Replace 'std::mutex' inside 'SyncSwitch' to 'fml::SharedMutex' (#32773)

Author: ColdPaleLight

fml/synchronization/sync_switch.cc

@@ -18,10 +18,12 @@ SyncSwitch::Handlers& SyncSwitch::Handlers::SetIfFalse(
   return *this;
 }
 
-SyncSwitch::SyncSwitch(bool value) : value_(value) {}
+SyncSwitch::SyncSwitch(bool value)
+    : mutex_(std::unique_ptr<fml::SharedMutex>(fml::SharedMutex::Create())),
+      value_(value) {}
 
 void SyncSwitch::Execute(const SyncSwitch::Handlers& handlers) const {
-  std::scoped_lock guard(mutex_);
+  fml::SharedLock lock(*mutex_);
   if (value_) {
     handlers.true_handler();
   } else {
@@ -30,7 +32,7 @@ void SyncSwitch::Execute(const SyncSwitch::Handlers& handlers) const {
 }
 
 void SyncSwitch::SetSwitch(bool value) {
-  std::scoped_lock guard(mutex_);
+  fml::UniqueLock lock(*mutex_);
   value_ = value;
 }
 

fml/synchronization/sync_switch.h

@@ -7,9 +7,10 @@
 
 #include <forward_list>
 #include <functional>
-#include <mutex>
+#include <memory>
 
 #include "flutter/fml/macros.h"
+#include "flutter/fml/synchronization/shared_mutex.h"
 
 namespace fml {
 
@@ -53,7 +54,7 @@ class SyncSwitch {
   void SetSwitch(bool value);
 
  private:
-  mutable std::mutex mutex_;
+  mutable std::unique_ptr<fml::SharedMutex> mutex_;
   bool value_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(SyncSwitch);

fml/synchronization/sync_switch_unittest.cc

@@ -4,6 +4,8 @@
 
 #include "flutter/fml/synchronization/sync_switch.h"
 
+#include <thread>
+
 #include "gtest/gtest.h"
 
 using fml::SyncSwitch;
@@ -28,3 +30,30 @@ TEST(SyncSwitchTest, NoopIfUndefined) {
   syncSwitch.Execute(SyncSwitch::Handlers());
   EXPECT_FALSE(switchValue);
 }
+
+TEST(SyncSwitchTest, SharedLock) {
+  SyncSwitch syncSwitch;
+  syncSwitch.SetSwitch(true);
+  bool switchValue1 = false;
+  bool switchValue2 = false;
+
+  std::thread thread1([&] {
+    syncSwitch.Execute(
+        SyncSwitch::Handlers()
+            .SetIfTrue([&] {
+              switchValue1 = true;
+
+              std::thread thread2([&]() {
+                syncSwitch.Execute(
+                    SyncSwitch::Handlers()
+                        .SetIfTrue([&] { switchValue2 = true; })
+                        .SetIfFalse([&] { switchValue2 = false; }));
+              });
+              thread2.join();
+            })
+            .SetIfFalse([&] { switchValue1 = false; }));
+  });
+  thread1.join();
+  EXPECT_TRUE(switchValue1);
+  EXPECT_TRUE(switchValue2);
+}