open-consul/api/watch/plan.go

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package watch
import (
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"context"
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"fmt"
"log"
"os"
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"reflect"
"time"
consulapi "github.com/hashicorp/consul/api"
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)
const (
// retryInterval is the base retry value
retryInterval = 5 * time.Second
// maximum back off time, this is to prevent
// exponential runaway
maxBackoffTime = 180 * time.Second
)
func (p *Plan) Run(address string) error {
return p.RunWithConfig(address, nil)
}
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// Run is used to run a watch plan
func (p *Plan) RunWithConfig(address string, conf *consulapi.Config) error {
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// Setup the client
p.address = address
if conf == nil {
conf = consulapi.DefaultConfig()
}
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conf.Address = address
conf.Datacenter = p.Datacenter
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conf.Token = p.Token
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client, err := consulapi.NewClient(conf)
if err != nil {
return fmt.Errorf("Failed to connect to agent: %v", err)
}
// Create the logger
output := p.LogOutput
if output == nil {
output = os.Stderr
}
logger := log.New(output, "", log.LstdFlags)
return p.RunWithClientAndLogger(client, logger)
}
// RunWithClientAndLogger runs a watch plan using an external client and
// log.Logger instance. Using this, the plan's Datacenter, Token and LogOutput
// fields are ignored and the passed client is expected to be configured as
// needed.
func (p *Plan) RunWithClientAndLogger(client *consulapi.Client,
logger *log.Logger) error {
p.client = client
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// Loop until we are canceled
failures := 0
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OUTER:
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for !p.shouldStop() {
// Invoke the handler
blockParamVal, result, err := p.Watcher(p)
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// Check if we should terminate since the function
// could have blocked for a while
if p.shouldStop() {
break
}
// Handle an error in the watch function
if err != nil {
// Perform an exponential backoff
failures++
if blockParamVal == nil {
p.lastParamVal = nil
} else {
p.lastParamVal = blockParamVal.Next(p.lastParamVal)
}
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retry := retryInterval * time.Duration(failures*failures)
if retry > maxBackoffTime {
retry = maxBackoffTime
}
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logger.Printf("[ERR] consul.watch: Watch (type: %s) errored: %v, retry in %v",
p.Type, err, retry)
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select {
case <-time.After(retry):
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continue OUTER
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case <-p.stopCh:
return nil
}
}
// Clear the failures
failures = 0
// If the index is unchanged do nothing
if p.lastParamVal != nil && p.lastParamVal.Equal(blockParamVal) {
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continue
}
// Update the index, look for change
oldParamVal := p.lastParamVal
p.lastParamVal = blockParamVal.Next(oldParamVal)
if oldParamVal != nil && reflect.DeepEqual(p.lastResult, result) {
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continue
}
// Handle the updated result
p.lastResult = result
// If a hybrid handler exists use that
if p.HybridHandler != nil {
p.HybridHandler(blockParamVal, result)
} else if p.Handler != nil {
idx, ok := blockParamVal.(WaitIndexVal)
if !ok {
logger.Printf("[ERR] consul.watch: Handler only supports index-based " +
" watches but non index-based watch run. Skipping Handler.")
}
p.Handler(uint64(idx), result)
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}
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}
return nil
}
// Stop is used to stop running the watch plan
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func (p *Plan) Stop() {
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p.stopLock.Lock()
defer p.stopLock.Unlock()
if p.stop {
return
}
p.stop = true
if p.cancelFunc != nil {
p.cancelFunc()
}
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close(p.stopCh)
}
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func (p *Plan) shouldStop() bool {
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select {
case <-p.stopCh:
return true
default:
return false
}
}
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func (p *Plan) setCancelFunc(cancel context.CancelFunc) {
p.stopLock.Lock()
defer p.stopLock.Unlock()
if p.shouldStop() {
// The watch is stopped and execute the new cancel func to stop watchFactory
cancel()
return
}
p.cancelFunc = cancel
}
func (p *Plan) IsStopped() bool {
p.stopLock.Lock()
defer p.stopLock.Unlock()
return p.stop
}