7.8 Transactions

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A transaction batches key creates and mutating value/key operations into an atomic unit.

int peios_reg_begin_transaction(void);
int peios_reg_commit(int txn_fd);
int peios_reg_txn_status(int txn_fd, uint32_t *state_out, int *terminal_errno_out);
  • peios_reg_begin_transaction starts one and returns a transaction fd (initially unbound; it binds to a source on first use), or -1/ENOMEM. Pass this fd as the txn_fd argument to the create and mutating calls to enlist them. Closing the fd without committing aborts the transaction — so a transaction is abort-by-default, which makes error paths safe.
  • peios_reg_commit atomically applies everything enlisted. On success the fd is terminal — close it. Errors tell you what to do: EINVAL (already committed / never bound), EBUSY (write-lock contention — the transaction stays active, retry the commit), EIO (source failure — stays active), ETIMEDOUT.
  • peios_reg_txn_status reads a transaction's state: state_out receives the REG_TXN_* state, and terminal_errno_out receives the errno that ended it (0 while active or after a clean commit). Both may be NULL.

The lifecycle: begin → enlist operations by passing txn_fd → commit (retry on EBUSY/EIO) → close, or just close to abort.

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