From 24253d2e1ebc178460eaa92449baa9e7fcd4bd01 Mon Sep 17 00:00:00 2001
From: Aaron Lindsay <aaron@aclindsay.com>
Date: Fri, 19 Jul 2013 22:15:53 -0400
Subject: [PATCH] server: Surround sqlite3 transactions with a lock to handle
 concurrency

---
 server/database.go | 27 +++++++++++++++++++++------
 server/server.go   |  9 ++++-----
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/server/database.go b/server/database.go
index 97e2961..d33c1df 100644
--- a/server/database.go
+++ b/server/database.go
@@ -4,9 +4,15 @@ import (
 	"asink"
 	"database/sql"
 	_ "github.com/mattn/go-sqlite3"
+	"sync"
 )
 
-func GetAndInitDB() (*sql.DB, error) {
+type AsinkDB struct {
+	db   *sql.DB
+	lock sync.Mutex
+}
+
+func GetAndInitDB() (*AsinkDB, error) {
 	dbLocation := "asink-server.db" //TODO make me configurable
 
 	db, err := sql.Open("sqlite3", dbLocation)
@@ -33,11 +39,14 @@ func GetAndInitDB() (*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) (err 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
 	}
@@ -47,6 +56,7 @@ func DatabaseAddEvent(db *sql.DB, e *asink.Event) (err error) {
 		if err != nil {
 			tx.Rollback()
 		}
+		adb.lock.Unlock()
 	}()
 
 	result, err := tx.Exec("INSERT INTO events (localid, type, status, path, hash, timestamp, permissions) VALUES (?,?,?,?,?,?,?);", e.LocalId, e.Type, e.Status, e.Path, e.Hash, e.Timestamp, e.Permissions)
@@ -67,8 +77,13 @@ func DatabaseAddEvent(db *sql.DB, e *asink.Event) (err error) {
 	return nil
 }
 
-func DatabaseRetrieveEvents(db *sql.DB, firstId uint64, maxEvents uint) (events []*asink.Event, err error) {
-	rows, err := db.Query("SELECT id, localid, type, status, path, hash, timestamp, permissions FROM events WHERE id >= ? ORDER BY id ASC LIMIT ?;", firstId, maxEvents)
+func (adb *AsinkDB) DatabaseRetrieveEvents(firstId uint64, maxEvents uint) (events []*asink.Event, err error) {
+	adb.lock.Lock()
+	//make sure the database gets unlocked on return
+	defer func() {
+		adb.lock.Unlock()
+	}()
+	rows, err := adb.db.Query("SELECT id, localid, type, status, path, hash, timestamp, permissions FROM events WHERE id >= ? ORDER BY id ASC LIMIT ?;", firstId, maxEvents)
 	if err != nil {
 		return nil, err
 	}
diff --git a/server/server.go b/server/server.go
index a023c9a..30562b8 100644
--- a/server/server.go
+++ b/server/server.go
@@ -2,7 +2,6 @@ package main
 
 import (
 	"asink"
-	"database/sql"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -15,7 +14,7 @@ import (
 //global variables
 var eventsRegexp *regexp.Regexp
 var port int = 8080
-var db *sql.DB
+var adb *AsinkDB
 
 func init() {
 	var err error
@@ -26,7 +25,7 @@ func init() {
 
 	eventsRegexp = regexp.MustCompile("^/events/([0-9]+)$")
 
-	db, err = GetAndInitDB()
+	adb, err = GetAndInitDB()
 	if err != nil {
 		panic(err)
 	}
@@ -74,7 +73,7 @@ func getEvents(w http.ResponseWriter, r *http.Request, nextEvent uint64) {
 		w.Write(b)
 	}()
 
-	events, err := DatabaseRetrieveEvents(db, nextEvent, 50)
+	events, err := adb.DatabaseRetrieveEvents(nextEvent, 50)
 	if err != nil {
 		panic(err)
 		error_message = err.Error()
@@ -126,7 +125,7 @@ func putEvents(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	for _, event := range events.Events {
-		err = DatabaseAddEvent(db, event)
+		err = adb.DatabaseAddEvent(event)
 		if err != nil {
 			//TODO should probably do this in a way that the caller knows how many of these have failed and doesn't re-try sending ones that succeeded
 			//i.e. add this to the return codes or something