WorkerThreadPool (plus friends): Overhaul unlock allowance zones

This fixes a rare but possible deadlock, maybe due to undefined behavior. The new implementation is safer, at the cost of some added boilerplate.

1 files changed, 6 insertions, 12 deletions

diff --git a/core/templates/command_queue_mt.h b/core/templates/command_queue_mt.h
index 1e6c6e42a9..8ef5dd3064 100644
--- a/core/templates/command_queue_mt.h
+++ b/core/templates/command_queue_mt.h
@@ -362,23 +362,24 @@ class CommandQueueMT {
 			return;
 		}
 
-		lock();
+		MutexLock lock(mutex);
 
-		uint32_t allowance_id = WorkerThreadPool::thread_enter_unlock_allowance_zone(&mutex);
 		while (flush_read_ptr < command_mem.size()) {
 			uint64_t size = *(uint64_t *)&command_mem[flush_read_ptr];
 			flush_read_ptr += 8;
 			CommandBase *cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
+			uint32_t allowance_id = WorkerThreadPool::thread_enter_unlock_allowance_zone(lock);
 			cmd->call();
+			WorkerThreadPool::thread_exit_unlock_allowance_zone(allowance_id);
 
 			// Handle potential realloc due to the command and unlock allowance.
 			cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
 
 			if (unlikely(cmd->sync)) {
 				sync_head++;
-				unlock(); // Give an opportunity to awaiters right away.
+				lock.~MutexLock(); // Give an opportunity to awaiters right away.
 				sync_cond_var.notify_all();
-				lock();
+				new (&lock) MutexLock(mutex);
 				// Handle potential realloc happened during unlock.
 				cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
 			}
@@ -387,14 +388,11 @@ class CommandQueueMT {
 
 			flush_read_ptr += size;
 		}
-		WorkerThreadPool::thread_exit_unlock_allowance_zone(allowance_id);
 
 		command_mem.clear();
 		flush_read_ptr = 0;
 
 		_prevent_sync_wraparound();
-
-		unlock();
 	}
 
 	_FORCE_INLINE_ void _wait_for_sync(MutexLock<BinaryMutex> &p_lock) {
@@ -410,9 +408,6 @@ class CommandQueueMT {
 	void _no_op() {}
 
 public:
-	void lock();
-	void unlock();
-
 	/* NORMAL PUSH COMMANDS */
 	DECL_PUSH(0)
 	SPACE_SEP_LIST(DECL_PUSH, 15)
@@ -446,9 +441,8 @@ public:
 	}
 
 	void set_pump_task_id(WorkerThreadPool::TaskID p_task_id) {
-		lock();
+		MutexLock lock(mutex);
 		pump_task_id = p_task_id;
-		unlock();
 	}
 
 	CommandQueueMT();