db: update FernDB

Add `mutex` field to the FernDB struct.

2 files changed, 20 insertions, 0 deletions

diff --git a/db/db.go b/db/db.go
index 2d6a4d5..6bc6d04 100644
--- a/db/db.go
+++ b/db/db.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"sync"
 
 	"ricketyspace.net/fern/file"
 )
@@ -15,6 +16,7 @@ import (
 var dbPath string
 
 type FernDB struct {
+	mutex *sync.Mutex // For writes to `downloaded`
 	// Key: feed-id
 	// Value: feed-id's entries that were downloaded
 	downloaded map[string][]string
@@ -42,6 +44,7 @@ func Open() (*FernDB, error) {
 	if err != nil {
 		// db does not exist yet; create an empty one.
 		db := new(FernDB)
+		db.mutex = new(sync.Mutex)
 		db.downloaded = make(map[string][]string)
 		return db, nil
 	}
@@ -58,6 +61,7 @@ func Open() (*FernDB, error) {
 
 	// Unmarshal db into an object.
 	db := new(FernDB)
+	db.mutex = new(sync.Mutex)
 	err = json.Unmarshal(bs, &db.downloaded)
 	if err != nil {
 		return nil, err
diff --git a/db/db_test.go b/db/db_test.go
index 5a2a983..e2308c1 100644
--- a/db/db_test.go
+++ b/db/db_test.go
@@ -46,6 +46,14 @@ func TestOpenNewDB(t *testing.T) {
 		return
 	}
 
+	// Verify that 'mutex' is initialized.
+	if db.mutex == nil {
+		t.Errorf("db.mutex is nil")
+		return
+	}
+	db.mutex.Lock()
+	db.mutex.Unlock()
+
 	// Verify that 'downloaded' is initialized
 	if db.downloaded == nil {
 		t.Errorf("db.downloaded is nil")
@@ -77,6 +85,14 @@ func TestOpenExistingDB(t *testing.T) {
 		return
 	}
 
+	// Verify that 'mutex' is initialized.
+	if db.mutex == nil {
+		t.Errorf("db.mutex is nil")
+		return
+	}
+	db.mutex.Lock()
+	db.mutex.Unlock()
+
 	// Validate db.downloaded.
 	var entries, expectedEntries []string
 	var ok bool