All examples are in a fictional language very close to Javascript. Short: A race condition can only occur between two or more threads / external state (one of them can be the OS). We cannot have race conditions inside a single thread process, non I/O doing program. But a single thread program can in many … Read more
Yes, race conditions (in the sense of a shared resource having an inconsistent value due to order of events) can still happen anywhere that there’s a point of suspension that could lead to other code being run (with threads its at any line), take for example this piece of async code that is entirely single … Read more
Django 1.4+ supports select_for_update, in earlier versions you may execute raw SQL queries e.g. select … for update which depending on underlying DB will lock the row from any updates, you can do whatever you want with that row until the end of transaction. e.g. from django.db import transaction @transaction.commit_manually() def add_points(request): user = User.objects.select_for_update().get(id=request.user.id) … Read more
Straight after the $wpdb->insert() that does the insert, do this: $lastid = $wpdb->insert_id; More information about how to do things the WordPress way can be found in the WordPress codex. The details above were found here on the wpdb class page
The race condition is, of course, between your program and some other code that operates on file (race condition always requires at least two parallel processes or threads, see this for details). That means using open() instead of exists() may really help only in two situations: You check for existence of a file that is … Read more
All Javascript event handler scripts are handled from one master event queue system. This means that event handlers run one at a time and one runs until completion before the next one that’s ready to go starts running. As such, there are none of the typical race conditions in Javascript that one would see in … Read more
Here’s 3 different approaches: Atomic update update table set tries=tries+1 where condition=value; and it will be done atomically. Use transactions If you do need to first select the value and update it in your application, you likely need to use transactions. That means you’ll have to use InnoDB, not MyISAM tables. Your query would be … Read more
No, this cannot happen. Yes, there are indeed “hidden” background threads that do the work for asychronous methods, but those don’t call callbacks. All execution of javascript does happen on the same thread, synchronously, sequentially. That data event callback will always be executed asynchronously, that is, after the current script/function ran to completion. While there … Read more
Yeah, there is a possible race in the using statement. The C# compiler transforms using (var obj = new Foo()) { // statements } to: var obj = new Foo(); try { // statements } finally { if (obj != null) obj.Dispose(); } The race occurs when the thread is aborted right between the obj … Read more
I think Bjarne is wrong about this, or at least, he’s simplifying things considerably. Most modern processors are capable of writing a byte without reading a complete word first, or rather, they behave “as if” this were the case. In particular, if you have a char array[2];, and thread one only accesses array[0] and thread … Read more