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>
23 using folly::StringPiece;
27 AsyncFileWriter::AsyncFileWriter(StringPiece path)
28 : AsyncFileWriter{File{path.str(), O_WRONLY | O_APPEND | O_CREAT}} {}
30 AsyncFileWriter::AsyncFileWriter(folly::File&& file)
31 : file_{std::move(file)}, ioThread_([this] { ioThread(); }) {}
33 AsyncFileWriter::~AsyncFileWriter() {
35 messageReady_.notify_one();
39 void AsyncFileWriter::writeMessage(StringPiece buffer) {
40 return writeMessage(buffer.str());
43 void AsyncFileWriter::writeMessage(std::string&& buffer) {
44 auto data = data_.lock();
45 if (data->currentBufferSize >= data->maxBufferBytes) {
50 data->currentBufferSize += buffer.size();
51 auto* queue = data->getCurrentQueue();
52 queue->emplace_back(std::move(buffer));
53 messageReady_.notify_one();
56 void AsyncFileWriter::flush() {
57 auto data = data_.lock();
58 auto start = data->ioThreadCounter;
60 // Wait until ioThreadCounter increments by at least two.
61 // Waiting for a single increment is not sufficient, as this happens after
62 // the I/O thread has swapped the queues, which is before it has actually
64 while (data->ioThreadCounter < start + 2) {
65 if (data->ioThreadDone) {
69 // Enqueue an empty string and wake the I/O thread.
70 // The empty string ensures that the I/O thread will break out of its wait
71 // loop and increment the ioThreadCounter, even if there is no other work
73 data->getCurrentQueue()->emplace_back();
74 messageReady_.notify_one();
76 // Wait for notification from the I/O thread that it has done work.
77 ioCV_.wait(data.getUniqueLock());
81 void AsyncFileWriter::ioThread() {
83 // With the lock held, grab a pointer to the current queue, then increment
84 // the ioThreadCounter index so that other threads will write into the
85 // other queue as we process this one.
86 std::vector<std::string>* ioQueue;
90 auto data = data_.lock();
91 ioQueue = data->getCurrentQueue();
92 while (ioQueue->empty() && !data->stop) {
93 messageReady_.wait(data.getUniqueLock());
96 ++data->ioThreadCounter;
97 numDiscarded = data->numDiscarded;
98 data->numDiscarded = 0;
99 data->currentBufferSize = 0;
104 // Write the log messages now that we have released the lock
107 } catch (const std::exception& ex) {
111 // clear() empties the vector, but the allocated capacity remains so we can
112 // just reuse it without having to re-allocate in most cases.
115 if (numDiscarded > 0) {
116 auto msg = getNumDiscardedMsg(numDiscarded);
118 auto ret = folly::writeFull(file_.fd(), msg.data(), msg.size());
119 // We currently ignore errors from writeFull() here.
120 // There's not much we can really do.
126 data_->ioThreadDone = true;
132 void AsyncFileWriter::performIO(std::vector<std::string>* ioQueue) {
133 // kNumIovecs controls the maximum number of strings we write at once in a
134 // single writev() call.
135 constexpr int kNumIovecs = 64;
136 std::array<iovec, kNumIovecs> iovecs;
139 while (idx < ioQueue->size()) {
141 while (numIovecs < kNumIovecs && idx < ioQueue->size()) {
142 const auto& str = (*ioQueue)[idx];
143 iovecs[numIovecs].iov_base = const_cast<char*>(str.data());
144 iovecs[numIovecs].iov_len = str.size();
149 auto ret = folly::writevFull(file_.fd(), iovecs.data(), numIovecs);
150 folly::checkUnixError(ret, "writeFull() failed");
154 void AsyncFileWriter::onIoError(const std::exception& ex) {
155 LoggerDB::internalWarning(
158 "error writing to log file ",
160 " in AsyncFileWriter: ",
161 folly::exceptionStr(ex));
164 std::string AsyncFileWriter::getNumDiscardedMsg(size_t numDiscarded) {
165 // We may want to make this customizable in the future (e.g., to allow it to
166 // conform to the LogFormatter style being used).
167 // For now just return a simple fixed message.
168 return folly::to<std::string>(
170 " log messages discarded: logging faster than we can write\n");