Fix data race.

conn.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"math"
 	"runtime"
+	"sync"
 )
 
 // Conn is a database connection handle.
@@ -17,6 +18,7 @@ type Conn struct {
 	handle uint32
 
 	arena     arena
+	mtx       sync.Mutex
 	interrupt context.Context
 	waiter    chan struct{}
 	pending   *Stmt
@@ -244,13 +246,7 @@ func (c *Conn) SetInterrupt(ctx context.Context) (old context.Context) {
 
 		case <-ctx.Done(): // Done was closed.
 
-			// This is safe to call from a goroutine
-			// because it doesn't touch the C stack.
-			_, err := c.api.interrupt.Call(c.ctx, uint64(c.handle))
-			if err != nil {
-				panic(err)
-			}
-
+			c.sendInterrupt()
 			// Wait for the next call to SetInterrupt.
 			<-waiter
 		}
@@ -265,11 +261,19 @@ func (c *Conn) checkInterrupt() bool {
 	if c.interrupt == nil || c.interrupt.Err() == nil {
 		return false
 	}
+	c.sendInterrupt()
+	return true
+}
+
+func (c *Conn) sendInterrupt() {
+	c.mtx.Lock()
+	defer c.mtx.Unlock()
+	// This is safe to call from a goroutine
+	// because it doesn't touch the C stack.
 	_, err := c.api.interrupt.Call(c.ctx, uint64(c.handle))
 	if err != nil {
 		panic(err)
 	}
-	return true
 }
 
 // Savepoint creates a named SQLite transaction using SAVEPOINT.