First draft of circuit-breaker
Evan Huus
9 years ago
| 0 | package breaker | |
| 1 | ||
| 2 | import ( | |
| 3 | "errors" | |
| 4 | "fmt" | |
| 5 | "sync" | |
| 6 | "time" | |
| 7 | ) | |
| 8 | ||
| 9 | var BreakerOpen = errors.New("circuit breaker is open") | |
| 10 | ||
| 11 | type Panic struct { | |
| 12 | Value interface{} | |
| 13 | } | |
| 14 | ||
| 15 | func (p Panic) Error() string { | |
| 16 | return fmt.Sprint("panic:", p.Value) | |
| 17 | } | |
| 18 | ||
| 19 | type state int | |
| 20 | ||
| 21 | const ( | |
| 22 | closed state = iota | |
| 23 | open | |
| 24 | halfOpen | |
| 25 | ) | |
| 26 | ||
| 27 | type Breaker struct { | |
| 28 | errorThreshold, successThreshold int | |
| 29 | timeout time.Duration | |
| 30 | ||
| 31 | lock sync.RWMutex | |
| 32 | state state | |
| 33 | errors, successes int | |
| 34 | } | |
| 35 | ||
| 36 | func New(errorThreshold, successThreshold int, timeout time.Duration) *Breaker { | |
| 37 | return &Breaker{ | |
| 38 | errorThreshold: errorThreshold, | |
| 39 | successThreshold: successThreshold, | |
| 40 | timeout: timeout, | |
| 41 | } | |
| 42 | } | |
| 43 | ||
| 44 | func (b *Breaker) Run(x func() error) error { | |
| 45 | b.lock.RLock() | |
| 46 | state := b.state | |
| 47 | b.lock.RUnlock() | |
| 48 | ||
| 49 | if state == open { | |
| 50 | return BreakerOpen | |
| 51 | } | |
| 52 | ||
| 53 | result := func() (err error) { | |
| 54 | defer func() { | |
| 55 | if val := recover(); val != nil { | |
| 56 | err = Panic{Value: val} | |
| 57 | } | |
| 58 | }() | |
| 59 | return x() | |
| 60 | }() | |
| 61 | ||
| 62 | b.lock.Lock() | |
| 63 | defer b.lock.Unlock() | |
| 64 | ||
| 65 | if result == nil { | |
| 66 | if b.state == halfOpen { | |
| 67 | b.successes++ | |
| 68 | if b.successes == b.successThreshold { | |
| 69 | b.closeBreaker() | |
| 70 | } | |
| 71 | } | |
| 72 | } else { | |
| 73 | switch b.state { | |
| 74 | case closed: | |
| 75 | b.errors++ | |
| 76 | if b.errors == b.errorThreshold { | |
| 77 | b.openBreaker() | |
| 78 | } | |
| 79 | case halfOpen: | |
| 80 | b.openBreaker() | |
| 81 | } | |
| 82 | } | |
| 83 | ||
| 84 | return result | |
| 85 | } | |
| 86 | ||
| 87 | func (b *Breaker) openBreaker() { | |
| 88 | b.changeState(open) | |
| 89 | go b.timer() | |
| 90 | } | |
| 91 | ||
| 92 | func (b *Breaker) closeBreaker() { | |
| 93 | b.changeState(closed) | |
| 94 | } | |
| 95 | ||
| 96 | func (b *Breaker) timer() { | |
| 97 | time.Sleep(b.timeout) | |
| 98 | ||
| 99 | b.lock.Lock() | |
| 100 | defer b.lock.Unlock() | |
| 101 | ||
| 102 | b.changeState(halfOpen) | |
| 103 | } | |
| 104 | ||
| 105 | func (b *Breaker) changeState(newState state) { | |
| 106 | b.errors = 0 | |
| 107 | b.successes = 0 | |
| 108 | b.state = newState | |
| 109 | } |