Permalink
Cannot retrieve contributors at this time
Name already in use
A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
hystrix-go/hystrix/hystrix.go
Go to fileThis commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
299 lines (265 sloc)
8.03 KB
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
package hystrix | |
import ( | |
"context" | |
"fmt" | |
"sync" | |
"time" | |
) | |
type runFunc func() error | |
type fallbackFunc func(error) error | |
type runFuncC func(context.Context) error | |
type fallbackFuncC func(context.Context, error) error | |
// A CircuitError is an error which models various failure states of execution, | |
// such as the circuit being open or a timeout. | |
type CircuitError struct { | |
Message string | |
} | |
func (e CircuitError) Error() string { | |
return "hystrix: " + e.Message | |
} | |
// command models the state used for a single execution on a circuit. "hystrix command" is commonly | |
// used to describe the pairing of your run/fallback functions with a circuit. | |
type command struct { | |
sync.Mutex | |
ticket *struct{} | |
start time.Time | |
errChan chan error | |
finished chan bool | |
circuit *CircuitBreaker | |
run runFuncC | |
fallback fallbackFuncC | |
runDuration time.Duration | |
events []string | |
} | |
var ( | |
// ErrMaxConcurrency occurs when too many of the same named command are executed at the same time. | |
ErrMaxConcurrency = CircuitError{Message: "max concurrency"} | |
// ErrCircuitOpen returns when an execution attempt "short circuits". This happens due to the circuit being measured as unhealthy. | |
ErrCircuitOpen = CircuitError{Message: "circuit open"} | |
// ErrTimeout occurs when the provided function takes too long to execute. | |
ErrTimeout = CircuitError{Message: "timeout"} | |
) | |
// Go runs your function while tracking the health of previous calls to it. | |
// If your function begins slowing down or failing repeatedly, we will block | |
// new calls to it for you to give the dependent service time to repair. | |
// | |
// Define a fallback function if you want to define some code to execute during outages. | |
func Go(name string, run runFunc, fallback fallbackFunc) chan error { | |
runC := func(ctx context.Context) error { | |
return run() | |
} | |
var fallbackC fallbackFuncC | |
if fallback != nil { | |
fallbackC = func(ctx context.Context, err error) error { | |
return fallback(err) | |
} | |
} | |
return GoC(context.Background(), name, runC, fallbackC) | |
} | |
// GoC runs your function while tracking the health of previous calls to it. | |
// If your function begins slowing down or failing repeatedly, we will block | |
// new calls to it for you to give the dependent service time to repair. | |
// | |
// Define a fallback function if you want to define some code to execute during outages. | |
func GoC(ctx context.Context, name string, run runFuncC, fallback fallbackFuncC) chan error { | |
cmd := &command{ | |
run: run, | |
fallback: fallback, | |
start: time.Now(), | |
errChan: make(chan error, 1), | |
finished: make(chan bool, 1), | |
} | |
// dont have methods with explicit params and returns | |
// let data come in and out naturally, like with any closure | |
// explicit error return to give place for us to kill switch the operation (fallback) | |
circuit, _, err := GetCircuit(name) | |
if err != nil { | |
cmd.errChan <- err | |
return cmd.errChan | |
} | |
cmd.circuit = circuit | |
ticketCond := sync.NewCond(cmd) | |
ticketChecked := false | |
// When the caller extracts error from returned errChan, it's assumed that | |
// the ticket's been returned to executorPool. Therefore, returnTicket() can | |
// not run after cmd.errorWithFallback(). | |
returnTicket := func() { | |
cmd.Lock() | |
// Avoid releasing before a ticket is acquired. | |
for !ticketChecked { | |
ticketCond.Wait() | |
} | |
cmd.circuit.executorPool.Return(cmd.ticket) | |
cmd.Unlock() | |
} | |
// Shared by the following two goroutines. It ensures only the faster | |
// goroutine runs errWithFallback() and reportAllEvent(). | |
returnOnce := &sync.Once{} | |
reportAllEvent := func() { | |
err := cmd.circuit.ReportEvent(cmd.events, cmd.start, cmd.runDuration) | |
if err != nil { | |
log.Printf(err.Error()) | |
} | |
} | |
go func() { | |
defer func() { cmd.finished <- true }() | |
// Circuits get opened when recent executions have shown to have a high error rate. | |
// Rejecting new executions allows backends to recover, and the circuit will allow | |
// new traffic when it feels a healthly state has returned. | |
if !cmd.circuit.AllowRequest() { | |
cmd.Lock() | |
// It's safe for another goroutine to go ahead releasing a nil ticket. | |
ticketChecked = true | |
ticketCond.Signal() | |
cmd.Unlock() | |
returnOnce.Do(func() { | |
returnTicket() | |
cmd.errorWithFallback(ctx, ErrCircuitOpen) | |
reportAllEvent() | |
}) | |
return | |
} | |
// As backends falter, requests take longer but don't always fail. | |
// | |
// When requests slow down but the incoming rate of requests stays the same, you have to | |
// run more at a time to keep up. By controlling concurrency during these situations, you can | |
// shed load which accumulates due to the increasing ratio of active commands to incoming requests. | |
cmd.Lock() | |
select { | |
case cmd.ticket = <-circuit.executorPool.Tickets: | |
ticketChecked = true | |
ticketCond.Signal() | |
cmd.Unlock() | |
default: | |
ticketChecked = true | |
ticketCond.Signal() | |
cmd.Unlock() | |
returnOnce.Do(func() { | |
returnTicket() | |
cmd.errorWithFallback(ctx, ErrMaxConcurrency) | |
reportAllEvent() | |
}) | |
return | |
} | |
runStart := time.Now() | |
runErr := run(ctx) | |
returnOnce.Do(func() { | |
defer reportAllEvent() | |
cmd.runDuration = time.Since(runStart) | |
returnTicket() | |
if runErr != nil { | |
cmd.errorWithFallback(ctx, runErr) | |
return | |
} | |
cmd.reportEvent("success") | |
}) | |
}() | |
go func() { | |
timer := time.NewTimer(getSettings(name).Timeout) | |
defer timer.Stop() | |
select { | |
case <-cmd.finished: | |
// returnOnce has been executed in another goroutine | |
case <-ctx.Done(): | |
returnOnce.Do(func() { | |
returnTicket() | |
cmd.errorWithFallback(ctx, ctx.Err()) | |
reportAllEvent() | |
}) | |
return | |
case <-timer.C: | |
returnOnce.Do(func() { | |
returnTicket() | |
cmd.errorWithFallback(ctx, ErrTimeout) | |
reportAllEvent() | |
}) | |
return | |
} | |
}() | |
return cmd.errChan | |
} | |
// Do runs your function in a synchronous manner, blocking until either your function succeeds | |
// or an error is returned, including hystrix circuit errors | |
func Do(name string, run runFunc, fallback fallbackFunc) error { | |
runC := func(ctx context.Context) error { | |
return run() | |
} | |
var fallbackC fallbackFuncC | |
if fallback != nil { | |
fallbackC = func(ctx context.Context, err error) error { | |
return fallback(err) | |
} | |
} | |
return DoC(context.Background(), name, runC, fallbackC) | |
} | |
// DoC runs your function in a synchronous manner, blocking until either your function succeeds | |
// or an error is returned, including hystrix circuit errors | |
func DoC(ctx context.Context, name string, run runFuncC, fallback fallbackFuncC) error { | |
done := make(chan struct{}, 1) | |
r := func(ctx context.Context) error { | |
err := run(ctx) | |
if err != nil { | |
return err | |
} | |
done <- struct{}{} | |
return nil | |
} | |
f := func(ctx context.Context, e error) error { | |
err := fallback(ctx, e) | |
if err != nil { | |
return err | |
} | |
done <- struct{}{} | |
return nil | |
} | |
var errChan chan error | |
if fallback == nil { | |
errChan = GoC(ctx, name, r, nil) | |
} else { | |
errChan = GoC(ctx, name, r, f) | |
} | |
select { | |
case <-done: | |
return nil | |
case err := <-errChan: | |
return err | |
} | |
} | |
func (c *command) reportEvent(eventType string) { | |
c.Lock() | |
defer c.Unlock() | |
c.events = append(c.events, eventType) | |
} | |
// errorWithFallback triggers the fallback while reporting the appropriate metric events. | |
func (c *command) errorWithFallback(ctx context.Context, err error) { | |
eventType := "failure" | |
if err == ErrCircuitOpen { | |
eventType = "short-circuit" | |
} else if err == ErrMaxConcurrency { | |
eventType = "rejected" | |
} else if err == ErrTimeout { | |
eventType = "timeout" | |
} else if err == context.Canceled { | |
eventType = "context_canceled" | |
} else if err == context.DeadlineExceeded { | |
eventType = "context_deadline_exceeded" | |
} | |
c.reportEvent(eventType) | |
fallbackErr := c.tryFallback(ctx, err) | |
if fallbackErr != nil { | |
c.errChan <- fallbackErr | |
} | |
} | |
func (c *command) tryFallback(ctx context.Context, err error) error { | |
if c.fallback == nil { | |
// If we don't have a fallback return the original error. | |
return err | |
} | |
fallbackErr := c.fallback(ctx, err) | |
if fallbackErr != nil { | |
c.reportEvent("fallback-failure") | |
return fmt.Errorf("fallback failed with '%v'. run error was '%v'", fallbackErr, err) | |
} | |
c.reportEvent("fallback-success") | |
return nil | |
} |