public:

virtual ~WorkerCacheInterface() {}

// Updates *workers with strings naming the remote worker tasks to

// which open channels have been established.

virtual void ListWorkers(std::vector<string>* workers) = 0;

// If "target" names a remote task for which an RPC channel exists

// or can be constructed, returns a new WorkerInterface object

// wrapping that channel. Ownership passes to the caller.

// TODO(tucker): rename this to CreateWorker() or something that

// makes it more obvious this is a constructor that transfers

// ownership, not a cache lookup.

virtual WorkerInterface* CreateWorker(const string& target) = 0;

// Set *ba with the BusAdjacency of the specified remote device

// within its local environment. Returns true if the device bus

// affinity was set, using only locally cached data. Returns false

// if status data for that device was not available. Never blocks.

// TODO(mrry,tucker): Maybe remove.

virtual bool GetDeviceBusNonBlocking(const string& device,

BusAdjacency* ba) = 0;

// Set *ba with the BusAdjacency of the specified remote device

// within its local environment. Callback gets Status::OK if the

// device bus affinity was set.

// TODO(mrry,tucker): Maybe remove.

virtual void GetDeviceBusAsync(const string& device, BusAdjacency* ba,

StatusCallback done) = 0;

// Start/stop logging activity.

virtual void SetLogging(bool active) {}

// Discard any saved log data.

virtual void ClearLogs() {}

// Return logs for the identified step in *ss. Any returned data will no

// longer be stored.

virtual bool RetrieveLogs(int64 step_id, StepStats* ss) { return false; }