Operating Systems

• Processes can communicate with each other through inter-process communication mechanisms such as pipes, shared memory, and message queues.
• An operating system's primary function is to allocate and manage computer resources efficiently so that multiple users or applications can run simultaneously without interfering with one another.
• Operating systems are designed to manage computer hardware, including input/output devices such as keyboards, mice, printers, and storage devices like hard drives and optical disks.
• File systems store data and allow it to be accessed by various applications.
• Memory management involves allocating physical RAM to running programs and managing virtual memory swapped between disk and RAM.
• There are three main states for a process and all threads: Running, Ready, Blocked.
• Blocking process is an important concept in process management.
• An OS knows it can make no useful progress so it is ineligible to run until it can make progress.
• A blocked process will always transition through ready before running.
• A running process can block based on kernel requests for temporarily unavailable resources.
• Ready processes move to running when the scheduler selects them.
• Most OSes provide a manual mechanism for the user to block a process (ready or running).
• The main responsibilities of process management include scheduling, blocking, creating, and destroying.
• Scheduling in process management is across both processes and threads, not strictly processes.
• Blocking is a crucial concept in process management.
• The kernel still needs to lock critical sections, which involves disabling interrupts and using spinlocks.
• Semaphores are a superset that maintains a counter.
• “Down” or “P” decrements the counter if it's greater than 0 or blocks the caller.
• “Up” or “V” unblocks a process, if available, or increments the counter.
• 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.
• Very common in computing to have a producer / consumer program.
• “producer” adds data to a fixed size queue at a particular rate.
• “consumer” remove and processes data.
• Semaphore – more general than mutex; can be used as a counter