Revert "Guard the service protocol's global handlers list with a read…

…er/writer lock (flutter#6888) flutter#6895" (flutter#6899)

ci/licenses_golden/licenses_flutter

@@ -164,8 +164,6 @@ FILE: ../../../flutter/fml/platform/posix/file_posix.cc
 FILE: ../../../flutter/fml/platform/posix/mapping_posix.cc
 FILE: ../../../flutter/fml/platform/posix/native_library_posix.cc
 FILE: ../../../flutter/fml/platform/posix/paths_posix.cc
-FILE: ../../../flutter/fml/platform/posix/shared_mutex_posix.cc
-FILE: ../../../flutter/fml/platform/posix/shared_mutex_posix.h
 FILE: ../../../flutter/fml/platform/win/errors_win.cc
 FILE: ../../../flutter/fml/platform/win/errors_win.h
 FILE: ../../../flutter/fml/platform/win/file_win.cc
@@ -178,13 +176,9 @@ FILE: ../../../flutter/fml/platform/win/wstring_conversion.h
 FILE: ../../../flutter/fml/string_view.cc
 FILE: ../../../flutter/fml/string_view.h
 FILE: ../../../flutter/fml/string_view_unittest.cc
-FILE: ../../../flutter/fml/synchronization/atomic_object.h
 FILE: ../../../flutter/fml/synchronization/count_down_latch.cc
 FILE: ../../../flutter/fml/synchronization/count_down_latch.h
 FILE: ../../../flutter/fml/synchronization/count_down_latch_unittests.cc
-FILE: ../../../flutter/fml/synchronization/shared_mutex.h
-FILE: ../../../flutter/fml/synchronization/shared_mutex_std.cc
-FILE: ../../../flutter/fml/synchronization/shared_mutex_std.h
 FILE: ../../../flutter/fml/synchronization/thread_annotations.h
 FILE: ../../../flutter/fml/synchronization/thread_annotations_unittest.cc
 FILE: ../../../flutter/fml/synchronization/thread_checker.h

fml/BUILD.gn

@@ -46,10 +46,8 @@ source_set("fml") {
     "paths.h",
     "string_view.cc",
     "string_view.h",
-    "synchronization/atomic_object.h",
     "synchronization/count_down_latch.cc",
     "synchronization/count_down_latch.h",
-    "synchronization/shared_mutex.h",
     "synchronization/thread_annotations.h",
     "synchronization/thread_checker.h",
     "synchronization/waitable_event.cc",
@@ -85,12 +83,6 @@ source_set("fml") {
 
   libs = []
 
-  if (is_ios || is_mac) {
-    sources += [ "platform/posix/shared_mutex_posix.cc" ]
-  } else {
-    sources += [ "synchronization/shared_mutex_std.cc" ]
-  }
-
   if (is_ios || is_mac) {
     sources += [
       "platform/darwin/cf_utils.cc",

runtime/service_protocol.cc

@@ -45,30 +45,29 @@ ServiceProtocol::ServiceProtocol()
           kRunInViewExtensionName,
           kFlushUIThreadTasksExtensionName,
           kSetAssetBundlePathExtensionName,
-      }),
-      handlers_mutex_(fml::SharedMutex::Create()) {}
+      }) {}
 
 ServiceProtocol::~ServiceProtocol() {
   ToggleHooks(false);
 }
 
 void ServiceProtocol::AddHandler(Handler* handler,
                                  Handler::Description description) {
-  fml::UniqueLock lock(*handlers_mutex_);
+  std::lock_guard<std::mutex> lock(handlers_mutex_);
   handlers_.emplace(handler, description);
 }
 
 void ServiceProtocol::RemoveHandler(Handler* handler) {
-  fml::UniqueLock lock(*handlers_mutex_);
+  std::lock_guard<std::mutex> lock(handlers_mutex_);
   handlers_.erase(handler);
 }
 
 void ServiceProtocol::SetHandlerDescription(Handler* handler,
                                             Handler::Description description) {
-  fml::SharedLock lock(*handlers_mutex_);
+  std::lock_guard<std::mutex> lock(handlers_mutex_);
   auto it = handlers_.find(handler);
   if (it != handlers_.end())
-    it->second.Store(description);
+    it->second = description;
 }
 
 void ServiceProtocol::ToggleHooks(bool set) {
@@ -176,7 +175,7 @@ bool ServiceProtocol::HandleMessage(fml::StringView method,
     return HandleListViewsMethod(response);
   }
 
-  fml::SharedLock lock(*handlers_mutex_);
+  std::lock_guard<std::mutex> lock(handlers_mutex_);
 
   if (handlers_.size() == 0) {
     WriteServerErrorResponse(response,
@@ -247,11 +246,12 @@ void ServiceProtocol::Handler::Description::Write(
 
 bool ServiceProtocol::HandleListViewsMethod(
     rapidjson::Document& response) const {
-  fml::SharedLock lock(*handlers_mutex_);
+  // Collect handler descriptions on their respective task runners.
+  std::lock_guard<std::mutex> lock(handlers_mutex_);
   std::vector<std::pair<intptr_t, Handler::Description>> descriptions;
   for (const auto& handler : handlers_) {
     descriptions.emplace_back(reinterpret_cast<intptr_t>(handler.first),
-                              handler.second.Load());
+                              handler.second);
   }
 
   auto& allocator = response.GetAllocator();

runtime/service_protocol.h

@@ -6,14 +6,13 @@
 #define FLUTTER_RUNTIME_SERVICE_PROTOCOL_H_
 
 #include <map>
+#include <mutex>
 #include <set>
 #include <string>
 
 #include "flutter/fml/compiler_specific.h"
 #include "flutter/fml/macros.h"
 #include "flutter/fml/string_view.h"
-#include "flutter/fml/synchronization/atomic_object.h"
-#include "flutter/fml/synchronization/shared_mutex.h"
 #include "flutter/fml/synchronization/thread_annotations.h"
 #include "flutter/fml/task_runner.h"
 #include "rapidjson/document.h"
@@ -73,8 +72,8 @@ class ServiceProtocol {
 
  private:
   const std::set<fml::StringView> endpoints_;
-  std::unique_ptr<fml::SharedMutex> handlers_mutex_;
-  std::map<Handler*, fml::AtomicObject<Handler::Description>> handlers_;
+  mutable std::mutex handlers_mutex_;
+  std::map<Handler*, Handler::Description> handlers_;
 
   FML_WARN_UNUSED_RESULT
   static bool HandleMessage(const char* method,