Lock

Nov 3, 2023

• Dijkstra’s Banker’s Algorithm
• What causes deadlock?
  • Mutual exclusion: Threads claim exclusive control of resources that they require (e.g., a thread grabs a lock).
  • Hold-and-wait: Threads hold resources allocated to them (e.g., locks that they have already acquired) while waiting for additional resources (e.g., locks that they wish to acquire).
  • No preemption: Resources (e.g., locks) cannot be forcibly removed from threads that are holding them.
  • Circular wait: There exists a circular chain of threads such that each thread holds one or more resources (e.g., locks) that are being requested by the next thread in the chain.
• How to avoid deadlocks
  • Circular Wait
  • Hold and Wait
• What to do when deadlock happens
  • Kill the one used the least resources.
  • Fight for resources (wait for resources).

• A binary Semaphore
  It acts as a gatekeeper to a section of code, allowing only one thread to enter at a time and blocking access to all others.