Revert of [Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid code duplication.

components/sync/engine/model_safe_worker.cc

Index: components/sync/engine/model_safe_worker.cc
diff --git a/components/sync/engine/model_safe_worker.cc b/components/sync/engine/model_safe_worker.cc
index 773571675ba7806755af26c9d2ab6b1b7bec18f6..530f206599673cf1b91239e5d40aeff463b0406c 100644
--- a/components/sync/engine/model_safe_worker.cc
+++ b/components/sync/engine/model_safe_worker.cc
@@ -4,9 +4,6 @@
 
 #include "components/sync/engine/model_safe_worker.h"
 
-#include <utility>
-
-#include "base/bind.h"
 #include "base/json/json_writer.h"
 #include "base/values.h"
 
@@ -72,86 +69,24 @@
   }
 }
 
-ModelSafeWorker::ModelSafeWorker()
-    : work_done_or_abandoned_(base::WaitableEvent::ResetPolicy::AUTOMATIC,
-                              base::WaitableEvent::InitialState::NOT_SIGNALED) {
-}
+ModelSafeWorker::ModelSafeWorker() {}
 ModelSafeWorker::~ModelSafeWorker() {}
 
 void ModelSafeWorker::RequestStop() {
-  base::AutoLock auto_lock(lock_);
-
-  // Set stop flag to prevent any *further* WorkCallback from starting to run
-  // (note that one may alreay be running).
-  stopped_ = true;
-
-  // If no work is running, unblock DoWorkAndWaitUntilDone(). If work is
-  // running, it is unsafe to return from DoWorkAndWaitUntilDone().
-  // ScopedSignalWorkDoneOrAbandoned will take care of signaling the event when
-  // the work is done.
-  if (!is_work_running_)
-    work_done_or_abandoned_.Signal();
+  // Set stop flag. This prevents any *further* tasks from being posted to
+  // worker threads (see DoWorkAndWaitUntilDone below), but note that one may
+  // already be posted.
+  stopped_.Set();
 }
 
-SyncerError ModelSafeWorker::DoWorkAndWaitUntilDone(WorkCallback work) {
-  {
-    // It is important to check |stopped_| and reset |work_done_or_abandoned_|
-    // atomically to prevent this race:
-    //
-    // Thread  Action
-    // Sync    Sees that |stopped_| is false.
-    // UI      Calls RequestStop(). Signals |work_done_or_abandoned_|.
-    // Sync    Resets |work_done_or_abandoned_|.
-    //         Waits on |work_done_or_abandoned_| forever since the task may not
-    //         run after RequestStop() is called.
-    base::AutoLock auto_lock(lock_);
-    if (stopped_)
-      return CANNOT_DO_WORK;
-    DCHECK(!is_work_running_);
-    work_done_or_abandoned_.Reset();
-  }
-
-  SyncerError error = UNSET;
-  bool did_run = false;
-  ScheduleWork(base::BindOnce(
-      &ModelSafeWorker::DoWork, this, base::Passed(std::move(work)),
-      base::Passed(base::ScopedClosureRunner(base::Bind(
-          [](scoped_refptr<ModelSafeWorker> worker) {
-            worker->work_done_or_abandoned_.Signal();
-          },
-          make_scoped_refptr(this)))),
-      base::Unretained(&error), base::Unretained(&did_run)));
-
-  // Unblocked when the task runs or is deleted or when RequestStop() is called
-  // before the task starts running.
-  work_done_or_abandoned_.Wait();
-
-  return did_run ? error : CANNOT_DO_WORK;
+SyncerError ModelSafeWorker::DoWorkAndWaitUntilDone(const WorkCallback& work) {
+  if (stopped_.IsSet())
+    return CANNOT_DO_WORK;
+  return DoWorkAndWaitUntilDoneImpl(work);
 }
 
-void ModelSafeWorker::DoWork(WorkCallback work,
-                             base::ScopedClosureRunner scoped_closure_runner,
-                             SyncerError* error,
-                             bool* did_run) {
-  {
-    base::AutoLock auto_lock(lock_);
-    if (stopped_)
-      return;
-
-    // Set |is_work_running_| to make sure that DoWorkAndWaitUntilDone() doesn't
-    // return while |work| is running.
-    DCHECK(!is_work_running_);
-    is_work_running_ = true;
-  }
-
-  *error = std::move(work).Run();
-  *did_run = true;
-
-  {
-    base::AutoLock auto_lock(lock_);
-    DCHECK(is_work_running_);
-    is_work_running_ = false;
-  }
+bool ModelSafeWorker::IsStopped() {
+  return stopped_.IsSet();
 }
 
 }  // namespace syncer