ircd:Ⓜ️:vm: Add an opts.unique bypass option for condition.

include/ircd/m/vm.h

@@ -243,6 +243,11 @@ struct ircd::m::vm::opts
 	/// replayed through the system (not recommended).
 	bool replays {false};
 
+	/// Bypass check for another evaluation of the same event_id already
+	/// occurring. If this is false (not recommended) two duplicate events
+	/// being evaluated may race through the core.
+	bool unique {true};
+
 	/// If the input event has a reference to already-strung json we can use
 	/// that directly when writing to the DB. When this is false we will
 	/// re-stringify the event internally either from a referenced source or

matrix/vm_eval.cc

@@ -329,10 +329,11 @@ ircd::m::vm::eval::operator()(const vector_view<m::event> &events)
 			// evaluation is finished. If the other was successful, the exists()
 			// check will skip this, otherwise we have to try again here because
 			// this evaluator might be using different options/credentials.
-			sequence::dock.wait([&event]
-			{
-				return eval::count(event.event_id) == 0;
-			});
+			if(likely(opts->unique))
+				sequence::dock.wait([&event]
+				{
+					return eval::count(event.event_id) == 0;
+				});
 
 			if(likely(!opts->replays) && m::exists(event.event_id))
 				continue;

matrix/vm_execute.cc

@@ -436,14 +436,13 @@ ircd::m::vm::execute_pdu(eval &eval,
 
 	// Wait for any pending duplicate evals before proceeding.
 	assert(eval::count(event_id));
-	sequence::dock.wait([&event_id]
-	{
-		return eval::count(event_id) <= 1;
-	});
+	if(likely(opts.unique))
+		sequence::dock.wait([&event_id]
+		{
+			return eval::count(event_id) <= 1;
+		});
 
-	// This branch won't be taken anymore with the above condition added; but
-	// leaving the code for reference right now.
-	if((false) && unlikely(eval::count(event_id) > 1))
+	if(likely(opts.unique) && unlikely(eval::count(event_id) > 1))
 		throw error
 		{
 			fault::EXISTS, "Event is already being evaluated."