lease: initial lessor impl

lease/lessor.go

@@ -0,0 +1,174 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// 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 lease
+
+import (
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/coreos/etcd/pkg/idutil"
+)
+
+var (
+	minLeaseTerm = 5 * time.Second
+)
+
+// a lessor is the owner of leases. It can grant, revoke,
+// renew and modify leases for lessee.
+// TODO: persist lease on to stable backend for failure recovery.
+// TODO: use clockwork for testability.
+type lessor struct {
+	mu sync.Mutex
+	// TODO: probably this should be a heap with a secondary
+	// id index.
+	// Now it is O(N) to loop over the leases to find expired ones.
+	// We want to make Grant, Revoke, and FindExpired all O(logN) and
+	// Renew O(1).
+	// FindExpired and Renew should be the most frequent operations.
+	leaseMap map[uint64]*lease
+
+	idgen *idutil.Generator
+}
+
+func NewLessor(lessorID uint8) *lessor {
+	return &lessor{
+		leaseMap: make(map[uint64]*lease),
+		idgen:    idutil.NewGenerator(lessorID, time.Now()),
+	}
+}
+
+// Grant grants a lease that expires at least at the given expiry
+// time.
+// TODO: when leassor is under highload, it should give out lease
+// with longer term to reduce renew load.
+func (le *lessor) Grant(expiry time.Time) *lease {
+	expiry = minExpiry(time.Now(), expiry)
+
+	id := le.idgen.Next()
+
+	le.mu.Lock()
+	defer le.mu.Unlock()
+
+	l := &lease{id: id, expiry: expiry}
+	if _, ok := le.leaseMap[id]; ok {
+		panic("lease: unexpected duplicate ID!")
+	}
+
+	le.leaseMap[id] = l
+	return l
+}
+
+// Revoke revokes a lease with given ID. The item attached to the
+// given lease will be removed. If the ID does not exist, an error
+// will be returned.
+func (le *lessor) Revoke(id uint64) error {
+	le.mu.Lock()
+	defer le.mu.Unlock()
+
+	l := le.leaseMap[id]
+	if l == nil {
+		return fmt.Errorf("lease: cannot find lease %x", id)
+	}
+
+	delete(le.leaseMap, l.id)
+
+	// TODO: remove attached items
+	return nil
+}
+
+// Renew renews an existing lease with at least the given expiry.
+// If the given lease does not exist or has expired, an error will
+// be returned.
+func (le *lessor) Renew(id uint64, expiry time.Time) error {
+	le.mu.Lock()
+	defer le.mu.Unlock()
+
+	l := le.leaseMap[id]
+	if l == nil {
+		return fmt.Errorf("lease: cannot find lease %x", id)
+	}
+
+	l.expiry = minExpiry(time.Now(), expiry)
+	return nil
+}
+
+// Attach attaches items to the lease with given ID. When the lease
+// expires, the attached items will be automatically removed.
+// If the given lease does not exist, an error will be returned.
+func (le *lessor) Attach(id uint64, items []leaseItem) error {
+	le.mu.Lock()
+	defer le.mu.Unlock()
+
+	l := le.leaseMap[id]
+	if l == nil {
+		return fmt.Errorf("lease: cannot find lease %x", id)
+	}
+
+	for _, it := range items {
+		l.itemSet[it] = struct{}{}
+	}
+	return nil
+}
+
+// findExpiredLeases loops all the leases in the leaseMap and returns the expired
+// leases that needed to be revoked.
+func (le *lessor) findExpiredLeases() []*lease {
+	le.mu.Lock()
+	defer le.mu.Unlock()
+
+	leases := make([]*lease, 0, 16)
+	now := time.Now()
+
+	for _, l := range le.leaseMap {
+		if l.expiry.Sub(now) <= 0 {
+			leases = append(leases, l)
+		}
+	}
+
+	return leases
+}
+
+// get gets the lease with given id.
+// get is a helper fucntion for testing, at least for now.
+func (le *lessor) get(id uint64) *lease {
+	le.mu.Lock()
+	defer le.mu.Unlock()
+
+	return le.leaseMap[id]
+}
+
+type lease struct {
+	id uint64
+
+	itemSet map[leaseItem]struct{}
+	// expiry time in unixnano
+	expiry time.Time
+}
+
+type leaseItem struct {
+	key      string
+	endRange string
+}
+
+// minExpiry returns a minimal expiry. A minimal expiry is the larger on
+// between now + minLeaseTerm and the given expectedExpiry.
+func minExpiry(now time.Time, expectedExpiry time.Time) time.Time {
+	minExpiry := time.Now().Add(minLeaseTerm)
+	if expectedExpiry.Sub(minExpiry) < 0 {
+		expectedExpiry = minExpiry
+	}
+	return expectedExpiry
+}

lease/lessor_test.go

@@ -0,0 +1,75 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// 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 lease
+
+import (
+	"reflect"
+	"testing"
+	"time"
+)
+
+// TestLessorGrant ensures Lessor can grant wanted lease.
+// The granted lease should have a unique ID with a term
+// that is greater than minLeaseTerm.
+func TestLessorGrant(t *testing.T) {
+	le := NewLessor(1)
+
+	l := le.Grant(time.Now().Add(time.Second))
+	gl := le.get(l.id)
+
+	if !reflect.DeepEqual(gl, l) {
+		t.Errorf("lease = %v, want %v", gl, l)
+	}
+	if l.expiry.Sub(time.Now()) < minLeaseTerm-time.Second {
+		t.Errorf("term = %v, want at least %v", l.expiry.Sub(time.Now()), minLeaseTerm-time.Second)
+	}
+
+	nl := le.Grant(time.Now().Add(time.Second))
+	if nl.id == l.id {
+		t.Errorf("new lease.id = %x, want != %x", nl.id, l.id)
+	}
+}
+
+// TestLessorRevoke ensures Lessor can revoke a lease.
+// The revoked lease cannot be got from Lessor again.
+func TestLessorRevoke(t *testing.T) {
+	le := NewLessor(1)
+
+	// grant a lease with long term (100 seconds) to
+	// avoid early termination during the test.
+	l := le.Grant(time.Now().Add(100 * time.Second))
+
+	err := le.Revoke(l.id)
+	if err != nil {
+		t.Fatal("failed to revoke lease:", err)
+	}
+
+	if le.get(l.id) != nil {
+		t.Errorf("got revoked lease %x", l.id)
+	}
+}
+
+// TestLessorRenew ensures Lessor can renew an existing lease.
+func TestLessorRenew(t *testing.T) {
+	le := NewLessor(1)
+	l := le.Grant(time.Now().Add(5 * time.Second))
+
+	le.Renew(l.id, time.Now().Add(100*time.Second))
+	l = le.get(l.id)
+
+	if l.expiry.Sub(time.Now()) < 95*time.Second {
+		t.Errorf("failed to renew the lease for 100 seconds")
+	}
+}