fix(OnceFlag): add isSet and check before waiting (#6316)

CHANGELOG.md

@@ -68,7 +68,7 @@
 - Dev: Refactored `Button` and friends. (#6102, #6255, #6266, #6302, #6268)
 - Dev: Made Settings & Account button on Linux/macOS SVGs. (#6267)
 - Dev: Emoji style / set is now stored lowercase (and matched case-insensitively). Changing emoji style from this point on and then running an old version might mean you will use the Twitter emoji style by default. (#6300)
-- Dev: `OnceFlag`'s internal flag is now atomic. (#6237)
+- Dev: Refactored `OnceFlag`. (#6237, #6316)
 - Dev: Bumped clang-format requirement to 19. (#6236)
 
 ## 2.5.3

src/util/OnceFlag.cpp

@@ -16,6 +16,10 @@ void OnceFlag::set()
 bool OnceFlag::waitFor(std::chrono::milliseconds ms)
 {
     std::unique_lock lock(this->mutex);
+    if (this->flag.load(std::memory_order::relaxed))
+    {
+        return true;
+    }
     return this->condvar.wait_for(lock, ms, [this] {
         return this->flag.load(std::memory_order::relaxed);
     });
@@ -24,9 +28,19 @@ bool OnceFlag::waitFor(std::chrono::milliseconds ms)
 void OnceFlag::wait()
 {
     std::unique_lock lock(this->mutex);
+    if (this->flag.load(std::memory_order::relaxed))
+    {
+        return;
+    }
     this->condvar.wait(lock, [this] {
         return this->flag.load(std::memory_order::relaxed);
     });
 }
 
+bool OnceFlag::isSet()
+{
+    std::unique_lock lock(this->mutex);
+    return this->flag.load(std::memory_order::relaxed);
+}
+
 }  // namespace chatterino

src/util/OnceFlag.hpp

@@ -31,6 +31,9 @@ public:
     /// The calling thread will be suspended during the wait.
     void wait();
 
+    /// Is the flag currently set?
+    bool isSet();
+
 private:
     std::mutex mutex;
     std::condition_variable condvar;

tests/src/OnceFlag.cpp

@@ -79,10 +79,31 @@ TEST(OnceFlag, waitForTimeout)
     });
 
     startedFlag.wait();
+    ASSERT_TRUE(startedFlag.isSet());
     startedAckFlag.set();
+    ASSERT_TRUE(startedAckFlag.isSet());
 
     ASSERT_FALSE(stoppedFlag.waitFor(std::chrono::milliseconds{25}));
     stoppedFlag.wait();
+    ASSERT_TRUE(stoppedFlag.isSet());
 
     t.join();
 }
+
+TEST(OnceFlag, alreadySet)
+{
+    OnceFlag flag;
+    flag.set();
+    ASSERT_TRUE(flag.isSet());
+
+    auto start = std::chrono::system_clock::now();
+    flag.wait();
+    auto stop = std::chrono::system_clock::now();
+    ASSERT_LT(stop - start, std::chrono::milliseconds{10});
+
+    start = std::chrono::system_clock::now();
+    ASSERT_TRUE(flag.waitFor(std::chrono::milliseconds{0}));
+    stop = std::chrono::system_clock::now();
+
+    ASSERT_LT(stop - start, std::chrono::milliseconds{10});
+}