Add parallel usage test and race detector.

Makefile

@@ -14,6 +14,11 @@ fmt:
 	@go fmt ./...
 
 test: fmt
+	@echo "=== TESTS ==="
 	@go test -v -cover -test.run=$(TEST)
+	@echo ""
+	@echo ""
+	@echo "=== RACE DETECTOR ==="
+	@go test -v -race -test.run=Parallel
 
 .PHONY: bench cover fmt test

db.go

@@ -239,10 +239,6 @@ func (db *DB) Close() {
 }
 
 func (db *DB) close() {
-	// Wait for pending transactions before closing and unmapping the data.
-	// db.mmaplock.Lock()
-	// defer db.mmaplock.Unlock()
-
 	// TODO(benbjohnson): Undo everything in Open().
 	db.freelist = nil
 	db.path = ""

db_test.go

@@ -259,3 +259,10 @@ func withOpenDB(fn func(*DB, string)) {
 		fn(db, path)
 	})
 }
+
+func trunc(b []byte, length int) []byte {
+	if length < len(b) {
+		return b[:length]
+	}
+	return b
+}

functional_test.go

@@ -0,0 +1,124 @@
+package bolt
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"testing"
+	"testing/quick"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Ensure that multiple threads can use the DB without race detector errors.
+func TestParallelTransactions(t *testing.T) {
+	var mutex sync.RWMutex
+
+	err := quick.Check(func(numReaders, batchSize uint, items testdata) bool {
+		// Limit the readers & writers to something reasonable.
+		numReaders = (numReaders % 10) + 1
+		batchSize = (batchSize % 50) + 1
+
+		// Maintain the current dataset.
+		var current testdata
+
+		withOpenDB(func(db *DB, path string) {
+			db.CreateBucket("widgets")
+
+			// Maintain a set of concurrent readers.
+			var wg sync.WaitGroup
+			var c = make(chan bool, 0)
+			go func() {
+				var readers = make(chan int, numReaders)
+				for {
+					wg.Add(1)
+
+					// Attempt to start a new reader unless we're stopped.
+					select {
+					case readers <- 0:
+					case <-c:
+						wg.Done()
+						return
+					}
+
+					go func() {
+						mutex.RLock()
+						local := current
+						txn, err := db.Transaction()
+						mutex.RUnlock()
+						if !assert.NoError(t, err) {
+							t.FailNow()
+						}
+
+						// Verify all data is in for local data list.
+						for _, item := range local {
+							value, err := txn.Get("widgets", item.Key)
+							if !assert.NoError(t, err) || !assert.Equal(t, value, item.Value) {
+								txn.Close()
+								wg.Done()
+								t.FailNow()
+							}
+						}
+
+						txn.Close()
+						wg.Done()
+						<-readers
+					}()
+				}
+			}()
+
+			// Batch insert items.
+			pending := items
+			for {
+				// Determine next batch.
+				currentBatchSize := int(batchSize)
+				if currentBatchSize > len(pending) {
+					currentBatchSize = len(pending)
+				}
+				batchItems := pending[0:currentBatchSize]
+				pending = pending[currentBatchSize:]
+
+				// Start write transaction.
+				txn, err := db.RWTransaction()
+				if !assert.NoError(t, err) {
+					t.FailNow()
+				}
+
+				// Insert whole batch.
+				for _, item := range batchItems {
+					err := txn.Put("widgets", item.Key, item.Value)
+					if !assert.NoError(t, err) {
+						t.FailNow()
+					}
+				}
+
+				// Commit and update the current list.
+				mutex.Lock()
+				err = txn.Commit()
+				current = append(current, batchItems...)
+				mutex.Unlock()
+				if !assert.NoError(t, err) {
+					t.FailNow()
+				}
+
+				// If there are no more left then exit.
+				if len(pending) == 0 {
+					break
+				}
+
+				time.Sleep(1 * time.Millisecond)
+			}
+
+			// Notify readers to stop.
+			close(c)
+
+			// Wait for readers to finish.
+			wg.Wait()
+		})
+		fmt.Fprint(os.Stderr, ".")
+		return true
+	}, qconfig())
+	assert.NoError(t, err)
+	fmt.Fprint(os.Stderr, "\n")
+}

rwtransaction.go

@@ -20,9 +20,7 @@ func (t *RWTransaction) init(db *DB) {
 	t.Transaction.init(db)
 	t.pages = make(map[pgid]*page)
 
-	// Copy the meta and increase the transaction id. 
+	// Increment the transaction id. 
-	t.meta = &meta{}
-	db.meta().copy(t.meta)
 	t.meta.txnid += txnid(1)
 }
 

transaction.go

@@ -20,9 +20,13 @@ type txnid uint64
 // init initializes the transaction and associates it with a database.
 func (t *Transaction) init(db *DB) {
 	t.db = db
-	t.meta = db.meta()
 	t.pages = nil
 
+	// Copy the meta page since it can be changed by the writer.
+	t.meta = &meta{}
+	db.meta().copy(t.meta)
+
+	// Read in the buckets page.
 	t.buckets = &buckets{}
 	t.buckets.read(t.page(t.meta.buckets))
 }