github.com/weaviate/weaviate@v1.24.6/adapters/repos/db/indexcounter/counter.go (about)

     1  //                           _       _
     2  // __      _____  __ ___   ___  __ _| |_ ___
     3  // \ \ /\ / / _ \/ _` \ \ / / |/ _` | __/ _ \
     4  //  \ V  V /  __/ (_| |\ V /| | (_| | ||  __/
     5  //   \_/\_/ \___|\__,_| \_/ |_|\__,_|\__\___|
     6  //
     7  //  Copyright © 2016 - 2024 Weaviate B.V. All rights reserved.
     8  //
     9  //  CONTACT: hello@weaviate.io
    10  //
    11  
    12  package indexcounter
    13  
    14  import (
    15  	"encoding/binary"
    16  	"fmt"
    17  	"os"
    18  	"sync"
    19  
    20  	"github.com/pkg/errors"
    21  )
    22  
    23  type Counter struct {
    24  	count uint64
    25  	sync.Mutex
    26  	f *os.File
    27  }
    28  
    29  func New(shardPath string) (*Counter, error) {
    30  	fileName := fmt.Sprintf("%s/indexcount", shardPath)
    31  	f, err := os.OpenFile(fileName, os.O_RDWR|os.O_CREATE, 0o666)
    32  	if err != nil {
    33  		return nil, err
    34  	}
    35  
    36  	stat, err := f.Stat()
    37  	if err != nil {
    38  		return nil, err
    39  	}
    40  
    41  	var initialCount uint64 = 0
    42  	if stat.Size() > 0 {
    43  		// the file has existed before, we need to initialize with its content
    44  		err := binary.Read(f, binary.LittleEndian, &initialCount)
    45  		if err != nil {
    46  			return nil, errors.Wrap(err, "read initial count from file")
    47  		}
    48  
    49  	}
    50  
    51  	return &Counter{
    52  		count: initialCount,
    53  		f:     f,
    54  	}, nil
    55  }
    56  
    57  func (c *Counter) Get() uint64 {
    58  	c.Lock()
    59  	defer c.Unlock()
    60  	return c.count
    61  }
    62  
    63  func (c *Counter) GetAndInc() (uint64, error) {
    64  	c.Lock()
    65  	defer c.Unlock()
    66  	before := c.count
    67  	c.count++
    68  	c.f.Seek(0, 0)
    69  	err := binary.Write(c.f, binary.LittleEndian, &c.count)
    70  	if err != nil {
    71  		return 0, errors.Wrap(err, "increase counter on disk")
    72  	}
    73  	c.f.Seek(0, 0)
    74  	return before, nil
    75  }
    76  
    77  // PreviewNext can be used to check if there is data present in the index, if
    78  // it returns 0, you can be certain that no data exists
    79  func (c *Counter) PreviewNext() uint64 {
    80  	c.Lock()
    81  	defer c.Unlock()
    82  
    83  	return c.count
    84  }
    85  
    86  func (c *Counter) Drop() error {
    87  	c.Lock()
    88  	defer c.Unlock()
    89  	if c.f == nil {
    90  		return nil
    91  	}
    92  	filename := c.FileName()
    93  	c.f.Close()
    94  	err := os.Remove(filename)
    95  	if err != nil {
    96  		return errors.Wrap(err, "drop counter file")
    97  	}
    98  	return nil
    99  }
   100  
   101  func (c *Counter) FileName() string {
   102  	return c.f.Name()
   103  }