Race conditions

• Different program behavior depending on which thread gets there first
• "Unsynchronized access of a shared resource leads to erroneous program behavior"
  • hardware, kernel resource, memory
  • memory - data race - most common form

💡 · critical region - region of code which needs synchronisation.
· Eliminate races by synchronising thread access to critical regions.

Dead locks

• Two threads both waiting for each other to finish.

• One thread blocked on a mutex it already holds.

  How to avoid?

  • Lock data not code - are multiple locks really required?
  • Have a specific order for obtaining locks when multiple data locks are required.
  • Release in opposite order obtained.