Created attachment 220017 [details]
vala file 

A lambda within 'Thread.create' (and I assume 'new Thread', but I have no way of testing it) allocates a user data block, but doesn't ref it before creating the thread, and unrefs it when the parent thread leaves the scope in which the thread was created.

That means that the data block can be deallocated before any information is ever used.

The relevant part of the c code generated was:

GThread* main_inner_scope (Foo* foo) {
...
	Block1Data* _data1_;
...
	_tmp2_ = g_thread_create (___lambda2__gthread_func, _data1_, TRUE, &_inner_error_);
...	
	block1_data_unref (_data1_);
...
	return result;
}

I think the g_thread_create call should be structured as '_tmp2_ = g_thread_create (___lambda2__gthread_func, block1_data_ref(_data1_), TRUE, &_inner_error_);', with a matching block1_data_unref within the lambda function after it's no longer needed.