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randomWRR: remove lock for accessing WRR.items #6666

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merged 5 commits into from
Oct 7, 2023
Merged

randomWRR: remove lock for accessing WRR.items #6666

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b36c982
randomWRR: attain lock before read in String()
arvindbr8 Sep 27, 2023
4847f78
Merge branch 'master' into i_5970
arvindbr8 Oct 5, 2023
269b3c0
update random.go by removing mutex
arvindbr8 Oct 6, 2023
e8c6f7e
Merge branch 'master' into i_5970
arvindbr8 Oct 6, 2023
84f59a7
address comments
arvindbr8 Oct 6, 2023
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2 changes: 2 additions & 0 deletions internal/wrr/random.go
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Original file line number Diff line number Diff line change
Expand Up @@ -87,5 +87,7 @@ func (rw *randomWRR) Add(item any, weight int64) {
}

func (rw *randomWRR) String() string {
rw.mu.Lock()
defer rw.mu.Unlock()
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This is risky as we'll deadlock if String is ever called while the lock is held.

Note that String is called indirectly, too, e.g. fmt.Sprint(rw). I don't think I like this. Maybe we should just exclude the items from what is printed and print only static info instead, with a different method that can retrieve the detailed data as a string if needed.

Consider:

func (rw *randomWRR) Whatever() {
	rw.mu.Lock()
	defer rw.mu.Unlock()
	...
	if badThing {
		rw.logger.Warningf("saw bad thing in %s", rw)
	}
	// or:
	if rw.logger.V(2) {
		rw.logger.Infof("saw weird thing in %s", rw)
	}
}

We'd deadlock in rare cases that might not be covered in tests.

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I just noticed that rw.mu is of type sync.RWMutex. Which means i could prolly use mu.RLock() in String(), which would avoid deadlocks on the mutex? wdyt? @dfawley

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Spoke with him offline.. my b, rLock still blocks on wLock.

return fmt.Sprint(rw.items)
}
18 changes: 18 additions & 0 deletions internal/wrr/random_test.go
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Why is this file empty?

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+1

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oops. I had initially thought about adding a unit test for this package. But i realized this was basically covered by other tests indirectly. Removed

Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
/*
*
* Copyright 2023 gRPC 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 wrr