// GetWork requests one or more work units to perform. The work unit
// attempts are associated with workerID, which need not have been
// previously registered. If there is no work to do, may return
// neither work nor an error.
//
// Each work unit is returned as a cborrpc.PythonTuple holding the
// work spec name, work unit key as a byte slice, and work unit data
// dictionary. If options does not contain "max_jobs" or if that
// value is 1, returns a tuple or nil, otherwise returns a slice of
// tuples (maybe 1 or none).
func (jobs *JobServer) GetWork(workerID string, options map[string]interface{}) (interface{}, string, error) {
// This is the Big Kahuna. The Python Coordinate server tries
// to be extra clever with its return value, returning None if
// there is no work, a concrete value if one work unit was
// requested, and a list if more than one was requested, and
// this same rule is enforced in the client code. So, this will
// return either exactly one PythonTuple or a list of PythonTuple.
var (
attempts []coordinate.Attempt
err error
gwOptions GetWorkOptions
worker coordinate.Worker
)
err = decode(&gwOptions, options)
if err == nil {
worker, err = jobs.Namespace.Worker(workerID)
}
if err == nil {
if gwOptions.MaxJobs < 1 {
gwOptions.MaxJobs = 1
}
req := coordinate.AttemptRequest{
NumberOfWorkUnits: gwOptions.MaxJobs,
Runtimes: []string{""},
WorkSpecs: gwOptions.WorkSpecNames,
}
attempts, err = worker.RequestAttempts(req)
}
if err != nil {
return nil, "", err
}
// successful return
if gwOptions.MaxJobs == 1 {
if len(attempts) == 0 {
tuple := cborrpc.PythonTuple{
Items: []interface{}{nil, nil, nil},
}
return tuple, "", nil
}
if len(attempts) == 1 {
tuple, err := getWorkTuple(attempts[0])
if err != nil {
return nil, "", err
}
return tuple, "", nil
}
}
result := make([]cborrpc.PythonTuple, len(attempts))
for i, attempt := range attempts {
tuple, err := getWorkTuple(attempt)
if err != nil {
return nil, "", err
}
result[i] = tuple
}
return result, "", nil
}
// doWork gets attempts and runs them. It assumes it is running in its
// own goroutine. It signals gotWork when the call to RequestAttempts
// returns, and signals finished immediately before returning.
func (w *Worker) doWork(id string, worker coordinate.Worker, ctx context.Context, gotWork chan<- bool, finished chan<- string) {
// When we finish, signal the finished channel with our own ID
defer func() {
finished <- id
}()
attempts, err := worker.RequestAttempts(coordinate.AttemptRequest{
Runtimes: []string{"go"},
NumberOfWorkUnits: w.MaxAttempts,
})
if err != nil {
// Handle the error if we can, but otherwise act just like
// we got no attempts back
if w.ErrorHandler != nil {
w.ErrorHandler(err)
}
gotWork <- false
return
}
if len(attempts) == 0 {
// Nothing to do
gotWork <- false
return
}
// Otherwise we have actual work (and at least one attempt).
gotWork <- true
// See if we can find a task for the work spec
spec := attempts[0].WorkUnit().WorkSpec()
task := spec.Name()
data, err := spec.Data()
if err == nil {
aTask, present := data["task"]
if present {
bTask, ok := aTask.(string)
if ok {
task = bTask
}
}
}
// Try to find the task function
var taskFn func(context.Context, []coordinate.Attempt)
if err == nil {
taskFn = w.Tasks[task]
if taskFn == nil {
err = fmt.Errorf("No such task function %q", task)
}
}
if err == nil {
taskCtx, cancellation := context.WithCancel(ctx)
w.cancellations[id] = cancellation
taskFn(taskCtx, attempts)
// It appears to be recommended to call this; calling
// it multiple times is documented to have no effect
cancellation()
} else {
failure := map[string]interface{}{
"traceback": err.Error(),
}
// Try to fail all the attempts, ignoring errors
for _, attempt := range attempts {
_ = attempt.Fail(failure)
}
}
}