[cdc_rsync] Improve throughput for local copies (#74)

On Windows, fclose() seems to be very expensive for large files, where
closing a 1 GB file takes up to 5 seconds. This CL calls fclose() in
background threads. This tremendously improves local syncs, e.g.
copying a 4.5 GB, 300 files data set takes only 7 seconds instead of
30 seconds.

Also increases the buffer size for copying from 16K to 128K (better
throughput for local copies), and adds a timestamp to debug and
verbose console logs (useful when comparing client and server logs).

cdc_rsync/cdc_rsync_client.cc

@@ -623,7 +623,7 @@ absl::Status CdcRsyncClient::SendMissingFiles() {
 
   ParallelFileOpener file_opener(&files_, missing_file_indices_);
 
-  constexpr size_t kBufferSize = 16000;
+  constexpr size_t kBufferSize = 128 * 1024;
   for (uint32_t server_index = 0; server_index < missing_file_indices_.size();
        ++server_index) {
     uint32_t client_index = missing_file_indices_[server_index];

cdc_rsync_server/cdc_rsync_server.cc

@@ -32,6 +32,13 @@ namespace cdc_ft {
 
 namespace {
 
+// Number of files for which to call fclose() and finalize files in parallel.
+constexpr size_t kNumFinalizerThreads = 8;
+
+// Max 16 files in the patcher and finalizer queues to prevent that too many
+// files are open concurrently.
+constexpr size_t kMaxQueueSize = 16;
+
 // Suffix for the patched file created from the basis file and the diff.
 constexpr char kIntermediatePathSuffix[] = ".__cdc_rsync_temp__";
 
@@ -49,6 +56,9 @@ uint16_t kExecutableBits =
 // |target_filepath| match, writes an intermediate file and replaces
 // the file at |target_filepath| with the intermediate file when all data has
 // been received.
+// Each PatchTask is queued twice, once to create the patched file, and once in
+// a different thread pool to close and finalize the patched file. This is
+// because fclose() can take a long time to finish, so it could block patching.
 class PatchTask : public Task {
  public:
   PatchTask(const std::string& base_filepath,
@@ -57,38 +67,69 @@ class PatchTask : public Task {
       : base_filepath_(base_filepath),
         target_filepath_(target_filepath),
         file_(file),
-        cdc_(cdc) {}
+        cdc_(cdc),
+        need_intermediate_file_(target_filepath_ == base_filepath_),
+        patched_filepath_(target_filepath_ == base_filepath_
+                              ? base_filepath_ + kIntermediatePathSuffix
+                              : target_filepath_) {}
 
   virtual ~PatchTask() = default;
 
+  PatchTask(const PatchTask& other) = delete;
+  PatchTask& operator=(const PatchTask& other) = delete;
+
   const ChangedFileInfo& File() const { return file_; }
 
   const absl::Status& Status() const { return status_; }
 
   // Task:
   void ThreadRun(IsCancelledPredicate is_cancelled) override {
-    bool need_intermediate_file = target_filepath_ == base_filepath_;
+    // Each PatchTask is queued twice, once to apply the patch and once to
-    std::string patched_filepath =
+    // close and finalize the patched file.
-        need_intermediate_file ? base_filepath_ + kIntermediatePathSuffix
+    switch (state_) {
-                               : target_filepath_;
+      case State::kPatching:
+        Patch();
+        state_ = State::kFinalizing;
+        break;
+      case State::kFinalizing:
+        Finalize();
+        state_ = State::kDone;
+        break;
+      default:
+        assert(!"Invalid state");
+    }
+  }
 
-    absl::StatusOr<FILE*> patched_file = path::OpenFile(patched_filepath, "wb");
+ private:
-    if (!patched_file.ok()) {
+  void Patch() {
-      status_ = patched_file.status();
+    absl::StatusOr<FILE*> patched_fp = path::OpenFile(patched_filepath_, "wb");
+    if (!patched_fp.ok()) {
+      status_ = patched_fp.status();
       return;
     }
+    patched_fp_ = *patched_fp;
 
     // Receive diff stream from server and apply.
-    bool is_executable = false;
+    status_ =
-    status_ = cdc_->ReceiveDiffAndPatch(base_filepath_, *patched_file,
+        cdc_->ReceiveDiffAndPatch(base_filepath_, patched_fp_, &is_executable_);
-                                        &is_executable);
+
-    fclose(*patched_file);
+    // The file is closed by Finalize() in a separate thread pool since fclose()
+    // takes a while on some systems.
+  }
+
+  void Finalize() {
+    if (patched_fp_) {
+      fclose(patched_fp_);
+      patched_fp_ = nullptr;
+    }
+
     if (!status_.ok()) {
+      // Some error occurred during Patch().
       return;
     }
 
     // These bits are OR'ed on top of the mode bits.
-    uint16_t mode_or_bits = is_executable ? kExecutableBits : 0;
+    uint16_t mode_or_bits = is_executable_ ? kExecutableBits : 0;
 
     // Store mode from the original base path.
     path::Stats stats;
@@ -99,13 +140,13 @@ class PatchTask : public Task {
       return;
     }
 
-    if (need_intermediate_file) {
+    if (need_intermediate_file_) {
       // Replace |base_filepath_| (==|target_filepath_|) by the intermediate
       // file |patched_filepath|.
-      status_ = path::ReplaceFile(target_filepath_, patched_filepath);
+      status_ = path::ReplaceFile(target_filepath_, patched_filepath_);
       if (!status_.ok()) {
         status_ = WrapStatus(status_, "ReplaceFile() for '%s' by '%s' failed",
-                             base_filepath_, patched_filepath);
+                             base_filepath_, patched_filepath_);
         return;
       }
     } else {
@@ -126,11 +167,82 @@ class PatchTask : public Task {
     status_ = path::SetFileTime(target_filepath_, file_.client_modified_time);
   }
 
+  const std::string base_filepath_;
+  const std::string target_filepath_;
+  const ChangedFileInfo file_;
+  CdcInterface* const cdc_;
+  const bool need_intermediate_file_ = false;
+  const std::string patched_filepath_;
+
+  FILE* patched_fp_ = nullptr;
+  bool is_executable_ = false;
+  absl::Status status_;
+
+  // This task is queued twice, once to patch and once to close and finalize the
+  // patched file.
+  enum class State { kPatching, kFinalizing, kDone };
+  State state_ = State::kPatching;
+};
+
+// Background task that closes a file and sets the mtime and perms. This is done
+// in the background since closing a file might block for a long time.
+class FinalizeCopiedFileTask : public Task {
+ public:
+  // Finalize |file| with given path |filepath|. |status| is the status from
+  // writing the file. On error, the file is only closed.
+  FinalizeCopiedFileTask(FILE* fp, FileInfo file, std::string filepath,
+                         bool is_executable, absl::Status status)
+      : fp_(fp),
+        file_(std::move(file)),
+        filepath_(std::move(filepath)),
+        is_executable_(is_executable),
+        status_(status) {}
+  virtual ~FinalizeCopiedFileTask() = default;
+
+  FinalizeCopiedFileTask(const FinalizeCopiedFileTask& other) = delete;
+  FinalizeCopiedFileTask& operator=(const FinalizeCopiedFileTask& other) =
+      delete;
+
+  const absl::Status& Status() const { return status_; }
+
+  // Task:
+  void ThreadRun(IsCancelledPredicate is_cancelled) override {
+    assert(fp_);
+    fclose(fp_);
+
+    if (!status_.ok()) {
+      // Writing the file failed, nothing to finalize.
+      status_ = WrapStatus(status_, "Failed to write file %s", filepath_);
+      return;
+    }
+
+    // Set file write time.
+    status_ = path::SetFileTime(filepath_, file_.modified_time);
+    if (!status_.ok()) {
+      status_ =
+          WrapStatus(status_, "Failed to set file mod time for %s", filepath_);
+      return;
+    }
+
+    // Set executable bit, but just print warnings as it's not critical.
+    if (is_executable_) {
+      path::Stats stats;
+      status_ = path::GetStats(filepath_, &stats);
+      if (status_.ok()) {
+        status_ = path::ChangeMode(filepath_, stats.mode | kExecutableBits);
+      }
+      if (!status_.ok()) {
+        LOG_WARNING("Failed to set executable bit on '%s': %s", filepath_,
+                    status_.ToString());
+      }
+    }
+  }
+
  private:
-  std::string base_filepath_;
+  FILE* const fp_ = nullptr;
-  std::string target_filepath_;
+  const FileInfo file_;
-  ChangedFileInfo file_;
+  const std::string filepath_;
-  CdcInterface* cdc_;
+  const bool is_executable_;
   absl::Status status_;
 };
 
@@ -550,6 +662,8 @@ absl::Status CdcRsyncServer::HandleSendMissingFileData() {
     }
   }
 
+  Threadpool finalize_pool(kNumFinalizerThreads);
+
   for (uint32_t server_index = 0; server_index < diff_.missing_files.size();
        server_index++) {
     const FileInfo& file = diff_.missing_files[server_index];
@@ -569,8 +683,8 @@ absl::Status CdcRsyncServer::HandleSendMissingFileData() {
                         request.server_index(), server_index);
     }
 
-    // Verify that there is no directory existing with the same name.
+    // Remove |filepath| if it is a directory.
-    if (path::Exists(filepath) && path::DirExists(filepath)) {
+    if (path::DirExists(filepath)) {
       assert(!diff_.extraneous_dirs.empty());
       status = path::RemoveFile(filepath);
       if (!status.ok()) {
@@ -619,27 +733,25 @@ absl::Status CdcRsyncServer::HandleSendMissingFileData() {
     }
 
     status = path::StreamWriteFileContents(*fp, handler);
-    fclose(*fp);
+    finalize_pool.QueueTask(std::make_unique<FinalizeCopiedFileTask>(
-    if (!status.ok()) {
+        *fp, file, filepath, is_executable, status));
-      return WrapStatus(status, "Failed to write file %s", filepath);
+    finalize_pool.WaitForQueuedTasksAtMost(kMaxQueueSize);
+
+    // Drain finalize pool for the last file.
+    if (server_index + 1 == diff_.missing_files.size()) {
+      finalize_pool.Wait();
     }
 
-    // Set file write time.
+    // Check the results of completed tasks.
-    status = path::SetFileTime(filepath, file.modified_time);
+    for (std::unique_ptr<Task> task = finalize_pool.TryGetCompletedTask();
-    if (!status.ok()) {
+         task != nullptr; task = finalize_pool.TryGetCompletedTask()) {
-      return WrapStatus(status, "Failed to set file mod time for %s", filepath);
+      const FinalizeCopiedFileTask* finalize_task =
-    }
+          static_cast<FinalizeCopiedFileTask*>(task.get());
-
+      if (!finalize_task->Status().ok()) {
-    // Set executable bit, but just print warnings as it's not critical.
+        // Close and finish files that have already been copied, so we don't
-    if (is_executable) {
+        // discard several already copied files because one failed.
-      path::Stats stats;
+        finalize_pool.Wait();
-      status = path::GetStats(filepath, &stats);
+        return finalize_task->Status();
-      if (status.ok()) {
-        status = path::ChangeMode(filepath, stats.mode | kExecutableBits);
-      }
-      if (!status.ok()) {
-        LOG_WARNING("Failed to set executable bit on '%s': %s", filepath,
-                    status.ToString());
       }
     }
   }
@@ -678,11 +790,22 @@ absl::Status CdcRsyncServer::SyncChangedFiles() {
   CdcInterface cdc(message_pump_.get());
 
   // Pipeline sending signatures and patching files:
-  // MAIN THREAD:   Send signatures to client.
+  // MAIN THREAD:       Send signatures to client.
-  //                Only sends to the socket.
+  //                    Only sends to the socket.
-  // WORKER THREAD: Receive diffs from client and patch file.
+  // PATCHER THREAD:    Receive diffs from client and create patch file.
-  //                Only reads from the socket.
+  //                    Only reads from the socket.
-  Threadpool pool(1);
+  // FINALIZER THREADS: Close patched files and finalize them.
+  Threadpool patch_pool(1);
+  Threadpool finalize_pool(kNumFinalizerThreads);
+
+  // Forward finished patch task immediately to finalize pool.
+  patch_pool.SetTaskCompletedCallback(
+      [&finalize_pool](std::unique_ptr<Task> task) {
+        // Spin if there are too many outstanding tasks, in order to limit the
+        // max number of outstanding tasks.
+        finalize_pool.QueueTask(std::move(task));
+        finalize_pool.WaitForQueuedTasksAtMost(kMaxQueueSize);
+      });
 
   for (uint32_t server_index = 0; server_index < diff_.changed_files.size();
        server_index++) {
@@ -708,25 +831,28 @@ absl::Status CdcRsyncServer::SyncChangedFiles() {
     }
 
     // Queue patching task.
-    pool.QueueTask(std::make_unique<PatchTask>(base_filepath, target_filepath,
+    patch_pool.QueueTask(std::make_unique<PatchTask>(
-                                               file, &cdc));
+        base_filepath, target_filepath, file, &cdc));
 
-    // Wait for the last file to finish.
+    // Drain pools for the last file.
     if (server_index + 1 == diff_.changed_files.size()) {
-      pool.Wait();
+      patch_pool.Wait();
+      finalize_pool.Wait();
     }
 
     // Check the results of completed tasks.
-    std::unique_ptr<Task> task = pool.TryGetCompletedTask();
+    for (std::unique_ptr<Task> task = finalize_pool.TryGetCompletedTask();
-    while (task) {
+         task != nullptr; task = finalize_pool.TryGetCompletedTask()) {
-      PatchTask* patch_task = static_cast<PatchTask*>(task.get());
+      const PatchTask* patch_task = static_cast<PatchTask*>(task.get());
       const std::string& task_path = patch_task->File().filepath;
       if (!patch_task->Status().ok()) {
+        // Close and finish files that have already been synced, so we don't
+        // discard several already synced files because one failed.
+        finalize_pool.Wait();
         return WrapStatus(patch_task->Status(), "Failed to patch file '%s'",
                           task_path);
       }
       LOG_INFO("Finished patching file %s", task_path.c_str());
-      task = pool.TryGetCompletedTask();
     }
   }
 

common/BUILD

@@ -158,6 +158,7 @@ cc_library(
     deps = [
         ":clock",
         ":platform",
+        ":stopwatch",
         "@com_google_absl//absl/strings:str_format",
         "@com_google_absl//absl/synchronization",
     ],

common/log.cc

@@ -126,21 +126,22 @@ void ConsoleLog::WriteLogMessage(LogLevel level, const char* file, int line,
   absl::MutexLock lock(&mutex_);
 
   // Show leaner log messages in non-verbose mode.
-  bool show_file_func = GetLogLevel() <= LogLevel::kDebug;
+  bool show_time_file_func = GetLogLevel() <= LogLevel::kDebug;
   FILE* stdfile = level >= LogLevel::kError ? stderr : stdout;
 #if PLATFORM_WINDOWS
   HANDLE hConsole = GetStdHandle(STD_OUTPUT_HANDLE);
   SetConsoleTextAttribute(hConsole, GetConsoleColor(level));
-  if (show_file_func) {
+  if (show_time_file_func) {
-    fprintf(stdfile, "%s(%i): %s(): %s\n", file, line, func, message);
+    fprintf(stdfile, "%0.3f %s(%i): %s(): %s\n", stopwatch_.ElapsedSeconds(),
+            file, line, func, message);
   } else {
     fprintf(stdfile, "%s\n", message);
   }
   SetConsoleTextAttribute(hConsole, kLightGray);
 #else
-  if (show_file_func) {
+  if (show_time_file_func) {
-    fprintf(stdfile, "%-7s %s(%i): %s(): %s\n", GetLogLevelString(level), file,
+    fprintf(stdfile, "%-7s %0.3f %s(%i): %s(): %s\n", GetLogLevelString(level),
-            line, func, message);
+            stopwatch_.ElapsedSeconds(), file, line, func, message);
   } else {
     fprintf(stdfile, "%-7s %s\n", GetLogLevelString(level), message);
   }

common/log.h

@@ -22,6 +22,7 @@
 #include "absl/strings/str_format.h"
 #include "absl/synchronization/mutex.h"
 #include "common/clock.h"
+#include "common/stopwatch.h"
 
 namespace cdc_ft {
 
@@ -120,6 +121,7 @@ class ConsoleLog : public Log {
       ABSL_LOCKS_EXCLUDED(mutex_);
 
  private:
+  Stopwatch stopwatch_;
   absl::Mutex mutex_;
 };
 

common/threadpool.cc

@@ -45,6 +45,11 @@ void Threadpool::Shutdown() {
   for (auto& worker : workers_) {
     if (worker.joinable()) worker.join();
   }
+
+  // Discard all completed tasks.
+  absl::MutexLock lock(&completed_tasks_mutex_);
+  std::queue<std::unique_ptr<Task>> empty;
+  std::swap(completed_tasks_, empty);
 }
 
 void Threadpool::QueueTask(std::unique_ptr<Task> task) {
@@ -77,6 +82,21 @@ std::unique_ptr<Task> Threadpool::GetCompletedTask() {
   return task;
 }
 
+void Threadpool::SetTaskCompletedCallback(TaskCompletedCallback cb) {
+  absl::MutexLock lock(&completed_tasks_mutex_);
+  on_task_completed_ = std::move(cb);
+}
+
+bool Threadpool::WaitForQueuedTasksAtMost(size_t count,
+                                          absl::Duration timeout) const {
+  absl::MutexLock lock(&task_queue_mutex_);
+  auto cond = [this, count]() ABSL_EXCLUSIVE_LOCKS_REQUIRED(task_queue_mutex_) {
+    return shutdown_ || outstanding_task_count_ <= count;
+  };
+  return task_queue_mutex_.AwaitWithTimeout(absl::Condition(&cond), timeout) &&
+         outstanding_task_count_ <= count;
+}
+
 void Threadpool::ThreadWorkerMain() {
   bool task_finished = false;
   for (;;) {
@@ -85,7 +105,8 @@ void Threadpool::ThreadWorkerMain() {
       absl::MutexLock lock(&task_queue_mutex_);
 
       // Decrease task count here, so we don't have to lock again at the end of
-      // the loop.
+      // the loop. It is important to first push the task, then decrease this
+      // count. Otherwise, there's a race between Wait() and GetCompletedTask().
       if (task_finished) {
         assert(outstanding_task_count_ > 0);
         --outstanding_task_count_;
@@ -104,17 +125,18 @@ void Threadpool::ThreadWorkerMain() {
     }
 
     // Run task, but make it cancellable.
-    task->ThreadRun([this]() ABSL_EXCLUSIVE_LOCKS_REQUIRED(
+    task->ThreadRun([this]() ABSL_LOCKS_EXCLUDED(task_queue_mutex_) -> bool {
-                        task_queue_mutex_) -> bool { return shutdown_; });
-
-    {
       absl::MutexLock lock(&task_queue_mutex_);
-      if (shutdown_) break;
+      return shutdown_;
-    }
+    });
 
     // Push task to completed queue.
     absl::MutexLock lock(&completed_tasks_mutex_);
-    completed_tasks_.push(std::move(task));
+    if (on_task_completed_) {
+      on_task_completed_(std::move(task));
+    } else {
+      completed_tasks_.push(std::move(task));
+    }
     task_finished = true;
   }
 }

common/threadpool.h

@@ -18,7 +18,6 @@
 #define COMMON_THREADPOOL_H_
 
 #include <atomic>
-#include <condition_variable>
 #include <functional>
 #include <memory>
 #include <queue>
@@ -57,7 +56,8 @@ class Threadpool {
   void QueueTask(std::unique_ptr<Task> task)
       ABSL_LOCKS_EXCLUDED(task_queue_mutex_);
 
-  // If available, returns the next completed task.
+  // Returns the next completed task if available or nullptr all are either
+  // queued or in progress.
   // For a single worker thread (|num_threads| == 1), tasks are completed in
   // FIFO order. This is no longer the case for multiple threads
   // (|num_threads| > 1). Tasks that got queued later might complete first.
@@ -71,6 +71,14 @@ class Threadpool {
   std::unique_ptr<Task> GetCompletedTask()
       ABSL_LOCKS_EXCLUDED(completed_tasks_mutex_);
 
+  using TaskCompletedCallback = std::function<void(std::unique_ptr<Task>)>;
+
+  // Set a callback that is called immediately in a background thread when a
+  // task is completed. The task will not be put onto the completed queue, so
+  // if this callback is set, do not call (Try)GetCompletedTask.
+  void SetTaskCompletedCallback(TaskCompletedCallback cb)
+      ABSL_LOCKS_EXCLUDED(completed_tasks_mutex_);
+
   // Returns the total number of worker threads in the pool.
   size_t NumThreads() const { return workers_.size(); }
 
@@ -80,6 +88,14 @@ class Threadpool {
     return outstanding_task_count_;
   }
 
+  // Block until the number of queued tasks drops below or equal to |count|, or
+  // until the timeout is exceeded, or until Shutdown() is called, whatever
+  // comes sooner. Returns true if less than or equal to |count| tasks are
+  // queued.
+  bool WaitForQueuedTasksAtMost(
+      size_t count, absl::Duration timeout = absl::InfiniteDuration()) const
+      ABSL_LOCKS_EXCLUDED(mutex_);
+
  private:
   // Background thread worker method. Picks tasks and runs them.
   void ThreadWorkerMain()
@@ -94,6 +110,8 @@ class Threadpool {
   absl::Mutex completed_tasks_mutex_;
   std::queue<std::unique_ptr<Task>> completed_tasks_
       ABSL_GUARDED_BY(completed_tasks_mutex_);
+  TaskCompletedCallback on_task_completed_
+      ABSL_GUARDED_BY(completed_tasks_mutex_);
 
   std::vector<std::thread> workers_;
 };

common/threadpool_test.cc

@@ -151,5 +151,37 @@ TEST_F(ThreadpoolTest, GetCompletedTask) {
   EXPECT_EQ(completed_task.get(), task);
 }
 
+TEST_F(ThreadpoolTest, SetTaskCompletedCallback) {
+  auto task_func = [](Task::IsCancelledPredicate) { /* empty */ };
+
+  Semaphore task_finished(0);
+  Threadpool pool(1);
+  std::atomic_bool finished = false;
+  pool.SetTaskCompletedCallback(
+      [&task_finished, &finished](std::unique_ptr<Task> task) {
+        finished = true;
+        task_finished.Signal();
+      });
+  pool.QueueTask(std::make_unique<TestTask>(task_func));
+  task_finished.Wait();
+  EXPECT_TRUE(finished);
+  EXPECT_FALSE(pool.TryGetCompletedTask());
+}
+
+TEST_F(ThreadpoolTest, WaitForQueuedTasksAtMost) {
+  Semaphore task_signal(0);
+  auto task_func = [&task_signal](Task::IsCancelledPredicate) {
+    task_signal.Wait();
+  };
+  Threadpool pool(1);
+  pool.QueueTask(std::make_unique<TestTask>(task_func));
+  pool.QueueTask(std::make_unique<TestTask>(task_func));
+  EXPECT_FALSE(pool.WaitForQueuedTasksAtMost(1, absl::Milliseconds(10)));
+  task_signal.Signal();
+  EXPECT_TRUE(pool.WaitForQueuedTasksAtMost(1, absl::Milliseconds(5000)));
+  EXPECT_EQ(pool.NumQueuedTasks(), 1);
+  task_signal.Signal();
+}
+
 }  // namespace
 }  // namespace cdc_ft

integration_tests/cdc_rsync/output_test.py

@@ -115,7 +115,7 @@ class OutputTest(test_base.CdcRsyncTest):
 
     # server-side output
     self._assert_regex(
-        r'DEBUG   server_socket\.cc\([0-9]+\): Receive\(\): EOF\(\) detected',
+        r'DEBUG   \d+\.\d{3} server_socket\.cc\([0-9]+\): Receive\(\): EOF\(\) detected',
         output)
 
     # TODO: Add a check here, as currently the output is misleading
@@ -139,7 +139,7 @@ class OutputTest(test_base.CdcRsyncTest):
 
     # server-side output
     self._assert_regex(
-        r'VERBOSE message_pump\.cc\([0-9]+\): ThreadDoReceivePacket\(\): Received packet of size',
+        r'VERBOSE \d+\.\d{3} message_pump\.cc\([0-9]+\): ThreadDoReceivePacket\(\): Received packet of size',
         output)
 
   def test_quiet(self):