Deadlocks
, Definition
• Multiprogramming environment: several processes compete for a fini
number of resources.
• A process requests resources: if the resources are not available at that
time, the process enters a waiting state.
• What if the requests resources are held by other waiting processes?
• This situation is called a deadlock.
, Deadlock System Model
• System consists of m resources: 𝑅1, 𝑅2 ,· · · , 𝑅𝑚
• Resource types: CPU cycles, memory space, I/O devices
• Each resource type 𝑅𝑖 has 𝑊𝑖 instances.
• Each process utilizes a resource as follows:
o Request
o Use
o Release
, Deadlock Characterization
• Deadlock can arise if four conditions hold simultaneously:
o Mutual exclusion
o Hold and wait
o No preemption
o Circular wait
, Definition
• Multiprogramming environment: several processes compete for a fini
number of resources.
• A process requests resources: if the resources are not available at that
time, the process enters a waiting state.
• What if the requests resources are held by other waiting processes?
• This situation is called a deadlock.
, Deadlock System Model
• System consists of m resources: 𝑅1, 𝑅2 ,· · · , 𝑅𝑚
• Resource types: CPU cycles, memory space, I/O devices
• Each resource type 𝑅𝑖 has 𝑊𝑖 instances.
• Each process utilizes a resource as follows:
o Request
o Use
o Release
, Deadlock Characterization
• Deadlock can arise if four conditions hold simultaneously:
o Mutual exclusion
o Hold and wait
o No preemption
o Circular wait
