Deadlock Detection Algorithm1

1
Deadlock Detection Algorithm-1

• Inputs
• N Number of Processes
• M Number of Resource Classes
• Blocked Set of Processes
• READY Set of Processes
• unsigned int Free_Resources M // Each
  Integer ? Number of Instances / Resource
• unsigned int Allocation N M // Current
  Allocation Status
• unsigned int Requested_Resources N,M
• Finished Set of Processes

2
Deadlock Detection Algorithm-2

• 1. repeat until Set Running is Empty
• (a) Select a Process Pj from the Set READY
  
• (b) Delete Pj from Set READY and add it to
  Set Finished
• ( c) for (k 1 k lt M k)
• Free_Resources k ? Free_Resources k
• 
  Allocation j ,k
• (d) while Blocked contains a Process Pl
  such that
• for (k 1 k lt M k)
• Requested_Resources l ,k lt
  Free_Resources k

3
Deadlock Detection Algorithm-3

• (i) for (k 1 k lt M k)
• Free_Resources k ? Free_Resources k
• - Requested_Resources l,
  k
• Allocation l, k ? Allocation l , k
• Requested_ Resources I ,
  k
• (ii) Delete Pl from the Set Blocked and Add it
  to Set READY
• 2. if Set Blocked is NOT Empty then
• Declare Processes in the Set Blocked
  to be Deadlocked.

4
Recovery from Deadlock situation - 1

• Abort all processes. Extreme Case.
• Back up all deadlocked processes up to certain
  predefined checkpoint restart
• Involves too much overhead.
• Successively preempt occupied resources
  forcibly. Not always possible.

5
Recovery from Deadlock situation - 2

• Successively abort deadlocked processes based on
  any of the following criteria Mostly used.
• Lowest Priority.
• Least number of resources used.
• Least CPU time consumed.
• Least Output generated.
• Most estimated time left.

6
Deadlock Handling Techniques Practical usage

• Resource Type Technique Used
• Disk Swap Space Prevention
  / Avoidance
• --------------------------------------------------
  ------------------------------
• Main Memory Prevention
  by Preemption
• (
  Handled by Virtual Memory )
• --------------------------------------------------
  ---------------------------
• Peripherals
  Prevention by Ordering
• --------------------------------------------------
  ---------------------------
• Consumable Detect
  Recover by
• 
  successively aborting
• 
  processes