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Diffstat (limited to 'vendor/github.com/lib/pq/example/listen')
-rw-r--r-- | vendor/github.com/lib/pq/example/listen/doc.go | 98 |
1 files changed, 98 insertions, 0 deletions
diff --git a/vendor/github.com/lib/pq/example/listen/doc.go b/vendor/github.com/lib/pq/example/listen/doc.go new file mode 100644 index 000000000..91e2ddbad --- /dev/null +++ b/vendor/github.com/lib/pq/example/listen/doc.go @@ -0,0 +1,98 @@ +/* + +Package listen is a self-contained Go program which uses the LISTEN / NOTIFY +mechanism to avoid polling the database while waiting for more work to arrive. + + // + // You can see the program in action by defining a function similar to + // the following: + // + // CREATE OR REPLACE FUNCTION public.get_work() + // RETURNS bigint + // LANGUAGE sql + // AS $$ + // SELECT CASE WHEN random() >= 0.2 THEN int8 '1' END + // $$ + // ; + + package main + + import ( + "database/sql" + "fmt" + "time" + + "github.com/lib/pq" + ) + + func doWork(db *sql.DB, work int64) { + // work here + } + + func getWork(db *sql.DB) { + for { + // get work from the database here + var work sql.NullInt64 + err := db.QueryRow("SELECT get_work()").Scan(&work) + if err != nil { + fmt.Println("call to get_work() failed: ", err) + time.Sleep(10 * time.Second) + continue + } + if !work.Valid { + // no more work to do + fmt.Println("ran out of work") + return + } + + fmt.Println("starting work on ", work.Int64) + go doWork(db, work.Int64) + } + } + + func waitForNotification(l *pq.Listener) { + select { + case <-l.Notify: + fmt.Println("received notification, new work available") + case <-time.After(90 * time.Second): + go l.Ping() + // Check if there's more work available, just in case it takes + // a while for the Listener to notice connection loss and + // reconnect. + fmt.Println("received no work for 90 seconds, checking for new work") + } + } + + func main() { + var conninfo string = "" + + db, err := sql.Open("postgres", conninfo) + if err != nil { + panic(err) + } + + reportProblem := func(ev pq.ListenerEventType, err error) { + if err != nil { + fmt.Println(err.Error()) + } + } + + minReconn := 10 * time.Second + maxReconn := time.Minute + listener := pq.NewListener(conninfo, minReconn, maxReconn, reportProblem) + err = listener.Listen("getwork") + if err != nil { + panic(err) + } + + fmt.Println("entering main loop") + for { + // process all available work before waiting for notifications + getWork(db) + waitForNotification(listener) + } + } + + +*/ +package listen |