OS Week 4

• Mutex is a basic lock that allows for one thread at a time, also known as mutual exclusion.
• Disable interrupts are necessary when using a Mutex.
• Mutex locks variables.
• Mutex: A basic lock that allows for one thread at a time, enforcing mutual exclusion.
• Disable interrupts: Mutex requires the CPU to disable interrupts.
• Lock variables: Mutex can lock variables.
• Peterson’s Solution: Two threads can be synchronized using Peterson’s Solution which adds another variable.
• Atomic test and set (TST): Performs both the test and set operations in a single instruction.
• Kernel provided mutex: The kernel still needs to lock critical sections, such as disable interrupts and spinlocks.
• Semaphores: A mutex superset that maintains a counter.
• “Down” or “P”: Decrements the counter if it's positive or blocks the caller.
• “Up” or “V”: Unblocks a process, if available, or increments the counter.
• Producer/Consumer Model: This model is very common in computing, where a producer adds data to a fixed size queue at a particular rate, and a consumer removes and processes data.
• Manage buffer capacity with two semaphores: “remaining” item semaphore (init 0) and “available” slot semaphore (init buffer size).
• Producer decrements remaining semaphore before adding to queue, and increments available semaphore when done.
• Consumer decrements available semaphore before removing from queue, and increments remaining semaphore when done.
• Note that, depending on buffer implementation, additional locking may be necessary to protect the data structure.