Constant ZX_ERR_STOP 

pub const ZX_ERR_STOP: i32 = -60;

An indicate to not call again.

The flow control values ZX_ERR_STOP, ZX_ERR_NEXT, and ZX_ERR_ASYNC are not errors and will never be returned by a system call or public API. They allow callbacks to request their caller perform some other operation.

For example, a callback might be called on every event until it returns something other than ZX_OK. This status allows differentiation between “stop due to an error” and “stop because work is done.”