Tools

Banker's Algorithm

1. Understanding the Key Elements of the Problem

1.1 Processes

  • Processes represent the competing entities that request and release resources in a system.
  • A process may request multiple resources before starting execution.
  • A process must release the resources after completing its task.
  • The system should ensure that no process holds resources indefinitely, causing deadlock.

Example:

  • A file download process requests CPU time, disk space, and network bandwidth.
  • A video rendering process requests GPU power and memory.

1.2 Resources

Resources are the limited components required for process execution.

Resources can be classified as:

  • CPU cycles
  • Memory blocks
  • Disk I/O slots
  • Network ports

Resources can be available, allocated, or in use.

Example:

  • Disk space and memory are shared resources that multiple processes may need simultaneously.
  • If one process holds a disk and another holds memory, both may end up waiting for each other → Deadlock

1.3 Maximum Demand

  • The maximum demand of a process refers to the maximum number of resources that the process may need during its execution.
  • A process declares its maximum demand at the start of execution.
  • The system uses this information to calculate whether the process can be granted resources without leading to a deadlock.

Example:

  • A video encoding process may need up to 4 CPU cores, but it may work with only 2 if that’s what’s available.

1.4 Allocation

  • The allocation represents the number of resources currently assigned to a process.
  • If a process is allocated fewer resources than its maximum demand, it may remain in a waiting state.

Example:

  • A file transfer process may be allocated one network port but needs two to reach maximum efficiency.

1.5 Need

The need is calculated as:
Need = Maximum Demand − Allocated Resources

  • The system checks the need value to decide if resources can be safely allocated without leading to a deadlock.

Example:

  • If a process needs 3 memory blocks and only 2 are available, the request is denied.

2. What is Synchronization?

Synchronization refers to the mechanism by which the operating system coordinates resource allocation among competing processes to avoid conflicts and deadlocks.

In the context of the Banker's Algorithm, synchronization ensures that:

  • Resources are allocated only if the system can remain in a safe state.
  • The system prevents deadlock by allowing processes to wait until enough resources become available.
  • Resources are released once a process completes its execution, allowing other processes to proceed.

3. Key Synchronization Mechanisms in Banker's Algorithm

3.1 Safe State

  • A system is in a safe state if there is a sequence of processes such that each process can complete with the currently available resources.
  • A resource request is granted only if the system remains in a safe state after allocation.
  • If granting a request results in an unsafe state, the request is denied.

Example:

  • If Process A is granted disk space but Process B then waits for memory, the system becomes unsafe → Request denied.

3.2 Resource Allocation Matrix

The Resource Allocation Matrix tracks how many resources each process currently holds.

Process CPU Memory Disk
P1 1 2 1
P2 2 1 0
  • P1 holds 1 CPU, 2 memory blocks, and 1 disk.
  • P2 holds 2 CPUs and 1 memory block.

3.3 Available Vector

The Available Vector represents the number of resources currently available for allocation.

CPU Memory Disk
1 2 1

3.4 Need Matrix

The Need Matrix calculates how many more resources each process will need to complete execution.

Need = Max Demand − Allocated

Process CPU Memory Disk
P1 1 1 1
P2 0 1 1

4. Potential Unsafe Scenarios Without Synchronization

4.1 Deadlock

  • If the system allocates resources without checking the safe state, it may enter a deadlock.

Example:

  • P1 holds CPU and waits for Memory.
  • P2 holds Memory and waits for CPU.
  • Neither process can proceed → Deadlock

4.2 Starvation

  • A process may be left waiting indefinitely if resources are repeatedly allocated to other processes.

Example:

  • P1 continuously acquires the CPU.
  • P2 never gets a turn → Starvation

4.3 Resource Hoarding

  • If one process holds resources without releasing them, it may prevent others from proceeding.

Example:

  • A process locks disk access but does not release it → Resource wastage

5. Why We Need Synchronization

The Banker's Algorithm ensures that resources are allocated fairly and safely to avoid system instability.

Example (Dining Philosophers Problem):

  • Philosophers must acquire two chopsticks to eat.
  • If all philosophers hold one chopstick → Deadlock.
  • If one philosopher repeatedly gets to eat → Starvation.

In the Banker's Algorithm:

  • The system calculates future availability before granting resources.
  • Ensures that no process can hold a resource indefinitely.