slots

nimony/lib/std/ioring/core/slots.nim

• type Slot = object
    op: OpContext
    gen: uint32
    inUse: bool
    nextInFd: int64
    prevInFd: int64

• type SlotArena = object
    slots: seq
    freelist: seq
    fdHeads: Table

• proc init(a: var SlotArena; capacity: int64)
• proc allocSlot(a: var SlotArena; op: OpContext): int64
• proc freeSlot(a: var SlotArena; idx: int64)
• proc hasPendingForFd(a: var SlotArena; fd: int32): bool

  var, like slotsForFd, purely to avoid copying the arena — see there.

• iterator slotsForFd(a: var SlotArena; fd: int32): int64

  Yield every in-use slot index for fd, O(k) in the number of ops on this fd rather than O(MaxOps).

  a is var even though nothing here writes to it: the callers all pass a seq element (gSlots[lane].slotsForFd(...)), and for a non-var parameter that materialises a copy of the whole arena — MaxOps slots, each with a 128-byte Sockaddr_storage inside, plus the fdHeads table — on every call, i.e. megabytes memcpy'd per I/O event. var passes the arena itself.

  The body may free the slot it was handed (complete/closeFd both do), so the successor is read before yielding — reading a.slots[cur] after the body ran would inspect a slot that is back on the freelist.

• iterator pendingFds(a: var SlotArena): int32

  Every fd that has at least one in-flight slot. The table is mutated by freeSlot, so a caller that completes ops must collect the fds first and dispatch afterwards — never complete from inside this loop.