Add locking to mbtiles commits -- sqlite3 doesn't allow concurrent transactions.

lib/mbtiles.js

@@ -368,11 +368,23 @@ MBTiles.prototype.write = function(table, id, row, callback) {
 // - @param {Function(err)} callback
 MBTiles.prototype._commit = function(callback) {
     var mbtiles = this;
+
+    // If no pending commits our work's done.
+    if (!mbtiles._pending) return callback();
+
+    // If already committing wait in line.
+    if (mbtiles._committing) return mbtiles.once('commit', function() {
+        mbtiles._commit(callback);
+    });
+
+    var writes = mbtiles._writes;
+    mbtiles._clearCaches();
+    mbtiles._committing = true;
     mbtiles._db.serialize(function() {
         mbtiles._db.run('BEGIN');
 
         var statements = {};
-        Object.keys(mbtiles._writes).forEach(function(table) {
+        Object.keys(writes).forEach(function(table) {
             switch (table) {
             case 'map':
                 // Insert map table. This has to be so complicate due to a design flaw
@@ -384,8 +396,8 @@ MBTiles.prototype._commit = function(callback) {
                     COALESCE(?, (SELECT tile_id FROM map WHERE zoom_level = ? AND tile_column = ? AND tile_row = ?)),\
                     COALESCE(?, (SELECT grid_id FROM map WHERE zoom_level = ? AND tile_column = ? AND tile_row = ?)))';
                 statements['map'] = mbtiles._db.prepare(sql);
-                for (var id in mbtiles._writes[table]) {
-                    var row = mbtiles._writes[table][id];
+                for (var id in writes[table]) {
+                    var row = writes[table][id];
                     statements['map'].run(
                         row.zoom_level, row.tile_column, row.tile_row,
                         row.tile_id, row.zoom_level, row.tile_column, row.tile_row,
@@ -397,8 +409,8 @@ MBTiles.prototype._commit = function(callback) {
                 var rows = [];
                 var args = [];
                 var fields = [];
-                for (var id in mbtiles._writes[table]) {
-                    var record = mbtiles._writes[table][id];
+                for (var id in writes[table]) {
+                    var record = writes[table][id];
                     var row = [];
                     for (var field in record) {
                         row.push(record[field]);
@@ -417,7 +429,11 @@ MBTiles.prototype._commit = function(callback) {
             }
         });
 
-        mbtiles._db.run('COMMIT', callback);
+        mbtiles._db.run('COMMIT', function(err) {
+            mbtiles._committing = false;
+            mbtiles.emit('commit');
+            callback(err);
+        });
         mbtiles._clearCaches();
     });
 };

test/commit.test.js

@@ -0,0 +1,32 @@
+require('sqlite3').verbose();
+
+var fs = require('fs');
+var assert = require('assert');
+var MBTiles = require('..');
+var fixtureDir = __dirname + '/fixtures/output';
+var image = fs.readFileSync(__dirname + '/fixtures/images/plain_1_0_0_0.png');
+
+describe('write', function() {
+    before(function(done) {
+        // Recreate output directory to remove previous tests.
+        try { fs.unlinkSync(fixtureDir + '/commit_1.mbtiles'); } catch(err) {}
+        try { fs.mkdirSync(fixtureDir, 0755); } catch(err) {}
+        done();
+    });
+    it('test mbtiles commit lock', function(done) {
+        var remaining = 10;
+        new MBTiles('mbtiles://' + fixtureDir + '/commit_1.mbtiles?batch=1', function(err, mbtiles) {
+            assert.ifError(err);
+            mbtiles.startWriting(function(err) {
+                assert.ifError(err);
+                for (var i = 0; i < remaining; i++) mbtiles.putTile(0,0,0,image,putcb);
+                assert.equal(mbtiles._committing, true);
+                assert.equal(mbtiles._events.commit.length, 19);
+            });
+        });
+        function putcb(err) {
+            assert.ifError(err);
+            if (!--remaining) done();
+        }
+    });
+});