Does lock() guarantee acquired in order requested?

by

IIRC, it’s highly likely to be in that order, but it’s not guaranteed. I believe there are at least theoretically cases where a thread will be woken spuriously, note that it still doesn’t have the lock, and go to the back of the queue. It’s possible that’s only for Wait/Notify, but I have a sneaking suspicion it’s for locking as well.

I definitely wouldn’t rely on it – if you need things to occur in a sequence, build up a Queue<T> or something similar.

EDIT: I’ve just found this within Joe Duffy’s Concurrent Programming on Windows which basically agrees:

Because monitors use kernel objects internally, they exhibit the same roughly-FIFO behavior that the OS synchronization mechanisms also exhibit (described in the previous chapter). Monitors are unfair, so if another thread tries to acquire the lock before an awakened waiting thread tries to acquire the lock, the sneaky thread is permitted to acquire a lock.

The “roughly-FIFO” bit is what I was thinking of before, and the “sneaky thread” bit is further evidence that you shouldn’t make assumptions about FIFO ordering.

More Related Contents:

  1. What does a lock statement do under the hood?
  2. Re-entrant locks in C#
  3. Is it OK to use a string as a lock object?
  4. Does a locked object stay locked if an exception occurs inside it?
  5. How expensive is the lock statement?
  6. Monitor vs lock
  7. What are the differences between various threading synchronization options in C#?
  8. Do I need to lock or mark as volatile when accessing a simple boolean flag in C#?
  9. Lock (Monitor) internal implementation in .NET
  10. When is ReaderWriterLockSlim better than a simple lock?
  11. increment a count value outside parallel.foreach scope
  12. How to lock on an integer in C#?
  13. Synchronizing 2 processes using interprocess synchronizations objects – Mutex or AutoResetEvent
  14. Is a bool read/write atomic in C#
  15. How do I calculate someone’s age based on a DateTime type birthday?
  16. how to create an animated gif in .net
  17. Windows Forms Splash Screen – Show a form while loading main form
  18. AppSettings get value from .config file
  19. IEqualityComparer that uses ReferenceEquals
  20. Internal vs. Private Access Modifiers
  21. How to catch ALL exceptions/crashes in a .NET app [duplicate]
  22. How DataReader works?
  23. Return to an already open application when a user tries to open a new instance
  24. How do I programmatically save an image from a URL?
  25. smtpclient ” failure sending mail”
  26. CryptographicException “Key not valid for use in specified state.” while trying to export RSAParameters of a X509 private key
  27. Are global static classes and methods bad?
  28. Storyboards can’t find ControlTemplate elements
  29. Intern string literals misunderstanding?
  30. EPPlus – LoadFromCollection – Text converted to number

Leave a Comment