task: don't hold the mutex while disposing of pending Tasks

In the event that someday Barrier allows users to force execution of
its pending tasks prior to the destruction of the BarrierState object,
we'll be ready to submit those Tasks for execution without waiting for
the BarrierState mutex lock.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

lib/task.cc

@@ -791,11 +791,13 @@ namespace crucible {
 	void
 	BarrierState::release()
 	{
+		set<Task> tasks_local;
 		unique_lock<mutex> lock(m_mutex);
-		for (auto i : m_tasks) {
+		swap(tasks_local, m_tasks);
+		lock.unlock();
+		for (const auto &i : tasks_local) {
 			i.run();
 		}
-		m_tasks.clear();
 	}
 
 	BarrierState::~BarrierState()