9045b79bc2
This PR modifies how the metrics library handles `Enabled`: previously, the package `init` decided whether to serve real metrics or just dummy-types. This has several drawbacks: - During pkg init, we need to determine whether metrics are enabled or not. So we first hacked in a check if certain geth-specific commandline-flags were enabled. Then we added a similar check for geth-env-vars. Then we almost added a very elaborate check for toml-config-file, plus toml parsing. - Using "real" types and dummy types interchangeably means that everything is hidden behind interfaces. This has a performance penalty, and also it just adds a lot of code. This PR removes the interface stuff, uses concrete types, and allows for the setting of Enabled to happen later. It is still assumed that `metrics.Enable()` is invoked early on. The somewhat 'heavy' operations, such as ticking meters and exp-decay, now checks the enable-flag to prevent resource leak. The change may be large, but it's mostly pretty trivial, and from the last time I gutted the metrics, I ensured that we have fairly good test coverage. --------- Co-authored-by: Felix Lange <fjl@twurst.com>
92 lines
2.5 KiB
Go
92 lines
2.5 KiB
Go
package metrics
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import (
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"math"
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"sync"
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"sync/atomic"
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"time"
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)
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// EWMASnapshot is a read-only copy of an EWMA.
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type EWMASnapshot float64
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// Rate returns the rate of events per second at the time the snapshot was
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// taken.
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func (a EWMASnapshot) Rate() float64 { return float64(a) }
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// NewEWMA constructs a new EWMA with the given alpha.
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func NewEWMA(alpha float64) *EWMA {
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return &EWMA{alpha: alpha}
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}
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// NewEWMA1 constructs a new EWMA for a one-minute moving average.
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func NewEWMA1() *EWMA {
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return NewEWMA(1 - math.Exp(-5.0/60.0/1))
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}
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// NewEWMA5 constructs a new EWMA for a five-minute moving average.
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func NewEWMA5() *EWMA {
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return NewEWMA(1 - math.Exp(-5.0/60.0/5))
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}
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// NewEWMA15 constructs a new EWMA for a fifteen-minute moving average.
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func NewEWMA15() *EWMA {
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return NewEWMA(1 - math.Exp(-5.0/60.0/15))
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}
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// EWMA continuously calculate an exponentially-weighted moving average
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// based on an outside source of clock ticks.
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type EWMA struct {
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uncounted atomic.Int64
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alpha float64
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rate atomic.Uint64
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init atomic.Bool
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mutex sync.Mutex
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}
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// Snapshot returns a read-only copy of the EWMA.
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func (a *EWMA) Snapshot() EWMASnapshot {
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r := math.Float64frombits(a.rate.Load()) * float64(time.Second)
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return EWMASnapshot(r)
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}
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// tick ticks the clock to update the moving average. It assumes it is called
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// every five seconds.
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func (a *EWMA) tick() {
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// Optimization to avoid mutex locking in the hot-path.
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if a.init.Load() {
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a.updateRate(a.fetchInstantRate())
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return
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}
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// Slow-path: this is only needed on the first tick() and preserves transactional updating
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// of init and rate in the else block. The first conditional is needed below because
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// a different thread could have set a.init = 1 between the time of the first atomic load and when
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// the lock was acquired.
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a.mutex.Lock()
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if a.init.Load() {
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// The fetchInstantRate() uses atomic loading, which is unnecessary in this critical section
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// but again, this section is only invoked on the first successful tick() operation.
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a.updateRate(a.fetchInstantRate())
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} else {
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a.init.Store(true)
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a.rate.Store(math.Float64bits(a.fetchInstantRate()))
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}
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a.mutex.Unlock()
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}
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func (a *EWMA) fetchInstantRate() float64 {
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count := a.uncounted.Swap(0)
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return float64(count) / float64(5*time.Second)
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}
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func (a *EWMA) updateRate(instantRate float64) {
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currentRate := math.Float64frombits(a.rate.Load())
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currentRate += a.alpha * (instantRate - currentRate)
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a.rate.Store(math.Float64bits(currentRate))
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}
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// Update adds n uncounted events.
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func (a *EWMA) Update(n int64) {
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a.uncounted.Add(n)
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}
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