pg_listen − set or change a callback for asynchronous notification messages
pg_listen conn notifyName [callbackCommand]
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 canceled.
After a 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 execute update or vwait to cause the idle loop to be entered.
You should not invoke the SQL statements LISTEN or UNLISTEN directly when using pg_listen. pgtcl takes care of issuing those statements for you. But if you want to send a notification message yourself, invoke the SQL NOTIFY statement using pg_exec.
conn |
The handle of the connection on which to listen for notifications. |
notifyName
The name of the notification condition to start or stop listening to.
callbackCommand
If present, provides the command string to execute when a matching notification arrives.
None