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concurrent_buffer.go
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concurrent_buffer.go
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package limiters
import (
"bytes"
"context"
"encoding/gob"
"fmt"
"sync"
"time"
"github.com/bradfitz/gomemcache/memcache"
"github.com/pkg/errors"
"github.com/redis/go-redis/v9"
)
// ConcurrentBufferBackend wraps the Add and Remove methods.
type ConcurrentBufferBackend interface {
// Add adds the request with the given key to the buffer and returns the total number of requests in it.
Add(ctx context.Context, key string) (int64, error)
// Remove removes the request from the buffer.
Remove(ctx context.Context, key string) error
}
// ConcurrentBuffer implements a limiter that allows concurrent requests up to the given capacity.
type ConcurrentBuffer struct {
locker DistLocker
backend ConcurrentBufferBackend
logger Logger
capacity int64
mu sync.Mutex
}
// NewConcurrentBuffer creates a new ConcurrentBuffer instance.
func NewConcurrentBuffer(locker DistLocker, concurrentStateBackend ConcurrentBufferBackend, capacity int64, logger Logger) *ConcurrentBuffer {
return &ConcurrentBuffer{locker: locker, backend: concurrentStateBackend, capacity: capacity, logger: logger}
}
// Limit puts the request identified by the key in a buffer.
func (c *ConcurrentBuffer) Limit(ctx context.Context, key string) error {
c.mu.Lock()
defer c.mu.Unlock()
if err := c.locker.Lock(ctx); err != nil {
return err
}
defer func() {
if err := c.locker.Unlock(ctx); err != nil {
c.logger.Log(err)
}
}()
// Optimistically add the new request.
counter, err := c.backend.Add(ctx, key)
if err != nil {
return err
}
if counter > c.capacity {
// Rollback the Add() operation.
if err = c.backend.Remove(ctx, key); err != nil {
c.logger.Log(err)
}
return ErrLimitExhausted
}
return nil
}
// Done removes the request identified by the key from the buffer.
func (c *ConcurrentBuffer) Done(ctx context.Context, key string) error {
return c.backend.Remove(ctx, key)
}
// ConcurrentBufferInMemory is an in-memory implementation of ConcurrentBufferBackend.
type ConcurrentBufferInMemory struct {
clock Clock
ttl time.Duration
mu sync.Mutex
registry *Registry
}
// NewConcurrentBufferInMemory creates a new instance of ConcurrentBufferInMemory.
// When the TTL of a key exceeds the key is removed from the buffer. This is needed in case if the process that added
// that key to the buffer did not call Done() for some reason.
func NewConcurrentBufferInMemory(registry *Registry, ttl time.Duration, clock Clock) *ConcurrentBufferInMemory {
return &ConcurrentBufferInMemory{clock: clock, ttl: ttl, registry: registry}
}
// Add adds the request with the given key to the buffer and returns the total number of requests in it.
// It also removes the keys with expired TTL.
func (c *ConcurrentBufferInMemory) Add(ctx context.Context, key string) (int64, error) {
c.mu.Lock()
defer c.mu.Unlock()
now := c.clock.Now()
c.registry.DeleteExpired(now)
c.registry.GetOrCreate(key, func() interface{} {
return struct{}{}
}, c.ttl, now)
return int64(c.registry.Len()), ctx.Err()
}
// Remove removes the request from the buffer.
func (c *ConcurrentBufferInMemory) Remove(_ context.Context, key string) error {
c.mu.Lock()
defer c.mu.Unlock()
c.registry.Delete(key)
return nil
}
// ConcurrentBufferRedis implements ConcurrentBufferBackend in Redis.
type ConcurrentBufferRedis struct {
clock Clock
cli redis.UniversalClient
key string
ttl time.Duration
}
// NewConcurrentBufferRedis creates a new instance of ConcurrentBufferRedis.
// When the TTL of a key exceeds the key is removed from the buffer. This is needed in case if the process that added
// that key to the buffer did not call Done() for some reason.
func NewConcurrentBufferRedis(cli redis.UniversalClient, key string, ttl time.Duration, clock Clock) *ConcurrentBufferRedis {
return &ConcurrentBufferRedis{clock: clock, cli: cli, key: key, ttl: ttl}
}
// Add adds the request with the given key to the sorted set in Redis and returns the total number of requests in it.
// It also removes the keys with expired TTL.
func (c *ConcurrentBufferRedis) Add(ctx context.Context, key string) (int64, error) {
var countCmd *redis.IntCmd
var err error
done := make(chan struct{})
go func() {
defer close(done)
_, err = c.cli.Pipelined(ctx, func(pipeliner redis.Pipeliner) error {
// Remove expired items.
now := c.clock.Now()
pipeliner.ZRemRangeByScore(ctx, c.key, "-inf", fmt.Sprintf("%d", now.Add(-c.ttl).UnixNano()))
pipeliner.ZAdd(ctx, c.key, redis.Z{
Score: float64(now.UnixNano()),
Member: key,
})
countCmd = pipeliner.ZCard(ctx, c.key)
return nil
})
}()
select {
case <-ctx.Done():
return 0, ctx.Err()
case <-done:
if err != nil {
return 0, errors.Wrap(err, "failed to add an item to redis set")
}
return countCmd.Val(), nil
}
}
// Remove removes the request identified by the key from the sorted set in Redis.
func (c *ConcurrentBufferRedis) Remove(ctx context.Context, key string) error {
return errors.Wrap(c.cli.ZRem(ctx, c.key, key).Err(), "failed to remove an item from redis set")
}
// ConcurrentBufferMemcached implements ConcurrentBufferBackend in Memcached.
type ConcurrentBufferMemcached struct {
clock Clock
cli *memcache.Client
key string
ttl time.Duration
}
// NewConcurrentBufferMemcached creates a new instance of ConcurrentBufferMemcached.
// When the TTL of a key exceeds the key is removed from the buffer. This is needed in case if the process that added
// that key to the buffer did not call Done() for some reason.
func NewConcurrentBufferMemcached(cli *memcache.Client, key string, ttl time.Duration, clock Clock) *ConcurrentBufferMemcached {
return &ConcurrentBufferMemcached{clock: clock, cli: cli, key: key, ttl: ttl}
}
type SortedSetNode struct {
CreatedAt int64
Value string
}
// Add adds the request with the given key to the slice in Memcached and returns the total number of requests in it.
// It also removes the keys with expired TTL.
func (c *ConcurrentBufferMemcached) Add(ctx context.Context, element string) (int64, error) {
var err error
done := make(chan struct{})
now := c.clock.Now()
var newNodes []SortedSetNode
var casId uint64 = 0
go func() {
defer close(done)
var item *memcache.Item
item, err = c.cli.Get(c.key)
if err != nil {
if !errors.Is(err, memcache.ErrCacheMiss) {
return
}
} else {
casId = item.CasID
b := bytes.NewBuffer(item.Value)
var oldNodes []SortedSetNode
_ = gob.NewDecoder(b).Decode(&oldNodes)
for _, node := range oldNodes {
if node.CreatedAt > now.UnixNano() && node.Value != element {
newNodes = append(newNodes, node)
}
}
}
newNodes = append(newNodes, SortedSetNode{CreatedAt: now.Add(c.ttl).UnixNano(), Value: element})
var b bytes.Buffer
_ = gob.NewEncoder(&b).Encode(newNodes)
item = &memcache.Item{
Key: c.key,
Value: b.Bytes(),
CasID: casId,
}
if casId > 0 {
err = c.cli.CompareAndSwap(item)
} else {
err = c.cli.Add(item)
}
}()
select {
case <-ctx.Done():
return 0, ctx.Err()
case <-done:
if err != nil {
if errors.Is(err, memcache.ErrCASConflict) || errors.Is(err, memcache.ErrNotStored) || errors.Is(err, memcache.ErrCacheMiss) {
return c.Add(ctx, element)
}
return 0, errors.Wrap(err, "failed to add in memcached")
}
return int64(len(newNodes)), nil
}
}
// Remove removes the request identified by the key from the slice in Memcached.
func (c *ConcurrentBufferMemcached) Remove(ctx context.Context, key string) error {
var err error
now := c.clock.Now()
var newNodes []SortedSetNode
var casID uint64
item, err := c.cli.Get(c.key)
if err != nil {
if errors.Is(err, memcache.ErrCacheMiss) {
return nil
}
return errors.Wrap(err, "failed to Get")
}
casID = item.CasID
var oldNodes []SortedSetNode
_ = gob.NewDecoder(bytes.NewBuffer(item.Value)).Decode(&oldNodes)
for _, node := range oldNodes {
if node.CreatedAt > now.UnixNano() && node.Value != key {
newNodes = append(newNodes, node)
}
}
var b bytes.Buffer
_ = gob.NewEncoder(&b).Encode(newNodes)
item = &memcache.Item{
Key: c.key,
Value: b.Bytes(),
CasID: casID,
}
err = c.cli.CompareAndSwap(item)
if err != nil && (errors.Is(err, memcache.ErrCASConflict) || errors.Is(err, memcache.ErrNotStored) || errors.Is(err, memcache.ErrCacheMiss)) {
return c.Remove(ctx, key)
}
return errors.Wrap(err, "failed to CompareAndSwap")
}