Skip to content

Extended time-in-force and reduce-only

The simulator now honours four order flags that real venues enforce on submit. Strategies built against GTC and POST_ONLY get the same behaviour as before; the new flags add coverage for the order types professional venues (Binance UM, Deribit, Bybit options) accept.

Flags

Flag Behaviour at submit
gtc (default) Rests until cancelled or filled.
ioc Take whatever crosses now, cancel the remainder. Never rests.
fok Atomic: fill the entire order at the best price or reject with fok_not_fillable. No partial fills.
gtd Like gtc, plus auto-cancel at expires_at_ns. Expiry fires on the next market event after the deadline.
post_only Reject any limit that would cross. Same as before this task.
reduce_only (orthogonal flag) Order may only reduce the open position. Rejected if it would open/grow; truncated if it would overshoot flat.

The TOB liquidity assumption for FOK is a simplification — only the best level is consulted. Deeper-walk FOK is a follow-up.

FOK mode (any-price vs single-price)

Real venues differ on what FOK means when crossing liquidity sits at a different price than the order's limit:

Mode Behaviour Used by
any_price Fill if TOB qty ≥ order qty and TOB crosses the limit. Default; most crypto venues
single_price Fill only if TOB price equals the order's limit and TOB qty ≥ order qty. CME, Eurex, most US equities

Single-price rejects with fok_unfillable when crossing liquidity sits at a more aggressive level than the limit. any_price accepts that same scenario.

exec.set_fok_mode("single_price")
print(exec.fok_mode())  # 'single_price'

exec.setFokMode("single_price");
exec.fokMode();  // 'single_price'

Apply from a strategy

"""Use FOK / IOC / GTD / reduce-only with SimulatedExecutor."""
import flox_py as flox

exec = flox.SimulatedExecutor()
exec.set_queue_model("tob", 1)
exec.on_best_levels(symbol=1, bid_price=50_000.0, bid_qty=5.0,
                    ask_price=50_001.0, ask_qty=5.0)

# FOK: fully fill or reject. Asks 5.0 available, request 1.0 → fills.
exec.submit_order(id=1, side="buy", price=50_001.0, quantity=1.0,
                  type="limit", symbol=1, tif="fok")

# IOC: take what crosses now, cancel remainder.
exec.submit_order(id=2, side="buy", price=50_001.0, quantity=0.5,
                  type="limit", symbol=1, tif="ioc")

# GTD: rests like GTC but auto-cancels at the absolute deadline.
expires = 5_000_000_000  # 5 seconds since simulator start
exec.submit_order(id=3, side="buy", price=49_500.0, quantity=1.0,
                  type="limit", symbol=1, tif="gtd",
                  expires_at_ns=expires)

# reduce_only: rejects if it would open / grow the position. After the
# two buys above we are long 1.5; a reduce-only sell shrinks toward
# flat. A reduce-only buy would be rejected.
exec.submit_order(id=4, side="sell", price=50_000.0, quantity=0.5,
                  type="limit", symbol=1, tif="ioc", reduce_only=True)

exec.submitOrder(1, 'buy', 50001.0, 1.0, 'limit', 1, { tif: 'fok' });
exec.submitOrder(2, 'sell', 50000.0, 0.5, 'limit', 1,
                  { tif: 'ioc', reduceOnly: true });

exec.submit_order_ex(1, "buy", 50001.0, 1.0, "limit", 1, "fok")
exec.submit_order_ex(2, "sell", 50000.0, 0.5, "limit", 1, "ioc",
                     reduce_only=True)

__flox_simulated_executor_submit_ex(exec, 1n, 0, 50001.0, 1.0, 1, 1, 2, 0, 0n);
// tif=2 (FOK), reduce_only=0

flox::Order o{};
o.id = 1; o.side = flox::Side::BUY;
o.price = flox::Price::fromDouble(50001.0);
o.quantity = flox::Quantity::fromDouble(1.0);
o.type = flox::OrderType::LIMIT;
o.timeInForce = flox::TimeInForce::FOK;
o.flags.reduceOnly = 1;
sim.submitOrder(o);

Reduce-only mechanics

The simulator maintains a per-symbol net position internally, updated in executeFill. A reduce-only submit is evaluated against that net:

  • Flat → reject with reduce_only.
  • Same side as the position → reject (would grow).
  • Opposite side that exactly reduces or zeros → accepted.
  • Opposite side that would flip the sign → truncated to flat.

The truncation is applied before the order enters the book / queue tracker, so the rest of the lifecycle (fills, queue position, etc.) operates on the truncated quantity.

GTD expiry timing

expires_at_ns is an absolute timestamp in the simulator's clock domain. The expiry fires at the next market event (book update / trade) past the deadline — there is no internal tick-driven scheduler. For deterministic expiry at exact times, advance the clock and fire any market event after the deadline.

Notes

  • POST_ONLY already rejected crossing limits before this task; the behaviour is unchanged.
  • IOC partial fills emit PARTIALLY_FILLED for the taken portion; the unfilled remainder emits CANCELED without a free-text reason field on cancel (the TIF tag is on the order itself).
  • The C ABI ships flox_simulated_executor_submit_order_ex for the extended-flag path. The legacy submit_order stays byte-compatible.