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Merge pull request #726 from hashicorp/f-blocked-evals
Job queue with the introduction of blocked evaluations
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# Set ourselves as thing one | ||
meta { | ||
thing = "two" | ||
ssd = "true" | ||
} | ||
} | ||
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package nomad | ||
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import ( | ||
"sync" | ||
"time" | ||
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"github.com/armon/go-metrics" | ||
"github.com/hashicorp/nomad/nomad/structs" | ||
) | ||
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const ( | ||
// unblockBuffer is the buffer size for the unblock channel. The buffer | ||
// should be large to ensure that the FSM doesn't block when calling Unblock | ||
// as this would apply back-pressure on Raft. | ||
unblockBuffer = 8096 | ||
) | ||
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// BlockedEvals is used to track evaluations that shouldn't be queued until a | ||
// certain class of nodes becomes available. An evaluation is put into the | ||
// blocked state when it is run through the scheduler and produced failed | ||
// allocations. It is unblocked when the capacity of a node that could run the | ||
// failed allocation becomes available. | ||
type BlockedEvals struct { | ||
evalBroker *EvalBroker | ||
enabled bool | ||
stats *BlockedStats | ||
l sync.RWMutex | ||
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// captured is the set of evaluations that are captured by computed node | ||
// classes. | ||
captured map[string]*structs.Evaluation | ||
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// escaped is the set of evaluations that have escaped computed node | ||
// classes. | ||
escaped map[string]*structs.Evaluation | ||
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// unblockCh is used to buffer unblocking of evaluations. | ||
capacityChangeCh chan string | ||
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// jobs is the map of blocked job and is used to ensure that only one | ||
// blocked eval exists for each job. | ||
jobs map[string]struct{} | ||
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// duplicates is the set of evaluations for jobs that had pre-existing | ||
// blocked evaluations. These should be marked as cancelled since only one | ||
// blocked eval is neeeded bper job. | ||
duplicates []*structs.Evaluation | ||
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// duplicateCh is used to signal that a duplicate eval was added to the | ||
// duplicate set. It can be used to unblock waiting callers looking for | ||
// duplicates. | ||
duplicateCh chan struct{} | ||
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// stopCh is used to stop any created goroutines. | ||
stopCh chan struct{} | ||
} | ||
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// BlockedStats returns all the stats about the blocked eval tracker. | ||
type BlockedStats struct { | ||
// TotalEscaped is the total number of blocked evaluations that have escaped | ||
// computed node classes. | ||
TotalEscaped int | ||
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// TotalBlocked is the total number of blocked evaluations. | ||
TotalBlocked int | ||
} | ||
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// NewBlockedEvals creates a new blocked eval tracker that will enqueue | ||
// unblocked evals into the passed broker. | ||
func NewBlockedEvals(evalBroker *EvalBroker) *BlockedEvals { | ||
return &BlockedEvals{ | ||
evalBroker: evalBroker, | ||
captured: make(map[string]*structs.Evaluation), | ||
escaped: make(map[string]*structs.Evaluation), | ||
jobs: make(map[string]struct{}), | ||
capacityChangeCh: make(chan string, unblockBuffer), | ||
duplicateCh: make(chan struct{}, 1), | ||
stopCh: make(chan struct{}), | ||
stats: new(BlockedStats), | ||
} | ||
} | ||
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// Enabled is used to check if the broker is enabled. | ||
func (b *BlockedEvals) Enabled() bool { | ||
b.l.RLock() | ||
defer b.l.RUnlock() | ||
return b.enabled | ||
} | ||
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// SetEnabled is used to control if the broker is enabled. The broker | ||
// should only be enabled on the active leader. | ||
func (b *BlockedEvals) SetEnabled(enabled bool) { | ||
b.l.Lock() | ||
if b.enabled == enabled { | ||
// No-op | ||
return | ||
} else if enabled { | ||
go b.watchCapacity() | ||
} else { | ||
close(b.stopCh) | ||
} | ||
b.enabled = enabled | ||
b.l.Unlock() | ||
if !enabled { | ||
b.Flush() | ||
} | ||
} | ||
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// Block tracks the passed evaluation and enqueues it into the eval broker when | ||
// a suitable node calls unblock. | ||
func (b *BlockedEvals) Block(eval *structs.Evaluation) { | ||
b.l.Lock() | ||
defer b.l.Unlock() | ||
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// Do nothing if not enabled | ||
if !b.enabled { | ||
return | ||
} | ||
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// Check if the job already has a blocked evaluation. If it does add it to | ||
// the list of duplicates. We omly ever want one blocked evaluation per job, | ||
// otherwise we would create unnecessary work for the scheduler as multiple | ||
// evals for the same job would be run, all producing the same outcome. | ||
if _, existing := b.jobs[eval.JobID]; existing { | ||
b.duplicates = append(b.duplicates, eval) | ||
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// Unblock any waiter. | ||
select { | ||
case b.duplicateCh <- struct{}{}: | ||
default: | ||
} | ||
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return | ||
} | ||
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// Mark the job as tracked. | ||
b.stats.TotalBlocked++ | ||
b.jobs[eval.JobID] = struct{}{} | ||
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// If the eval has escaped, meaning computed node classes could not capture | ||
// the constraints of the job, we store the eval separately as we have to | ||
// unblock it whenever node capacity changes. This is because we don't know | ||
// what node class is feasible for the jobs constraints. | ||
if eval.EscapedComputedClass { | ||
b.escaped[eval.ID] = eval | ||
b.stats.TotalEscaped++ | ||
return | ||
} | ||
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// Add the eval to the set of blocked evals whose jobs constraints are | ||
// captured by computed node class. | ||
b.captured[eval.ID] = eval | ||
} | ||
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// Unblock causes any evaluation that could potentially make progress on a | ||
// capacity change on the passed computed node class to be enqueued into the | ||
// eval broker. | ||
func (b *BlockedEvals) Unblock(computedClass string) { | ||
// Do nothing if not enabled | ||
if !b.enabled { | ||
return | ||
} | ||
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b.capacityChangeCh <- computedClass | ||
} | ||
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// watchCapacity is a long lived function that watches for capacity changes in | ||
// nodes and unblocks the correct set of evals. | ||
func (b *BlockedEvals) watchCapacity() { | ||
for { | ||
select { | ||
case <-b.stopCh: | ||
return | ||
case computedClass := <-b.capacityChangeCh: | ||
b.unblock(computedClass) | ||
} | ||
} | ||
} | ||
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// unblock unblocks all blocked evals that could run on the passed computed node | ||
// class. | ||
func (b *BlockedEvals) unblock(computedClass string) { | ||
b.l.Lock() | ||
defer b.l.Unlock() | ||
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// Protect against the case of a flush. | ||
if !b.enabled { | ||
return | ||
} | ||
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// Every eval that has escaped computed node class has to be unblocked | ||
// because any node could potentially be feasible. | ||
var unblocked []*structs.Evaluation | ||
if l := len(b.escaped); l != 0 { | ||
unblocked = make([]*structs.Evaluation, 0, l) | ||
for id, eval := range b.escaped { | ||
unblocked = append(unblocked, eval) | ||
delete(b.escaped, id) | ||
delete(b.jobs, eval.JobID) | ||
} | ||
} | ||
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// We unblock any eval that is explicitely eligible for the computed class | ||
// and also any eval that is not eligible or uneligible. This signifies that | ||
// when the evaluation was originally run through the scheduler, that it | ||
// never saw a node with the given computed class and thus needs to be | ||
// unblocked for correctness. | ||
for id, eval := range b.captured { | ||
if elig, ok := eval.ClassEligibility[computedClass]; ok && !elig { | ||
// Can skip because the eval has explicitely marked the node class | ||
// as ineligible. | ||
continue | ||
} | ||
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// The computed node class has never been seen by the eval so we unblock | ||
// it. | ||
unblocked = append(unblocked, eval) | ||
delete(b.jobs, eval.JobID) | ||
delete(b.captured, id) | ||
} | ||
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if l := len(unblocked); l != 0 { | ||
// Update the counters | ||
b.stats.TotalEscaped = 0 | ||
b.stats.TotalBlocked -= l | ||
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// Enqueue all the unblocked evals into the broker. | ||
b.evalBroker.EnqueueAll(unblocked) | ||
} | ||
} | ||
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// GetDuplicates returns all the duplicate evaluations and blocks until the | ||
// passed timeout. | ||
func (b *BlockedEvals) GetDuplicates(timeout time.Duration) []*structs.Evaluation { | ||
var timeoutTimer *time.Timer | ||
var timeoutCh <-chan time.Time | ||
SCAN: | ||
b.l.Lock() | ||
if len(b.duplicates) != 0 { | ||
dups := b.duplicates | ||
b.duplicates = nil | ||
b.l.Unlock() | ||
return dups | ||
} | ||
b.l.Unlock() | ||
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// Create the timer | ||
if timeoutTimer == nil && timeout != 0 { | ||
timeoutTimer = time.NewTimer(timeout) | ||
timeoutCh = timeoutTimer.C | ||
defer timeoutTimer.Stop() | ||
} | ||
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select { | ||
case <-b.stopCh: | ||
return nil | ||
case <-timeoutCh: | ||
return nil | ||
case <-b.duplicateCh: | ||
goto SCAN | ||
} | ||
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return nil | ||
} | ||
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// Flush is used to clear the state of blocked evaluations. | ||
func (b *BlockedEvals) Flush() { | ||
b.l.Lock() | ||
defer b.l.Unlock() | ||
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// Reset the blocked eval tracker. | ||
b.stats.TotalEscaped = 0 | ||
b.stats.TotalBlocked = 0 | ||
b.captured = make(map[string]*structs.Evaluation) | ||
b.escaped = make(map[string]*structs.Evaluation) | ||
b.jobs = make(map[string]struct{}) | ||
b.duplicates = nil | ||
b.capacityChangeCh = make(chan string, unblockBuffer) | ||
b.stopCh = make(chan struct{}) | ||
b.duplicateCh = make(chan struct{}, 1) | ||
} | ||
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// Stats is used to query the state of the blocked eval tracker. | ||
func (b *BlockedEvals) Stats() *BlockedStats { | ||
// Allocate a new stats struct | ||
stats := new(BlockedStats) | ||
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b.l.RLock() | ||
defer b.l.RUnlock() | ||
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// Copy all the stats | ||
stats.TotalEscaped = b.stats.TotalEscaped | ||
stats.TotalBlocked = b.stats.TotalBlocked | ||
return stats | ||
} | ||
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// EmitStats is used to export metrics about the blocked eval tracker while enabled | ||
func (b *BlockedEvals) EmitStats(period time.Duration, stopCh chan struct{}) { | ||
for { | ||
select { | ||
case <-time.After(period): | ||
stats := b.Stats() | ||
metrics.SetGauge([]string{"nomad", "blocked_evals", "total_blocked"}, float32(stats.TotalBlocked)) | ||
metrics.SetGauge([]string{"nomad", "blocked_evals", "total_escaped"}, float32(stats.TotalEscaped)) | ||
case <-stopCh: | ||
return | ||
} | ||
} | ||
} |
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