diff --git a/logging/BUILD.gn b/logging/BUILD.gn
index fac7e3d..6b1e549 100644
--- a/logging/BUILD.gn
+++ b/logging/BUILD.gn
@@ -40,6 +40,8 @@
     "rtc_event_log/rtc_event_log.cc",
     "rtc_event_log/rtc_event_log_factory.cc",
     "rtc_event_log/rtc_event_log_factory.h",
+    "rtc_event_log/rtc_event_log_helper_thread.cc",
+    "rtc_event_log/rtc_event_log_helper_thread.h",
   ]
 
   defines = []
@@ -52,8 +54,6 @@
     "../modules/rtp_rtcp",
     "../rtc_base:protobuf_utils",
     "../rtc_base:rtc_base_approved",
-    "../rtc_base:rtc_task_queue",
-    "../rtc_base:sequenced_task_checker",
     "../system_wrappers",
   ]
 
diff --git a/logging/rtc_event_log/rtc_event_log.cc b/logging/rtc_event_log/rtc_event_log.cc
index d1cad89..e661e67 100644
--- a/logging/rtc_event_log/rtc_event_log.cc
+++ b/logging/rtc_event_log/rtc_event_log.cc
@@ -10,14 +10,11 @@
 
 #include "webrtc/logging/rtc_event_log/rtc_event_log.h"
 
-#include <atomic>
-#include <deque>
-#include <functional>
 #include <limits>
-#include <memory>
 #include <utility>
 #include <vector>
 
+#include "webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h"
 #include "webrtc/modules/audio_coding/audio_network_adaptor/include/audio_network_adaptor.h"
 #include "webrtc/modules/remote_bitrate_estimator/include/bwe_defines.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
@@ -32,67 +29,30 @@
 #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/rtpfb.h"
 #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/sdes.h"
 #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/sender_report.h"
+#include "webrtc/rtc_base/atomicops.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/constructormagic.h"
 #include "webrtc/rtc_base/event.h"
-#include "webrtc/rtc_base/ignore_wundef.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/rtc_base/protobuf_utils.h"
-#include "webrtc/rtc_base/ptr_util.h"
-#include "webrtc/rtc_base/sequenced_task_checker.h"
-#include "webrtc/rtc_base/task_queue.h"
-#include "webrtc/rtc_base/thread_annotations.h"
+#include "webrtc/rtc_base/swap_queue.h"
+#include "webrtc/rtc_base/thread_checker.h"
 #include "webrtc/rtc_base/timeutils.h"
 #include "webrtc/system_wrappers/include/file_wrapper.h"
-#include "webrtc/typedefs.h"
 
 #ifdef ENABLE_RTC_EVENT_LOG
 // *.pb.h files are generated at build-time by the protobuf compiler.
-RTC_PUSH_IGNORING_WUNDEF()
 #ifdef WEBRTC_ANDROID_PLATFORM_BUILD
 #include "external/webrtc/webrtc/logging/rtc_event_log/rtc_event_log.pb.h"
 #else
 #include "webrtc/logging/rtc_event_log/rtc_event_log.pb.h"
 #endif
-RTC_POP_IGNORING_WUNDEF()
 #endif
 
 namespace webrtc {
 
 #ifdef ENABLE_RTC_EVENT_LOG
 
-namespace {
-const int kEventsInHistory = 10000;
-
-bool IsConfigEvent(const rtclog::Event& event) {
-  rtclog::Event_EventType event_type = event.type();
-  return event_type == rtclog::Event::VIDEO_RECEIVER_CONFIG_EVENT ||
-         event_type == rtclog::Event::VIDEO_SENDER_CONFIG_EVENT ||
-         event_type == rtclog::Event::AUDIO_RECEIVER_CONFIG_EVENT ||
-         event_type == rtclog::Event::AUDIO_SENDER_CONFIG_EVENT;
-}
-
-// TODO(eladalon): This class exists because C++11 doesn't allow transferring a
-// unique_ptr to a lambda (a copy constructor is required). We should get
-// rid of this when we move to C++14.
-template <typename T>
-class ResourceOwningTask final : public rtc::QueuedTask {
- public:
-  ResourceOwningTask(std::unique_ptr<T> resource,
-                     std::function<void(std::unique_ptr<T>)> handler)
-      : resource_(std::move(resource)), handler_(handler) {}
-
-  bool Run() override {
-    handler_(std::move(resource_));
-    return true;
-  }
-
- private:
-  std::unique_ptr<T> resource_;
-  std::function<void(std::unique_ptr<T>)> handler_;
-};
-}  // namespace
-
 class RtcEventLogImpl final : public RtcEventLog {
   friend std::unique_ptr<RtcEventLog> RtcEventLog::Create();
 
@@ -135,52 +95,24 @@
                              ProbeFailureReason failure_reason) override;
 
  private:
-  void StartLoggingInternal(std::unique_ptr<FileWrapper> file,
-                            int64_t max_size_bytes);
-
-  RtcEventLogImpl();  // Creation is done by RtcEventLog::Create.
+  // Private constructor to ensure that creation is done by RtcEventLog::Create.
+  RtcEventLogImpl();
 
   void StoreEvent(std::unique_ptr<rtclog::Event> event);
   void LogProbeResult(int id,
                       rtclog::BweProbeResult::ResultType result,
                       int bitrate_bps);
 
-  // Appends an event to the output protobuf string, returning true on success.
-  // Fails and returns false in case the limit on output size prevents the
-  // event from being added; in this case, the output string is left unchanged.
-  bool AppendEventToString(rtclog::Event* event,
-                           ProtoString* output_string) RTC_WARN_UNUSED_RESULT;
+  static volatile int log_count_;
 
-  void LogToMemory(std::unique_ptr<rtclog::Event> event);
+  // Message queue for passing control messages to the logging thread.
+  SwapQueue<RtcEventLogHelperThread::ControlMessage> message_queue_;
 
-  void StartLogFile();
-  void LogToFile(std::unique_ptr<rtclog::Event> event);
-  void StopLogFile(int64_t stop_time);
+  // Message queue for passing events to the logging thread.
+  SwapQueue<std::unique_ptr<rtclog::Event> > event_queue_;
 
-  // Observe a limit on the number of concurrent logs, so as not to run into
-  // OS-imposed limits on open files and/or threads/task-queues.
-  // TODO(eladalon): Known issue - there's a race over |log_count_|.
-  static std::atomic<int> log_count_;
-
-  // Make sure that the event log is "managed" - created/destroyed, as well
-  // as started/stopped - from the same thread/task-queue.
-  rtc::SequencedTaskChecker owner_sequence_checker_;
-
-  // History containing all past configuration events.
-  std::vector<std::unique_ptr<rtclog::Event>> config_history_
-      ACCESS_ON(task_queue_);
-
-  // History containing the most recent (non-configuration) events (~10s).
-  std::deque<std::unique_ptr<rtclog::Event>> history_ ACCESS_ON(task_queue_);
-
-  std::unique_ptr<FileWrapper> file_ ACCESS_ON(task_queue_);
-
-  size_t max_size_bytes_ ACCESS_ON(task_queue_);
-  size_t written_bytes_ ACCESS_ON(task_queue_);
-
-  // Keep this last to ensure it destructs first, or else tasks living on the
-  // queue might access other members after they've been torn down.
-  rtc::TaskQueue task_queue_;
+  RtcEventLogHelperThread helper_thread_;
+  rtc::ThreadChecker thread_checker_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(RtcEventLogImpl);
 };
@@ -232,46 +164,66 @@
   return rtclog::BweProbeResult::SUCCESS;
 }
 
+// The RTP and RTCP buffers reserve space for twice the expected number of
+// sent packets because they also contain received packets.
+static const int kEventsPerSecond = 1000;
+static const int kControlMessagesPerSecond = 10;
 }  // namespace
 
-std::atomic<int> RtcEventLogImpl::log_count_(0);
+volatile int RtcEventLogImpl::log_count_ = 0;
 
+// RtcEventLogImpl member functions.
 RtcEventLogImpl::RtcEventLogImpl()
-    : file_(FileWrapper::Create()),
-      max_size_bytes_(std::numeric_limits<decltype(max_size_bytes_)>::max()),
-      written_bytes_(0),
-      task_queue_("rtc_event_log") {}
+    // Allocate buffers for roughly one second of history.
+    : message_queue_(kControlMessagesPerSecond),
+      event_queue_(kEventsPerSecond),
+      helper_thread_(&message_queue_, &event_queue_),
+      thread_checker_() {
+  thread_checker_.DetachFromThread();
+}
 
 RtcEventLogImpl::~RtcEventLogImpl() {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&owner_sequence_checker_);
-
-  // If we're logging to the file, this will stop that. Blocking function.
-  StopLogging();
-
-  int count = std::atomic_fetch_sub(&RtcEventLogImpl::log_count_, 1) - 1;
+  // The RtcEventLogHelperThread destructor closes the file
+  // and waits for the thread to terminate.
+  int count = rtc::AtomicOps::Decrement(&RtcEventLogImpl::log_count_);
   RTC_DCHECK_GE(count, 0);
 }
 
 bool RtcEventLogImpl::StartLogging(const std::string& file_name,
                                    int64_t max_size_bytes) {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&owner_sequence_checker_);
-
-  auto file = rtc::WrapUnique<FileWrapper>(FileWrapper::Create());
-  if (!file->OpenFile(file_name.c_str(), false)) {
+  RTC_DCHECK(thread_checker_.CalledOnValidThread());
+  RtcEventLogHelperThread::ControlMessage message;
+  message.message_type = RtcEventLogHelperThread::ControlMessage::START_FILE;
+  message.max_size_bytes = max_size_bytes <= 0
+                               ? std::numeric_limits<int64_t>::max()
+                               : max_size_bytes;
+  message.start_time = rtc::TimeMicros();
+  message.stop_time = std::numeric_limits<int64_t>::max();
+  message.file.reset(FileWrapper::Create());
+  if (!message.file->OpenFile(file_name.c_str(), false)) {
     LOG(LS_ERROR) << "Can't open file. WebRTC event log not started.";
     return false;
   }
-
-  StartLoggingInternal(std::move(file), max_size_bytes);
-
+  if (!message_queue_.Insert(&message)) {
+    LOG(LS_ERROR) << "Message queue full. Can't start logging.";
+    return false;
+  }
+  helper_thread_.SignalNewEvent();
+  LOG(LS_INFO) << "Starting WebRTC event log.";
   return true;
 }
 
 bool RtcEventLogImpl::StartLogging(rtc::PlatformFile platform_file,
                                    int64_t max_size_bytes) {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&owner_sequence_checker_);
-
-  auto file = rtc::WrapUnique<FileWrapper>(FileWrapper::Create());
+  RTC_DCHECK(thread_checker_.CalledOnValidThread());
+  RtcEventLogHelperThread::ControlMessage message;
+  message.message_type = RtcEventLogHelperThread::ControlMessage::START_FILE;
+  message.max_size_bytes = max_size_bytes <= 0
+                               ? std::numeric_limits<int64_t>::max()
+                               : max_size_bytes;
+  message.start_time = rtc::TimeMicros();
+  message.stop_time = std::numeric_limits<int64_t>::max();
+  message.file.reset(FileWrapper::Create());
   FILE* file_handle = rtc::FdopenPlatformFileForWriting(platform_file);
   if (!file_handle) {
     LOG(LS_ERROR) << "Can't open file. WebRTC event log not started.";
@@ -282,36 +234,37 @@
     }
     return false;
   }
-  if (!file->OpenFromFileHandle(file_handle)) {
+  if (!message.file->OpenFromFileHandle(file_handle)) {
     LOG(LS_ERROR) << "Can't open file. WebRTC event log not started.";
     return false;
   }
-
-  StartLoggingInternal(std::move(file), max_size_bytes);
-
+  if (!message_queue_.Insert(&message)) {
+    LOG(LS_ERROR) << "Message queue full. Can't start logging.";
+    return false;
+  }
+  helper_thread_.SignalNewEvent();
+  LOG(LS_INFO) << "Starting WebRTC event log.";
   return true;
 }
 
 void RtcEventLogImpl::StopLogging() {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&owner_sequence_checker_);
-
+  RTC_DCHECK(thread_checker_.CalledOnValidThread());
+  RtcEventLogHelperThread::ControlMessage message;
+  message.message_type = RtcEventLogHelperThread::ControlMessage::STOP_FILE;
+  message.stop_time = rtc::TimeMicros();
+  while (!message_queue_.Insert(&message)) {
+    // TODO(terelius): We would like to have a blocking Insert function in the
+    // SwapQueue, but for the time being we will just clear any previous
+    // messages.
+    // Since StopLogging waits for the thread, it is essential that we don't
+    // clear any STOP_FILE messages. To ensure that there is only one call at a
+    // time, we require that all calls to StopLogging are made on the same
+    // thread.
+    LOG(LS_ERROR) << "Message queue full. Clearing queue to stop logging.";
+    message_queue_.Clear();
+  }
   LOG(LS_INFO) << "Stopping WebRTC event log.";
-
-  const int64_t stop_time = rtc::TimeMicros();
-
-  rtc::Event file_finished(true, false);
-
-  task_queue_.PostTask([this, stop_time, &file_finished]() {
-    RTC_DCHECK_RUN_ON(&task_queue_);
-    if (file_->is_open()) {
-      StopLogFile(stop_time);
-    }
-    file_finished.Set();
-  });
-
-  file_finished.Wait(rtc::Event::kForever);
-
-  LOG(LS_INFO) << "WebRTC event log successfully stopped.";
+  helper_thread_.WaitForFileFinished();
 }
 
 void RtcEventLogImpl::LogVideoReceiveStreamConfig(
@@ -612,197 +565,12 @@
   StoreEvent(std::move(event));
 }
 
-void RtcEventLogImpl::StartLoggingInternal(std::unique_ptr<FileWrapper> file,
-                                           int64_t max_size_bytes) {
-  LOG(LS_INFO) << "Starting WebRTC event log.";
-
-  max_size_bytes = (max_size_bytes <= 0)
-                       ? std::numeric_limits<decltype(max_size_bytes)>::max()
-                       : max_size_bytes;
-  auto file_handler = [this,
-                       max_size_bytes](std::unique_ptr<FileWrapper> file) {
-    RTC_DCHECK_RUN_ON(&task_queue_);
-    if (!file_->is_open()) {
-      max_size_bytes_ = max_size_bytes;
-      file_ = std::move(file);
-      StartLogFile();
-    } else {
-      // Already started. Ignore message and close file handle.
-      file->CloseFile();
-    }
-  };
-  task_queue_.PostTask(rtc::MakeUnique<ResourceOwningTask<FileWrapper>>(
-      std::move(file), file_handler));
-}
-
 void RtcEventLogImpl::StoreEvent(std::unique_ptr<rtclog::Event> event) {
-  RTC_DCHECK(event);
-
-  auto event_handler = [this](std::unique_ptr<rtclog::Event> rtclog_event) {
-    RTC_DCHECK_RUN_ON(&task_queue_);
-    if (file_->is_open()) {
-      LogToFile(std::move(rtclog_event));
-    } else {
-      LogToMemory(std::move(rtclog_event));
-    }
-  };
-
-  task_queue_.PostTask(rtc::MakeUnique<ResourceOwningTask<rtclog::Event>>(
-      std::move(event), event_handler));
-}
-
-bool RtcEventLogImpl::AppendEventToString(rtclog::Event* event,
-                                          ProtoString* output_string) {
-  RTC_DCHECK_RUN_ON(&task_queue_);
-
-  // Even though we're only serializing a single event during this call, what
-  // we intend to get is a list of events, with a tag and length preceding
-  // each actual event. To produce that, we serialize a list of a single event.
-  // If we later serialize additional events, the resulting ProtoString will
-  // be a proper concatenation of all those events.
-
-  rtclog::EventStream event_stream;
-  event_stream.add_stream();
-
-  // As a tweak, we swap the new event into the event-stream, write that to
-  // file, then swap back. This saves on some copying.
-  rtclog::Event* output_event = event_stream.mutable_stream(0);
-  output_event->Swap(event);
-
-  bool appended;
-  size_t potential_new_size =
-      written_bytes_ + output_string->size() + event_stream.ByteSize();
-  if (potential_new_size <= max_size_bytes_) {
-    event_stream.AppendToString(output_string);
-    appended = true;
-  } else {
-    appended = false;
+  RTC_DCHECK(event.get() != nullptr);
+  if (!event_queue_.Insert(&event)) {
+    LOG(LS_ERROR) << "WebRTC event log queue full. Dropping event.";
   }
-
-  // When the function returns, the original Event will be unchanged.
-  output_event->Swap(event);
-
-  return appended;
-}
-
-void RtcEventLogImpl::LogToMemory(std::unique_ptr<rtclog::Event> event) {
-  RTC_DCHECK_RUN_ON(&task_queue_);
-  RTC_DCHECK(!file_->is_open());
-
-  if (IsConfigEvent(*event.get())) {
-    config_history_.push_back(std::move(event));
-  } else {
-    history_.push_back(std::move(event));
-    if (history_.size() > kEventsInHistory) {
-      history_.pop_front();
-    }
-  }
-}
-
-void RtcEventLogImpl::StartLogFile() {
-  RTC_DCHECK_RUN_ON(&task_queue_);
-  RTC_DCHECK(file_->is_open());
-
-  ProtoString output_string;
-
-  // Create and serialize the LOG_START event.
-  // The timestamp used will correspond to when logging has started. The log
-  // may contain events earlier than the LOG_START event. (In general, the
-  // timestamps in the log are not monotonic.)
-  rtclog::Event start_event;
-  start_event.set_timestamp_us(rtc::TimeMicros());
-  start_event.set_type(rtclog::Event::LOG_START);
-  bool appended = AppendEventToString(&start_event, &output_string);
-
-  // Serialize the config information for all old streams, including streams
-  // which were already logged to previous files.
-  for (auto& event : config_history_) {
-    if (!appended) {
-      break;
-    }
-    appended = AppendEventToString(event.get(), &output_string);
-  }
-
-  // Serialize the events in the event queue.
-  while (appended && !history_.empty()) {
-    appended = AppendEventToString(history_.front().get(), &output_string);
-    if (appended) {
-      // Known issue - if writing to the file fails, these events will have
-      // been lost. If we try to open a new file, these events will be missing
-      // from it.
-      history_.pop_front();
-    }
-  }
-
-  // Write to file.
-  if (!file_->Write(output_string.data(), output_string.size())) {
-    LOG(LS_ERROR) << "FileWrapper failed to write WebRtcEventLog file.";
-    // The current FileWrapper implementation closes the file on error.
-    RTC_DCHECK(!file_->is_open());
-    return;
-  }
-  written_bytes_ += output_string.size();
-
-  if (!appended) {
-    RTC_DCHECK(file_->is_open());
-    StopLogFile(rtc::TimeMicros());
-  }
-}
-
-void RtcEventLogImpl::LogToFile(std::unique_ptr<rtclog::Event> event) {
-  RTC_DCHECK_RUN_ON(&task_queue_);
-  RTC_DCHECK(file_->is_open());
-
-  ProtoString output_string;
-
-  bool appended = AppendEventToString(event.get(), &output_string);
-
-  if (IsConfigEvent(*event.get())) {
-    config_history_.push_back(std::move(event));
-  }
-
-  if (!appended) {
-    RTC_DCHECK(file_->is_open());
-    history_.push_back(std::move(event));
-    StopLogFile(rtc::TimeMicros());
-    return;
-  }
-
-  // Write string to file.
-  if (file_->Write(output_string.data(), output_string.size())) {
-    written_bytes_ += output_string.size();
-  } else {
-    LOG(LS_ERROR) << "FileWrapper failed to write WebRtcEventLog file.";
-    // The current FileWrapper implementation closes the file on error.
-    RTC_DCHECK(!file_->is_open());
-  }
-}
-
-void RtcEventLogImpl::StopLogFile(int64_t stop_time) {
-  RTC_DCHECK_RUN_ON(&task_queue_);
-  RTC_DCHECK(file_->is_open());
-
-  ProtoString output_string;
-
-  rtclog::Event end_event;
-  end_event.set_timestamp_us(stop_time);
-  end_event.set_type(rtclog::Event::LOG_END);
-  bool appended = AppendEventToString(&end_event, &output_string);
-
-  if (appended) {
-    if (!file_->Write(output_string.data(), output_string.size())) {
-      LOG(LS_ERROR) << "FileWrapper failed to write WebRtcEventLog file.";
-      // The current FileWrapper implementation closes the file on error.
-      RTC_DCHECK(!file_->is_open());
-    }
-    written_bytes_ += output_string.size();
-  }
-
-  max_size_bytes_ = std::numeric_limits<decltype(max_size_bytes_)>::max();
-  written_bytes_ = 0;
-
-  file_->CloseFile();
-  RTC_DCHECK(!file_->is_open());
+  helper_thread_.SignalNewEvent();
 }
 
 bool RtcEventLog::ParseRtcEventLog(const std::string& file_name,
@@ -826,18 +594,17 @@
 // RtcEventLog member functions.
 std::unique_ptr<RtcEventLog> RtcEventLog::Create() {
 #ifdef ENABLE_RTC_EVENT_LOG
-  // TODO(eladalon): Known issue - there's a race over |log_count_| here.
   constexpr int kMaxLogCount = 5;
-  int count = 1 + std::atomic_fetch_add(&RtcEventLogImpl::log_count_, 1);
+  int count = rtc::AtomicOps::Increment(&RtcEventLogImpl::log_count_);
   if (count > kMaxLogCount) {
     LOG(LS_WARNING) << "Denied creation of additional WebRTC event logs. "
                     << count - 1 << " logs open already.";
-    std::atomic_fetch_sub(&RtcEventLogImpl::log_count_, 1);
+    rtc::AtomicOps::Decrement(&RtcEventLogImpl::log_count_);
     return std::unique_ptr<RtcEventLog>(new RtcEventLogNullImpl());
   }
   return std::unique_ptr<RtcEventLog>(new RtcEventLogImpl());
 #else
-  return CreateNull();
+  return std::unique_ptr<RtcEventLog>(new RtcEventLogNullImpl());
 #endif  // ENABLE_RTC_EVENT_LOG
 }
 
diff --git a/logging/rtc_event_log/rtc_event_log.h b/logging/rtc_event_log/rtc_event_log.h
index 087f5d9..d26dccb 100644
--- a/logging/rtc_event_log/rtc_event_log.h
+++ b/logging/rtc_event_log/rtc_event_log.h
@@ -98,17 +98,16 @@
                             int64_t max_size_bytes) = 0;
 
   // Deprecated. Pass an explicit file size limit.
-  RTC_DEPRECATED bool StartLogging(const std::string& file_name) {
+  bool StartLogging(const std::string& file_name) {
     return StartLogging(file_name, 10000000);
   }
 
   // Deprecated. Pass an explicit file size limit.
-  RTC_DEPRECATED bool StartLogging(rtc::PlatformFile platform_file) {
+  bool StartLogging(rtc::PlatformFile platform_file) {
     return StartLogging(platform_file, 10000000);
   }
 
-  // Stops logging to file and waits until the file has been closed, after
-  // which it would be permissible to read and/or modify it.
+  // Stops logging to file and waits until the thread has finished.
   virtual void StopLogging() = 0;
 
   // Logs configuration information for a video receive stream.
diff --git a/logging/rtc_event_log/rtc_event_log_helper_thread.cc b/logging/rtc_event_log/rtc_event_log_helper_thread.cc
new file mode 100644
index 0000000..a98336f
--- /dev/null
+++ b/logging/rtc_event_log/rtc_event_log_helper_thread.cc
@@ -0,0 +1,315 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h"
+
+#include <algorithm>
+
+#include "webrtc/rtc_base/checks.h"
+#include "webrtc/rtc_base/logging.h"
+#include "webrtc/rtc_base/timeutils.h"
+
+#ifdef ENABLE_RTC_EVENT_LOG
+
+namespace webrtc {
+
+namespace {
+const int kEventsInHistory = 10000;
+
+bool IsConfigEvent(const rtclog::Event& event) {
+  rtclog::Event_EventType event_type = event.type();
+  return event_type == rtclog::Event::VIDEO_RECEIVER_CONFIG_EVENT ||
+         event_type == rtclog::Event::VIDEO_SENDER_CONFIG_EVENT ||
+         event_type == rtclog::Event::AUDIO_RECEIVER_CONFIG_EVENT ||
+         event_type == rtclog::Event::AUDIO_SENDER_CONFIG_EVENT;
+}
+}  // namespace
+
+// RtcEventLogImpl member functions.
+RtcEventLogHelperThread::RtcEventLogHelperThread(
+    SwapQueue<ControlMessage>* message_queue,
+    SwapQueue<std::unique_ptr<rtclog::Event>>* event_queue)
+    : message_queue_(message_queue),
+      event_queue_(event_queue),
+      file_(FileWrapper::Create()),
+      thread_(&ThreadOutputFunction, this, "RtcEventLog thread"),
+      max_size_bytes_(std::numeric_limits<int64_t>::max()),
+      written_bytes_(0),
+      start_time_(0),
+      stop_time_(std::numeric_limits<int64_t>::max()),
+      has_recent_event_(false),
+      wake_periodically_(false, false),
+      wake_from_hibernation_(false, false),
+      file_finished_(false, false) {
+  RTC_DCHECK(message_queue_);
+  RTC_DCHECK(event_queue_);
+  thread_.Start();
+}
+
+RtcEventLogHelperThread::~RtcEventLogHelperThread() {
+  ControlMessage message;
+  message.message_type = ControlMessage::TERMINATE_THREAD;
+  message.stop_time = rtc::TimeMicros();
+  while (!message_queue_->Insert(&message)) {
+    // We can't destroy the event log until we have stopped the thread,
+    // so clear the message queue and try again. Note that if we clear
+    // any STOP_FILE events, then the threads calling StopLogging would likely
+    // wait indefinitely. However, there should not be any such calls as we
+    // are executing the destructor.
+    LOG(LS_WARNING) << "Clearing message queue to terminate thread.";
+    message_queue_->Clear();
+  }
+  wake_from_hibernation_.Set();
+  wake_periodically_.Set();  // Wake up the output thread.
+  thread_.Stop();            // Wait for the thread to terminate.
+}
+
+void RtcEventLogHelperThread::WaitForFileFinished() {
+  wake_from_hibernation_.Set();
+  wake_periodically_.Set();
+  file_finished_.Wait(rtc::Event::kForever);
+}
+
+void RtcEventLogHelperThread::SignalNewEvent() {
+  wake_from_hibernation_.Set();
+}
+
+bool RtcEventLogHelperThread::AppendEventToString(rtclog::Event* event) {
+  rtclog::EventStream event_stream;
+  event_stream.add_stream();
+  event_stream.mutable_stream(0)->Swap(event);
+  // We create a new event stream per event but because of the way protobufs
+  // are encoded, events can be merged by concatenating them. Therefore,
+  // it will look like a single stream when we read it back from file.
+  bool stop = true;
+  if (written_bytes_ + static_cast<int64_t>(output_string_.size()) +
+          event_stream.ByteSize() <=
+      max_size_bytes_) {
+    event_stream.AppendToString(&output_string_);
+    stop = false;
+  }
+  // Swap the event back so that we don't mix event types in the queues.
+  event_stream.mutable_stream(0)->Swap(event);
+  return stop;
+}
+
+bool RtcEventLogHelperThread::LogToMemory() {
+  RTC_DCHECK(!file_->is_open());
+  bool message_received = false;
+
+  // Process each event earlier than the current time and append it to the
+  // appropriate history_.
+  int64_t current_time = rtc::TimeMicros();
+  if (!has_recent_event_) {
+    has_recent_event_ = event_queue_->Remove(&most_recent_event_);
+  }
+  while (has_recent_event_ &&
+         most_recent_event_->timestamp_us() <= current_time) {
+    if (IsConfigEvent(*most_recent_event_)) {
+      config_history_.push_back(std::move(most_recent_event_));
+    } else {
+      history_.push_back(std::move(most_recent_event_));
+      if (history_.size() > kEventsInHistory)
+        history_.pop_front();
+    }
+    has_recent_event_ = event_queue_->Remove(&most_recent_event_);
+    message_received = true;
+  }
+  return message_received;
+}
+
+void RtcEventLogHelperThread::StartLogFile() {
+  RTC_DCHECK(file_->is_open());
+  bool stop = false;
+  output_string_.clear();
+
+  // Create and serialize the LOG_START event.
+  rtclog::Event start_event;
+  start_event.set_timestamp_us(start_time_);
+  start_event.set_type(rtclog::Event::LOG_START);
+  AppendEventToString(&start_event);
+
+  // Serialize the config information for all old streams.
+  for (auto& event : config_history_) {
+    AppendEventToString(event.get());
+  }
+
+  // Serialize the events in the event queue.
+  while (!history_.empty() && !stop) {
+    stop = AppendEventToString(history_.front().get());
+    if (!stop) {
+      history_.pop_front();
+    }
+  }
+
+  // Write to file.
+  if (!file_->Write(output_string_.data(), output_string_.size())) {
+    LOG(LS_ERROR) << "FileWrapper failed to write WebRtcEventLog file.";
+    // The current FileWrapper implementation closes the file on error.
+    RTC_DCHECK(!file_->is_open());
+    return;
+  }
+  written_bytes_ += output_string_.size();
+
+  // Free the allocated memory since we probably won't need this amount of
+  // space again.
+  output_string_.clear();
+  output_string_.shrink_to_fit();
+
+  if (stop) {
+    RTC_DCHECK(file_->is_open());
+    StopLogFile();
+  }
+}
+
+bool RtcEventLogHelperThread::LogToFile() {
+  RTC_DCHECK(file_->is_open());
+  output_string_.clear();
+  bool message_received = false;
+
+  // Append each event older than both the current time and the stop time
+  // to the output_string_.
+  int64_t current_time = rtc::TimeMicros();
+  int64_t time_limit = std::min(current_time, stop_time_);
+  if (!has_recent_event_) {
+    has_recent_event_ = event_queue_->Remove(&most_recent_event_);
+  }
+  bool stop = false;
+  while (!stop && has_recent_event_ &&
+         most_recent_event_->timestamp_us() <= time_limit) {
+    stop = AppendEventToString(most_recent_event_.get());
+    if (!stop) {
+      if (IsConfigEvent(*most_recent_event_)) {
+        config_history_.push_back(std::move(most_recent_event_));
+      }
+      has_recent_event_ = event_queue_->Remove(&most_recent_event_);
+    }
+    message_received = true;
+  }
+
+  // Write string to file.
+  if (!file_->Write(output_string_.data(), output_string_.size())) {
+    LOG(LS_ERROR) << "FileWrapper failed to write WebRtcEventLog file.";
+    // The current FileWrapper implementation closes the file on error.
+    RTC_DCHECK(!file_->is_open());
+    return message_received;
+  }
+  written_bytes_ += output_string_.size();
+
+  // We want to stop logging if we have reached the file size limit. We also
+  // want to stop logging if the remaining events are more recent than the
+  // time limit, or in other words if we have terminated the loop despite
+  // having more events in the queue.
+  if ((has_recent_event_ && most_recent_event_->timestamp_us() > stop_time_) ||
+      stop) {
+    RTC_DCHECK(file_->is_open());
+    StopLogFile();
+  }
+  return message_received;
+}
+
+void RtcEventLogHelperThread::StopLogFile() {
+  RTC_DCHECK(file_->is_open());
+  output_string_.clear();
+
+  rtclog::Event end_event;
+  // This function can be called either because we have reached the stop time,
+  // or because we have reached the log file size limit. Therefore, use the
+  // current time if we have not reached the time limit.
+  end_event.set_timestamp_us(
+      std::min(stop_time_, rtc::TimeMicros()));
+  end_event.set_type(rtclog::Event::LOG_END);
+  AppendEventToString(&end_event);
+
+  if (written_bytes_ + static_cast<int64_t>(output_string_.size()) <=
+      max_size_bytes_) {
+    if (!file_->Write(output_string_.data(), output_string_.size())) {
+      LOG(LS_ERROR) << "FileWrapper failed to write WebRtcEventLog file.";
+      // The current FileWrapper implementation closes the file on error.
+      RTC_DCHECK(!file_->is_open());
+    }
+    written_bytes_ += output_string_.size();
+  }
+
+  max_size_bytes_ = std::numeric_limits<int64_t>::max();
+  written_bytes_ = 0;
+  start_time_ = 0;
+  stop_time_ = std::numeric_limits<int64_t>::max();
+  output_string_.clear();
+  file_->CloseFile();
+  RTC_DCHECK(!file_->is_open());
+}
+
+void RtcEventLogHelperThread::ProcessEvents() {
+  ControlMessage message;
+
+  while (true) {
+    bool message_received = false;
+    // Process control messages.
+    while (message_queue_->Remove(&message)) {
+      switch (message.message_type) {
+        case ControlMessage::START_FILE:
+          if (!file_->is_open()) {
+            max_size_bytes_ = message.max_size_bytes;
+            start_time_ = message.start_time;
+            stop_time_ = message.stop_time;
+            file_.swap(message.file);
+            StartLogFile();
+          } else {
+            // Already started. Ignore message and close file handle.
+            message.file->CloseFile();
+          }
+          message_received = true;
+          break;
+        case ControlMessage::STOP_FILE:
+          if (file_->is_open()) {
+            stop_time_ = message.stop_time;
+            LogToFile();  // Log remaining events from message queues.
+          }
+          // LogToFile might stop on it's own so we need to recheck the state.
+          if (file_->is_open()) {
+            StopLogFile();
+          }
+          file_finished_.Set();
+          message_received = true;
+          break;
+        case ControlMessage::TERMINATE_THREAD:
+          if (file_->is_open()) {
+            StopLogFile();
+          }
+          return;
+      }
+    }
+
+    // Write events to file or memory.
+    if (file_->is_open()) {
+      message_received |= LogToFile();
+    } else {
+      message_received |= LogToMemory();
+    }
+
+    // Accumulate a new batch of events instead of processing them one at a
+    // time.
+    if (message_received) {
+      wake_periodically_.Wait(100);
+    } else {
+      wake_from_hibernation_.Wait(rtc::Event::kForever);
+    }
+  }
+}
+
+void RtcEventLogHelperThread::ThreadOutputFunction(void* obj) {
+  RtcEventLogHelperThread* helper = static_cast<RtcEventLogHelperThread*>(obj);
+  helper->ProcessEvents();
+}
+
+}  // namespace webrtc
+
+#endif  // ENABLE_RTC_EVENT_LOG
diff --git a/logging/rtc_event_log/rtc_event_log_helper_thread.h b/logging/rtc_event_log/rtc_event_log_helper_thread.h
new file mode 100644
index 0000000..0d9ad4d
--- /dev/null
+++ b/logging/rtc_event_log/rtc_event_log_helper_thread.h
@@ -0,0 +1,128 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_LOGGING_RTC_EVENT_LOG_RTC_EVENT_LOG_HELPER_THREAD_H_
+#define WEBRTC_LOGGING_RTC_EVENT_LOG_RTC_EVENT_LOG_HELPER_THREAD_H_
+
+#include <deque>
+#include <limits>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "webrtc/rtc_base/constructormagic.h"
+#include "webrtc/rtc_base/event.h"
+#include "webrtc/rtc_base/ignore_wundef.h"
+#include "webrtc/rtc_base/platform_thread.h"
+#include "webrtc/rtc_base/protobuf_utils.h"
+#include "webrtc/rtc_base/swap_queue.h"
+#include "webrtc/system_wrappers/include/file_wrapper.h"
+
+#ifdef ENABLE_RTC_EVENT_LOG
+// *.ph.h files are generated at build-time by the protobuf compiler.
+RTC_PUSH_IGNORING_WUNDEF()
+#ifdef WEBRTC_ANDROID_PLATFORM_BUILD
+#include "external/webrtc/webrtc/logging/rtc_event_log/rtc_event_log.pb.h"
+#else
+#include "webrtc/logging/rtc_event_log/rtc_event_log.pb.h"
+#endif
+RTC_POP_IGNORING_WUNDEF()
+#endif
+
+#ifdef ENABLE_RTC_EVENT_LOG
+
+namespace webrtc {
+
+class RtcEventLogHelperThread final {
+ public:
+  struct ControlMessage {
+    ControlMessage()
+        : message_type(STOP_FILE),
+          file(nullptr),
+          max_size_bytes(0),
+          start_time(0),
+          stop_time(0) {}
+    enum { START_FILE, STOP_FILE, TERMINATE_THREAD } message_type;
+
+    std::unique_ptr<FileWrapper> file;  // Only used with START_FILE.
+    int64_t max_size_bytes;             // Only used with START_FILE.
+    int64_t start_time;                 // Only used with START_FILE.
+    int64_t stop_time;                  // Used with all 3 message types.
+
+    friend void swap(ControlMessage& lhs, ControlMessage& rhs) {
+      using std::swap;
+      swap(lhs.message_type, rhs.message_type);
+      lhs.file.swap(rhs.file);
+      swap(lhs.max_size_bytes, rhs.max_size_bytes);
+      swap(lhs.start_time, rhs.start_time);
+      swap(lhs.stop_time, rhs.stop_time);
+    }
+  };
+
+  RtcEventLogHelperThread(
+      SwapQueue<ControlMessage>* message_queue,
+      SwapQueue<std::unique_ptr<rtclog::Event>>* event_queue);
+  ~RtcEventLogHelperThread();
+
+  // This function MUST be called once a STOP_FILE message is added to the
+  // signalling queue. The function will make sure that the output thread
+  // wakes up to read the message, and it blocks until the output thread has
+  // finished writing to the file.
+  void WaitForFileFinished();
+
+  // This fuction MUST be called once an event is added to the event queue.
+  void SignalNewEvent();
+
+ private:
+  static void ThreadOutputFunction(void* obj);
+
+  bool AppendEventToString(rtclog::Event* event);
+  bool LogToMemory();
+  void StartLogFile();
+  bool LogToFile();
+  void StopLogFile();
+  void ProcessEvents();
+
+  // Message queues for passing events to the logging thread.
+  SwapQueue<ControlMessage>* message_queue_;
+  SwapQueue<std::unique_ptr<rtclog::Event>>* event_queue_;
+
+  // History containing the most recent events (~ 10 s).
+  std::deque<std::unique_ptr<rtclog::Event>> history_;
+
+  // History containing all past configuration events.
+  std::vector<std::unique_ptr<rtclog::Event>> config_history_;
+
+  std::unique_ptr<FileWrapper> file_;
+  rtc::PlatformThread thread_;
+
+  int64_t max_size_bytes_;
+  int64_t written_bytes_;
+  int64_t start_time_;
+  int64_t stop_time_;
+
+  bool has_recent_event_;
+  std::unique_ptr<rtclog::Event> most_recent_event_;
+
+  // Temporary space for serializing profobuf data.
+  ProtoString output_string_;
+
+  rtc::Event wake_periodically_;
+  rtc::Event wake_from_hibernation_;
+  rtc::Event file_finished_;
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(RtcEventLogHelperThread);
+};
+
+}  // namespace webrtc
+
+#endif  // ENABLE_RTC_EVENT_LOG
+
+#endif  // WEBRTC_LOGGING_RTC_EVENT_LOG_RTC_EVENT_LOG_HELPER_THREAD_H_
diff --git a/pc/peerconnection.cc b/pc/peerconnection.cc
index 99b87c0..e22a09e 100644
--- a/pc/peerconnection.cc
+++ b/pc/peerconnection.cc
@@ -1337,11 +1337,11 @@
       rtc::Bind(&cricket::PortAllocator::DiscardCandidatePool,
                 port_allocator_.get()));
 
-  factory_->worker_thread()->Invoke<void>(RTC_FROM_HERE, [this] {
-    call_.reset();
-    // The event log must outlive call (and any other object that uses it).
-    event_log_.reset();
-  });
+  factory_->worker_thread()->Invoke<void>(RTC_FROM_HERE,
+                                          [this] { call_.reset(); });
+
+  // The event log must outlive call (and any other object that uses it).
+  event_log_.reset();
 }
 
 void PeerConnection::OnSessionStateChange(WebRtcSession* /*session*/,
diff --git a/pc/peerconnectionfactory.cc b/pc/peerconnectionfactory.cc
index 6da4669..d4ee405 100644
--- a/pc/peerconnectionfactory.cc
+++ b/pc/peerconnectionfactory.cc
@@ -262,9 +262,8 @@
                                allocator.get(), options_.network_ignore_mask));
 
   std::unique_ptr<RtcEventLog> event_log =
-      worker_thread_->Invoke<std::unique_ptr<RtcEventLog>>(
-          RTC_FROM_HERE,
-          rtc::Bind(&PeerConnectionFactory::CreateRtcEventLog_w, this));
+      event_log_factory_ ? event_log_factory_->CreateRtcEventLog()
+                         : rtc::MakeUnique<RtcEventLogNullImpl>();
 
   std::unique_ptr<Call> call = worker_thread_->Invoke<std::unique_ptr<Call>>(
       RTC_FROM_HERE,
@@ -332,11 +331,6 @@
   return network_thread_;
 }
 
-std::unique_ptr<RtcEventLog> PeerConnectionFactory::CreateRtcEventLog_w() {
-  return event_log_factory_ ? event_log_factory_->CreateRtcEventLog()
-                            : rtc::MakeUnique<RtcEventLogNullImpl>();
-}
-
 std::unique_ptr<Call> PeerConnectionFactory::CreateCall_w(
     RtcEventLog* event_log) {
   const int kMinBandwidthBps = 30000;
diff --git a/pc/peerconnectionfactory.h b/pc/peerconnectionfactory.h
index 82440e7..ebd3016 100644
--- a/pc/peerconnectionfactory.h
+++ b/pc/peerconnectionfactory.h
@@ -121,7 +121,6 @@
   virtual ~PeerConnectionFactory();
 
  private:
-  std::unique_ptr<RtcEventLog> CreateRtcEventLog_w();
   std::unique_ptr<Call> CreateCall_w(RtcEventLog* event_log);
 
   bool wraps_current_thread_;