Industries · Trading and HFT

For matching engines and feed handlers

ByteAsk joins the gdb session you already have open, finds the lock-order inversion, and cites ITCH and FIX by section.

Book a demo See it find the deadlock

The deadlock is found and fixed.

ByteAskAI pair-debuggerdone

❯ byteask "my gdb is stopped on the deadlock in orderd, take a look"

● Joined the bridge in your gdb. orderd is stopped.

▸ Two threads are stuck in __lll_lock_wait with no progress since 09:31.

▸ T7 (match) is blocked in OrderBook::cancel at order_book.cpp:214.

▸ T7 holds book_mtx_ and waits on risk_mtx_, owned by LWP 71154.

▸ T12 holds risk_mtx_ and waits on book_mtx_, owned by LWP 71149.

▸ That is a lock-order inversion between cancel() and on_fill().

✎ order_book.cpp

-std::lock_guard<std::mutex> bk(book_mtx_);

-std::lock_guard<std::mutex> rk(risk_mtx_);

+std::scoped_lock lk(book_mtx_, risk_mtx_);

▸ The same change is applied in risk_engine.cpp:87.

$ ninja -C build && ./build/stress --orders 5000000 --threads 16

✓ 5000000 orders, 0 stalls

▸ I want to run detach in your gdb. Approve? [y/n]

▸ Approved. Sent to your gdb.

✓The diff is ready for review.

gdbyour gdb, bridge armeddetached

(gdb) source ~/.byteask/byteask_gdb_bridge.py your session · 09:36

(gdb) byteask-bridge

ByteAsk bridge armed. The AI can attach now.

[byteask] (gdb) info threads

Id Target Id Frame

* 1 LWP 71142 "orderd" epoll_wait ()

2 LWP 71143 "io" io_uring_enter ()

7 LWP 71149 "match" __lll_lock_wait ()

9 LWP 71151 "md_feed" recvmsg ()

12 LWP 71154 "risk" __lll_lock_wait ()

[byteask] (gdb) thread 7

[Switching to thread 7 (LWP 71149 "match")]

[byteask] (gdb) bt

#0 __lll_lock_wait ()

#1 ___pthread_mutex_lock ()

#2 std::mutex::lock () at bits/std_mutex.h

#3 OrderBook::cancel (this=0x55d1a3f2c8e0, id=88213004) at order_book.cpp:214

[byteask] (gdb) frame 3

#3 OrderBook::cancel (this=0x55d1a3f2c8e0, id=88213004) at order_book.cpp:214

[byteask] (gdb) p risk_mtx_._M_mutex.__data.__owner

$1 = 71154 ← held by T12

[byteask] (gdb) thread 12

[Switching to thread 12 (LWP 71154 "risk")]

[byteask] (gdb) bt

#0 __lll_lock_wait ()

#1 ___pthread_mutex_lock ()

#2 std::mutex::lock () at bits/std_mutex.h

#3 RiskEngine::on_fill (this=0x55d1a3f30120, fill=...) at risk_engine.cpp:87

[byteask] (gdb) p book_mtx_._M_mutex.__data.__owner

$2 = 71149 ← held by T7 · cycle confirmed

[byteask] (gdb) detach

Detaching from program: /srv/orderd, process 71142

[Inferior 1 (process 71142) detached]

(gdb)

Recorded ByteAsk session on a trading service stopped in gdb: the orderd deadlock.

Standards it can cite

ITCH/OUCH · FIX · PTP

hft_ref: ITCH/OUCH · FIX · IEEE 1588 PTP

hft_refNasdaq TotalView-ITCH 5.0 Add Order No MPID Attribution message type A field layout length offsets page

Nasdaq TotalView-ITCH 5.0 Specification§1.3 Add Order Message · p.13

Add Order Message
   Name                    Offset   Length   Value       Notes
   Message Type            0        1        “A”         Add Order – No MPID Attribution Message.
   Stock Locate            1        2        Integer     Locate code identifying the security
   Tracking Number         3        2        Integer     Nasdaq internal tracking number
   Timestamp               5        6        Integer     Nanoseconds since midnight.
   Order Reference         11       8        Integer     The unique reference number assigned to the new order at
   Number                                                the time of receipt.
   Buy/Sell Indicator      19       1        Alpha       The type of order being added.
                                                         “B” = Buy Order.     “S” = Sell Order.
   Shares                  20       4        Integer     The total number of shares associated with the order being
                                                         added to the book.
   Stock                   24       8        Alpha       Stock symbol, right padded with spaces

ref E1_Nasdaq_ITCH-5.0:1.3:4:1 · captured 2026-09-11

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