Fixes that should hopefully protect against database corruption

- When opening the DB, always tell other Zotero instances to close it,
  regardless of whether they are holding the lock.
- Don't let database re-open after it has been closed. This also fixes
  some issues with connector switching.

chrome/content/zotero/xpcom/db.js

@@ -791,12 +791,17 @@ Zotero.DBConnection.prototype.checkException = function (e) {
 }
 
 
-Zotero.DBConnection.prototype.closeDatabase = function () {
+/**
+ * Close the database
+ * @param {Boolean} [permanent] If true, throw an error instead of
+ *     allowing code to re-open the database again
+ */
+Zotero.DBConnection.prototype.closeDatabase = function (permanent) {
 	if(this._connection) {
 		this.stopDummyStatement();
 		var deferred = Q.defer();
 		this._connection.asyncClose(deferred.resolve);
-		this._connection = undefined;
+		this._connection = permanent ? false : null;
 		return deferred.promise;
 	} else {
 		return Q();
@@ -1073,6 +1078,8 @@ Zotero.DBConnection.prototype.getSQLDataType = function(value) {
 Zotero.DBConnection.prototype._getDBConnection = function () {
 	if (this._connection) {
 		return this._connection;
+	} else if (this._connection === false) {
+		throw new Error("Database permanently closed; not re-opening");
 	}
 	
 	this._debug("Opening database '" + this._dbName + "'");

chrome/content/zotero/xpcom/ipc.js

@@ -62,10 +62,13 @@ Zotero.IPC = new function() {
 			 *    has been received if it is already initialized, SA sends an initComplete message 
 			 *    to Z4Fx.
 			 */
-			if(msg === "releaseLock" && !Zotero.isConnector) {
+			if(msg.substr(0, 11) === "releaseLock") {
 				// Standalone sends this to the Firefox extension to tell the Firefox extension to
 				// release its lock on the Zotero database
-				switchConnectorMode(true);
+				if(!Zotero.isConnector && (msg.length === 11 ||
+					                       msg.substr(12) === Zotero.getZoteroDirectory().persistentDescriptor)) {
+					switchConnectorMode(true);
+				}
 			} else if(msg === "lockReleased") {
 				// The Firefox extension sends this to Standalone to let Standalone know that it has
 				// released its lock

chrome/content/zotero/xpcom/zotero.js

@@ -759,6 +759,11 @@ Components.utils.import("resource://gre/modules/Services.jsm");
 			Zotero.DB.test();
 			
 			var dbfile = Zotero.getZoteroDatabase();
+
+			// Tell any other Zotero instances to release their lock,
+			// in case we lost the lock on the database (how?) and it's
+			// now open in two places at once
+			Zotero.IPC.broadcast("releaseLock "+dbfile.persistentDescriptor);
 			
 			// Test write access on Zotero data directory
 			if (!dbfile.parent.isWritable()) {
@@ -886,8 +891,8 @@ Components.utils.import("resource://gre/modules/Services.jsm");
 				// Zotero.DBConnection.getStatement() explicitly
 				Components.utils.forceGC();
 				
-				// unlock DB
-				return Zotero.DB.closeDatabase().then(function() {				
+				// close DB
+				return Zotero.DB.closeDatabase(true).then(function() {				
 					// broadcast that DB lock has been released
 					Zotero.IPC.broadcast("lockReleased");
 				});