聊聊dubbo-go的DefaultHealthChecker

func init() {
    extension.SethealthChecker(constant.DEFAULT_HEALTH_CHECKER, NewDefaultHealthChecker)
}

// DefaultHealthChecker is the default implementation of HealthChecker, which determines the health status of
// the invoker based on the number of successive bad request and the current active request.
type DefaultHealthChecker struct {
    // the limit of outstanding request
    outStandingRequestConutLimit int32
    // the threshold of successive-failure-request
    requestSuccessiveFailureThreshold int32
    // value of circuit-tripped timeout factor
    circuitTrippedTimeoutFactor int32
}

// NewDefaultHealthChecker constructs a new DefaultHealthChecker based on the url
func NewDefaultHealthChecker(url *common.URL) router.HealthChecker {
    return &DefaultHealthChecker{
        outStandingRequestConutLimit:      int32(url.GetParamInt(constant.OUTSTANDING_REQUEST_COUNT_LIMIT_KEY, math.MaxInt32)),
        requestSuccessiveFailureThreshold: int32(url.GetParamInt(constant.SUCCESSIVE_FAILED_REQUEST_THRESHOLD_KEY, constant.DEFAULT_SUCCESSIVE_FAILED_REQUEST_MAX_DIFF)),
        circuitTrippedTimeoutFactor:       int32(url.GetParamInt(constant.CIRCUIT_TRIPPED_TIMEOUT_FACTOR_KEY, constant.DEFAULT_CIRCUIT_TRIPPED_TIMEOUT_FACTOR)),
    }
}

// IsHealthy evaluates the healthy state on the given Invoker based on the number of successive bad request
// and the current active request
func (c *DefaultHealthChecker) IsHealthy(invoker protocol.Invoker) bool {
    urlStatus := protocol.GetURLStatus(invoker.GetUrl())
    if c.isCircuitBreakerTripped(urlStatus) || urlStatus.GetActive() > c.GetOutStandingRequestConutLimit() {
        logger.Debugf("Invoker [%s] is currently in circuitbreaker tripped state", invoker.GetUrl().Key())
        return false
    }
    return true
}

// isCircuitBreakerTripped determine whether the invoker is in the tripped state by the number of successive bad request
func (c *DefaultHealthChecker) isCircuitBreakerTripped(status *protocol.RPCStatus) bool {
    circuitBreakerTimeout := c.getCircuitBreakerTimeout(status)
    currentTime := protocol.CurrentTimeMillis()
    if circuitBreakerTimeout <= 0 {
        return false
    }
    return circuitBreakerTimeout > currentTime
}

// getCircuitBreakerTimeout get the timestamp recovered from tripped state, the unit is millisecond
func (c *DefaultHealthChecker) getCircuitBreakerTimeout(status *protocol.RPCStatus) int64 {
    sleepWindow := c.getCircuitBreakerSleepWindowTime(status)
    if sleepWindow <= 0 {
        return 0
    }
    return status.GetLastRequestFailedTimestamp() + sleepWindow
}

// getCircuitBreakerSleepWindowTime get the sleep window time of invoker, the unit is millisecond
func (c *DefaultHealthChecker) getCircuitBreakerSleepWindowTime(status *protocol.RPCStatus) int64 {

    successiveFailureCount := status.GetSuccessiveRequestFailureCount()
    diff := successiveFailureCount - c.GetRequestSuccessiveFailureThreshold()
    if diff < 0 {
        return 0
    } else if diff > constant.DEFAULT_SUCCESSIVE_FAILED_REQUEST_MAX_DIFF {
        diff = constant.DEFAULT_SUCCESSIVE_FAILED_REQUEST_MAX_DIFF
    }
    sleepWindow := (1 << diff) * c.GetCircuitTrippedTimeoutFactor()
    if sleepWindow > constant.MAX_CIRCUIT_TRIPPED_TIMEOUT_IN_MS {
        sleepWindow = constant.MAX_CIRCUIT_TRIPPED_TIMEOUT_IN_MS
    }
    return int64(sleepWindow)
}