*: use std::lock_guard instead of std::scoped_lock

std::lock_guard is a simpler template for locking just one mutex,
while std::scoped_lock is more complex because it allows locking
multiple mutexes, avoiding deadlocks.  This isn't what we need, so
let's use the simpler one.

Author: MaxKellermann

src/event/Loop.cxx

@@ -498,7 +498,7 @@ EventLoop::Run() noexcept
 		/* try to handle DeferEvents without WakeFD
 		   overhead */
 		{
-			const std::scoped_lock lock{mutex};
+			const std::lock_guard lock{mutex};
 			HandleInject();
 #endif
 
@@ -526,7 +526,7 @@ EventLoop::Run() noexcept
 
 #ifdef HAVE_THREADED_EVENT_LOOP
 		{
-			const std::scoped_lock lock{mutex};
+			const std::lock_guard lock{mutex};
 			busy = true;
 		}
 #endif
@@ -558,7 +558,7 @@ EventLoop::AddInject(InjectEvent &d) noexcept
 	bool must_wake;
 
 	{
-		const std::scoped_lock lock{mutex};
+		const std::lock_guard lock{mutex};
 		if (d.IsPending())
 			return;
 
@@ -577,7 +577,7 @@ EventLoop::AddInject(InjectEvent &d) noexcept
 void
 EventLoop::RemoveInject(InjectEvent &d) noexcept
 {
-	const std::scoped_lock protect{mutex};
+	const std::lock_guard protect{mutex};
 
 	if (d.IsPending())
 		inject.erase(inject.iterator_to(d));
@@ -605,7 +605,7 @@ EventLoop::OnWake() noexcept
 		return;
 	}
 
-	const std::scoped_lock lock{mutex};
+	const std::lock_guard lock{mutex};
 	HandleInject();
 }
 

src/event/Loop.hxx

@@ -244,7 +244,7 @@ public:
 	 */
 	void InjectBreak() noexcept {
 		{
-			const std::scoped_lock lock{mutex};
+			const std::lock_guard lock{mutex};
 			quit_injected = true;
 		}