fn: non-blocking resource tracker and notification (#841)

* fn: non-blocking resource tracker and notification

For some types of errors, we might want to notify
the actual caller if the error is directly 1-1 tied
to that request. If hotLauncher is triggered with
signaller, then here we send a back communication
error notification channel. This is passed to
checkLaunch to send back synchronous responses
to the caller that initiated this hot container
launch.

This is useful if we want to run the agent in
quick fail mode, where instead of waiting for
CPU/Mem to become available, we prefer to fail
quick in order not to hold up the caller.
To support this, non-blocking resource tracker
option/functions are now available.

* fn: test env var rename tweak

* fn: fixup merge

* fn: rebase test fix

* fn: merge fixup

* fn: test tweak down to 70MB for 128MB total

* fn: refactor token creation and use broadcast regardless

* fn: nb description

* fn: bugfix

api/agent/agent.go

@@ -315,6 +315,8 @@ func transformTimeout(e error, isRetriable bool) error {
 			return models.ErrCallTimeoutServerBusy
 		}
 		return models.ErrCallTimeout
+	} else if e == CapacityFull {
+		return models.ErrCallTimeoutServerBusy
 	}
 	return e
 }
@@ -402,9 +404,12 @@ func (a *agent) hotLauncher(ctx context.Context, call *call) {
 	ctx, span := trace.StartSpan(ctx, "agent_hot_launcher")
 	defer span.End()
 
+	var notifyChan chan error
+
 	for {
 		ctx, cancel := context.WithTimeout(ctx, timeout)
-		a.checkLaunch(ctx, call)
+		a.checkLaunch(ctx, call, notifyChan)
+		notifyChan = nil
 
 		select {
 		case <-a.shutWg.Closer(): // server shutdown
@@ -416,15 +421,25 @@ func (a *agent) hotLauncher(ctx context.Context, call *call) {
 				logger.Info("Hot function launcher timed out")
 				return
 			}
-		case <-call.slots.signaller:
+		case notifyChan = <-call.slots.signaller:
 			cancel()
 		}
 	}
 }
 
-func (a *agent) checkLaunch(ctx context.Context, call *call) {
+func tryNotify(notifyChan chan error, err error) {
+	if notifyChan != nil && err != nil {
+		select {
+		case notifyChan <- err:
+		default:
+		}
+	}
+}
+
+func (a *agent) checkLaunch(ctx context.Context, call *call, notifyChan chan error) {
 	curStats := call.slots.getStats()
 	isAsync := call.Type == models.TypeAsync
+	isNB := a.cfg.EnableNBResourceTracker
 	isNeeded := isNewContainerNeeded(&curStats)
 	common.Logger(ctx).WithFields(logrus.Fields{"currentStats": curStats, "isNeeded": isNeeded}).Debug("Hot function launcher stats")
 	if !isNeeded {
@@ -436,9 +451,28 @@ func (a *agent) checkLaunch(ctx context.Context, call *call) {
 
 	common.Logger(ctx).WithFields(logrus.Fields{"currentStats": call.slots.getStats(), "isNeeded": isNeeded}).Info("Hot function launcher starting hot container")
 
+	// WARNING: Tricky flow below. We are here because: isNeeded is set,
+	// in other words, we need to launch a new container at this time due to high load.
+	//
+	// For non-blocking mode, this means, if we cannot acquire resources (cpu+mem), then we need
+	// to notify the caller through notifyChan. This is not perfect as the callers and
+	// checkLaunch do not match 1-1. But this is OK, we can notify *any* waiter that
+	// has signalled us, this is because non-blocking mode is a system wide setting.
+	// The notifications are lossy, but callers will signal/poll again if this is the case
+	// or this may not matter if they've already acquired an empty slot.
+	//
+	// For Non-blocking mode, a.cfg.HotPoll should not be set to too high since a missed
+	// notify event from here will add a.cfg.HotPoll msec latency. Setting a.cfg.HotPoll may
+	// be an acceptable workaround for the short term since non-blocking mode likely to reduce
+	// the number of waiters which perhaps could compensate for more frequent polling.
+	//
+	// Non-blocking mode only applies to cpu+mem, and if isNeeded decided that we do not
+	// need to start a new container, then waiters will wait.
 	select {
-	case tok := <-a.resources.GetResourceToken(ctx, call.Memory, uint64(call.CPUs), isAsync):
-		if a.shutWg.AddSession(1) {
+	case tok := <-a.resources.GetResourceToken(ctx, call.Memory, uint64(call.CPUs), isAsync, isNB):
+		if tok != nil && tok.Error() != nil {
+			tryNotify(notifyChan, tok.Error())
+		} else if a.shutWg.AddSession(1) {
 			go func() {
 				// NOTE: runHot will not inherit the timeout from ctx (ignore timings)
 				a.runHot(ctx, call, tok, state)
@@ -466,12 +500,16 @@ func (a *agent) waitHot(ctx context.Context, call *call) (Slot, error) {
 
 	ch := call.slots.startDequeuer(ctx)
 
+	notifyChan := make(chan error)
+
 	// 1) if we can get a slot immediately, grab it.
 	// 2) if we don't, send a signaller every x msecs until we do.
 
 	sleep := 1 * time.Microsecond // pad, so time.After doesn't send immediately
 	for {
 		select {
+		case err := <-notifyChan:
+			return nil, err
 		case s := <-ch:
 			if call.slots.acquireSlot(s) {
 				if s.slot.Error() != nil {
@@ -493,7 +531,7 @@ func (a *agent) waitHot(ctx context.Context, call *call) (Slot, error) {
 		sleep = a.cfg.HotPoll
 		// send a notification to launchHot()
 		select {
-		case call.slots.signaller <- true:
+		case call.slots.signaller <- notifyChan:
 		default:
 		}
 	}
@@ -503,6 +541,8 @@ func (a *agent) waitHot(ctx context.Context, call *call) (Slot, error) {
 // returns the slot for that new container to run the request on.
 func (a *agent) launchCold(ctx context.Context, call *call) (Slot, error) {
 	isAsync := call.Type == models.TypeAsync
+	isNB := a.cfg.EnableNBResourceTracker
+
 	ch := make(chan Slot)
 
 	ctx, span := trace.StartSpan(ctx, "agent_launch_cold")
@@ -511,7 +551,11 @@ func (a *agent) launchCold(ctx context.Context, call *call) (Slot, error) {
 	call.containerState.UpdateState(ctx, ContainerStateWait, call.slots)
 
 	select {
-	case tok := <-a.resources.GetResourceToken(ctx, call.Memory, uint64(call.CPUs), isAsync):
+	case tok := <-a.resources.GetResourceToken(ctx, call.Memory, uint64(call.CPUs), isAsync, isNB):
+		if tok.Error() != nil {
+			return nil, tok.Error()
+		}
+
 		go a.prepCold(ctx, call, tok, ch)
 	case <-ctx.Done():
 		return nil, ctx.Err()

api/agent/config.go

@@ -9,44 +9,46 @@ import (
 )
 
 type AgentConfig struct {
-	MinDockerVersion   string        `json:"min_docker_version"`
-	FreezeIdle         time.Duration `json:"freeze_idle_msecs"`
-	EjectIdle          time.Duration `json:"eject_idle_msecs"`
-	HotPoll            time.Duration `json:"hot_poll_msecs"`
-	HotLauncherTimeout time.Duration `json:"hot_launcher_timeout_msecs"`
-	AsyncChewPoll      time.Duration `json:"async_chew_poll_msecs"`
-	CallEndTimeout     time.Duration `json:"call_end_timeout"`
-	MaxCallEndStacking uint64        `json:"max_call_end_stacking"`
-	MaxResponseSize    uint64        `json:"max_response_size_bytes"`
-	MaxLogSize         uint64        `json:"max_log_size_bytes"`
-	MaxTotalCPU        uint64        `json:"max_total_cpu_mcpus"`
-	MaxTotalMemory     uint64        `json:"max_total_memory_bytes"`
-	MaxFsSize          uint64        `json:"max_fs_size_mb"`
-	PreForkPoolSize    uint64        `json:"pre_fork_pool_size"`
-	PreForkImage       string        `json:"pre_fork_image"`
-	PreForkCmd         string        `json:"pre_fork_pool_cmd"`
-	PreForkUseOnce     uint64        `json:"pre_fork_use_once"`
-	PreForkNetworks    string        `json:"pre_fork_networks"`
+	MinDockerVersion        string        `json:"min_docker_version"`
+	FreezeIdle              time.Duration `json:"freeze_idle_msecs"`
+	EjectIdle               time.Duration `json:"eject_idle_msecs"`
+	HotPoll                 time.Duration `json:"hot_poll_msecs"`
+	HotLauncherTimeout      time.Duration `json:"hot_launcher_timeout_msecs"`
+	AsyncChewPoll           time.Duration `json:"async_chew_poll_msecs"`
+	CallEndTimeout          time.Duration `json:"call_end_timeout"`
+	MaxCallEndStacking      uint64        `json:"max_call_end_stacking"`
+	MaxResponseSize         uint64        `json:"max_response_size_bytes"`
+	MaxLogSize              uint64        `json:"max_log_size_bytes"`
+	MaxTotalCPU             uint64        `json:"max_total_cpu_mcpus"`
+	MaxTotalMemory          uint64        `json:"max_total_memory_bytes"`
+	MaxFsSize               uint64        `json:"max_fs_size_mb"`
+	PreForkPoolSize         uint64        `json:"pre_fork_pool_size"`
+	PreForkImage            string        `json:"pre_fork_image"`
+	PreForkCmd              string        `json:"pre_fork_pool_cmd"`
+	PreForkUseOnce          uint64        `json:"pre_fork_use_once"`
+	PreForkNetworks         string        `json:"pre_fork_networks"`
+	EnableNBResourceTracker bool          `json:"enable_nb_resource_tracker"`
 }
 
 const (
-	EnvFreezeIdle         = "FN_FREEZE_IDLE_MSECS"
-	EnvEjectIdle          = "FN_EJECT_IDLE_MSECS"
-	EnvHotPoll            = "FN_HOT_POLL_MSECS"
-	EnvHotLauncherTimeout = "FN_HOT_LAUNCHER_TIMEOUT_MSECS"
-	EnvAsyncChewPoll      = "FN_ASYNC_CHEW_POLL_MSECS"
-	EnvCallEndTimeout     = "FN_CALL_END_TIMEOUT_MSECS"
-	EnvMaxCallEndStacking = "FN_MAX_CALL_END_STACKING"
-	EnvMaxResponseSize    = "FN_MAX_RESPONSE_SIZE"
-	EnvMaxLogSize         = "FN_MAX_LOG_SIZE_BYTES"
-	EnvMaxTotalCPU        = "FN_MAX_TOTAL_CPU_MCPUS"
-	EnvMaxTotalMemory     = "FN_MAX_TOTAL_MEMORY_BYTES"
-	EnvMaxFsSize          = "FN_MAX_FS_SIZE_MB"
-	EnvPreForkPoolSize    = "FN_EXPERIMENTAL_PREFORK_POOL_SIZE"
-	EnvPreForkImage       = "FN_EXPERIMENTAL_PREFORK_IMAGE"
-	EnvPreForkCmd         = "FN_EXPERIMENTAL_PREFORK_CMD"
-	EnvPreForkUseOnce     = "FN_EXPERIMENTAL_PREFORK_USE_ONCE"
-	EnvPreForkNetworks    = "FN_EXPERIMENTAL_PREFORK_NETWORKS"
+	EnvFreezeIdle              = "FN_FREEZE_IDLE_MSECS"
+	EnvEjectIdle               = "FN_EJECT_IDLE_MSECS"
+	EnvHotPoll                 = "FN_HOT_POLL_MSECS"
+	EnvHotLauncherTimeout      = "FN_HOT_LAUNCHER_TIMEOUT_MSECS"
+	EnvAsyncChewPoll           = "FN_ASYNC_CHEW_POLL_MSECS"
+	EnvCallEndTimeout          = "FN_CALL_END_TIMEOUT_MSECS"
+	EnvMaxCallEndStacking      = "FN_MAX_CALL_END_STACKING"
+	EnvMaxResponseSize         = "FN_MAX_RESPONSE_SIZE"
+	EnvMaxLogSize              = "FN_MAX_LOG_SIZE_BYTES"
+	EnvMaxTotalCPU             = "FN_MAX_TOTAL_CPU_MCPUS"
+	EnvMaxTotalMemory          = "FN_MAX_TOTAL_MEMORY_BYTES"
+	EnvMaxFsSize               = "FN_MAX_FS_SIZE_MB"
+	EnvPreForkPoolSize         = "FN_EXPERIMENTAL_PREFORK_POOL_SIZE"
+	EnvPreForkImage            = "FN_EXPERIMENTAL_PREFORK_IMAGE"
+	EnvPreForkCmd              = "FN_EXPERIMENTAL_PREFORK_CMD"
+	EnvPreForkUseOnce          = "FN_EXPERIMENTAL_PREFORK_USE_ONCE"
+	EnvPreForkNetworks         = "FN_EXPERIMENTAL_PREFORK_NETWORKS"
+	EnvEnableNBResourceTracker = "FN_ENABLE_NB_RESOURCE_TRACKER"
 
 	MaxDisabledMsecs = time.Duration(math.MaxInt64)
 )
@@ -85,6 +87,10 @@ func NewAgentConfig() (*AgentConfig, error) {
 		return cfg, err
 	}
 
+	if _, ok := os.LookupEnv(EnvEnableNBResourceTracker); ok {
+		cfg.EnableNBResourceTracker = true
+	}
+
 	if cfg.EjectIdle == time.Duration(0) {
 		return cfg, fmt.Errorf("error %s cannot be zero", EnvEjectIdle)
 	}

api/agent/resource.go

@@ -23,6 +23,8 @@ const (
 	Mem1GB = 1024 * 1024 * 1024
 )
 
+var CapacityFull = errors.New("max capacity reached")
+
 // A simple resource (memory, cpu, disk, etc.) tracker for scheduling.
 // TODO: add cpu, disk, network IO for future
 type ResourceTracker interface {
@@ -34,8 +36,10 @@ type ResourceTracker interface {
 	// the channel will never receive anything. If it is not possible to fulfill this resource, the channel
 	// will never receive anything (use IsResourcePossible). If a resource token is available for the provided
 	// resource parameters, it will otherwise be sent once on the returned channel. The channel is never closed.
-	// Memory is expected to be provided in MB units.
-	GetResourceToken(ctx context.Context, memory, cpuQuota uint64, isAsync bool) <-chan ResourceToken
+	// if isNB is set, resource check is done and error token is returned without blocking.
+	// if isAsync is set, resource allocation specific for async requests is considered. (eg. always allow
+	// a sync only reserve area) Memory is expected to be provided in MB units.
+	GetResourceToken(ctx context.Context, memory, cpuQuota uint64, isAsync, isNB bool) <-chan ResourceToken
 
 	// IsResourcePossible returns whether it's possible to fulfill the requested resources on this
 	// machine. It must be called before GetResourceToken or GetResourceToken may hang.
@@ -88,13 +92,19 @@ func NewResourceTracker(cfg *AgentConfig) ResourceTracker {
 type ResourceToken interface {
 	// Close must be called by any thread that receives a token.
 	io.Closer
+	Error() error
 }
 
 type resourceToken struct {
 	once      sync.Once
+	err       error
 	decrement func()
 }
 
+func (t *resourceToken) Error() error {
+	return t.err
+}
+
 func (t *resourceToken) Close() error {
 	t.once.Do(func() {
 		t.decrement()
@@ -140,10 +150,93 @@ func (a *resourceTracker) GetResourceTokenWaiterCount() uint64 {
 	return waiters
 }
 
+func (a *resourceTracker) allocResourcesLocked(memory, cpuQuota uint64, isAsync bool) ResourceToken {
+
+	var asyncMem, syncMem uint64
+	var asyncCPU, syncCPU uint64
+
+	if isAsync {
+		// async uses async pool only
+		asyncMem = memory
+		asyncCPU = cpuQuota
+	} else {
+		// if sync fits async + sync pool
+		syncMem = minUint64(a.ramSyncTotal-a.ramSyncUsed, memory)
+		syncCPU = minUint64(a.cpuSyncTotal-a.cpuSyncUsed, cpuQuota)
+
+		asyncMem = memory - syncMem
+		asyncCPU = cpuQuota - syncCPU
+	}
+
+	a.ramAsyncUsed += asyncMem
+	a.ramSyncUsed += syncMem
+	a.cpuAsyncUsed += asyncCPU
+	a.cpuSyncUsed += syncCPU
+
+	return &resourceToken{decrement: func() {
+
+		a.cond.L.Lock()
+		a.ramAsyncUsed -= asyncMem
+		a.ramSyncUsed -= syncMem
+		a.cpuAsyncUsed -= asyncCPU
+		a.cpuSyncUsed -= syncCPU
+		a.cond.L.Unlock()
+
+		// WARNING: yes, we wake up everyone even async waiters when only sync pool has space, but
+		// the cost of this spurious wake up is unlikely to impact much performance. Simpler
+		// to use one cond variable for the time being.
+		a.cond.Broadcast()
+	}}
+}
+
+func (a *resourceTracker) getResourceTokenNB(memory uint64, cpuQuota uint64, isAsync bool) ResourceToken {
+	if !a.IsResourcePossible(memory, cpuQuota, isAsync) {
+		return &resourceToken{decrement: func() {}, err: CapacityFull}
+	}
+	memory = memory * Mem1MB
+
+	var t ResourceToken
+
+	a.cond.L.Lock()
+
+	if !a.isResourceAvailableLocked(memory, cpuQuota, isAsync) {
+		t = &resourceToken{decrement: func() {}, err: CapacityFull}
+	} else {
+		t = a.allocResourcesLocked(memory, cpuQuota, isAsync)
+	}
+
+	a.cond.L.Unlock()
+	return t
+}
+
+func (a *resourceTracker) getResourceTokenNBChan(ctx context.Context, memory uint64, cpuQuota uint64, isAsync bool) <-chan ResourceToken {
+	ctx, span := trace.StartSpan(ctx, "agent_get_resource_token_nbio_chan")
+
+	ch := make(chan ResourceToken)
+	go func() {
+		defer span.End()
+		t := a.getResourceTokenNB(memory, cpuQuota, isAsync)
+
+		select {
+		case ch <- t:
+		case <-ctx.Done():
+			// if we can't send b/c nobody is waiting anymore, need to decrement here
+			t.Close()
+		}
+	}()
+
+	return ch
+}
+
 // the received token should be passed directly to launch (unconditionally), launch
 // will close this token (i.e. the receiver should not call Close)
-func (a *resourceTracker) GetResourceToken(ctx context.Context, memory uint64, cpuQuota uint64, isAsync bool) <-chan ResourceToken {
+func (a *resourceTracker) GetResourceToken(ctx context.Context, memory uint64, cpuQuota uint64, isAsync, isNB bool) <-chan ResourceToken {
+	if isNB {
+		return a.getResourceTokenNBChan(ctx, memory, cpuQuota, isAsync)
+	}
+
 	ch := make(chan ResourceToken)
+
 	if !a.IsResourcePossible(memory, cpuQuota, isAsync) {
 		// return the channel, but never send anything.
 		return ch
@@ -186,43 +279,9 @@ func (a *resourceTracker) GetResourceToken(ctx context.Context, memory uint64, c
 			return
 		}
 
-		var asyncMem, syncMem uint64
-		var asyncCPU, syncCPU uint64
-
-		if isAsync {
-			// async uses async pool only
-			asyncMem = memory
-			asyncCPU = cpuQuota
-		} else {
-			// if sync fits async + sync pool
-			syncMem = minUint64(a.ramSyncTotal-a.ramSyncUsed, memory)
-			syncCPU = minUint64(a.cpuSyncTotal-a.cpuSyncUsed, cpuQuota)
-
-			asyncMem = memory - syncMem
-			asyncCPU = cpuQuota - syncCPU
-		}
-
-		a.ramAsyncUsed += asyncMem
-		a.ramSyncUsed += syncMem
-		a.cpuAsyncUsed += asyncCPU
-		a.cpuSyncUsed += syncCPU
+		t := a.allocResourcesLocked(memory, cpuQuota, isAsync)
 		c.L.Unlock()
 
-		t := &resourceToken{decrement: func() {
-
-			c.L.Lock()
-			a.ramAsyncUsed -= asyncMem
-			a.ramSyncUsed -= syncMem
-			a.cpuAsyncUsed -= asyncCPU
-			a.cpuSyncUsed -= syncCPU
-			c.L.Unlock()
-
-			// WARNING: yes, we wake up everyone even async waiters when only sync pool has space, but
-			// the cost of this spurious wake up is unlikely to impact much performance. Simpler
-			// to use one cond variable for the time being.
-			c.Broadcast()
-		}}
-
 		select {
 		case ch <- t:
 		case <-ctx.Done():

api/agent/resource_test.go

@@ -179,7 +179,7 @@ func TestResourceGetSimple(t *testing.T) {
 
 	// ask for 4GB and 10 CPU
 	ctx, cancel := context.WithCancel(context.Background())
-	ch := trI.GetResourceToken(ctx, 4*1024, 1000, false)
+	ch := trI.GetResourceToken(ctx, 4*1024, 1000, false, false)
 	defer cancel()
 
 	_, err := fetchToken(ch)
@@ -198,7 +198,7 @@ func TestResourceGetSimple(t *testing.T) {
 
 	// ask for another 4GB and 10 CPU
 	ctx, cancel = context.WithCancel(context.Background())
-	ch = trI.GetResourceToken(ctx, 4*1024, 1000, false)
+	ch = trI.GetResourceToken(ctx, 4*1024, 1000, false, false)
 	defer cancel()
 
 	_, err = fetchToken(ch)
@@ -226,6 +226,69 @@ func TestResourceGetSimple(t *testing.T) {
 	}
 }
 
+func TestResourceGetSimpleNB(t *testing.T) {
+
+	var vals trackerVals
+	trI := NewResourceTracker(nil)
+	tr := trI.(*resourceTracker)
+
+	vals.setDefaults()
+
+	// let's make it like CPU and MEM are 100% full
+	vals.mau = vals.mat
+	vals.cau = vals.cat
+
+	setTrackerTestVals(tr, &vals)
+
+	// ask for 4GB and 10 CPU
+	ctx, cancel := context.WithCancel(context.Background())
+	ch := trI.GetResourceToken(ctx, 4*1024, 1000, false, true)
+	defer cancel()
+
+	tok := <-ch
+	if tok.Error() == nil {
+		t.Fatalf("full system should not hand out token")
+	}
+
+	// reset back
+	vals.setDefaults()
+	setTrackerTestVals(tr, &vals)
+
+	tok1 := <-trI.GetResourceToken(ctx, 4*1024, 1000, false, true)
+	if tok1.Error() != nil {
+		t.Fatalf("empty system should hand out token")
+	}
+
+	// ask for another 4GB and 10 CPU
+	ctx, cancel = context.WithCancel(context.Background())
+	ch = trI.GetResourceToken(ctx, 4*1024, 1000, false, true)
+	defer cancel()
+
+	tok = <-ch
+	if tok.Error() == nil {
+		t.Fatalf("full system should not hand out token")
+	}
+
+	// close means, giant token resources released
+	tok1.Close()
+
+	tok = <-trI.GetResourceToken(ctx, 4*1024, 1000, false, true)
+	if tok.Error() != nil {
+		t.Fatalf("empty system should hand out token")
+	}
+
+	tok.Close()
+
+	// POOLS should all be empty now
+	getTrackerTestVals(tr, &vals)
+	if vals.msu != 0 || vals.mau != 0 {
+		t.Fatalf("faulty state MEM %#v", vals)
+	}
+	if vals.csu != 0 || vals.cau != 0 {
+		t.Fatalf("faulty state CPU %#v", vals)
+	}
+}
+
 func TestResourceGetCombo(t *testing.T) {
 
 	var vals trackerVals
@@ -237,7 +300,7 @@ func TestResourceGetCombo(t *testing.T) {
 
 	// impossible request
 	ctx, cancel := context.WithCancel(context.Background())
-	ch := trI.GetResourceToken(ctx, 20*1024, 20000, false)
+	ch := trI.GetResourceToken(ctx, 20*1024, 20000, false, false)
 	_, err := fetchToken(ch)
 	if err == nil {
 		t.Fatalf("impossible request should never return (error here)")
@@ -247,7 +310,7 @@ func TestResourceGetCombo(t *testing.T) {
 	ctx, cancel = context.WithCancel(context.Background())
 
 	// let's use up 2 GB of 3GB async pool
-	ch = trI.GetResourceToken(ctx, 2*1024, 10, true)
+	ch = trI.GetResourceToken(ctx, 2*1024, 10, true, false)
 	tok1, err := fetchToken(ch)
 	if err != nil {
 		t.Fatalf("empty async system should hand out token1")
@@ -257,7 +320,7 @@ func TestResourceGetCombo(t *testing.T) {
 	ctx, cancel = context.WithCancel(context.Background())
 
 	// remaining 1 GB async
-	ch = trI.GetResourceToken(ctx, 1*1024, 11, true)
+	ch = trI.GetResourceToken(ctx, 1*1024, 11, true, false)
 	tok2, err := fetchToken(ch)
 	if err != nil {
 		t.Fatalf("empty async system should hand out token2")
@@ -270,7 +333,7 @@ func TestResourceGetCombo(t *testing.T) {
 	// SYNC POOL HAS 1GB
 
 	// we no longer can get async token
-	ch = trI.GetResourceToken(ctx, 1*1024, 12, true)
+	ch = trI.GetResourceToken(ctx, 1*1024, 12, true, false)
 	_, err = fetchToken(ch)
 	if err == nil {
 		t.Fatalf("full async system should not hand out a token")
@@ -280,7 +343,7 @@ func TestResourceGetCombo(t *testing.T) {
 	ctx, cancel = context.WithCancel(context.Background())
 
 	// but we should get 1GB sync token
-	ch = trI.GetResourceToken(ctx, 1*1024, 13, false)
+	ch = trI.GetResourceToken(ctx, 1*1024, 13, false, false)
 	tok3, err := fetchToken(ch)
 	if err != nil {
 		t.Fatalf("empty sync system should hand out token3")
@@ -292,7 +355,7 @@ func TestResourceGetCombo(t *testing.T) {
 	// NOW ASYNC AND SYNC POOLS ARE FULL
 
 	// this should fail
-	ch = trI.GetResourceToken(ctx, 1*1024, 14, false)
+	ch = trI.GetResourceToken(ctx, 1*1024, 14, false, false)
 	_, err = fetchToken(ch)
 	if err == nil {
 		t.Fatalf("full system should not hand out a token")
@@ -308,7 +371,7 @@ func TestResourceGetCombo(t *testing.T) {
 	// SYNC POOL IS FULL
 
 	// async pool should provide this
-	ch = trI.GetResourceToken(ctx, 1*1024, 15, false)
+	ch = trI.GetResourceToken(ctx, 1*1024, 15, false, false)
 	tok4, err := fetchToken(ch)
 	if err != nil {
 		t.Fatalf("async system should hand out token4")
@@ -326,7 +389,7 @@ func TestResourceGetCombo(t *testing.T) {
 	// SYNC POOL HAS 1GB FREE
 
 	// now, we ask for 2GB sync token, it should be provided from both async+sync pools
-	ch = trI.GetResourceToken(ctx, 2*1024, 16, false)
+	ch = trI.GetResourceToken(ctx, 2*1024, 16, false, false)
 	tok5, err := fetchToken(ch)
 	if err != nil {
 		t.Fatalf("async+sync system should hand out token5")

api/agent/slots.go

@@ -50,7 +50,7 @@ type slotQueue struct {
 	cond      *sync.Cond
 	slots     []*slotToken
 	nextId    uint64
-	signaller chan bool
+	signaller chan chan error
 	statsLock sync.Mutex // protects stats below
 	stats     slotQueueStats
 }
@@ -67,7 +67,7 @@ func NewSlotQueue(key string) *slotQueue {
 		key:       key,
 		cond:      sync.NewCond(new(sync.Mutex)),
 		slots:     make([]*slotToken, 0),
-		signaller: make(chan bool, 1),
+		signaller: make(chan chan error, 1),
 	}
 
 	return obj