Implement query cancellation support within MCPKit, and add it to the task functionality:

 - MCPKit now supports cancelling the active query; for MySQL servers >= 5.0.0 a query kill is attempted from a new connection, and if that fails or for MySQL < 5 a reconnect is triggered.
 - TableDocument now supports enabling a cancel task button on the task interface, including an optional callback
 - Implement query cancellation for custom queries.  This addresses Issue #86.
 - Implement query cancellation for table content loads, filters, and sorts.

9 files changed, 327 insertions, 65 deletions

diff --git a/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.h b/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.h
index 548425e1..0442bf9f 100644
--- a/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.h
+++ b/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.h
@@ -111,6 +111,8 @@ static inline NSData* NSStringDataUsingLossyEncoding(NSString* self, NSInteger e
 	uint64_t connectionStartTime;
 	
 	BOOL retryAllowed;
+	BOOL queryCancelled;
+	BOOL queryCancelUsedReconnect;
 	BOOL delegateQueryLogging;
 	BOOL delegateResponseToWillQueryString;
 	
@@ -205,6 +207,9 @@ void performThreadedKeepAlive(void *ptr);
 - (id)queryString:(NSString *) query usingEncoding:(NSStringEncoding) encoding streamingResult:(NSInteger) streamResult;
 - (my_ulonglong)affectedRows;
 - (my_ulonglong)insertId;
+- (void)cancelCurrentQuery;
+- (BOOL)queryCancelled;
+- (BOOL)queryCancellationUsedReconnect;
 
 // Locking
 - (void)lockConnection;
diff --git a/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.m b/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.m
index e55568d5..7db3ec2d 100644
--- a/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.m
+++ b/Frameworks/MCPKit/MCPFoundationKit/MCPConnection.m
@@ -101,6 +101,8 @@ static BOOL	sTruncateLongFieldInLogs = YES;
 		connectionProxy = nil;
 		connectionStartTime = -1;
 		lastQueryExecutedAtTime = CGFLOAT_MAX;
+		queryCancelled = NO;
+		queryCancelUsedReconnect = NO;
 		
 		// Initialize ivar defaults
 		connectionTimeout = 10;
@@ -1261,6 +1263,9 @@ void performThreadedKeepAlive(void *ptr)
 	NSInteger		currentMaxAllowedPacket = -1;
 	BOOL			isQueryRetry = NO;
 	NSString		*queryErrorMessage = nil;
+
+	// Reset the query cancelled boolean
+	queryCancelled = NO;
 	
 	// If no connection is present, return nil.
 	if (!mConnected) {
@@ -1290,7 +1295,6 @@ void performThreadedKeepAlive(void *ptr)
 	// minimising the impact of performing lots of additional checks.
 	if ([self timeConnected] - lastQueryExecutedAtTime > 30
 		&& ![self checkConnection]) {
-			NSLog(@"returning nil!");
 			return nil;
 			}
 
@@ -1366,7 +1370,7 @@ void performThreadedKeepAlive(void *ptr)
 				// For normal result sets, fetch the results and unlock the connection
 				if (streamResultType == MCP_NO_STREAMING) {
 					theResult = [[MCPResult alloc] initWithMySQLPtr:mConnection encoding:mEncoding timeZone:mTimeZone];
-					[queryLock unlock];
+					if (!queryCancelled || !queryCancelUsedReconnect) [queryLock unlock];
 				
 				// For streaming result sets, fetch the result pointer and leave the connection locked
 				} else if (streamResultType == MCP_FAST_STREAMING) {
@@ -1394,16 +1398,23 @@ void performThreadedKeepAlive(void *ptr)
 			
 		// On failure, set the error messages and IDs
 		} else {
-			if (streamResultType == MCP_NO_STREAMING) [queryLock unlock];
-			else [self unlockConnection];
+			if (!queryCancelled || !queryCancelUsedReconnect) {
+				if (streamResultType == MCP_NO_STREAMING) [queryLock unlock];
+				else [self unlockConnection];
+			}
 			
-			queryErrorMessage = [[NSString alloc] initWithString:[self stringWithCString:mysql_error(mConnection)]];
-			queryErrorId = mysql_errno(mConnection);
-
-			// If the error was a connection error, retry once
-			if (!isQueryRetry && retryAllowed && [MCPConnection isErrorNumberConnectionError:queryErrorId]) {
-				isQueryRetry = YES;
-				continue;
+			if (queryCancelled) {
+				queryErrorMessage = [[NSString alloc] initWithString:NSLocalizedString(@"Query cancelled.", @"Query cancelled error")];
+				queryErrorId = 1152;
+			} else {			
+				queryErrorMessage = [[NSString alloc] initWithString:[self stringWithCString:mysql_error(mConnection)]];
+				queryErrorId = mysql_errno(mConnection);
+
+				// If the error was a connection error, retry once
+				if (!isQueryRetry && retryAllowed && [MCPConnection isErrorNumberConnectionError:queryErrorId]) {
+					isQueryRetry = YES;
+					continue;
+				}
 			}
 		}
 		
@@ -1464,6 +1475,104 @@ void performThreadedKeepAlive(void *ptr)
 	return 0;
 }
 
+/**
+ * Cancel the currently running query.  This tries to kill the current query, and if that
+ * isn't possible, resets the connection.
+ */
+- (void) cancelCurrentQuery
+{
+
+	// If not connected, return.
+	if (![self isConnected]) return;
+
+	// Check whether a query is actually being performed - if not, also return.
+	if ([queryLock tryLock]) {
+		[queryLock unlock];
+		return;
+	}
+
+	// Set queryCancelled to prevent query retries
+	queryCancelled = YES;
+
+	// For MySQL server versions >=5, try to kill the connection.  This requires
+	// setting up a new connection, and running a KILL QUERY via it.
+	if ([self serverMajorVersion] >= 5) {
+
+		MYSQL *killerConnection = mysql_init(NULL);
+		if (killerConnection) {
+			const char *theLogin = [self cStringFromString:connectionLogin];
+			const char *theHost;
+			const char *thePass;
+			const char *theSocket;
+			void *connectionSetupStatus;
+
+			mysql_options(killerConnection, MYSQL_OPT_CONNECT_TIMEOUT, (const void *)&connectionTimeout);
+
+			// Set up the host, socket and password as per the connect method
+			if (!connectionHost || ![connectionHost length]) {
+				theHost = NULL;
+			} else {
+				theHost = [self cStringFromString:connectionHost];
+			}
+			if (connectionSocket == nil || ![connectionSocket length]) {
+				theSocket = kMCPConnectionDefaultSocket;
+			} else {
+				theSocket = [self cStringFromString:connectionSocket];
+			}
+			if (!connectionPassword) {
+				if (delegate && [delegate respondsToSelector:@selector(keychainPasswordForConnection:)]) {
+					thePass = [self cStringFromString:[delegate keychainPasswordForConnection:self]];
+				}
+			} else {		
+				thePass = [self cStringFromString:connectionPassword];
+			}
+			
+			// Connect
+			connectionSetupStatus = mysql_real_connect(killerConnection, theHost, theLogin, thePass, NULL, connectionPort, theSocket, mConnectionFlags);
+			thePass = NULL;
+			if (connectionSetupStatus) {
+				NSStringEncoding killerConnectionEncoding = [MCPConnection encodingForMySQLEncoding:mysql_character_set_name(killerConnection)];
+				NSString *killerQueryString = [NSString stringWithFormat:@"KILL QUERY %lu", mConnection->thread_id];
+				NSData *encodedKillerQueryData = NSStringDataUsingLossyEncoding(killerQueryString, killerConnectionEncoding, 1);
+				const char *killerQueryCString = [encodedKillerQueryData bytes];
+				unsigned long killerQueryCStringLength = [encodedKillerQueryData length];
+				if (mysql_real_query(killerConnection, killerQueryCString, killerQueryCStringLength) == 0) {
+					mysql_close(killerConnection);
+					queryCancelUsedReconnect = NO;
+					return;
+				}
+				mysql_close(killerConnection);
+			}
+		}
+	}
+
+	// Reset the connection
+	[self unlockConnection];
+	[self reconnect];
+
+	// Set queryCancelled again to handle requery cleanups, and return.
+	queryCancelled = YES;
+	queryCancelUsedReconnect = YES;
+}
+
+/**
+ * Return whether the last query was cancelled
+ */
+- (BOOL)queryCancelled
+{
+	return queryCancelled;
+}
+
+/**
+ * If the last query was cancelled, returns whether that cancellation
+ * required a connection reset.  If the last query was not cancelled
+ * the behaviour is undefined.
+ */
+- (BOOL)queryCancellationUsedReconnect
+{
+	return queryCancelUsedReconnect;
+}
+
 #pragma mark -
 #pragma mark Connection locking
 
@@ -1483,6 +1592,13 @@ void performThreadedKeepAlive(void *ptr)
  */
 - (void)unlockConnection
 {
+
+	// Make sure the unlock is performed safely - eg for reconnected queries
+	if ([queryLock tryLock]) {
+		[queryLock unlock];
+		return;
+	}
+
 	if ([NSThread isMainThread]) [queryLock unlock];
 	else [queryLock performSelectorOnMainThread:@selector(unlock) withObject:nil waitUntilDone:YES];
 }
diff --git a/Interfaces/English.lproj/ProgressIndicatorLayer.xib b/Interfaces/English.lproj/ProgressIndicatorLayer.xib
index 33adda95..de3df433 100644
--- a/Interfaces/English.lproj/ProgressIndicatorLayer.xib
+++ b/Interfaces/English.lproj/ProgressIndicatorLayer.xib
@@ -3,7 +3,7 @@
 	<data>
 		<int key="IBDocument.SystemTarget">1050</int>
 		<string key="IBDocument.SystemVersion">10B504</string>
-		<string key="IBDocument.InterfaceBuilderVersion">732</string>
+		<string key="IBDocument.InterfaceBuilderVersion">740</string>
 		<string key="IBDocument.AppKitVersion">1038.2</string>
 		<string key="IBDocument.HIToolboxVersion">437.00</string>
 		<object class="NSMutableDictionary" key="IBDocument.PluginVersions">
@@ -15,7 +15,7 @@
 			</object>
 			<object class="NSMutableArray" key="dict.values">
 				<bool key="EncodedWithXMLCoder">YES</bool>
-				<string>732</string>
+				<string>740</string>
 				<string>1.2.1</string>
 			</object>
 		</object>
@@ -117,8 +117,8 @@
 									</object>
 									<object class="BWTransparentButton" id="540103856">
 										<reference key="NSNextResponder" ref="950529842"/>
-										<int key="NSvFlags">-2147483358</int>
-										<string key="NSFrame">{{89, 4}, {81, 28}}</string>
+										<int key="NSvFlags">290</int>
+										<string key="NSFrame">{{64, 4}, {132, 28}}</string>
 										<reference key="NSSuperview" ref="950529842"/>
 										<bool key="NSEnabled">YES</bool>
 										<object class="BWTransparentButtonCell" key="NSCell" id="1030687082">
@@ -217,6 +217,14 @@
 					</object>
 					<int key="connectionID">34</int>
 				</object>
+				<object class="IBConnectionRecord">
+					<object class="IBActionConnection" key="connection">
+						<string key="label">cancelTask:</string>
+						<reference key="source" ref="1001"/>
+						<reference key="destination" ref="540103856"/>
+					</object>
+					<int key="connectionID">35</int>
+				</object>
 			</object>
 			<object class="IBMutableOrderedSet" key="objectRecords">
 				<object class="NSArray" key="orderedObjects">
@@ -259,22 +267,13 @@
 						<reference key="object" ref="450247213"/>
 						<object class="NSMutableArray" key="children">
 							<bool key="EncodedWithXMLCoder">YES</bool>
-							<reference ref="540103856"/>
 							<reference ref="545295640"/>
+							<reference ref="540103856"/>
 							<reference ref="602680912"/>
 						</object>
 						<reference key="parent" ref="1005"/>
 					</object>
 					<object class="IBObjectRecord">
-						<int key="objectID">17</int>
-						<reference key="object" ref="540103856"/>
-						<object class="NSMutableArray" key="children">
-							<bool key="EncodedWithXMLCoder">YES</bool>
-							<reference ref="1030687082"/>
-						</object>
-						<reference key="parent" ref="450247213"/>
-					</object>
-					<object class="IBObjectRecord">
 						<int key="objectID">15</int>
 						<reference key="object" ref="545295640"/>
 						<object class="NSMutableArray" key="children">
@@ -294,6 +293,15 @@
 						<reference key="parent" ref="545295640"/>
 					</object>
 					<object class="IBObjectRecord">
+						<int key="objectID">17</int>
+						<reference key="object" ref="540103856"/>
+						<object class="NSMutableArray" key="children">
+							<bool key="EncodedWithXMLCoder">YES</bool>
+							<reference ref="1030687082"/>
+						</object>
+						<reference key="parent" ref="450247213"/>
+					</object>
+					<object class="IBObjectRecord">
 						<int key="objectID">18</int>
 						<reference key="object" ref="1030687082"/>
 						<reference key="parent" ref="540103856"/>
@@ -373,7 +381,7 @@
 				</object>
 			</object>
 			<nil key="sourceID"/>
-			<int key="maxID">34</int>
+			<int key="maxID">37</int>
 		</object>
 		<object class="IBClassDescriber" key="IBDocument.Classes">
 			<object class="NSMutableArray" key="referencedPartialClassDescriptions">
@@ -555,6 +563,7 @@
 							<string>addDatabase:</string>
 							<string>analyzeTable:</string>
 							<string>backForwardInHistory:</string>
+							<string>cancelTask:</string>
 							<string>checkTable:</string>
 							<string>checksumTable:</string>
 							<string>chooseDatabase:</string>
@@ -636,6 +645,7 @@
 							<string>id</string>
 							<string>id</string>
 							<string>id</string>
+							<string>id</string>
 						</object>
 					</object>
 					<object class="NSMutableDictionary" key="outlets">
@@ -690,6 +700,7 @@
 							<string>tableWindow</string>
 							<string>tablesListInstance</string>
 							<string>taskCancelButton</string>
+							<string>taskCancellationCallbackObject</string>
 							<string>taskDescriptionText</string>
 							<string>taskProgressIndicator</string>
 							<string>taskProgressLayer</string>
@@ -754,6 +765,7 @@
 							<string>NSButton</string>
 							<string>id</string>
 							<string>id</string>
+							<string>id</string>
 							<string>NSBox</string>
 							<string>id</string>
 							<string>id</string>
diff --git a/Source/CustomQuery.m b/Source/CustomQuery.m
index f515f335..dc0d9b76 100644
--- a/Source/CustomQuery.m
+++ b/Source/CustomQuery.m
@@ -388,6 +388,7 @@
 	MCPStreamingResult	*streamingResult  = nil;
 	NSMutableString		*errors     = [NSMutableString string];
 	SEL					callbackMethod = NULL;
+	NSString			*taskButtonString;
 	
 	int i, totalQueriesRun = 0, totalAffectedRows = 0;
 	double executionTime = 0;
@@ -425,6 +426,13 @@
 	long queryCount = [queries count];
 	NSMutableArray *tempQueries = [NSMutableArray arrayWithCapacity:queryCount];
 
+	// Enable task cancellation
+	if (queryCount > 1)
+		taskButtonString = NSLocalizedString(@"Stop queries", @"Stop queries string");
+	else
+		taskButtonString = NSLocalizedString(@"Stop query", @"Stop query string");
+	[tableDocumentInstance enableTaskCancellationWithTitle:taskButtonString callbackObject:nil callbackFunction:NULL];
+
 	// Perform the supplied queries in series
 	for ( i = 0 ; i < queryCount ; i++ ) {
 
@@ -450,7 +458,7 @@
 
 		// If this is the last query, retrieve and store the result; otherwise,
 		// discard the result without fully loading.
-		if (totalQueriesRun == queryCount) {
+		if (totalQueriesRun == queryCount || [mySQLConnection queryCancelled]) {
 
 			// get column definitions for the result array
 			if (cqColumnDefinition) [cqColumnDefinition release];
@@ -507,7 +515,17 @@
 			totalAffectedRows += [streamingResult numOfRows];
 
 		// Store any error messages
-		if ( ![[mySQLConnection getLastErrorMessage] isEqualToString:@""] ) {
+		if ( ![[mySQLConnection getLastErrorMessage] isEqualToString:@""] || [mySQLConnection queryCancelled]) {
+
+			NSString *errorString;
+			if ([mySQLConnection queryCancelled]) {
+				if ([mySQLConnection queryCancellationUsedReconnect])
+					errorString = NSLocalizedString(@"Query cancelled.  Please note that to cancel the query the connection had to be reset; transactions and connection variables were reset.", @"Query cancel by resetting connection error");
+				else
+					errorString = NSLocalizedString(@"Query cancelled.", @"Query cancelled error");
+			} else {
+				errorString = [mySQLConnection getLastErrorMessage];
+			}
 
 			// If the query errored, append error to the error log for display at the end
 			if ( queryCount > 1 ) {
@@ -519,35 +537,37 @@
 					// Update error text for the user
 					[errors appendString:[NSString stringWithFormat:NSLocalizedString(@"[ERROR in query %d] %@\n", @"error text when multiple custom query failed"),
 										i+1,
-										[mySQLConnection getLastErrorMessage]]];
+										errorString]];
 					[errorText setStringValue:errors];
+
 					// ask the user to continue after detecting an error
-					NSAlert *alert = [[[NSAlert alloc] init] autorelease];
-					[alert addButtonWithTitle:NSLocalizedString(@"Run All", @"run all button")];
-					[alert addButtonWithTitle:NSLocalizedString(@"Continue", @"continue button")];
-					[alert addButtonWithTitle:NSLocalizedString(@"Stop", @"stop button")];
-					[alert setMessageText:NSLocalizedString(@"MySQL Error", @"mysql error message")];
-					[alert setInformativeText:[mySQLConnection getLastErrorMessage]];
-					[alert setAlertStyle:NSWarningAlertStyle];
-					int choice = [alert runModal];
-					switch (choice){
-						case NSAlertFirstButtonReturn:
-							suppressErrorSheet = YES;
-						case NSAlertSecondButtonReturn:
-							break;
-						default:
-							if(i < queryCount-1) // output that message only if it was not the last one
-								[errors appendString:NSLocalizedString(@"Execution stopped!\n", @"execution stopped message")];
-							i = queryCount; // break for loop; for safety reasons stop the execution of the following queries
+					if (![mySQLConnection queryCancelled]) {
+						NSAlert *alert = [[[NSAlert alloc] init] autorelease];
+						[alert addButtonWithTitle:NSLocalizedString(@"Run All", @"run all button")];
+						[alert addButtonWithTitle:NSLocalizedString(@"Continue", @"continue button")];
+						[alert addButtonWithTitle:NSLocalizedString(@"Stop", @"stop button")];
+						[alert setMessageText:NSLocalizedString(@"MySQL Error", @"mysql error message")];
+						[alert setInformativeText:[mySQLConnection getLastErrorMessage]];
+						[alert setAlertStyle:NSWarningAlertStyle];
+						int choice = [alert runModal];
+						switch (choice){
+							case NSAlertFirstButtonReturn:
+								suppressErrorSheet = YES;
+							case NSAlertSecondButtonReturn:
+								break;
+							default:
+								if(i < queryCount-1) // output that message only if it was not the last one
+									[errors appendString:NSLocalizedString(@"Execution stopped!\n", @"execution stopped message")];
+								i = queryCount; // break for loop; for safety reasons stop the execution of the following queries
+						}
 					}
-
 				} else {
 					[errors appendString:[NSString stringWithFormat:NSLocalizedString(@"[ERROR in query %d] %@\n", @"error text when multiple custom query failed"),
 											i+1,
-											[mySQLConnection getLastErrorMessage]]];
+											errorString]];
 				}
 			} else {
-				[errors setString:[mySQLConnection getLastErrorMessage]];
+				[errors setString:errorString];
 			}
 		} else {
 			// Check if table/db list needs an update
@@ -557,6 +577,9 @@
 			if(!databaseWasChanged && [query isMatchedByRegex:@"(?i)\\b(use|drop\\s+database|drop\\s+schema)\\b\\s+."])
 				databaseWasChanged = YES;
 		}
+
+		// If the query was cancelled, end all queries.
+		if ([mySQLConnection queryCancelled]) break;
 	}
 
 	// Reload table list if at least one query began with drop, alter, rename, or create
@@ -605,7 +628,7 @@
 	}
 
 	// Error checking
-	if ( [errors length] && !queryIsTableSorter ) {
+	if ( [mySQLConnection queryCancelled] || ([errors length] && !queryIsTableSorter)) {
 		// set the error text
 		[errorText setStringValue:errors];
 		// select the line x of the first error if error message contains "at line x"
@@ -656,7 +679,18 @@
 	}
 	
 	// Set up the status string
-	if ( totalQueriesRun > 1 ) {
+	if ( [mySQLConnection queryCancelled] ) {
+		if (totalQueriesRun > 1) {
+			[affectedRowsText setStringValue:[NSString stringWithFormat:NSLocalizedString(@"Cancelled in query %i, after %@", @"text showing multiple queries were cancelled"),
+                                              totalQueriesRun,
+                                              [NSString stringForTimeInterval:executionTime]
+                                              ]];
+		} else {
+			[affectedRowsText setStringValue:[NSString stringWithFormat:NSLocalizedString(@"Cancelled after %@", @"text showing a query was cancelled"),
+                                              [NSString stringForTimeInterval:executionTime]
+                                              ]];
+		}
+	} else if ( totalQueriesRun > 1 ) {
 		if (totalAffectedRows==1) {
 			[affectedRowsText setStringValue:[NSString stringWithFormat:NSLocalizedString(@"1 row affected in total, by %i queries taking %@", @"text showing one row has been affected by multiple queries"),
                                               totalQueriesRun,
diff --git a/Source/TableContent.h b/Source/TableContent.h
index 889a79e5..d0cc0ec3 100644
--- a/Source/TableContent.h
+++ b/Source/TableContent.h
@@ -65,7 +65,7 @@
 	NSString *compareType;
 	NSNumber *sortCol;
 	BOOL isEditingRow, isEditingNewRow, isSavingRow, isDesc, setLimit;
-	BOOL isFiltered, isLimited, maxNumRowsIsEstimate;
+	BOOL isFiltered, isLimited, isInterruptedLoad, maxNumRowsIsEstimate;
 	NSUserDefaults *prefs;
 	int currentlyEditingRow, maxNumRows;
 
diff --git a/Source/TableContent.m b/Source/TableContent.m
index 552fbd41..d5c9e8d1 100644
--- a/Source/TableContent.m
+++ b/Source/TableContent.m
@@ -86,6 +86,7 @@
 
 		isFiltered = NO;
 		isLimited = NO;
+		isInterruptedLoad = NO;
 		
 		prefs = [NSUserDefaults standardUserDefaults];
 		
@@ -532,7 +533,10 @@
 		rowsToLoad = rowsToLoad - ([limitRowsField intValue]-1);
 		if (rowsToLoad > [prefs integerForKey:SPLimitResultsValue]) rowsToLoad = [prefs integerForKey:SPLimitResultsValue];
 	}
-	
+
+	// If within a task, allow this query to be cancelled
+	[tableDocumentInstance enableTaskCancellationWithTitle:NSLocalizedString(@"Stop", @"Stop load") callbackObject:nil callbackFunction:NULL];
+
 	// Perform and process the query
 	[tableContentView performSelectorOnMainThread:@selector(noteNumberOfRowsChanged) withObject:nil waitUntilDone:YES]; 
 	[self setUsedQuery:queryString];
@@ -541,7 +545,7 @@
 	[streamingResult release];
 
 	// If the result is empty, and a limit is active, reset the limit
-	if ([prefs boolForKey:SPLimitResults] && queryStringBeforeLimit && !tableRowsCount) {
+	if ([prefs boolForKey:SPLimitResults] && queryStringBeforeLimit && !tableRowsCount && ![mySQLConnection queryCancelled]) {
 		[limitRowsField setStringValue:@"1"];
 		queryString = [NSMutableString stringWithFormat:@"%@ LIMIT 0,%d", queryStringBeforeLimit, [prefs integerForKey:SPLimitResultsValue]];
 		[self setUsedQuery:queryString];
@@ -549,6 +553,14 @@
 		[self processResultIntoDataStorage:streamingResult approximateRowCount:[prefs integerForKey:SPLimitResultsValue]];
 		[streamingResult release];
 	}
+	
+	if ([mySQLConnection queryCancelled] || ![[mySQLConnection getLastErrorMessage] isEqualToString:@""])
+		isInterruptedLoad = YES;
+	else 
+		isInterruptedLoad = NO;
+
+	// End cancellation ability
+	[tableDocumentInstance disableTaskCancellation];
 
 	if ([prefs boolForKey:SPLimitResults]
 		&& ([limitRowsField intValue] > 1
@@ -821,8 +833,15 @@
 	NSString *rowString;
 	NSMutableString *countString = [NSMutableString string];
 
+	// If the result is partial due to an error or query cancellation, show a very basic count
+	if (isInterruptedLoad) {
+		if (tableRowsCount == 1)
+			[countString appendFormat:NSLocalizedString(@"%d row in partial load", @"text showing a single row a partially loaded result"), tableRowsCount];
+		else
+			[countString appendFormat:NSLocalizedString(@"%d rows in partial load", @"text showing how many rows are in a partially loaded result"), tableRowsCount];
+		
 	// If no filter or limit is active, show just the count of rows in the table
-	if (!isFiltered && !isLimited) {
+	} else if (!isFiltered && !isLimited) {
 		if (tableRowsCount == 1)
 			[countString appendFormat:NSLocalizedString(@"%d row in table", @"text showing a single row in the result"), tableRowsCount];
 		else
@@ -1128,7 +1147,7 @@
 	
 	NSString *contextInfo = @"removerow";
 	
-	if (([tableContentView numberOfSelectedRows] == [tableContentView numberOfRows]) && !isFiltered && !isLimited) {
+	if (([tableContentView numberOfSelectedRows] == [tableContentView numberOfRows]) && !isFiltered && !isLimited && !isInterruptedLoad) {
 		
 		contextInfo = @"removeallrows";
 		
@@ -2288,7 +2307,7 @@
 	BOOL checkStatusCount = NO;
 
 	// For unfiltered and non-limited tables, use the result count - and update the status count
-	if (!isLimited && !isFiltered) {
+	if (!isLimited && !isFiltered && !isInterruptedLoad) {
 		maxNumRows = tableRowsCount;
 		maxNumRowsIsEstimate = NO;
 		[tableDataInstance setStatusValue:[NSString stringWithFormat:@"%d", maxNumRows] forKey:@"Rows"];
diff --git a/Source/TableDocument.h b/Source/TableDocument.h
index f9e96730..db4b48ae 100644
--- a/Source/TableDocument.h
+++ b/Source/TableDocument.h
@@ -138,6 +138,9 @@
 	float taskProgressValueDisplayInterval;
 	NSTimer *taskDrawTimer;
 	NSViewAnimation *taskFadeAnimator;
+	BOOL taskCanBeCancelled;
+	id taskCancellationCallbackObject;
+	SEL taskCancellationCallbackSelector;
 
 	NSToolbar *mainToolbar;
 	NSToolbarItem *chooseDatabaseToolbarItem;
@@ -186,6 +189,9 @@
 - (void) setTaskPercentage:(float)taskPercentage;
 - (void) setTaskProgressToIndeterminate;
 - (void) endTask;
+- (void) enableTaskCancellationWithTitle:(NSString *)buttonTitle callbackObject:(id)callbackObject callbackFunction:(SEL)callbackFunction;
+- (void) disableTaskCancellation;
+- (IBAction) cancelTask:(id)sender;
 - (BOOL) isWorking;
 - (void) setDatabaseListIsSelectable:(BOOL)isSelectable;
 - (void) centerTaskWindow;
diff --git a/Source/TableDocument.m b/Source/TableDocument.m
index fa07e143..78df5e16 100644
--- a/Source/TableDocument.m
+++ b/Source/TableDocument.m
@@ -103,6 +103,9 @@
 		taskProgressValueDisplayInterval = 1;
 		taskDrawTimer = nil;
 		taskFadeAnimator = nil;
+		taskCanBeCancelled = NO;
+		taskCancellationCallbackObject = nil;
+		taskCancellationCallbackSelector = NULL;
 
 		keyChainID = nil;
 	}
@@ -223,15 +226,17 @@
 		NSLog(@"Progress indicator layer could not be loaded; progress display will not function correctly.");
 	}
 
-	// Set up the progress indicator child window and later - add to main window, change indicator color and size
+	// Set up the progress indicator child window and layer - add to main window, change indicator color and size
+	[taskProgressIndicator setForeColor:[NSColor whiteColor]];
 	taskProgressWindow = [[NSWindow alloc] initWithContentRect:[taskProgressLayer bounds] styleMask:NSBorderlessWindowMask backing:NSBackingStoreBuffered defer:NO];
 	[taskProgressWindow setOpaque:NO];
-	[taskProgressWindow setIgnoresMouseEvents:YES];
 	[taskProgressWindow setBackgroundColor:[NSColor clearColor]];
 	[taskProgressWindow setAlphaValue:0.0];
-	[[taskProgressWindow contentView] addSubview:taskProgressLayer];
+	[taskProgressWindow orderWindow:NSWindowAbove relativeTo:[tableWindow windowNumber]];
 	[tableWindow addChildWindow:taskProgressWindow ordered:NSWindowAbove];
-	[taskProgressIndicator setForeColor:[NSColor whiteColor]];
+	[taskProgressWindow release];
+	[taskProgressWindow setContentView:taskProgressLayer];
+	[self centerTaskWindow];
 }
 
 /**
@@ -1258,7 +1263,7 @@
 		[historyControl setEnabled:NO];
 		databaseListIsSelectable = NO;
 		[[NSNotificationCenter defaultCenter] postNotificationName:SPDocumentTaskStartNotification object:self];
-
+		
 		// Schedule appearance of the task window in the near future
 		taskDrawTimer = [[NSTimer scheduledTimerWithTimeInterval:0.25 target:self selector:@selector(showTaskProgressWindow:) userInfo:nil repeats:NO] retain];
 	}
@@ -1333,6 +1338,9 @@
 	// Decrement the working level
 	_isWorkingLevel--;
 
+	// Ensure cancellation interface is reset
+	[self disableTaskCancellation];
+
 	// If all tasks have ended, re-enable the interface
 	if (!_isWorkingLevel) {
 
@@ -1358,6 +1366,57 @@
 }
 
 /**
+ * Allow a task to be cancelled, enabling the button with a supplied title
+ * and optionally supplying a callback object and function.
+ */
+- (void) enableTaskCancellationWithTitle:(NSString *)buttonTitle callbackObject:(id)callbackObject callbackFunction:(SEL)callbackFunction
+{
+
+	// If no task is active, return
+	if (!_isWorkingLevel) return;
+
+	if (callbackObject && callbackFunction) {
+		taskCancellationCallbackObject = callbackObject;
+		taskCancellationCallbackSelector = callbackFunction;
+	}
+	taskCanBeCancelled = YES;
+
+	[taskCancelButton setTitle:buttonTitle];
+	[taskCancelButton setEnabled:YES];
+	[taskCancelButton setHidden:NO];
+}
+
+/**
+ * Disable task cancellation.  Called automatically at the end of a task.
+ */
+- (void) disableTaskCancellation
+{
+
+	// If no task is active, return
+	if (!_isWorkingLevel) return;
+	
+	taskCanBeCancelled = NO;
+	taskCancellationCallbackObject = nil;
+	taskCancellationCallbackSelector = NULL;
+	[taskCancelButton setHidden:YES];
+}
+
+/**
+ * Action sent by the cancel button when it's active.
+ */
+- (IBAction) cancelTask:(id)sender
+{
+	if (!taskCanBeCancelled) return;
+
+	[taskCancelButton setEnabled:NO];
+	[mySQLConnection cancelCurrentQuery];
+
+	if (taskCancellationCallbackObject && taskCancellationCallbackSelector) {
+		[taskCancellationCallbackObject performSelector:taskCancellationCallbackSelector];
+	}
+}
+
+/**
  * Returns whether the document is busy performing a task - allows UI or actions
  * to be restricted as appropriate.
  */
@@ -3553,7 +3612,6 @@
 	if (spfSession) [spfSession release];
 	if (spfDocData) [spfDocData release];
 	if (keyChainID) [keyChainID release];
-	if (taskProgressWindow) [taskProgressWindow release];
 	
 	[super dealloc];
 }
diff --git a/Source/TableSource.m b/Source/TableSource.m
index 932d9cdd..6228e6f1 100644
--- a/Source/TableSource.m
+++ b/Source/TableSource.m
@@ -1033,8 +1033,20 @@ returns a dictionary containing enum/set field names as key and possible values
 }
 
 - (id)tableView:(NSTableView *)aTableView objectValueForTableColumn:(NSTableColumn *)aTableColumn row:(int)rowIndex
-{	
-	return [(aTableView == tableSourceView) ? [tableFields objectAtIndex:rowIndex] : [indexes objectAtIndex:rowIndex] objectForKey:[aTableColumn identifier]];
+{
+	NSDictionary *theRow;
+
+	if (aTableView == tableSourceView) {
+		
+		// Return a placeholder if the table is reloading
+		if (rowIndex >= [tableFields count]) return @"...";
+
+		theRow = [tableFields objectAtIndex:rowIndex];
+	} else {
+		theRow = [indexes objectAtIndex:rowIndex];
+	}
+
+	return [theRow objectForKey:[aTableColumn identifier]];
 }
 
 - (void)tableView:(NSTableView *)aTableView setObjectValue:(id)anObject forTableColumn:(NSTableColumn *)aTableColumn row:(int)rowIndex