src/kudu/util/cloud/instance_detector.h

// Licensed to the Apache Software Foundation (ASF) under one
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// to you under the Apache License, Version 2.0 (the
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// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
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// specific language governing permissions and limitations
// under the License.

#pragma once

#include <cstddef>
#include <memory>
#include <vector>

#include "kudu/gutil/port.h"
#include "kudu/gutil/ref_counted.h"
#include "kudu/util/cloud/instance_metadata.h"
#include "kudu/util/condition_variable.h"
#include "kudu/util/mutex.h"
#include "kudu/util/status.h"
#include "kudu/util/thread.h"

namespace kudu {

namespace cloud {

// Cloud instance detector. Provides an interface to retieve metadata about
// machines/instances run by public cloud vendors.
class InstanceDetector {
 public:
  // Instantiate the detector for all known types of cloud instances.
  InstanceDetector();

  // The destructor awaits for the detector threads to join (if any spawn).
  virtual ~InstanceDetector();

  // Perform the auto-detection of a cloud instance this object is running at.
  // This method must not be invoked more than once. It's a synchronous call
  // and it can take some time to complete. On success, returns Status::OK()
  // and provides the instance's metadata object via the 'metadata' output
  // parameter. In case of a failure, no valid metadata is provided in the
  // 'metadata' output parameter, and this method returns
  //
  //   * Status::NotFound()   if the auto-detection didn't recognize any known
  //                          instance types: most likely, the auto-detection
  //                          was run in a non-cloud environment or at a VM of
  //                          unknown/not-yet-supported cloud type
  //
  //   * other non-OK status  an unexpected error happened while trying to
  //                          determine the type of the environment
  //
  // TODO(aserbin): do we need async version of this method?
  Status Detect(std::unique_ptr<InstanceMetadata>* metadata) WARN_UNUSED_RESULT;

 private:
  static const size_t kNoIdx;

  // Get metadata for the specified instance. In case of success, store the
  // specified index 'idx' in 'result_detector_idx_' field.
  void GetInstanceInfo(InstanceMetadata* imd, size_t idx);

  // Mutex and associated condition variable.
  Mutex mutex_;
  ConditionVariable cv_;

  struct DetectorInfo {
    std::unique_ptr<InstanceMetadata> metadata;
    scoped_refptr<Thread> runner;
  };
  std::vector<DetectorInfo> detectors_;

  // Number of detector threads starting/running.
  size_t num_running_detectors_;

  // The index of the matched detector thread in the detectors_ container;
  // access to the field is guarded by the 'mutex_'.
  size_t result_detector_idx_;
};

} // namespace cloud
} // namespace kudu