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opentelemetry-go/internal/metric/async.go
Joshua MacDonald 1fab21ddbf
Support use of synchronous instruments in async callbacks (#725)
* Support use of synchronous instruments in async callbacks

* Add a test
2020-05-19 21:33:10 -07:00

162 lines
5.2 KiB
Go

// Copyright The OpenTelemetry Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package metric
import (
"context"
"errors"
"fmt"
"os"
"sync"
"go.opentelemetry.io/otel/api/kv"
"go.opentelemetry.io/otel/api/metric"
)
var ErrInvalidAsyncRunner = errors.New("unknown async runner type")
// AsyncCollector is an interface used between the MeterImpl and the
// AsyncInstrumentState helper below. This interface is implemented by
// the SDK to provide support for running observer callbacks.
type AsyncCollector interface {
// CollectAsync passes a batch of observations to the MeterImpl.
CollectAsync([]kv.KeyValue, ...metric.Observation)
}
// AsyncInstrumentState manages an ordered set of asynchronous
// instruments and the distinct runners, taking into account batch
// observer callbacks.
type AsyncInstrumentState struct {
lock sync.Mutex
// errorHandler will be called in case of an invalid
// metric.AsyncRunner, i.e., one that does not implement
// either the single-or batch-runner interfaces.
errorHandler func(error)
errorOnce sync.Once
// runnerMap keeps the set of runners that will run each
// collection interval. Singletons are entered with a real
// instrument each, batch observers are entered with a nil
// instrument, ensuring that when a singleton callback is used
// repeatedly, it is excuted repeatedly in the interval, while
// when a batch callback is used repeatedly, it only executes
// once per interval.
runnerMap map[asyncRunnerPair]struct{}
// runners maintains the set of runners in the order they were
// registered.
runners []asyncRunnerPair
// instruments maintains the set of instruments in the order
// they were registered.
instruments []metric.AsyncImpl
}
// asyncRunnerPair is a map entry for Observer callback runners.
type asyncRunnerPair struct {
// runner is used as a map key here. The API ensures
// that all callbacks are pointers for this reason.
runner metric.AsyncRunner
// inst refers to a non-nil instrument when `runner` is a
// AsyncSingleRunner.
inst metric.AsyncImpl
}
// NewAsyncInstrumentState returns a new *AsyncInstrumentState, for
// use by MeterImpl to manage running the set of observer callbacks in
// the correct order.
//
// errorHandler is used to print an error condition. If errorHandler
// nil, the default error handler will be used that prints to
// os.Stderr. Only the first error is passed to the handler, after
// which errors are skipped.
func NewAsyncInstrumentState(errorHandler func(error)) *AsyncInstrumentState {
if errorHandler == nil {
errorHandler = func(err error) {
fmt.Fprintln(os.Stderr, "Metrics Async state error:", err)
}
}
return &AsyncInstrumentState{
errorHandler: errorHandler,
runnerMap: map[asyncRunnerPair]struct{}{},
}
}
// Instruments returns the asynchronous instruments managed by this
// object, the set that should be checkpointed after observers are
// run.
func (a *AsyncInstrumentState) Instruments() []metric.AsyncImpl {
a.lock.Lock()
defer a.lock.Unlock()
return a.instruments
}
// Register adds a new asynchronous instrument to by managed by this
// object. This should be called during NewAsyncInstrument() and
// assumes that errors (e.g., duplicate registration) have already
// been checked.
func (a *AsyncInstrumentState) Register(inst metric.AsyncImpl, runner metric.AsyncRunner) {
a.lock.Lock()
defer a.lock.Unlock()
a.instruments = append(a.instruments, inst)
// asyncRunnerPair reflects this callback in the asyncRunners
// list. If this is a batch runner, the instrument is nil.
// If this is a single-Observer runner, the instrument is
// included. This ensures that batch callbacks are called
// once and single callbacks are called once per instrument.
rp := asyncRunnerPair{
runner: runner,
}
if _, ok := runner.(metric.AsyncSingleRunner); ok {
rp.inst = inst
}
if _, ok := a.runnerMap[rp]; !ok {
a.runnerMap[rp] = struct{}{}
a.runners = append(a.runners, rp)
}
}
// Run executes the complete set of observer callbacks.
func (a *AsyncInstrumentState) Run(ctx context.Context, collector AsyncCollector) {
a.lock.Lock()
runners := a.runners
a.lock.Unlock()
for _, rp := range runners {
// The runner must be a single or batch runner, no
// other implementations are possible because the
// interface has un-exported methods.
if singleRunner, ok := rp.runner.(metric.AsyncSingleRunner); ok {
singleRunner.Run(ctx, rp.inst, collector.CollectAsync)
continue
}
if multiRunner, ok := rp.runner.(metric.AsyncBatchRunner); ok {
multiRunner.Run(ctx, collector.CollectAsync)
continue
}
a.errorOnce.Do(func() {
a.errorHandler(fmt.Errorf("%w: type %T (reported once)", ErrInvalidAsyncRunner, rp))
})
}
}