pg_listen creates, changes, or
cancels a request to listen for asynchronous notification
messages from the PostgreSQL
server. With a callbackCommand
parameter, the request is established, or the command string of
an already existing request is replaced. With no callbackCommand parameter, a prior request is
pg_listen request is
established, the specified command string is executed whenever a
notification message bearing the given name arrives from the
server. This occurs when any PostgreSQL client application issues a
NOTIFY command referencing that name. The command string
is executed from the Tcl idle loop. That is the normal idle state
of an application written with Tk. In non-Tk Tcl shells, you can
vwait to cause the idle loop to be entered.
You should not invoke the SQL statements LISTEN or UNLISTEN
directly when using
pgtcl takes care of issuing
those statements for you. But if you want to send a notification
message yourself, invoke the SQL NOTIFY
The handle of the connection on which to listen for notifications.
The name of the notification condition to start or stop listening to.
If present, provides the command string to execute when a matching notification arrives.