| 1 | package calendar |
| 2 | |
| 3 | import ( |
| 4 | "context" |
| 5 | "time" |
| 6 | ) |
| 7 | |
| 8 | // The drain's budgets: what a send may use of one, and what is kept |
| 9 | // back for recording its outcome. |
| 10 | |
| 11 | // keepReserve is the part of every budget that belongs to bookkeeping, |
| 12 | // not sending: sends stop this long before the deadline, and the |
| 13 | // outcome of the last one is recorded inside it. |
| 14 | const keepReserve = 2 * time.Second |
| 15 | |
| 16 | // sendBudget is what a send may use of ctx: everything but the |
| 17 | // reserve. A context with no deadline is left alone. |
| 18 | func sendBudget(ctx context.Context) (context.Context, context.CancelFunc) { |
| 19 | if dl, ok := ctx.Deadline(); ok { |
| 20 | return context.WithDeadline(ctx, dl.Add(-keepReserve)) |
| 21 | } |
| 22 | return context.WithCancel(ctx) |
| 23 | } |
| 24 | |
| 25 | // keep is the bookkeeping context: what a send's outcome is recorded |
| 26 | // under. Detached from cancellation — a send that ran out its budget |
| 27 | // still has to be marked failed or deferred, or the lease does the |
| 28 | // same job five minutes later at the cost of a duplicate — and bounded |
| 29 | // by what is left of ctx's own deadline, floored at keepFloor so a |
| 30 | // late claim still gets its outcome recorded. That floor is the whole |
| 31 | // of the overrun a budget can suffer. |
| 32 | func keep(ctx context.Context) context.Context { |
| 33 | left := keepReserve |
| 34 | if dl, ok := ctx.Deadline(); ok { |
| 35 | if until := time.Until(dl); until < left { |
| 36 | left = until |
| 37 | } |
| 38 | } |
| 39 | if left < keepFloor { |
| 40 | left = keepFloor |
| 41 | } |
| 42 | k, cancel := context.WithTimeout(context.WithoutCancel(ctx), left) |
| 43 | _ = cancel // released by the timeout; the store calls are short |
| 44 | return k |
| 45 | } |
| 46 | |
| 47 | // keepFloor is the least a bookkeeping call is given, whatever the |
| 48 | // clock says. |
| 49 | const keepFloor = time.Second |
| 50 | |
amadan