Initial commit of sync engine code to browser/sync....

chrome/browser/sync/engine/model_safe_worker.h

+// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
+#define CHROME_BROWSER_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
+
+#include "chrome/browser/sync/util/closure.h"
+#include "chrome/browser/sync/util/sync_types.h"
+
+namespace browser_sync {
+
+// The Syncer uses a ModelSafeWorker for all tasks that could potentially
+// modify syncable entries (e.g under a WriteTransaction). The ModelSafeWorker
+// only knows how to do one thing, and that is take some work (in a fully
+// pre-bound callback) and have it performed (as in Run()) from a thread which
+// is guaranteed to be "model-safe", where "safe" refers to not allowing us to
+// cause an embedding application model to fall out of sync with the
+// syncable::Directory due to a race.
+class ModelSafeWorker {
+ public:
+  ModelSafeWorker() { }
+  virtual ~ModelSafeWorker() { }
+
+  // Any time the Syncer performs model modifications (e.g employing a
+  // WriteTransaction), it should be done by this method to ensure it is done
+  // from a model-safe thread.
+  //
+  // TODO(timsteele): For now this is non-reentrant, meaning the work being
+  // done should be at a high enough level in the stack that
+  // DoWorkAndWaitUntilDone won't be called again by invoking Run() on |work|.
+  // This is not strictly necessary; it may be best to call
+  // DoWorkAndWaitUntilDone at lower levels, such as within ApplyUpdates, but
+  // this is sufficient to simplify and test out our dispatching approach.
+  virtual void DoWorkAndWaitUntilDone(Closure* work) {
+    work->Run();  // By default, do the work on the current thread.
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ModelSafeWorker);
+};
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_ENGINE_MODEL_SAFE_WORKER_H_