chore: use condition variable to shutdown websocket pools (#5721)

src/util/OnceFlag.cpp

@@ -0,0 +1,33 @@
+#include "util/OnceFlag.hpp"
+
+namespace chatterino {
+
+OnceFlag::OnceFlag() = default;
+OnceFlag::~OnceFlag() = default;
+
+void OnceFlag::set()
+{
+    {
+        std::unique_lock guard(this->mutex);
+        this->flag = true;
+    }
+    this->condvar.notify_all();
+}
+
+bool OnceFlag::waitFor(std::chrono::milliseconds ms)
+{
+    std::unique_lock lock(this->mutex);
+    return this->condvar.wait_for(lock, ms, [this] {
+        return this->flag;
+    });
+}
+
+void OnceFlag::wait()
+{
+    std::unique_lock lock(this->mutex);
+    this->condvar.wait(lock, [this] {
+        return this->flag;
+    });
+}
+
+}  // namespace chatterino