What happens to in-flight TxF writes when a Windows 8 transaction hits its timeout?

The short answer

When a TxF transaction exceeds its timeout (roughly 60 seconds by default), the Windows Transaction Manager aborts it, and rollback is complete. No portion of your uncommitted writes ever becomes visible in the target file — not to other readers, and not after the abort. The file reverts to its exact pre-transaction state. Atomicity is the entire point of TxF, and a timeout-triggered abort goes through the same rollback path as an explicit RollbackTransaction call.

The practical consequence for your retry design is the opposite of what you hoped: you cannot retry a failed write inside the same transaction after a timeout abort, because the transaction no longer exists. Your retry logic must detect the abort, start a brand-new transaction, and redo the write from scratch.

What state the handles are in after an abort

Your transaction handle remains a valid handle object, but the transaction it refers to is gone. Any transacted file handles created with CreateFileTransacted against that transaction are similarly orphaned. The next operation you attempt — whether a write or CommitTransaction — will fail with a transaction-related error such as ERROR_TRANSACTION_NOT_FOUND or a code indicating the transaction is no longer active. Always check GetLastError() after every transacted I/O call, not just at commit time, so you learn about the abort at the first failing operation instead of at commit.

Is the timeout configurable?

Not through the standard Win32 TxF surface. CreateTransaction accepts a timeout parameter in milliseconds, and passing 0 selects the system default — but the system can still abort a transaction for other reasons (resource pressure, log issues), so treating the timeout as a hard guarantee is unsafe either way. Design as if any transaction can be aborted at any time.

Detecting the abort

There is no supported API to poll a transaction's liveness. Detection is reactive:

1. Check the return value and GetLastError() on every transacted write and on CommitTransaction.
2. On a transaction-state error, close the orphaned handles, call RollbackTransaction defensively (it will simply fail harmlessly if the transaction is already gone), then open a new transaction and retry the whole unit of work.
3. Make your write operation idempotent at the transaction level: since rollback is complete, re-running the full write in a fresh transaction cannot duplicate data — duplication only becomes a risk if you mix transacted and non-transacted writes to the same file.

Verify it yourself

Because the ~60-second figure is a guideline that can vary with build and load, confirm on your target Windows 8 machines:

1. Start a transaction, write recognizable bytes to a test file, sleep past the timeout, then attempt CommitTransaction.
2. Assert the commit fails, record the exact error code, and read the file non-transacted to confirm its contents are unchanged.
3. Optionally trace with Process Monitor to confirm no partial data reaches the file during the abort window.

One caveat worth flagging

TxF is effectively deprecated in later Windows versions and unsupported on ReFS and network shares. If this component has a long life ahead of it, consider whether a write-temp-file-then-atomic-rename pattern (e.g., ReplaceFile) meets your durability goals with a supported API. That decision hinges on one detail you didn't mention: whether you need multi-file atomicity. TxF's real advantage is atomic updates across several files; for a single file, rename-based replacement is simpler and future-proof.