37.11 Transaction Queues

You can use a transaction queue to communicate with a subprocess using transactions. First use tq-create to create a transaction queue communicating with a specified process. Then you can call tq-enqueue to send a transaction.

Function: tq-create process

This function creates and returns a transaction queue communicating with process. The argument process should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server, possibly on another machine.

Function: tq-enqueue queue question regexp closure fn

This function sends a transaction to queue queue. Specifying the queue has the effect of specifying the subprocess to talk to.

The argument question is the outgoing message that starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.

The argument regexp is a regular expression that should match text at the end of the entire answer, but nothing before; that's how tq-enqueue determines where the answer ends.

The return value of tq-enqueue itself is not meaningful.

Function: tq-close queue

Shut down transaction queue queue, waiting for all pending transactions to complete, and then terminate the connection or child process.

Transaction queues are implemented by means of a filter function. See section 37.9.2 Process Filter Functions.