146 * mutual exclusion) In this case, pending() returns a snapshot
147 * of the current number of pending requests.
149 explicit AsyncIO(size_t capacity, PollMode pollMode=NOT_POLLABLE);
153 * Wait for at least minRequests to complete. Returns the requests that
154 * have completed; the returned range is valid until the next call to
155 * wait(). minRequests may be 0 to not block.
157 Range<Op**> wait(size_t minRequests);
160 * Return the number of pending requests.
162 size_t pending() const { return pending_; }
165 * Return the maximum number of requests that can be kept outstanding
168 size_t capacity() const { return capacity_; }
171 * Return the accumulative number of submitted I/O, since this object
174 size_t totalSubmits() const { return submitted_; }
177 * If POLLABLE, return a file descriptor that can be passed to poll / epoll
178 * and will become readable when any async IO operations have completed.
179 * If NOT_POLLABLE, return -1.
181 int pollFd() const { return pollFd_; }
184 * If POLLABLE, call instead of wait after the file descriptor returned
185 * by pollFd() became readable. The returned range is valid until the next
186 * call to pollCompleted().
188 Range<Op**> pollCompleted();
191 * Submit an op for execution.
196 void decrementPending();
197 void initializeContext();
199 Range<Op**> doWait(size_t minRequests, size_t maxRequests);
202 std::atomic<bool> ctxSet_;
203 std::mutex initMutex_;
205 std::atomic<size_t> pending_;
206 std::atomic<size_t> submitted_;
207 const size_t capacity_;
209 std::vector<Op*> completed_;
213 * Wrapper around AsyncIO that allows you to schedule more requests than
214 * the AsyncIO's object capacity. Other requests are queued and processed
220 * Create a queue, using the given AsyncIO object.
221 * The AsyncIO object may not be used by anything else until the
222 * queue is destroyed.
224 explicit AsyncIOQueue(AsyncIO* asyncIO);
227 size_t queued() const { return queue_.size(); }
230 * Submit an op to the AsyncIO queue. The op will be queued until
231 * the AsyncIO object has room.
233 void submit(AsyncIOOp* op);
236 * Submit a delayed op to the AsyncIO queue; this allows you to postpone
237 * creation of the Op (which may require allocating memory, etc) until
238 * the AsyncIO object has room.
240 typedef std::function<AsyncIOOp*()> OpFactory;
241 void submit(OpFactory op);
244 void onCompleted(AsyncIOOp* op);
249 std::deque<OpFactory> queue_;