forked from hashicorp/nomad
/
blocked_evals.go
307 lines (264 loc) · 8.51 KB
/
blocked_evals.go
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package nomad
import (
"sync"
"time"
"github.com/armon/go-metrics"
"github.com/hashicorp/nomad/nomad/structs"
)
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
)
// 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
// captured is the set of evaluations that are captured by computed node
// classes.
captured map[string]*structs.Evaluation
// escaped is the set of evaluations that have escaped computed node
// classes.
escaped map[string]*structs.Evaluation
// unblockCh is used to buffer unblocking of evaluations.
capacityChangeCh chan string
// 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{}
// 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
// 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{}
// stopCh is used to stop any created goroutines.
stopCh chan struct{}
}
// 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
// TotalBlocked is the total number of blocked evaluations.
TotalBlocked int
}
// 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),
}
}
// 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
}
// 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()
}
}
// 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()
// Do nothing if not enabled
if !b.enabled {
return
}
// 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)
// Unblock any waiter.
select {
case b.duplicateCh <- struct{}{}:
default:
}
return
}
// Mark the job as tracked.
b.stats.TotalBlocked++
b.jobs[eval.JobID] = struct{}{}
// 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
}
// Add the eval to the set of blocked evals whose jobs constraints are
// captured by computed node class.
b.captured[eval.ID] = eval
}
// 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
}
b.capacityChangeCh <- computedClass
}
// 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)
}
}
}
// 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()
// Protect against the case of a flush.
if !b.enabled {
return
}
// 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)
}
}
// 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
}
// 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)
}
if l := len(unblocked); l != 0 {
// Update the counters
b.stats.TotalEscaped = 0
b.stats.TotalBlocked -= l
// Enqueue all the unblocked evals into the broker.
b.evalBroker.EnqueueAll(unblocked)
}
}
// 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()
// Create the timer
if timeoutTimer == nil && timeout != 0 {
timeoutTimer = time.NewTimer(timeout)
timeoutCh = timeoutTimer.C
defer timeoutTimer.Stop()
}
select {
case <-b.stopCh:
return nil
case <-timeoutCh:
return nil
case <-b.duplicateCh:
goto SCAN
}
}
// Flush is used to clear the state of blocked evaluations.
func (b *BlockedEvals) Flush() {
b.l.Lock()
defer b.l.Unlock()
// 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)
}
// 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)
b.l.RLock()
defer b.l.RUnlock()
// Copy all the stats
stats.TotalEscaped = b.stats.TotalEscaped
stats.TotalBlocked = b.stats.TotalBlocked
return stats
}
// 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
}
}
}