[RocksDB] Fix PosixLogger and AutoRollLogger thread safety

Summary:
PosixLogger and AutoRollLogger do not seem to be thread safe.
For PosixLogger, log_size_ is not atomically updated.
For AutoRollLogger, the underlying logger_ might be deleted by
one thread while still being accessed by another.

Test Plan: make check

Reviewers: kailiu, dhruba, heyongqiang

Reviewed By: kailiu

CC: leveldb, zshao, sheki

Differential Revision: https://reviews.facebook.net/D9699

util/auto_roll_logger.cc

 #include "util/auto_roll_logger.h"
+#include "util/mutexlock.h"
 
 using namespace std;
 
@@ -35,17 +36,26 @@ void AutoRollLogger::RollLogFile() {
 void AutoRollLogger::Logv(const char* format, va_list ap) {
   assert(GetStatus().ok());
 
-  if (kLogFileTimeToRoll > 0 && LogExpired()) {
-    RollLogFile();
-    ResetLogger();
-  }
-
-  logger_->Logv(format, ap);
+  std::shared_ptr<Logger> logger;
+  {
+    MutexLock l(&mutex_);
+    if ((kLogFileTimeToRoll > 0 && LogExpired()) ||
+        (kMaxLogFileSize > 0 && logger_->GetLogFileSize() >= kMaxLogFileSize)) {
+      RollLogFile();
+      ResetLogger();
+    }
 
-  if (kMaxLogFileSize > 0 && logger_->GetLogFileSize() > kMaxLogFileSize) {
-    RollLogFile();
-    ResetLogger();
+    // pin down the current logger_ instance before releasing the mutex.
+    logger = logger_;
   }
+
+  // Another thread could have put a new Logger instance into logger_ by now.
+  // However, since logger is still hanging on to the previous instance
+  // (reference count is not zero), we don't have to worry about it being
+  // deleted while we are accessing it.
+  // Note that logv itself is not mutex protected to allow maximum concurrency,
+  // as thread safety should have been handled by the underlying logger.
+  logger->Logv(format, ap);
 }
 
 bool AutoRollLogger::LogExpired() {

util/auto_roll_logger.h

@@ -8,8 +8,9 @@
 #ifndef STORAGE_LEVELDB_UTIL_AUTO_ROLL_LOGGER_H
 #define STORAGE_LEVELDB_UTIL_AUTO_ROLL_LOGGER_H
 
-#include "util/posix_logger.h"
 #include "db/filename.h"
+#include "port/port.h"
+#include "util/posix_logger.h"
 
 namespace leveldb {
 
@@ -29,7 +30,8 @@ class AutoRollLogger : public Logger {
      cached_now(static_cast<uint64_t>(env_->NowMicros() * 1e-6)),
      ctime_(cached_now),
      cached_now_access_count(0),
-     call_NowMicros_every_N_records_(100) {
+     call_NowMicros_every_N_records_(100),
+     mutex_() {
     env->GetAbsolutePath(dbname, &db_absolute_path_);
     log_fname_ = InfoLogFileName(dbname_, db_absolute_path_, db_log_dir_);
     RollLogFile();
@@ -75,6 +77,7 @@ class AutoRollLogger : public Logger {
   uint64_t ctime_;
   uint64_t cached_now_access_count;
   uint64_t call_NowMicros_every_N_records_;
+  port::Mutex mutex_;
 };
 
 // Facade to craete logger automatically

util/auto_roll_logger_test.cc

@@ -78,7 +78,11 @@ void AutoRollLoggerTest::RollLogFileBySizeTest(AutoRollLogger* logger,
 
   // Now the log file will be rolled
   LogMessage(logger, log_message.c_str());
-  ASSERT_TRUE(0 == logger->GetLogFileSize());
+  // Since rotation is checked before actual logging, we need to
+  // trigger the rotation by logging another message.
+  LogMessage(logger, log_message.c_str());
+
+  ASSERT_TRUE(message_size == logger->GetLogFileSize());
 }
 
 uint64_t AutoRollLoggerTest::RollLogFileByTimeTest(

util/posix_logger.h

@@ -18,6 +18,7 @@
 #include <linux/falloc.h>
 #endif
 #include "leveldb/env.h"
+#include <atomic>
 
 namespace leveldb {
 
@@ -27,8 +28,7 @@ class PosixLogger : public Logger {
  private:
   FILE* file_;
   uint64_t (*gettid_)();  // Return the thread id for the current thread
-
-  size_t log_size_;
+  std::atomic_size_t log_size_;
   int fd_;
  public:
   PosixLogger(FILE* f, uint64_t (*gettid)()) :
@@ -100,10 +100,11 @@ class PosixLogger : public Logger {
       // If this write would cross a boundary of kDebugLogChunkSize
       // space, pre-allocate more space to avoid overly large
       // allocations from filesystem allocsize options.
+      const size_t log_size = log_size_;
       const int last_allocation_chunk =
-        ((kDebugLogChunkSize - 1 + log_size_) / kDebugLogChunkSize);
+        ((kDebugLogChunkSize - 1 + log_size) / kDebugLogChunkSize);
       const int desired_allocation_chunk =
-        ((kDebugLogChunkSize - 1 + log_size_ + write_size) /
+        ((kDebugLogChunkSize - 1 + log_size + write_size) /
            kDebugLogChunkSize);
       if (last_allocation_chunk != desired_allocation_chunk) {
         fallocate(fd_, FALLOC_FL_KEEP_SIZE, 0,