C practice in Operating Systems

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• Count the CPUs

  A CPU-availability mask stores many yes/no flags in one integer; population count measures how many are set.

  bits. Free with an account.

• Count the Forks

  Starting from one process, n complete duplication rounds produce 2 to the power n processes.

  fork. Free with an account.

• Name the State

  Map the five model states to distinct characters and use ? for an unknown value.

  states. Free with an account.

• The Turnaround Desk

  Waiting = completion - arrival - CPU burst, for this no-I/O model.

  metrics. Free with an account.

• Ring Around the Buffer

  Accept an operation only when occupancy permits it; otherwise count a failure without changing occupancy.

  ring. Free with an account.

• Round the Robin

  On each turn, execute min(quantum, remaining work), then record completion exactly when the remaining work reaches zero.

  rr. Free with an account.

• Spin the Lock

  Remember the old value, store one, then return the old value.

  locks. Free with an account.

• Wait on the Semaphore

  A wait consumes one permit only when capacity is available.

  semaphores. Free with an account.

• Catch the Cycle

  A cycle exists if some node can follow one or more dependency links back to itself.

  deadlock. Free with an account.

• Split the Address

  With a power-of-two page size, the high address bits identify the virtual page.

  paging. Free with an account.

• The Tightest Hole

  Filter eligible free blocks, then choose the smallest size with earliest-index ties.

  fit. Free with an account.

• Walk the Table

  Physical address = mapped frame times page size + original page offset.

  pagetable. Free with an account.

• Evict the Stale

  On every access record its time; on a miss use the first empty slot or the least-recently-used occupied slot.

  lru. Free with an account.

• Raise the Dead Disk

  Missing value = parity XOR every surviving data value.

  raid. Free with an account.

• Sweep the Disk

  At each step, serve the nearest remaining request from the current head position.

  elevator. Free with an account.

• XOR the Stripe

  XOR parity summarizes a stripe and can help reconstruct one missing data word.

  raid. Free with an account.

• Ask the Oracle

  On a full-memory miss, replace the page needed farthest after the current request.

  optimal. Free with an account.

• Banker's Hours

  Repeatedly finish any eligible unfinished process and add its allocation to a private work vector.

  deadlock. Free with an account.

• Boot to Idle

  Run round-robin once, then report makespan, identity changes and mean completion time scaled by 100.

  fullrun. Free with an account.

• Hand Out the FD

  The lowest free descriptor is a hole in an occupancy mask, not the number of open descriptors.

  files. Free with an account.