2 * Copyright 2004-present 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.
16 #include <folly/experimental/logging/AsyncFileWriter.h>
18 #include <folly/Exception.h>
19 #include <folly/FileUtil.h>
20 #include <folly/experimental/logging/LoggerDB.h>
21 #include <folly/system/ThreadName.h>
24 using folly::StringPiece;
28 AsyncFileWriter::AsyncFileWriter(StringPiece path)
29 : AsyncFileWriter{File{path.str(), O_WRONLY | O_APPEND | O_CREAT}} {}
31 AsyncFileWriter::AsyncFileWriter(folly::File&& file)
32 : file_{std::move(file)}, ioThread_([this] { ioThread(); }) {}
34 AsyncFileWriter::~AsyncFileWriter() {
36 messageReady_.notify_one();
40 void AsyncFileWriter::writeMessage(StringPiece buffer, uint32_t flags) {
41 return writeMessage(buffer.str(), flags);
44 void AsyncFileWriter::writeMessage(std::string&& buffer, uint32_t flags) {
45 auto data = data_.lock();
46 if ((data->currentBufferSize >= data->maxBufferBytes) &&
47 !(flags & NEVER_DISCARD)) {
52 data->currentBufferSize += buffer.size();
53 auto* queue = data->getCurrentQueue();
54 queue->emplace_back(std::move(buffer));
55 messageReady_.notify_one();
58 void AsyncFileWriter::flush() {
59 auto data = data_.lock();
60 auto start = data->ioThreadCounter;
62 // Wait until ioThreadCounter increments by at least two.
63 // Waiting for a single increment is not sufficient, as this happens after
64 // the I/O thread has swapped the queues, which is before it has actually
66 while (data->ioThreadCounter < start + 2) {
67 if (data->ioThreadDone) {
71 // Enqueue an empty string and wake the I/O thread.
72 // The empty string ensures that the I/O thread will break out of its wait
73 // loop and increment the ioThreadCounter, even if there is no other work
75 data->getCurrentQueue()->emplace_back();
76 messageReady_.notify_one();
78 // Wait for notification from the I/O thread that it has done work.
79 ioCV_.wait(data.getUniqueLock());
83 void AsyncFileWriter::ioThread() {
84 folly::setThreadName("log_writer");
87 // With the lock held, grab a pointer to the current queue, then increment
88 // the ioThreadCounter index so that other threads will write into the
89 // other queue as we process this one.
90 std::vector<std::string>* ioQueue;
94 auto data = data_.lock();
95 ioQueue = data->getCurrentQueue();
96 while (ioQueue->empty() && !data->stop) {
97 messageReady_.wait(data.getUniqueLock());
100 ++data->ioThreadCounter;
101 numDiscarded = data->numDiscarded;
102 data->numDiscarded = 0;
103 data->currentBufferSize = 0;
108 // Write the log messages now that we have released the lock
111 } catch (const std::exception& ex) {
115 // clear() empties the vector, but the allocated capacity remains so we can
116 // just reuse it without having to re-allocate in most cases.
119 if (numDiscarded > 0) {
120 auto msg = getNumDiscardedMsg(numDiscarded);
122 auto ret = folly::writeFull(file_.fd(), msg.data(), msg.size());
123 // We currently ignore errors from writeFull() here.
124 // There's not much we can really do.
130 data_->ioThreadDone = true;
136 void AsyncFileWriter::performIO(std::vector<std::string>* ioQueue) {
137 // kNumIovecs controls the maximum number of strings we write at once in a
138 // single writev() call.
139 constexpr int kNumIovecs = 64;
140 std::array<iovec, kNumIovecs> iovecs;
143 while (idx < ioQueue->size()) {
145 while (numIovecs < kNumIovecs && idx < ioQueue->size()) {
146 const auto& str = (*ioQueue)[idx];
147 iovecs[numIovecs].iov_base = const_cast<char*>(str.data());
148 iovecs[numIovecs].iov_len = str.size();
153 auto ret = folly::writevFull(file_.fd(), iovecs.data(), numIovecs);
154 folly::checkUnixError(ret, "writeFull() failed");
158 void AsyncFileWriter::onIoError(const std::exception& ex) {
159 LoggerDB::internalWarning(
162 "error writing to log file ",
164 " in AsyncFileWriter: ",
165 folly::exceptionStr(ex));
168 std::string AsyncFileWriter::getNumDiscardedMsg(size_t numDiscarded) {
169 // We may want to make this customizable in the future (e.g., to allow it to
170 // conform to the LogFormatter style being used).
171 // For now just return a simple fixed message.
172 return folly::to<std::string>(
174 " log messages discarded: logging faster than we can write\n");