s6-ftrigrd is a helper program that manages a set of subscriptions to fifodirs as well as regular expressions on events. It takes orders from its client program that controls it via the ftrigr library, and notifies it when desired events happen.
s6-ftrigrd is not meant to be called directly.
s6-ftrigrd handles the grunt work of creating fifos in a fifodir for a subscriber. It also wakes up on every event, and compares the chain of events it received on a given fifodir with the client-provided regexp. If the chain of events matches the regexp, it notifies the client.
The connection management between the client and s6-ftrigrd is entirely done by the textclient library from skalibs.
s6-ftrigrd is entirely asynchronous. It stores unread notifications into heap memory; it can grow in size if there are a lot of events and the client fails to read them. To avoid uncontrolled growth, make sure your client calls ftrigr_update() as soon as ftrigr_fd() becomes readable.
A s6-ftrigrd instance can only handle up to FTRIGRD_MAX (defined in s6/ftrigr.h) subscriptions at once. By default, this number is 1000, which is more than enough for any reasonable system.