github.com/m3db/m3@v1.5.0/src/cmd/services/m3coordinator/downsample/async_downsampler.go (about)

     1  // Copyright (c) 2018 Uber Technologies, Inc.
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE.
    20  
    21  package downsample
    22  
    23  import (
    24  	"errors"
    25  	"fmt"
    26  	"sync"
    27  
    28  	"github.com/m3db/m3/src/metrics/rules/view"
    29  )
    30  
    31  const (
    32  	errNewDownsamplerFailFmt = "downsampler failed to initialize: %v"
    33  )
    34  
    35  var (
    36  	errDownsamplerUninitialized = errors.New("downsampler is not yet initialized")
    37  )
    38  
    39  // asyncDownsampler is an asynchronous downsampler that can be lazily
    40  // initialized, it will return errors on calls to its methods until it is
    41  // initialized.
    42  // This is useful when a component needs to be built with a downsampler that
    43  // might not be able to wait for to it be constructed (i.e. HTTP handlers
    44  // need to be registered immediately but can respond with errors until
    45  // the downsampler downstream services have been discovered/connected to).
    46  type asyncDownsampler struct {
    47  	sync.RWMutex
    48  	downsampler Downsampler
    49  	done        chan<- struct{}
    50  	err         error
    51  }
    52  
    53  // NewDownsamplerFn creates a downsampler.
    54  type NewDownsamplerFn func() (Downsampler, error)
    55  
    56  // NewAsyncDownsampler is a downsampler that is lazily initialized.
    57  func NewAsyncDownsampler(
    58  	fn NewDownsamplerFn,
    59  	done chan<- struct{},
    60  ) Downsampler {
    61  	asyncDownsampler := &asyncDownsampler{
    62  		done: done,
    63  		err:  errDownsamplerUninitialized,
    64  	}
    65  
    66  	go func() {
    67  		asyncDownsampler.Lock()
    68  		defer asyncDownsampler.Unlock()
    69  
    70  		if asyncDownsampler.done != nil {
    71  			defer func() {
    72  				asyncDownsampler.done <- struct{}{}
    73  			}()
    74  		}
    75  		downsampler, err := fn()
    76  
    77  		if err != nil {
    78  			asyncDownsampler.err = fmt.Errorf(errNewDownsamplerFailFmt, err)
    79  			return
    80  		}
    81  
    82  		asyncDownsampler.downsampler = downsampler
    83  		asyncDownsampler.err = nil
    84  	}()
    85  
    86  	return asyncDownsampler
    87  }
    88  
    89  func (d *asyncDownsampler) LatestRollupRules(namespace []byte, timeNanos int64) ([]view.RollupRule, error) {
    90  	d.RLock()
    91  	defer d.RUnlock()
    92  	return d.downsampler.LatestRollupRules(namespace, timeNanos)
    93  }
    94  
    95  func (d *asyncDownsampler) NewMetricsAppender() (MetricsAppender, error) {
    96  	d.RLock()
    97  	defer d.RUnlock()
    98  	if d.err != nil {
    99  		return nil, d.err
   100  	}
   101  	return d.downsampler.NewMetricsAppender()
   102  }
   103  
   104  func (d *asyncDownsampler) Enabled() bool {
   105  	d.RLock()
   106  	defer d.RUnlock()
   107  	if d.err != nil {
   108  		return false
   109  	}
   110  	return d.downsampler.Enabled()
   111  }