Restructure FilesystemCopierAction to use ping-pong buffers.

filesystem_copier_action.cc

Index: filesystem_copier_action.cc
diff --git a/filesystem_copier_action.cc b/filesystem_copier_action.cc
index 1452b4dbffed38399e04f39d462a6b5313d139b0..f3f71bdbee4b107ddfc7ccba92e1e68cb168da91 100755
--- a/filesystem_copier_action.cc
+++ b/filesystem_copier_action.cc
@@ -32,9 +32,32 @@ using std::vector;
 namespace chromeos_update_engine {
 
 namespace {
-const off_t kCopyFileBufferSize = 2 * 1024 * 1024;
+const off_t kCopyFileBufferSize = 512 * 1024;
 }  // namespace {}
 
+FilesystemCopierAction::FilesystemCopierAction(
+    bool copying_kernel_install_path)
+    : copying_kernel_install_path_(copying_kernel_install_path),
+      src_stream_(NULL),
+      dst_stream_(NULL),
+      read_done_(false),
+      failed_(false),
+      cancelled_(false),
+      filesystem_size_(kint64max) {
+  // A lot of code works on the implicit assumption that processing is done on
+  // exactly 2 ping-pong buffers.
+  COMPILE_ASSERT(arraysize(buffer_) == 2 &&
+                 arraysize(buffer_state_) == 2 &&
+                 arraysize(buffer_valid_size_) == 2 &&
+                 arraysize(canceller_) == 2,
+                 ping_pong_buffers_not_two);
+  for (int i = 0; i < 2; ++i) {
+    buffer_state_[i] = kBufferStateEmpty;
+    buffer_valid_size_[i] = 0;
+    canceller_[i] = NULL;
+  }
+}
+
 void FilesystemCopierAction::PerformAction() {
   // Will tell the ActionProcessor we've failed if we return.
   ScopedActionCompleter abort_action_completer(processor_, this);
@@ -84,35 +107,35 @@ void FilesystemCopierAction::PerformAction() {
   src_stream_ = g_unix_input_stream_new(src_fd, TRUE);
   dst_stream_ = g_unix_output_stream_new(dst_fd, TRUE);
 
-  buffer_.resize(kCopyFileBufferSize);
-
-  // Set up the first read
-  canceller_ = g_cancellable_new();
+  for (int i = 0; i < 2; i++) {
+    buffer_[i].resize(kCopyFileBufferSize);
+    canceller_[i] = g_cancellable_new();
+  }
 
-  g_input_stream_read_async(src_stream_,
-                            &buffer_[0],
-                            GetBytesToRead(),
-                            G_PRIORITY_DEFAULT,
-                            canceller_,
-                            &FilesystemCopierAction::StaticAsyncReadyCallback,
-                            this);
-  read_in_flight_ = true;
+  // Start the first read.
+  SpawnAsyncActions();
 
   abort_action_completer.set_should_complete(false);
 }
 
 void FilesystemCopierAction::TerminateProcessing() {
-  if (canceller_) {
-    g_cancellable_cancel(canceller_);
+  for (int i = 0; i < 2; i++) {
+    if (canceller_[i]) {
+      g_cancellable_cancel(canceller_[i]);
+    }
   }
 }
 
-void FilesystemCopierAction::Cleanup(bool success, bool was_cancelled) {
+void FilesystemCopierAction::Cleanup(bool success) {
+  for (int i = 0; i < 2; i++) {
+    g_object_unref(canceller_[i]);
+    canceller_[i] = NULL;
+  }
   g_object_unref(src_stream_);
   src_stream_ = NULL;
   g_object_unref(dst_stream_);
   dst_stream_ = NULL;
-  if (was_cancelled)
+  if (cancelled_)
     return;
   if (success && HasOutputPipe())
     SetOutputObject(install_plan_);
@@ -121,85 +144,141 @@ void FilesystemCopierAction::Cleanup(bool success, bool was_cancelled) {
       success ? kActionCodeSuccess : kActionCodeError);
 }
 
-void FilesystemCopierAction::AsyncReadyCallback(GObject *source_object,
-                                                GAsyncResult *res) {
+void FilesystemCopierAction::AsyncReadReadyCallback(GObject *source_object,
+                                                    GAsyncResult *res) {
+  int index = buffer_state_[0] == kBufferStateReading ? 0 : 1;
+  CHECK(buffer_state_[index] == kBufferStateReading);
+
   GError* error = NULL;
-  CHECK(canceller_);
-  bool was_cancelled = g_cancellable_is_cancelled(canceller_) == TRUE;
-  g_object_unref(canceller_);
-  canceller_ = NULL;
-
-  if (read_in_flight_) {
-    ssize_t bytes_read = g_input_stream_read_finish(src_stream_, res, &error);
-    if (bytes_read < 0) {
-      LOG(ERROR) << "Read failed:" << utils::GetGErrorMessage(error);
-      Cleanup(false, was_cancelled);
-      return;
-    }
+  CHECK(canceller_[index]);
+  cancelled_ = g_cancellable_is_cancelled(canceller_[index]) == TRUE;
 
-    if (bytes_read == 0) {
-      // We're done!
-      if (!hasher_.Finalize()) {
-        LOG(ERROR) << "Unable to finalize the hash.";
-        Cleanup(false, was_cancelled);
-        return;
-      }
-      LOG(INFO) << "hash: " << hasher_.hash();
-      if (copying_kernel_install_path_) {
-        install_plan_.current_kernel_hash = hasher_.raw_hash();
-      } else {
-        install_plan_.current_rootfs_hash = hasher_.raw_hash();
-      }
-      Cleanup(true, was_cancelled);
-      return;
-    }
-    if (!hasher_.Update(buffer_.data(), bytes_read)) {
-      LOG(ERROR) << "Unable to update the hash.";
-      Cleanup(false, was_cancelled);
-      return;
-    }
+  ssize_t bytes_read = g_input_stream_read_finish(src_stream_, res, &error);
+  if (bytes_read < 0) {
+    LOG(ERROR) << "Read failed: " << utils::GetGErrorMessage(error);
+    failed_ = true;
+    buffer_state_[index] = kBufferStateEmpty;
+  } else if (bytes_read == 0) {
+    read_done_ = true;
+    buffer_state_[index] = kBufferStateEmpty;
+  } else {
+    buffer_valid_size_[index] = bytes_read;
+    buffer_state_[index] = kBufferStateFull;
+  }
+
+  if (bytes_read > 0) {
     filesystem_size_ -= bytes_read;
+  }
 
-    // Kick off a write
-    read_in_flight_ = false;
-    buffer_valid_size_ = bytes_read;
-    canceller_ = g_cancellable_new();
-    g_output_stream_write_async(
-        dst_stream_,
-        &buffer_[0],
-        bytes_read,
-        G_PRIORITY_DEFAULT,
-        canceller_,
-        &FilesystemCopierAction::StaticAsyncReadyCallback,
-        this);
-    return;
+  SpawnAsyncActions();
+
+  if (bytes_read > 0) {
+    if (!hasher_.Update(buffer_[index].data(), bytes_read)) {
+      LOG(ERROR) << "Unable to update the hash.";
+      failed_ = true;
+    }
   }
+}
+
+void FilesystemCopierAction::StaticAsyncReadReadyCallback(
+    GObject *source_object,
+    GAsyncResult *res,
+    gpointer user_data) {
+  reinterpret_cast<FilesystemCopierAction*>(user_data)->
+      AsyncReadReadyCallback(source_object, res);
+}
+
+void FilesystemCopierAction::AsyncWriteReadyCallback(GObject *source_object,
+                                                     GAsyncResult *res) {
+  int index = buffer_state_[0] == kBufferStateWriting ? 0 : 1;
+  CHECK(buffer_state_[index] == kBufferStateWriting);
+  buffer_state_[index] = kBufferStateEmpty;
+
+  GError* error = NULL;
+  CHECK(canceller_[index]);
+  cancelled_ = g_cancellable_is_cancelled(canceller_[index]) == TRUE;
 
   ssize_t bytes_written = g_output_stream_write_finish(dst_stream_,
                                                        res,
                                                        &error);
-  if (bytes_written < static_cast<ssize_t>(buffer_valid_size_)) {
+  if (bytes_written < static_cast<ssize_t>(buffer_valid_size_[index])) {
     if (bytes_written < 0) {
-      LOG(ERROR) << "Write failed:" << utils::GetGErrorMessage(error);
+      LOG(ERROR) << "Write failed: " << utils::GetGErrorMessage(error);
     } else {
       LOG(ERROR) << "Write was short: wrote " << bytes_written
-                 << " but expected to write " << buffer_valid_size_;
+                 << " but expected to write " << buffer_valid_size_[index];
     }
-    Cleanup(false, was_cancelled);
-    return;
+    failed_ = true;
   }
 
-  // Kick off a read
-  read_in_flight_ = true;
-  canceller_ = g_cancellable_new();
-  g_input_stream_read_async(
-      src_stream_,
-      &buffer_[0],
-      GetBytesToRead(),
-      G_PRIORITY_DEFAULT,
-      canceller_,
-      &FilesystemCopierAction::StaticAsyncReadyCallback,
-      this);
+  SpawnAsyncActions();
+}
+
+void FilesystemCopierAction::StaticAsyncWriteReadyCallback(
+    GObject *source_object,
+    GAsyncResult *res,
+    gpointer user_data) {
+  reinterpret_cast<FilesystemCopierAction*>(user_data)->
+      AsyncWriteReadyCallback(source_object, res);
+}
+
+void FilesystemCopierAction::SpawnAsyncActions() {
+  bool reading = false;
+  bool writing = false;
+  for (int i = 0; i < 2; i++) {
+    if (buffer_state_[i] == kBufferStateReading) {
+      reading = true;
+    }
+    if (buffer_state_[i] == kBufferStateWriting) {
+      writing = true;
+    }
+  }
+  if (failed_ || cancelled_) {
+    if (!reading && !writing) {
+      Cleanup(false);
+    }
+    return;
+  }
+  for (int i = 0; i < 2; i++) {
+    if (!reading && !read_done_ && buffer_state_[i] == kBufferStateEmpty) {
+      g_input_stream_read_async(
+          src_stream_,
+          buffer_[i].data(),
+          GetBytesToRead(),
+          G_PRIORITY_DEFAULT,
+          canceller_[i],
+          &FilesystemCopierAction::StaticAsyncReadReadyCallback,
+          this);
+      reading = true;
+      buffer_state_[i] = kBufferStateReading;
+    } else if (!writing && buffer_state_[i] == kBufferStateFull) {
+      g_output_stream_write_async(
+          dst_stream_,
+          buffer_[i].data(),
+          buffer_valid_size_[i],
+          G_PRIORITY_DEFAULT,
+          canceller_[i],
+          &FilesystemCopierAction::StaticAsyncWriteReadyCallback,
+          this);
+      writing = true;
+      buffer_state_[i] = kBufferStateWriting;
+    }
+  }
+  if (!reading && !writing) {
+    // We're done!
+    if (hasher_.Finalize()) {
+      LOG(INFO) << "hash: " << hasher_.hash();
+      if (copying_kernel_install_path_) {
+        install_plan_.current_kernel_hash = hasher_.raw_hash();
+      } else {
+        install_plan_.current_rootfs_hash = hasher_.raw_hash();
+      }
+      Cleanup(true);
+    } else {
+      LOG(ERROR) << "Unable to finalize the hash.";
+      Cleanup(false);
+    }
+  }
 }
 
 void FilesystemCopierAction::DetermineFilesystemSize(int fd) {
@@ -214,7 +293,7 @@ void FilesystemCopierAction::DetermineFilesystemSize(int fd) {
 }
 
 int64_t FilesystemCopierAction::GetBytesToRead() {
-  return std::min(static_cast<int64_t>(buffer_.size()), filesystem_size_);
+  return std::min(static_cast<int64_t>(buffer_[0].size()), filesystem_size_);
 }
 
 }  // namespace chromeos_update_engine