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// Copyright (c) 2018 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
//
// Logger implementation for the Windows platform.
#ifndef STORAGE_LEVELDB_UTIL_WINDOWS_LOGGER_H_
#define STORAGE_LEVELDB_UTIL_WINDOWS_LOGGER_H_
#include <cassert>
#include <cstdarg>
#include <cstdio>
#include <ctime>
#include <sstream>
#include <thread>
#include "leveldb/env.h"
namespace leveldb {
class WindowsLogger final : public Logger {
public:
// Creates a logger that writes to the given file.
//
// The PosixLogger instance takes ownership of the file handle.
explicit WindowsLogger(std::FILE* fp) : fp_(fp) { assert(fp != nullptr); }
~WindowsLogger() override { std::fclose(fp_); }
void Logv(const char* format, va_list arguments) override {
// Record the time as close to the Logv() call as possible.
SYSTEMTIME now_components;
::GetLocalTime(&now_components);
// Record the thread ID.
constexpr const int kMaxThreadIdSize = 32;
std::ostringstream thread_stream;
thread_stream << std::this_thread::get_id();
std::string thread_id = thread_stream.str();
if (thread_id.size() > kMaxThreadIdSize) {
thread_id.resize(kMaxThreadIdSize);
}
// We first attempt to print into a stack-allocated buffer. If this attempt
// fails, we make a second attempt with a dynamically allocated buffer.
constexpr const int kStackBufferSize = 512;
char stack_buffer[kStackBufferSize];
static_assert(sizeof(stack_buffer) == static_cast<size_t>(kStackBufferSize),
"sizeof(char) is expected to be 1 in C++");
int dynamic_buffer_size = 0; // Computed in the first iteration.
for (int iteration = 0; iteration < 2; ++iteration) {
const int buffer_size =
(iteration == 0) ? kStackBufferSize : dynamic_buffer_size;
char* const buffer =
(iteration == 0) ? stack_buffer : new char[dynamic_buffer_size];
// Print the header into the buffer.
int buffer_offset = snprintf(
buffer, buffer_size, "%04d/%02d/%02d-%02d:%02d:%02d.%06d %s ",
now_components.wYear, now_components.wMonth, now_components.wDay,
now_components.wHour, now_components.wMinute, now_components.wSecond,
static_cast<int>(now_components.wMilliseconds * 1000),
thread_id.c_str());
// The header can be at most 28 characters (10 date + 15 time +
// 3 delimiters) plus the thread ID, which should fit comfortably into the
// static buffer.
assert(buffer_offset <= 28 + kMaxThreadIdSize);
static_assert(28 + kMaxThreadIdSize < kStackBufferSize,
"stack-allocated buffer may not fit the message header");
assert(buffer_offset < buffer_size);
// Print the message into the buffer.
std::va_list arguments_copy;
va_copy(arguments_copy, arguments);
buffer_offset +=
std::vsnprintf(buffer + buffer_offset, buffer_size - buffer_offset,
format, arguments_copy);
va_end(arguments_copy);
// The code below may append a newline at the end of the buffer, which
// requires an extra character.
if (buffer_offset >= buffer_size - 1) {
// The message did not fit into the buffer.
if (iteration == 0) {
// Re-run the loop and use a dynamically-allocated buffer. The buffer
// will be large enough for the log message, an extra newline and a
// null terminator.
dynamic_buffer_size = buffer_offset + 2;
continue;
}
// The dynamically-allocated buffer was incorrectly sized. This should
// not happen, assuming a correct implementation of (v)snprintf. Fail
// in tests, recover by truncating the log message in production.
assert(false);
buffer_offset = buffer_size - 1;
}
// Add a newline if necessary.
if (buffer[buffer_offset - 1] != '\n') {
buffer[buffer_offset] = '\n';
++buffer_offset;
}
assert(buffer_offset <= buffer_size);
std::fwrite(buffer, 1, buffer_offset, fp_);
std::fflush(fp_);
if (iteration != 0) {
delete[] buffer;
}
break;
}
}
private:
std::FILE* const fp_;
};
} // namespace leveldb
#endif // STORAGE_LEVELDB_UTIL_WINDOWS_LOGGER_H_
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