Final feature work on the SPMySQL branch before merging:

 - Add a ping keepalive managing object to prevent retain cycles from the NSTimer
 - Add -[SPMySQLConnection copy] support
 - Refactor Hans-Jörg Bibiko's database structure retrieval, moving it out of the MySQL framework and building it around a copy of the connection.  This reduces the amount of connections-over-time used by Sequel Pro to two constant connections (addressing Issue #1097) and improves robustness.
 - Use the database structure retrieval connection for faster query cancellation without an extra connection required, if possible

1 files changed, 647 insertions, 0 deletions

diff --git a/Source/SPDatabaseStructure.m b/Source/SPDatabaseStructure.m
new file mode 100644
index 00000000..35637093
--- /dev/null
+++ b/Source/SPDatabaseStructure.m
@@ -0,0 +1,647 @@
+//
+//  $Id$
+//
+//  SPDatabaseStructure.m
+//  sequel-pro
+//
+//  Created by Hans-Jörg Bibiko on March 25, 2010
+//  Copyright (c) 2010 Hans-Jörg Bibiko. All rights reserved.
+//
+//  This program is free software; you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation; either version 2 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program; if not, write to the Free Software
+//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+//
+//  More info at <http://code.google.com/p/sequel-pro/>
+
+#import "SPDatabaseStructure.h"
+#import "SPDatabaseDocument.h"
+#import "SPConnectionDelegate.h"
+#import "SPTablesList.h"
+#import "RegexKitLite.h"
+#import "SPMySQL.h"
+#import <pthread.h>
+
+@interface SPDatabaseStructure (Private_API)
+
+- (void)_updateGlobalVariablesWithStructure:(NSDictionary *)aStructure keys:(NSArray *)theKeys;
+- (void)_cloneConnectionFromConnection:(SPMySQLConnection *)aConnection;
+- (BOOL)_ensureConnection;
+
+@end
+
+#pragma mark -
+
+@implementation SPDatabaseStructure
+
+#pragma mark -
+#pragma mark Setup and teardown
+
+/**
+ * Prevent SPDatabaseStructure from being init'd normally.
+ */
+- (id)init
+{
+	[NSException raise:NSInternalInconsistencyException format:@"SPDatabaseStructures should not be init'd directly; use initWithDelegate: instead."];
+	return nil;
+}
+
+/**
+ * Standard init method, constructing the SPDatabaseStructure around a SPMySQL
+ * connection pointer and a delegate.
+ */
+- (id)initWithDelegate:(SPDatabaseDocument *)theDelegate
+{
+	if ((self = [super init])) {
+
+		// Keep a weak reference to the delegate
+		delegate = theDelegate;
+
+		// Start with no root connection
+		mySQLConnection = nil;
+
+		// Set up empty structure and keys storage
+		structureRetrievalThreads = [[NSMutableArray alloc] init];
+		structure = [[NSMutableDictionary alloc] initWithCapacity:1];
+		allKeysofDbStructure = [[NSMutableArray alloc] initWithCapacity:20];
+
+		// Set up the connection, thread management and data locks
+		pthread_mutex_init(&threadManagementLock, NULL);
+		pthread_mutex_init(&dataLock, NULL);
+		pthread_mutex_init(&connectionCheckLock, NULL);
+	}
+
+	return self;
+}
+
+/**
+ * Rather than supplying a connection to SPDatabaseStructure, the class instead
+ * will set up its own connection to allow background querying.  The supplied
+ * connection will be used to look up details for the clone process.
+ */
+- (void)setConnectionToClone:(SPMySQLConnection *)aConnection
+{
+
+	// Perform the task in a background thread to avoid blocking the UI
+	[NSThread detachNewThreadSelector:@selector(_cloneConnectionFromConnection:) toTarget:self withObject:aConnection];
+}
+
+- (void)dealloc
+{
+
+	// Ensure all the retrieval threads have ended
+	pthread_mutex_lock(&threadManagementLock);
+	if ([structureRetrievalThreads count]) {
+		for (NSThread *eachThread in structureRetrievalThreads) {
+			[eachThread cancel];
+		}
+		while ([structureRetrievalThreads count]) {
+			pthread_mutex_unlock(&threadManagementLock);
+			usleep(100000);
+			pthread_mutex_lock(&threadManagementLock);
+		}
+	}
+	pthread_mutex_unlock(&threadManagementLock);
+	[structureRetrievalThreads release];
+
+	pthread_mutex_destroy(&threadManagementLock);
+	pthread_mutex_destroy(&dataLock);
+	pthread_mutex_destroy(&connectionCheckLock);
+	delegate = nil;
+
+	if (mySQLConnection) [mySQLConnection release], mySQLConnection = nil;
+	if (structure) [structure release], structure = nil;
+	if (allKeysofDbStructure) [allKeysofDbStructure release], allKeysofDbStructure = nil;
+
+	[super dealloc];
+}
+
+#pragma mark -
+#pragma mark Information
+
+- (SPMySQLConnection *)connection
+{
+	return mySQLConnection;
+}
+
+#pragma mark -
+#pragma mark Structure retrieval from the server
+
+/**
+ * Updates the dict containing the structure of all available databases (mainly for completion/navigator)
+ * executed on the helper connection.
+ * Should always be executed on a background thread.
+ */
+- (void)queryDbStructureWithUserInfo:(NSDictionary*)userInfo
+{
+	NSAutoreleasePool *queryPool = [[NSAutoreleasePool alloc] init];
+	BOOL structureWasUpdated = NO;
+
+	// Lock the management lock
+	pthread_mutex_lock(&threadManagementLock);
+
+	// If 'cancelQuerying' is set try to interrupt any current querying
+	if (userInfo && [userInfo objectForKey:@"cancelQuerying"]) {
+		for (NSThread *eachThread in structureRetrievalThreads) {
+			[eachThread cancel];
+		}
+	}
+
+	// Add this thread to the group
+	[structureRetrievalThreads addObject:[NSThread currentThread]];
+
+	// Only allow one request to be running against the server at any one time, to prevent
+	// escessive server i/o or slowdown.  Loop until this is the first thread in the array
+	while ([structureRetrievalThreads objectAtIndex:0] != [NSThread currentThread]) {
+		if ([[NSThread currentThread] isCancelled]) {
+			[structureRetrievalThreads removeObject:[NSThread currentThread]];
+			pthread_mutex_unlock(&threadManagementLock);
+			[queryPool release];
+			return;
+		}
+			
+		pthread_mutex_unlock(&threadManagementLock);
+		usleep(1000000);
+		pthread_mutex_lock(&threadManagementLock);
+	}
+	pthread_mutex_unlock(&threadManagementLock);
+
+	// This thread is now first on the stack, and about to process the structure.
+	[[NSNotificationCenter defaultCenter] postNotificationName:@"SPDBStructureIsUpdating" object:delegate];
+
+	NSString *connectionID;
+	if([delegate respondsToSelector:@selector(connectionID)])
+		connectionID = [NSString stringWithString:[delegate connectionID]];
+	else
+		connectionID = @"_";
+
+	// Re-init with already cached data from navigator controller
+	NSMutableDictionary *queriedStructure = [NSMutableDictionary dictionary];
+	NSDictionary *dbstructure = [delegate getDbStructure];
+	if (dbstructure) [queriedStructure setDictionary:[NSMutableDictionary dictionaryWithDictionary:dbstructure]];
+
+	NSMutableArray *queriedStructureKeys = [NSMutableArray array];
+	NSArray *dbStructureKeys = [delegate allSchemaKeys];
+	if (dbStructureKeys) [queriedStructureKeys setArray:dbStructureKeys];
+
+	// Retrieve all the databases known of by the delegate
+	NSMutableArray *connectionDatabases = [NSMutableArray array];
+	[connectionDatabases addObjectsFromArray:[delegate allSystemDatabaseNames]];
+	[connectionDatabases addObjectsFromArray:[delegate allDatabaseNames]];
+
+	// Add all known databases coming from connection if they aren't parsed yet
+	for (id db in connectionDatabases) {
+		NSString *dbid = [NSString stringWithFormat:@"%@%@%@", connectionID, SPUniqueSchemaDelimiter, db];
+		if(![queriedStructure objectForKey:dbid]) {
+			structureWasUpdated = YES;
+			[queriedStructure setObject:db forKey:dbid];
+			[queriedStructureKeys addObject:dbid];
+		}
+	}
+
+	// Check the existing databases in the 'structure' and 'allKeysOfDbStructure' stores,
+	// and remove any that are no longer found in the connectionDatabases list (indicating deletion).
+	// Iterate through extracted keys to avoid <NSCFDictionary> mutation while being enumerated.
+	NSArray *keys = [queriedStructure allKeys];
+	for(id key in keys) {
+		NSString *db = [[key componentsSeparatedByString:SPUniqueSchemaDelimiter] objectAtIndex:1];
+		if(![connectionDatabases containsObject:db]) {
+			structureWasUpdated = YES;
+			[queriedStructure removeObjectForKey:key];
+			NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT SELF BEGINSWITH %@", [NSString stringWithFormat:@"%@%@", key, SPUniqueSchemaDelimiter]];
+			[queriedStructureKeys filterUsingPredicate:predicate];
+			[queriedStructureKeys removeObject:key];
+		}
+	}
+
+	NSString *currentDatabase = nil;
+	if ([delegate respondsToSelector:@selector(database)])
+		currentDatabase = [delegate database];
+
+	// Determine whether the database details need to be queried.
+	BOOL shouldQueryStructure = YES;
+	NSString *db_id = nil;
+
+	// If no database is selected, no need to check further
+	if(!currentDatabase || (currentDatabase && ![currentDatabase length])) {
+		shouldQueryStructure = NO;
+
+	// Otherwise, build up the schema key for the database to be retrieved.
+	} else {
+		db_id = [NSString stringWithFormat:@"%@%@%@", connectionID, SPUniqueSchemaDelimiter, currentDatabase];
+
+		// Check to see if a cache already exists for the database.
+		if ([queriedStructure objectForKey:db_id] && [[queriedStructure objectForKey:db_id] isKindOfClass:[NSDictionary class]]) {
+
+			// The cache is available. If the `mysql` or `information_schema` databases are being queried,
+			// never requery as their structure will never change.
+			// 5.5.3+ also has performance_schema meta database
+			if ([currentDatabase isEqualToString:@"mysql"] || [currentDatabase isEqualToString:@"information_schema"] || [currentDatabase isEqualToString:@"performance_schema"]) {
+				shouldQueryStructure = NO;
+
+			// Otherwise, if the forceUpdate flag wasn't supplied or evaluates to false, also don't update.
+			} else if (userInfo == nil || ![userInfo objectForKey:@"forceUpdate"] || ![[userInfo objectForKey:@"forceUpdate"] boolValue]) {
+				shouldQueryStructure = NO;
+			}
+		}
+	}
+
+	// If it has been determined that no new structure needs to be retrieved, clean up and return.
+	if (!shouldQueryStructure) {
+
+		// Update the global variables
+		[self _updateGlobalVariablesWithStructure:queriedStructure keys:queriedStructureKeys];
+
+		if (structureWasUpdated) {
+			[[NSNotificationCenter defaultCenter] postNotificationName:@"SPDBStructureWasUpdated" object:delegate];
+		}
+
+		pthread_mutex_lock(&threadManagementLock);
+		[structureRetrievalThreads removeObject:[NSThread currentThread]];
+		pthread_mutex_unlock(&threadManagementLock);
+
+		[queryPool release];
+		return;
+	}
+
+	// Retrieve the tables and views for this database from SPTablesList
+	NSMutableArray *tablesAndViews = [NSMutableArray array];
+	for (id aTable in [[delegate valueForKeyPath:@"tablesListInstance"] allTableNames]) {
+		NSDictionary *aTableDict = [NSDictionary dictionaryWithObjectsAndKeys:
+										aTable, @"name",
+										@"0", @"type",
+										nil];
+		[tablesAndViews addObject:aTableDict];
+	}
+	for (id aView in [[delegate valueForKeyPath:@"tablesListInstance"] allViewNames]) {
+		NSDictionary *aViewDict = [NSDictionary dictionaryWithObjectsAndKeys:
+										aView, @"name",
+										@"1", @"type",
+										nil];
+		[tablesAndViews addObject:aViewDict];
+	}
+
+	// Do not parse more than 2000 tables/views per db
+	if ([tablesAndViews count] > 2000) {
+		NSLog(@"%lu items in database %@. Only 2000 items can be parsed. Stopped parsing.", (unsigned long)[tablesAndViews count], currentDatabase);
+
+		pthread_mutex_lock(&threadManagementLock);
+		[structureRetrievalThreads removeObject:[NSThread currentThread]];
+		pthread_mutex_unlock(&threadManagementLock);
+
+		[queryPool release];
+		return;
+	}
+
+	// For future usage - currently unused
+	// If the affected item name and type - for example, table type and table name - were supplied, extract it.
+	NSString *affectedItem = nil;
+	NSInteger affectedItemType = -1;
+	if(userInfo && [userInfo objectForKey:@"affectedItem"]) {
+		affectedItem = [userInfo objectForKey:@"affectedItem"];
+		if([userInfo objectForKey:@"affectedItemType"])
+			affectedItemType = [[userInfo objectForKey:@"affectedItemType"] intValue];
+		else
+			affectedItem = nil;
+	}
+
+	// Delete all stored data for the database to be updated, leaving the structure key
+	[queriedStructure removeObjectForKey:db_id];
+	NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT SELF BEGINSWITH %@", [NSString stringWithFormat:@"%@%@", db_id, SPUniqueSchemaDelimiter]];
+	[queriedStructureKeys filterUsingPredicate:predicate];
+
+	// Set up the database as an empty mutable dictionary ready for tables, and store a reference
+	[queriedStructure setObject:[NSMutableDictionary dictionary] forKey:db_id];
+	NSMutableDictionary *databaseStructure = [queriedStructure objectForKey:db_id];
+
+	NSString *currentDatabaseEscaped = [currentDatabase stringByReplacingOccurrencesOfString:@"`" withString:@"``"];
+
+	NSUInteger uniqueCounter = 0; // used to make field data unique
+	SPMySQLResult *theResult;
+
+	// Loop through the known tables and views, retrieving details for each
+	for (NSDictionary *aTableDict in tablesAndViews) {
+
+		// Extract the name
+		NSString *aTableName = [aTableDict objectForKey:@"name"];
+
+		if(!aTableName) continue;
+		if(![aTableName isKindOfClass:[NSString class]]) continue;
+		if(![aTableName length]) continue;
+
+		BOOL cancelThread = NO;
+
+		// If the thread has been cancelled, abort without saving
+		if ([[NSThread currentThread] isCancelled]) cancelThread = YES;
+
+		// Check connection state before use
+		while (!cancelThread && pthread_mutex_trylock(&connectionCheckLock)) {
+			usleep(100000);
+			if ([[NSThread currentThread] isCancelled]) {
+				cancelThread = YES;
+				break;
+			}
+		}
+
+		if (cancelThread) {
+			pthread_mutex_trylock(&connectionCheckLock);
+			pthread_mutex_unlock(&connectionCheckLock);
+			pthread_mutex_lock(&threadManagementLock);
+			[structureRetrievalThreads removeObject:[NSThread currentThread]];
+			pthread_mutex_unlock(&threadManagementLock);
+
+			[queryPool release];
+			return;
+		}
+
+		if (![self _ensureConnection]) {
+			pthread_mutex_unlock(&connectionCheckLock);
+			pthread_mutex_lock(&threadManagementLock);
+			[structureRetrievalThreads removeObject:[NSThread currentThread]];
+			pthread_mutex_unlock(&threadManagementLock);
+
+			[queryPool release];
+			return;
+		}
+		pthread_mutex_unlock(&connectionCheckLock);
+
+		// Retrieve the column details
+		theResult = [mySQLConnection queryString:[NSString stringWithFormat:@"SHOW FULL COLUMNS FROM `%@` FROM `%@`", [aTableName stringByReplacingOccurrencesOfString:@"`" withString:@"``"], currentDatabaseEscaped]];
+		if (!theResult) {
+			continue;
+		}
+		[theResult setDefaultRowReturnType:SPMySQLResultRowAsArray];
+		[theResult setReturnDataAsStrings:YES];
+
+		// Add a structure key for this table
+		NSString *table_id = [NSString stringWithFormat:@"%@%@%@", db_id, SPUniqueSchemaDelimiter, aTableName];
+		[queriedStructureKeys addObject:table_id];
+
+		// Add a mutable dictionary to the structure and store a reference
+		[databaseStructure setObject:[NSMutableDictionary dictionary] forKey:table_id];
+		NSMutableDictionary *tableStructure = [databaseStructure objectForKey:table_id];
+
+		// Loop through the fields, extracting details for each
+		for (NSArray *row in theResult) {
+			NSString *field = [row objectAtIndex:0];
+			NSString *type = [row objectAtIndex:1];
+			NSString *type_display = [type stringByReplacingOccurrencesOfRegex:@"\\(.*?,.*?\\)" withString:@"(…)"];
+			NSString *collation = [row objectAtIndex:2];
+			NSString *isnull = [row objectAtIndex:3];
+			NSString *key = [row objectAtIndex:4];
+			NSString *def = [row objectAtIndex:5];
+			NSString *extra = [row objectAtIndex:6];
+			NSString *priv = [row objectAtIndex:7];
+			NSString *comment;
+			if ([row count] > 8) {
+				comment = [row objectAtIndex:8];
+			} else {
+				comment = @"";
+			}
+
+			NSString *charset = @"";
+			if (![collation isNSNull]) {
+				NSArray *a = [collation componentsSeparatedByString:@"_"];
+				charset = [a objectAtIndex:0];
+			}
+
+			// Add a structure key for this field
+			NSString *field_id = [NSString stringWithFormat:@"%@%@%@", table_id, SPUniqueSchemaDelimiter, field];
+			[queriedStructureKeys addObject:field_id];
+
+			[tableStructure setObject:[NSArray arrayWithObjects:type, def, isnull, charset, collation, key, extra, priv, comment, type_display, [NSNumber numberWithUnsignedLongLong:uniqueCounter], nil] forKey:field_id];
+			[tableStructure setObject:[aTableDict objectForKey:@"type"] forKey:@"  struct_type  "];
+			uniqueCounter++;
+		}
+
+		// Allow a tiny pause between iterations
+		usleep(10);
+	}
+
+	// If the MySQL version is higher than 5, also retrieve function/procedure details via the information_schema table
+	if ([mySQLConnection serverMajorVersion] >= 5) {
+		BOOL cancelThread = NO;
+
+		if ([[NSThread currentThread] isCancelled]) cancelThread = YES;
+
+		// Check connection state before use
+		while (!cancelThread && pthread_mutex_trylock(&connectionCheckLock)) {
+			usleep(100000);
+			if ([[NSThread currentThread] isCancelled]) {
+				cancelThread = YES;
+				break;
+			}
+		}
+
+		if (!cancelThread) {
+			if (![self _ensureConnection]) cancelThread = YES;
+			pthread_mutex_unlock(&connectionCheckLock);
+		};
+
+		// Return if the thread is due to be cancelled
+		if (cancelThread) {
+			pthread_mutex_trylock(&connectionCheckLock);
+			pthread_mutex_unlock(&connectionCheckLock);
+			pthread_mutex_lock(&threadManagementLock);
+			[structureRetrievalThreads removeObject:[NSThread currentThread]];
+			pthread_mutex_unlock(&threadManagementLock);
+
+			[queryPool release];
+			return;
+		}
+
+		// Retrieve the column details
+		theResult = [mySQLConnection queryString:[NSString stringWithFormat:@"SELECT * FROM `information_schema`.`ROUTINES` WHERE `information_schema`.`ROUTINES`.`ROUTINE_SCHEMA` = '%@'", [currentDatabase stringByReplacingOccurrencesOfString:@"'" withString:@"\\'"]]];
+		[theResult setDefaultRowReturnType:SPMySQLResultRowAsArray];
+
+		// Loop through the rows and extract the function details
+		for (NSArray *row in theResult) {
+			NSString *fname = [row objectAtIndex:0];
+			NSString *type = ([[row objectAtIndex:4] isEqualToString:@"FUNCTION"]) ? @"3" : @"2";
+			NSString *dtd = [row objectAtIndex:5];
+			NSString *det = [row objectAtIndex:11];
+			NSString *dataaccess = [row objectAtIndex:12];
+			NSString *security_type = [row objectAtIndex:14];
+			NSString *definer = [row objectAtIndex:19];
+
+			// Generate "table" and "field" names and add to structure key store
+			NSString *table_id = [NSString stringWithFormat:@"%@%@%@", db_id, SPUniqueSchemaDelimiter, fname];
+			NSString *field_id = [NSString stringWithFormat:@"%@%@%@", table_id, SPUniqueSchemaDelimiter, fname];
+			[queriedStructureKeys addObject:table_id];
+			[queriedStructureKeys addObject:field_id];
+
+			// Ensure that a dictionary exists for this "table" name
+			if(![[queriedStructure valueForKey:db_id] valueForKey:table_id])
+				[[queriedStructure valueForKey:db_id] setObject:[NSMutableDictionary dictionary] forKey:table_id];
+
+			// Add the "field" details
+			[[[queriedStructure valueForKey:db_id] valueForKey:table_id] setObject:
+				[NSArray arrayWithObjects:dtd, dataaccess, det, security_type, definer, [NSNumber numberWithUnsignedLongLong:uniqueCounter], nil] forKey:field_id];
+			[[[queriedStructure valueForKey:db_id] valueForKey:table_id] setObject:type forKey:@"  struct_type  "];
+			uniqueCounter++;
+		}
+	}
+
+	// Update the global variables
+	[self _updateGlobalVariablesWithStructure:queriedStructure keys:queriedStructureKeys];
+
+	// Notify that the structure querying has been performed
+	[[NSNotificationCenter defaultCenter] postNotificationName:@"SPDBStructureWasUpdated" object:delegate];
+
+	// Remove this thread from the processing stack
+	pthread_mutex_lock(&threadManagementLock);
+	[structureRetrievalThreads removeObject:[NSThread currentThread]];
+	pthread_mutex_unlock(&threadManagementLock);
+	
+	[queryPool release];
+}
+
+- (BOOL)isQueryingDatabaseStructure
+{
+	pthread_mutex_lock(&threadManagementLock);
+	BOOL returnValue = ([structureRetrievalThreads count] > 0);
+	pthread_mutex_unlock(&threadManagementLock);
+
+	return returnValue;
+}
+
+#pragma mark -
+#pragma mark Structure information
+
+/**
+ * Returns a dict containing the structure of all available databases
+ */
+- (NSDictionary *)structure
+{
+	pthread_mutex_lock(&dataLock);
+	NSDictionary *d = [NSDictionary dictionaryWithDictionary:structure];
+	pthread_mutex_unlock(&dataLock);
+
+	return d;
+}
+
+/**
+ * Returns all keys of the db structure
+ */
+- (NSArray *)allStructureKeys
+{
+	pthread_mutex_lock(&dataLock);
+	NSArray *r = [NSArray arrayWithArray:allKeysofDbStructure];
+	pthread_mutex_unlock(&dataLock);
+
+	return r;
+}
+
+#pragma mark -
+#pragma mark SPMySQLConnection delegate methods
+
+/**
+ * Forward keychain password requests to the database object.
+ */
+- (NSString *)keychainPasswordForConnection:(id)connection
+{
+	return [delegate keychainPasswordForConnection:connection];
+}
+
+@end
+
+#pragma mark -
+#pragma mark Private API
+
+@implementation SPDatabaseStructure (Private_API)
+
+/**
+ * Update the global variables, using the data lock for multithreading safety.
+ */
+- (void)_updateGlobalVariablesWithStructure:(NSDictionary *)aStructure keys:(NSArray *)theKeys
+{
+
+	NSString *connectionID = [delegate connectionID];
+
+	// Return if the delegate indicates disconnection
+	if([connectionID length] < 2) return;
+
+	pthread_mutex_lock(&dataLock);
+
+	[structure setObject:aStructure forKey:connectionID];
+	[allKeysofDbStructure setArray:theKeys];
+
+	pthread_mutex_unlock(&dataLock);
+}
+
+/**
+ * Set up a new connection in a background thread
+ */
+- (void)_cloneConnectionFromConnection:(SPMySQLConnection *)aConnection
+{
+	NSAutoreleasePool *connectionPool = [[NSAutoreleasePool alloc] init];
+
+	pthread_mutex_lock(&connectionCheckLock);
+
+	// If a connection is already set, ensure it's idle before releasing it
+	if (mySQLConnection) {
+		pthread_mutex_lock(&threadManagementLock);
+		if ([structureRetrievalThreads count]) {
+			for (NSThread *eachThread in structureRetrievalThreads) {
+				[eachThread cancel];
+			}
+			while ([structureRetrievalThreads count]) {
+				pthread_mutex_unlock(&threadManagementLock);
+				usleep(100000);
+				pthread_mutex_lock(&threadManagementLock);
+			}
+		}
+		pthread_mutex_unlock(&threadManagementLock);
+
+		[mySQLConnection release];
+		mySQLConnection = nil;
+	}
+
+	// Create a copy of the supplied connection
+	mySQLConnection = [aConnection copy];
+
+	// Set the delegate to this instance
+	[mySQLConnection setDelegate:self];
+
+	// Trigger the connection
+	[self _ensureConnection];
+
+	pthread_mutex_unlock(&connectionCheckLock);
+
+	[connectionPool drain];
+}
+
+- (BOOL)_ensureConnection
+{
+	if (!mySQLConnection) return NO;
+
+	// Check the connection state
+	if ([mySQLConnection isConnected] && [mySQLConnection checkConnection]) return YES;
+
+	// The connection isn't connected.  Check the parent connection state, and if that
+	// also isn't connected, return.
+	if (![[delegate getConnection] isConnected]) return NO;
+
+	// Copy the local port from the parent connection, in case a proxy has changed
+	[mySQLConnection setPort:[[delegate getConnection] port]];
+
+	// Attempt a connection
+	if (![mySQLConnection connect]) return NO;
+
+	// Ensure the encoding is set to UTF8
+	[mySQLConnection setEncoding:@"utf8"];
+
+	// Return success
+	return YES;
+}
+
+@end
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