From 11bcf164c652e429b222b49a1e4c5e23163c3515 Mon Sep 17 00:00:00 2001
From: Aaron Lindsay <aaron@aclindsay.com>
Date: Sun, 10 Mar 2013 23:13:30 -0400
Subject: [PATCH] Surround sqlite3 transactions with a lock to handle
 concurrency

---
 client/asink.go    | 13 ++++++-------
 client/database.go | 38 ++++++++++++++++++++++++++++++++------
 2 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/client/asink.go b/client/asink.go
index 9b7cd86..c9b46ee 100644
--- a/client/asink.go
+++ b/client/asink.go
@@ -5,7 +5,6 @@ import (
 	"asink/util"
 	"bytes"
 	"code.google.com/p/goconf/conf"
-	"database/sql"
 	"encoding/json"
 	"errors"
 	"flag"
@@ -23,7 +22,7 @@ type AsinkGlobals struct {
 	syncDir        string
 	cacheDir       string
 	tmpDir         string
-	db             *sql.DB
+	db             *AsinkDB
 	storage        Storage
 	server         string
 	port           int
@@ -91,13 +90,13 @@ func main() {
 
 	for {
 		event := <-fileUpdates
-		ProcessEvent(globals, event)
+		go ProcessEvent(globals, event)
 	}
 }
 
 func ProcessEvent(globals AsinkGlobals, event *asink.Event) {
 	//add to database
-	err := DatabaseAddEvent(globals.db, event)
+	err := globals.db.DatabaseAddEvent(event)
 	if err != nil {
 		panic(err)
 	}
@@ -129,7 +128,7 @@ func ProcessEvent(globals AsinkGlobals, event *asink.Event) {
 		event.Status |= asink.CACHED
 
 		//update database
-		err = DatabaseUpdateEvent(globals.db, event)
+		err = globals.db.DatabaseUpdateEvent(event)
 		if err != nil {
 			panic(err)
 		}
@@ -142,7 +141,7 @@ func ProcessEvent(globals AsinkGlobals, event *asink.Event) {
 		event.Status |= asink.UPLOADED
 
 		//update database again
-		err = DatabaseUpdateEvent(globals.db, event)
+		err = globals.db.DatabaseUpdateEvent(event)
 		if err != nil {
 			panic(err)
 		}
@@ -156,7 +155,7 @@ func ProcessEvent(globals AsinkGlobals, event *asink.Event) {
 	}
 
 	event.Status |= asink.ON_SERVER
-	err = DatabaseUpdateEvent(globals.db, event)
+	err = globals.db.DatabaseUpdateEvent(event)
 	if err != nil {
 		panic(err) //TODO probably, definitely, none of these should panic
 	}
diff --git a/client/database.go b/client/database.go
index e4eefb1..3c7baf9 100644
--- a/client/database.go
+++ b/client/database.go
@@ -7,9 +7,15 @@ import (
 	"errors"
 	_ "github.com/mattn/go-sqlite3"
 	"strconv"
+	"sync"
 )
 
-func GetAndInitDB(config *conf.ConfigFile) (*sql.DB, error) {
+type AsinkDB struct {
+	db *sql.DB
+	lock sync.Mutex
+}
+
+func GetAndInitDB(config *conf.ConfigFile) (*AsinkDB, error) {
 	dbLocation, err := config.GetString("local", "dblocation")
 	if err != nil {
 		return nil, errors.New("Error: database location not specified in config file.")
@@ -41,14 +47,25 @@ func GetAndInitDB(config *conf.ConfigFile) (*sql.DB, error) {
 		return nil, err
 	}
 
-	return db, nil
+	ret := new(AsinkDB)
+	ret.db = db
+	return ret, nil
 }
 
-func DatabaseAddEvent(db *sql.DB, e *asink.Event) error {
-	tx, err := db.Begin()
+func (adb *AsinkDB) DatabaseAddEvent(e *asink.Event) (err error) {
+	adb.lock.Lock()
+	tx, err := adb.db.Begin()
 	if err != nil {
 		return err
 	}
+	//make sure the transaction gets rolled back on error, and the database gets unlocked
+	defer func() {
+		if err != nil {
+			tx.Rollback()
+		}
+		adb.lock.Unlock()
+	}()
+
 	result, err := tx.Exec("INSERT INTO events (id, type, status, path, hash, timestamp, permissions) VALUES (?,?,?,?,?,?,?);", e.Id, e.Type, e.Status, e.Path, e.Hash, e.Timestamp, e.Permissions)
 	if err != nil {
 		return err
@@ -67,15 +84,24 @@ func DatabaseAddEvent(db *sql.DB, e *asink.Event) error {
 	return nil
 }
 
-func DatabaseUpdateEvent(db *sql.DB, e *asink.Event) error {
+func (adb *AsinkDB) DatabaseUpdateEvent(e *asink.Event) (err error) {
 	if !e.InDB {
 		return errors.New("Attempting to update an event in the database which hasn't been previously added.")
 	}
 
-	tx, err := db.Begin()
+	adb.lock.Lock()
+	tx, err := adb.db.Begin()
 	if err != nil {
 		return err
 	}
+	//make sure the transaction gets rolled back on error, and the database gets unlocked
+	defer func() {
+		if err != nil {
+			tx.Rollback()
+		}
+		adb.lock.Unlock()
+	}()
+
 	result, err := tx.Exec("UPDATE events SET id=?, type=?, status=?, path=?, hash=?, timestamp=?, permissions=? WHERE localid=?;", e.Id, e.Type, e.Status, e.Path, e.Hash, e.Timestamp, e.Permissions, e.LocalId)
 	if err != nil {
 		return err