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[core] avoid stuck updateTaskStatus due to mulitple mesos updates
The issue described in OCTRL-953 occurs when we schedule kill of a task and while waiting for an acknowledgment, we receive two mesos updates: ``` [2024-11-11T12:14:02+01:00] TRACE scheduler: task status update received detector=TRG message= srcHost=alio2-cr1-flp163 state=TASK_FAILED task=2qwA9EYEgnY [2024-11-11T12:14:02+01:00] TRACE scheduler: task status update received detector=TRG message=Reconciliation: Task is unknown to the agent srcHost=alio2-cr1-flp163 state=TASK_LOST task=2qwA9EYEgnY ``` Which then trigger the discussed ack. Since it's inclear to me whether we can surely ignore TASK_LOST and trust that we will always receive either TASK_FAILED or TASK_FINISHED, I went for the approach of improving safeAcks to produce an error when subsequent acks are sent instead of blocking some goroutines.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,124 @@ | ||
| /* | ||
| * === This file is part of ALICE O² === | ||
| * | ||
| * Copyright 2020 CERN and copyright holders of ALICE O². | ||
| * Author: Miltiadis Alexis <[email protected]> | ||
| * | ||
| * This program is free software: you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License as published by | ||
| * the Free Software Foundation, either version 3 of the License, or | ||
| * (at your option) any later version. | ||
| * | ||
| * This program is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
| * | ||
| * In applying this license CERN does not waive the privileges and | ||
| * immunities granted to it by virtue of its status as an | ||
| * Intergovernmental Organization or submit itself to any jurisdiction. | ||
| */ | ||
|
|
||
| package safeacks | ||
|
|
||
| import ( | ||
| "fmt" | ||
| "sync" | ||
| ) | ||
|
|
||
| // SafeAcks is a thread safe structure which allows to handle acknowledgment exchanges | ||
| // with N senders and one receiver. The first sender succeeds, then an error is returned for the subsequent ones. | ||
| // This way, subsequent senders are not stuck sending an acknowledgment when nothing expects it anymore. | ||
| // The signaling design is inspired by point 2 in https://go101.org/article/channel-closing.html | ||
| // SafeAcks can be used to acknowledge that an action happened to the task such as task KILLED. | ||
| // At the moment we utilize SafeAcks to acknowledge that all the requested tasks were killed by mesos (task/manager.go). | ||
| type SafeAcks struct { | ||
| mu sync.RWMutex | ||
| acks map[string]ackChannels | ||
| } | ||
|
|
||
| type ackChannels struct { | ||
| // the channel to send the ack to | ||
| ack chan struct{} | ||
| // the channel to close when acks are no longer expected | ||
| stop chan struct{} | ||
| } | ||
|
|
||
| func (a *SafeAcks) deleteKey(key string) { | ||
| a.mu.Lock() | ||
| defer a.mu.Unlock() | ||
|
|
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| delete(a.acks, key) | ||
| } | ||
|
|
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| func (a *SafeAcks) ExpectsAck(key string) bool { | ||
| a.mu.RLock() | ||
| defer a.mu.RUnlock() | ||
|
|
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| _, ok := a.acks[key] | ||
|
|
||
| return ok | ||
| } | ||
|
|
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| func (a *SafeAcks) RegisterAck(key string) error { | ||
| a.mu.Lock() | ||
| defer a.mu.Unlock() | ||
|
|
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| if _, hasKey := a.acks[key]; hasKey { | ||
| return fmt.Errorf("an acknowledgment was already registered for key '%s'", key) | ||
| } | ||
|
|
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| a.acks[key] = ackChannels{make(chan struct{}), make(chan struct{})} | ||
| return nil | ||
| } | ||
|
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| func (a *SafeAcks) getValue(key string) (ackChannels ackChannels, ok bool) { | ||
| a.mu.Lock() | ||
| defer a.mu.Unlock() | ||
|
|
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| ackChannels, ok = a.acks[key] | ||
| return | ||
| } | ||
|
|
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| // TrySendAck checks if an acknowledgment is expected and if it is, it blocks until it is received. | ||
| // If an acknowledgment is not expected at the moment of the call (or already was received), nil is returned. | ||
| // If more than one goroutine attempts to send an acknowledgment before it is received, all but one goroutines will | ||
| // receive an error. | ||
| func (a *SafeAcks) TrySendAck(key string) error { | ||
| channels, ok := a.getValue(key) | ||
| if !ok { | ||
| // fixme: perhaps we should return an error also here, but returning nil preserves the original behaviour | ||
| // of safeAcks before the refactoring. Perhaps the rest of the code assumes it's ok to blindly try sending | ||
| // an ack "just in case", so I would not change it lightly. | ||
| return nil | ||
| } | ||
|
|
||
| select { | ||
| case <-channels.stop: | ||
| return fmt.Errorf("an acknowledgment has been already received for key '%s'", key) | ||
| case channels.ack <- struct{}{}: | ||
| return nil | ||
| } | ||
| } | ||
|
|
||
| // TryReceiveAck blocks until an acknowledgment is received and then returns true. | ||
| // It will return false if an acknowledgment for a given key is not expected. | ||
| func (a *SafeAcks) TryReceiveAck(key string) bool { | ||
| channels, ok := a.getValue(key) | ||
| if !ok { | ||
| return false | ||
| } | ||
| <-channels.ack | ||
| close(channels.stop) | ||
| a.deleteKey(key) | ||
| return true | ||
| } | ||
|
|
||
| func NewAcks() *SafeAcks { | ||
| return &SafeAcks{ | ||
| acks: make(map[string]ackChannels), | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,118 @@ | ||
| package safeacks | ||
|
|
||
| import ( | ||
| . "github.com/onsi/ginkgo/v2" | ||
| . "github.com/onsi/gomega" | ||
| "sync" | ||
| "testing" | ||
| "time" | ||
| ) | ||
|
|
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| var _ = Describe("SafeAcks", func() { | ||
| var sa *SafeAcks | ||
|
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| BeforeEach(func() { | ||
| sa = NewAcks() | ||
| }) | ||
|
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| Describe("RegisterAck", func() { | ||
| It("should register a new ack", func(ctx SpecContext) { | ||
| err := sa.RegisterAck("test") | ||
| Expect(err).NotTo(HaveOccurred()) | ||
| Expect(sa.ExpectsAck("test")).To(BeTrue()) | ||
| }, SpecTimeout(5*time.Second)) | ||
|
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| It("should return error when an ack is already registered", func(ctx SpecContext) { | ||
| err := sa.RegisterAck("test") | ||
| Expect(err).NotTo(HaveOccurred()) | ||
| Expect(sa.ExpectsAck("test")).To(BeTrue()) | ||
|
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| err = sa.RegisterAck("test") | ||
| Expect(err).To(HaveOccurred()) | ||
|
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| Expect(sa.ExpectsAck("test")).To(BeTrue()) | ||
| }, SpecTimeout(5*time.Second)) | ||
| }) | ||
| // TODO add timeout for this test | ||
| Describe("TrySendAck and TryReceiveAck", func() { | ||
| It("should return nil for non-existent key", func(ctx SpecContext) { | ||
| err := sa.TrySendAck("nonexistent") | ||
| Expect(err).To(BeNil()) | ||
| }, SpecTimeout(5*time.Second)) | ||
|
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| It("should send ack successfully", func(ctx SpecContext) { | ||
| err := sa.RegisterAck("test") | ||
| Expect(err).NotTo(HaveOccurred()) | ||
|
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| var wg sync.WaitGroup | ||
| wg.Add(1) | ||
|
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| go func() { | ||
| defer wg.Done() | ||
| err := sa.TrySendAck("test") | ||
| Expect(err).To(BeNil()) | ||
| }() | ||
| Expect(sa.TryReceiveAck("test")).To(BeTrue()) | ||
|
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| wg.Wait() | ||
| }, SpecTimeout(5*time.Second)) | ||
|
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| It("should return error when ack was already sent once", func(ctx SpecContext) { | ||
| err := sa.RegisterAck("test") | ||
| Expect(err).NotTo(HaveOccurred()) | ||
|
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| result1 := make(chan error) | ||
| result2 := make(chan error) | ||
| go func() { | ||
| result1 <- sa.TrySendAck("test") | ||
| }() | ||
|
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| go func() { | ||
| result2 <- sa.TrySendAck("test") | ||
| }() | ||
|
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| // I really don't like relying on a sleep call to test this, but I see no other way... | ||
| // The goal is to have both `TrySendAck` blocked at channel send before invoking TryReceiveAck. | ||
| // Hopefully 1 second is enough to avoid having a shaky test. | ||
| time.Sleep(1000 * time.Millisecond) | ||
|
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| ok := sa.TryReceiveAck("test") | ||
| Expect(ok).To(BeTrue()) | ||
|
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| oneErrorHaveOccured := (<-result1 != nil) != (<-result2 != nil) | ||
| Expect(oneErrorHaveOccured).To(BeTrue()) | ||
| }, SpecTimeout(5*time.Second)) | ||
| }) | ||
|
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| Describe("ExpectsAck", func() { | ||
| It("should return false for non-existent key", func(ctx SpecContext) { | ||
| Expect(sa.ExpectsAck("nonexistent")).To(BeFalse()) | ||
| }, SpecTimeout(5*time.Second)) | ||
|
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| It("should return true for registered key", func(ctx SpecContext) { | ||
| err := sa.RegisterAck("test") | ||
| Expect(err).NotTo(HaveOccurred()) | ||
| Expect(sa.ExpectsAck("test")).To(BeTrue()) | ||
| }, SpecTimeout(5*time.Second)) | ||
|
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| It("should not be permanently blocked by another call", func(ctx SpecContext) { | ||
| err := sa.RegisterAck("test") | ||
| Expect(err).NotTo(HaveOccurred()) | ||
| go func() { | ||
| sa.TryReceiveAck("test") | ||
| }() | ||
|
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| // I really don't like relying on a sleep call to test this, but I see no other way... | ||
| // The goal is to have `TryReceiveAck` blocked at channel receive before invoking ExpectsAck. | ||
| // Hopefully 1 second is enough to avoid having a shaky test. | ||
| time.Sleep(1000 * time.Millisecond) | ||
|
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| Expect(sa.ExpectsAck("test")).To(BeTrue()) | ||
| }, SpecTimeout(5*time.Second)) | ||
| }) | ||
| }) | ||
|
|
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| func TestSafeAcks(t *testing.T) { | ||
| RegisterFailHandler(Fail) | ||
| RunSpecs(t, "Component SafeAcks Test Suite") | ||
| } |
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