func Trigger(db *sublevel.DB, taskDb *sublevel.DB, filter FilterFunc, taskfunc ProcessFunc) *Task {
wo := levigo.NewWriteOptions()
ro := levigo.NewReadOptions()
task := &Task{db: db, filter: filter, processFunc: taskfunc, taskDb: taskDb, wo: wo, ro: ro, running: make(map[string]bool)}
var run func(taskKey []byte)
run = func(taskKey []byte) {
taskKeyStr := string(taskKey)
var ok bool
// println("RUN", string(key), string(value), string(taskKey))
hookfunc := func(key, value []byte, hook *sublevel.Hook) {
ok = taskfunc(key, value)
}
for {
it := task.taskDb.NewIterator(task.ro)
for it.Seek(taskKey); it.Valid(); it.Next() {
if !bytes.HasPrefix(it.Key(), taskKey) || len(taskKey)+16 != len(it.Key()) {
break
}
key := it.Value()
val, err := task.db.Get(task.ro, it.Value())
if err != nil {
continue
}
if len(val) == 0 {
val = nil
}
// println("RUN", string(key), string(val), string(taskKey))
// This lock avoids that the processing is interrupted by a call to Close()
task.closeMutex.Lock()
// Execute taskfunc in the context of a new hook, commit to disk, then call after
ok = true
db.RunHook(wo, hookfunc, nil, key, val)
if ok {
taskDb.Delete(wo, it.Key())
}
task.closeMutex.Unlock()
}
it.Close()
task.runningMutex.Lock()
state := task.running[taskKeyStr]
if !state {
delete(task.running, taskKeyStr)
task.runningMutex.Unlock()
break
}
task.running[taskKeyStr] = false
task.runningMutex.Unlock()
}
}
// Hook into the db to watch for changes
task.pre = func(key, value []byte, hook *sublevel.Hook) {
// println("PRE", string(key), string(value))
// Is this change relevant?
taskKey := filter(key, value)
if taskKey == nil {
return
}
// Write a DB row so the task is not forgotten if the system is terminated now
now := uniclock.Next()
nowBytes := []byte(fmt.Sprintf("%016x", now))
hook.Put(append(taskKey, nowBytes...), key, taskDb)
}
task.post = func(key, value []byte) {
// println("POST", string(key), string(value))
// Is this change relevant?
taskKey := filter(key, value)
if taskKey == nil {
return
}
taskKeyStr := string(taskKey)
// println("POSTtask", "'" + taskKeyStr + "'")
task.runningMutex.Lock()
defer task.runningMutex.Unlock()
if _, ok := task.running[taskKeyStr]; ok {
task.running[taskKeyStr] = true
} else {
task.running[taskKeyStr] = false
go run(taskKey)
}
}
db.Pre(task.pre)
db.Post(task.post)
return task
}
