SVEN CASES OF DEADLOCKS / DEADLOCK MODELING AND MULTIPROCESSING CONFIGURATIONS

Deadlock

occur in operating systems when two or more processes are unable to proceed because each is waiting for the other to release resources. Here are seven specific cases of deadlocks:

Case 1: Deadlocks on File Request

When jobs request and hold files during execution, deadlocks can occur. Other programs requiring these files are put on hold until the deadlock is resolved.

Case 2: Deadlocks in Database

Deadlocks can arise when multiple processes lock database records.

Case 3: Deadlocks in Dedicated Device Allocation

Occurs when limited dedicated devices (e.g., printers, plotters) are allocated.

Case 4: Deadlocks in Multiple Device Allocation

Happens when several processes request and hold multiple devices, preventing each other from proceeding.

Case 5: Deadlocks in Spooling

In systems where devices like printers are spooled with temporary disk storage, deadlocks can arise if the spooling mechanism interferes with job requirements.

Case 6: Deadlocks in Network

A congested network can lead to deadlocks if protocols to control message flow are absent.

Case 7: Deadlocks in Disk Sharing

Deadlocks can occur when multiple processes access different areas of the same disk without control mechanisms.

Deadlock Modeling

is a method used to represent and analyze deadlocks in operating systems using directed graphs

HOLT

A computer scientist/programmer demonstrated how the four necessary conditions for deadlock can be modeled using directed graphs.

Resource Allocation Graphs

The ______________ help in visualizing deadlocks.

CIRCLES

Processes are represented as

SQUARES

Resources are represented as

An arc from a resource (square) to a process (circle)

indicates that the resource has been allocated to the process.

An arc from a process (circle) to a resource (square)

indicates that the process is requesting the resource and is in a waiting state.

FIGURE A

Holding a Resource

FIGURE B

Requesting a Resource

FIGURE C

Deadlock

1. Master/Slave Multiprocessing Configuration

2. Loosely Coupled Multiprocessing Configuration

3. Symmetric Multiprocessing (SMP) Configuration

3 Typical Multiprocessing Configurations

Master/Slave Multiprocessing Configuration

• Asymmetric architecture.

• Master processor controls all system operations, including process management, 1/0 operations, and memory management.

• Slave processors execute tasks assigned by the master but cannot control system resources independently.

Loosely Coupled Multiprocessing Configuration

• Each processor has its own CPU, memory, and 1/0 devices.

• Each processor runs an independent operating system.

• Processors communicate and cooperate through interconnection networks.

• Global tables track jobs allocated to each processor.

Symmetric Multiprocessing (SMP) Configuration

• Decentralized processor scheduling

• Single copy of the OS manages all processors.

• Global process table stored in shared memory.

• Each processor uses the same scheduling algorithm to select tasks.