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Add fswatch library to watch and batch filesystem events, use in allo…
…cator (#2792) This pull refactors the fsnotify code in allocator/main out to a shared library, and in that shared library implements a batched notification processor. Closes #1816: This takes a slightly different approach than specified in the issue, instead choosing to just delay processing until after a batch processing period. I chose 1s - it's far longer than necessary, but still much shorter than it takes for the secret changes to propagate to the container anyways. I considered the approach in #1816 of trying to parse the actual events, but it's too fiddly to get exactly right: e.g. maybe you only refresh on "write", but then "chmod" could make the file readable whereas it wasn't before, "rename" could expose a file that wasn't there before, etc.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,81 @@ | ||
| // Copyright 2022 Google LLC All Rights Reserved. | ||
| // | ||
| // 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 fswatch provies Watch(), a utility function to watch a filesystem path. | ||
| package fswatch | ||
|
|
||
| import ( | ||
| "time" | ||
|
|
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| "github.com/sirupsen/logrus" | ||
| "gopkg.in/fsnotify.v1" | ||
| ) | ||
|
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| // Watch watches the filesystem path `path`. When anything changes, changes are | ||
| // batched for the period `batchFor`, then `processEvent` is called. | ||
| // | ||
| // Returns a cancel() function to terminate the watch. | ||
| func Watch(logger *logrus.Entry, path string, batchFor time.Duration, processEvent func()) (func(), error) { | ||
| logger = logger.WithField("path", path) | ||
| watcher, err := fsnotify.NewWatcher() | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| cancelChan := make(chan struct{}) | ||
| cancel := func() { | ||
| close(cancelChan) | ||
| _ = watcher.Close() | ||
| } | ||
| if err := watcher.Add(path); err != nil { | ||
| cancel() | ||
| return nil, err | ||
| } | ||
|
|
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| go batchWatch(batchFor, watcher.Events, watcher.Errors, cancelChan, processEvent, func(error) { | ||
| logger.WithError(err).Errorf("error watching path") | ||
| }) | ||
| return cancel, nil | ||
| } | ||
|
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| // batchWatch: watch for events; when an event occurs, keep draining events for duration `batchFor`, then call processEvent(). | ||
| // Intended for batching of rapid-fire events where we want to process the batch once, like filesystem update notifications. | ||
| func batchWatch(batchFor time.Duration, events chan fsnotify.Event, errors chan error, cancelChan chan struct{}, processEvent func(), onError func(error)) { | ||
| // Pattern shamelessly stolen from https://blog.gopheracademy.com/advent-2013/day-24-channel-buffering-patterns/ | ||
| timer := time.NewTimer(0) | ||
| var timerCh <-chan time.Time | ||
|
|
||
| for { | ||
| select { | ||
| // start a timer when an event occurs, otherwise ignore event | ||
| case <-events: | ||
| if timerCh == nil { | ||
| timer.Reset(batchFor) | ||
| timerCh = timer.C | ||
| } | ||
|
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| // on timer, run the batch; nil channels are silently ignored | ||
| case <-timerCh: | ||
| processEvent() | ||
| timerCh = nil | ||
|
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| // handle errors | ||
| case err := <-errors: | ||
| onError(err) | ||
|
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| // on cancel, abort | ||
| case <-cancelChan: | ||
| return | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,66 @@ | ||
| // Copyright 2022 Google LLC All Rights Reserved. | ||
| // | ||
| // 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 fswatch | ||
|
|
||
| import ( | ||
| "errors" | ||
| "testing" | ||
| "time" | ||
|
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| "github.com/stretchr/testify/assert" | ||
| "gopkg.in/fsnotify.v1" | ||
| ) | ||
|
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| func TestBatchWatch(t *testing.T) { | ||
| eventChan := make(chan fsnotify.Event) | ||
| errorChan := make(chan error) | ||
| cancelChan := make(chan struct{}) | ||
| defer close(cancelChan) | ||
|
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| eventOut := make(chan struct{}, 1) // only allow one event | ||
| errorCount := 0 | ||
|
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| go batchWatch(time.Second, eventChan, errorChan, cancelChan, func() { | ||
| select { | ||
| case eventOut <- struct{}{}: | ||
| // capacity | ||
| default: | ||
| assert.FailNow(t, "second event written - did not want") | ||
| } | ||
| }, func(error) { | ||
| errorCount++ | ||
| }) | ||
|
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| drainEventAndErrors := func(wantErrors int) { | ||
| timeout := time.NewTimer(2 * time.Second) | ||
| select { | ||
| case <-eventOut: | ||
| case <-timeout.C: | ||
| assert.FailNow(t, "no event in 2s") | ||
| } | ||
| assert.Equal(t, wantErrors, errorCount) | ||
| } | ||
|
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| for i := 0; i < 10; i++ { | ||
| eventChan <- fsnotify.Event{} | ||
| } | ||
| drainEventAndErrors(0) | ||
|
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| for i := 0; i < 10; i++ { | ||
| errorChan <- errors.New("some error") | ||
| eventChan <- fsnotify.Event{} | ||
| } | ||
| drainEventAndErrors(10) | ||
| } |