Add module for transactions cache (#440)

* Add transactions cache, write tests.

Add a transactions module in dendrite/common. This is needed for idempotent APIs.

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

* Use cycling double map instead, improve code logic, remove unneeded test

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

* Update code comments

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

* Use two constructors for default and custom cleanupPeriod
Add code comments

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>
This commit is contained in:
Anant Prakash 2018-05-16 16:06:40 +05:30 committed by Erik Johnston
parent 4c807e082f
commit 8861437c26
2 changed files with 138 additions and 0 deletions

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// 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 transactions
import (
"sync"
"time"
"github.com/matrix-org/util"
)
// DefaultCleanupPeriod represents the default time duration after which cacheCleanService runs.
const DefaultCleanupPeriod time.Duration = 30 * time.Minute
type txnsMap map[string]*util.JSONResponse
// Cache represents a temporary store for response entries.
// Entries are evicted after a certain period, defined by cleanupPeriod.
// This works by keeping two maps of entries, and cycling the maps after the cleanupPeriod.
type Cache struct {
sync.RWMutex
txnsMaps [2]txnsMap
cleanupPeriod time.Duration
}
// New is a wrapper which calls NewWithCleanupPeriod with DefaultCleanupPeriod as argument.
func New() *Cache {
return NewWithCleanupPeriod(DefaultCleanupPeriod)
}
// NewWithCleanupPeriod creates a new Cache object, starts cacheCleanService.
// Takes cleanupPeriod as argument.
// Returns a reference to newly created Cache.
func NewWithCleanupPeriod(cleanupPeriod time.Duration) *Cache {
t := Cache{txnsMaps: [2]txnsMap{make(txnsMap), make(txnsMap)}}
t.cleanupPeriod = cleanupPeriod
// Start clean service as the Cache is created
go cacheCleanService(&t)
return &t
}
// FetchTransaction looks up an entry for txnID in Cache.
// Looks in both the txnMaps.
// Returns (JSON response, true) if txnID is found, else the returned bool is false.
func (t *Cache) FetchTransaction(txnID string) (*util.JSONResponse, bool) {
t.RLock()
defer t.RUnlock()
for _, txns := range t.txnsMaps {
res, ok := txns[txnID]
if ok {
return res, true
}
}
return nil, false
}
// AddTransaction adds an entry for txnID in Cache for later access.
// Adds to the front txnMap.
func (t *Cache) AddTransaction(txnID string, res *util.JSONResponse) {
t.Lock()
defer t.Unlock()
t.txnsMaps[0][txnID] = res
}
// cacheCleanService is responsible for cleaning up entries after cleanupPeriod.
// It guarantees that an entry will be present in cache for at least cleanupPeriod & at most 2 * cleanupPeriod.
// This cycles the txnMaps forward, i.e. back map is assigned the front and front is assigned an empty map.
func cacheCleanService(t *Cache) {
ticker := time.Tick(t.cleanupPeriod)
for range ticker {
t.Lock()
t.txnsMaps[1] = t.txnsMaps[0]
t.txnsMaps[0] = make(txnsMap)
t.Unlock()
}
}

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// 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 transactions
import (
"net/http"
"testing"
"github.com/matrix-org/util"
)
type fakeType struct {
ID string `json:"ID"`
}
var (
fakeTxnID = "aRandomTxnID"
fakeResponse = &util.JSONResponse{Code: http.StatusOK, JSON: fakeType{ID: "0"}}
)
// TestCache creates a New Cache and tests AddTransaction & FetchTransaction
func TestCache(t *testing.T) {
fakeTxnCache := New()
fakeTxnCache.AddTransaction(fakeTxnID, fakeResponse)
// Add entries for noise.
for i := 1; i <= 100; i++ {
fakeTxnCache.AddTransaction(
fakeTxnID+string(i),
&util.JSONResponse{Code: http.StatusOK, JSON: fakeType{ID: string(i)}},
)
}
testResponse, ok := fakeTxnCache.FetchTransaction(fakeTxnID)
if !ok {
t.Error("Failed to retrieve entry for txnID: ", fakeTxnID)
} else if testResponse.JSON != fakeResponse.JSON {
t.Error("Fetched response incorrect. Expected: ", fakeResponse.JSON, " got: ", testResponse.JSON)
}
}