github.com/google/cadvisor@v0.49.1/summary/buffer.go (about)

     1  // Copyright 2015 Google Inc. All Rights Reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package summary
    16  
    17  import (
    18  	info "github.com/google/cadvisor/info/v2"
    19  )
    20  
    21  // Manages a buffer of usage samples.
    22  // This is similar to stats buffer in cache/memory.
    23  // The main difference is that we do not pre-allocate the buffer as most containers
    24  // won't live that long.
    25  type SamplesBuffer struct {
    26  	// list of collected samples.
    27  	samples []info.Usage
    28  	// maximum size this buffer can grow to.
    29  	maxSize int
    30  	// index for the latest sample.
    31  	index int
    32  }
    33  
    34  // Initializes an empty buffer.
    35  func NewSamplesBuffer(size int) *SamplesBuffer {
    36  	return &SamplesBuffer{
    37  		index:   -1,
    38  		maxSize: size,
    39  	}
    40  }
    41  
    42  // Returns the current number of samples in the buffer.
    43  func (s *SamplesBuffer) Size() int {
    44  	return len(s.samples)
    45  }
    46  
    47  // Add an element to the buffer. Oldest one is overwritten if required.
    48  func (s *SamplesBuffer) Add(stat info.Usage) {
    49  	if len(s.samples) < s.maxSize {
    50  		s.samples = append(s.samples, stat)
    51  		s.index++
    52  		return
    53  	}
    54  	s.index = (s.index + 1) % s.maxSize
    55  	s.samples[s.index] = stat
    56  }
    57  
    58  // Returns pointers to the last 'n' stats.
    59  func (s *SamplesBuffer) RecentStats(n int) []*info.Usage {
    60  	if n > len(s.samples) {
    61  		n = len(s.samples)
    62  	}
    63  	start := s.index - (n - 1)
    64  	if start < 0 {
    65  		start += len(s.samples)
    66  	}
    67  
    68  	out := make([]*info.Usage, n)
    69  	for i := 0; i < n; i++ {
    70  		index := (start + i) % len(s.samples)
    71  		out[i] = &s.samples[index]
    72  	}
    73  	return out
    74  }