Operating Systems - Deadlock and Race Conditions

Tutorial 6

• Deadlock, Starvation, and Race Conditions:
  • Deadlock: Occurs when two or more threads are blocked indefinitely, waiting for each other to release resources.
  • Starvation: Occurs when a low priority thread is constantly denied resources by higher priority threads.
  • Race Condition: Occurs when multiple threads interact negatively, resulting in unpredictable outcomes due to the order of their instructions.

Tutorial 6 - Resource Graph

• Deadlock Identification: A directed graph can reveal if a system is currently deadlocked or not. It shows resources and processes.
• Blocked Processes: Check for any process that is waiting for a resource that is unavailable.
• Process Reduction: Removing a process from the graph and updating it to reveal other states of the system.
• System Stability: A system is stable if a process' request can be granted without leading to further instability.

Tutorial 7

• Parallel Processing (Multiprocessing): Two or more processors working simultaneously.

• Multiprocessing Benefits:

  • Higher throughput (faster completion of tasks)
  • Increased computing power

• Multiprocessing Levels:

  • Job Level: Synchronization not needed.
  • Process Level: Moderate synchronization required.
  • Thread Level: High synchronization required

• Master/Slave Configuration Disadvantages:

  • Master failure means the entire system fails.
  • Inefficient resource utilization.
  • High interrupt frequency

• Symmetric Configuration Advantages:

  • Increased reliability
  • Efficient resource usage
  • Load balancing
  • Graceful degradation in case of failures

• Test and Set Locking Drawbacks:

  • Starvation: Processes can get stuck waiting for the critical section.
  • Resource Consumption: Waiting processes consume resources if they remain endlessly waiting.

Tutorial 7 - Semaphores

• Semaphores: Flag that tracks the availability of a resource (ON/OFF).

• Wait Operation: Testing a resource (blocking process if unavailable).

• Signal Operation: Indicating a resource is available (unblocking a process).

• Synchronization Role: Manages CPU/memory/IO device access to prevent simultaneous access causing issues.

Tutorial 8

• Secondary Storage: Permanent memory - examples include punch cards, Blu-ray discs, floppy disks, magnetic tapes, USB drives, CDs, cloud storage.
• Primary Storage (Main Memory): Temporary memory; data lost when power off; used for CPU processing.
• Buffering: Storing data temporarily before sending to a slower device (monitor, hard drive).
• Blocking: Grouping data records into blocks for efficient access/storage.

Tutorial 8 - Disk Capacity Calculations

• Calculations : Using formulas for calculating waste in space, number of tracks, rotational speed and total time to transfer data

Tutorial 9

• File Management Criteria:

  • File organization (sequential, direct, indexed).
  • Record structure (fixed-length, variable-length).
  • Access control (matrix, lists, capabilities).
  • Storage method (contiguous, non-contiguous, indexed).

• File Manager Responsibilities:

  • Tracking file locations.
  • Managing storage allocation and access.
  • Assigning files.
  • Deallocating files.

• User-File Manager Communication: Commands such as OPEN, COPY, DELETE, RENAME.

• Fixed vs. Variable Length Records:

  • Fixed Length: Easier direct access, sequential access speedier.
  • Variable Length: Adaptable to varying record sizes, but more complex to address.

• Absolute vs. Relative File Names:

  • Absolute: Full path (e.g., c:/documents/filename.txt).
  • Relative: Path relative to the current directory (e.g., filename.txt).

Tutorial 9 - Other Topics

• File Organization Types: Sequential, direct, indexed sequential storage (contiguous, noncontiguous, indexed).

Tutorial 10

• Noncontiguous File Storage: Diagrammed examples of non-contiguous storage: showing how different files take up different parts of the storage space, with links between different areas. This shows where files are located in memory and how to find them when needed.
• Index Tables: Tables showing how to refer to different storage locations and how different parts of a file are stored across the storage space using pointers that link to where the file begins, or how long it is.

Tutorial 10 - Access Control for Files

• Access Control Matrix: Describes what type of access (read, write, delete, execute) different users have to different files.

• Access Control List (ACL): Lists what access each user has to a specific file. (e.g. User 2010 can only read and execute (R-E-) on File 1)

• WORLD category: All users that are not included in other groups.