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authorMax <post@wickenrode.com>2016-02-12 01:16:45 +0100
committerMax <post@wickenrode.com>2016-02-12 01:16:45 +0100
commit4341c2a1d270f7a6ede47616ddf79135bcd37cfd (patch)
treed9bdb052369815e196c7daec7f68940ae2f889e5
parente168cbf3a71d244bb32fbe3904da7d47d2b668db (diff)
downloadsequelpro-release-1.1.1-rc1.tar.gz
sequelpro-release-1.1.1-rc1.tar.bz2
sequelpro-release-1.1.1-rc1.zip
Fix for #2353 ("Attempted to connect a connection that is not disconnected")release-1.1.1-rc1
Backport of 3aadea1be33212ca50e7faffcd0620ea976f9d59
-rw-r--r--Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Querying & Preparation.m6
-rw-r--r--Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Server Info.m3
-rw-r--r--Frameworks/SPMySQLFramework/Source/SPMySQLConnection.m13
-rw-r--r--Source/SPDatabaseStructure.h1
-rw-r--r--Source/SPDatabaseStructure.m374
5 files changed, 207 insertions, 190 deletions
diff --git a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Querying & Preparation.m b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Querying & Preparation.m
index 48f4fc1e..1a8628c1 100644
--- a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Querying & Preparation.m
+++ b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Querying & Preparation.m
@@ -58,6 +58,9 @@
* Take a string and escapes any special character for safe use within a query; correctly
* escapes any characters within the string using the current connection encoding.
* Allows control over whether to also wrap the string in single quotes.
+ *
+ * WARNING: This method may return nil if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
*/
- (NSString *)escapeString:(NSString *)theString includingQuotes:(BOOL)includeQuotes
{
@@ -221,6 +224,9 @@
* the connection encoding.
* The result type desired can be specified, supporting either standard or streaming
* result sets.
+ *
+ * WARNING: This method may return nil if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
*/
- (id)queryString:(NSString *)theQueryString usingEncoding:(NSStringEncoding)theEncoding withResultType:(SPMySQLResultType)theReturnType
{
diff --git a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Server Info.m b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Server Info.m
index c9bf0bfd..74d40c6a 100644
--- a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Server Info.m
+++ b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Server Info.m
@@ -124,6 +124,9 @@
* the resulting process list defaults to the short form; run a manual SHOW FULL PROCESSLIST
* to retrieve tasks in non-truncated form.
* Returns nil on error.
+ *
+ * WARNING: This method may return nil if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
*/
- (SPMySQLResult *)listProcesses
{
diff --git a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection.m b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection.m
index 3b60e9ef..2acc0d4a 100644
--- a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection.m
+++ b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection.m
@@ -263,6 +263,9 @@ const char *SPMySQLSSLPermissibleCiphers = "DHE-RSA-AES256-SHA:AES256-SHA:DHE-RS
* Error checks extensively - if this method fails, it will ask how to proceed and loop depending
* on the status, not returning control until either a connection has been established or
* the connection and document have been closed.
+ *
+ * WARNING: This method may exit early returning NO if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
*/
- (BOOL)reconnect
{
@@ -311,10 +314,12 @@ const char *SPMySQLSSLPermissibleCiphers = "DHE-RSA-AES256-SHA:AES256-SHA:DHE-RS
* Checks whether the connection to the server is still active. This verifies
* the connection using a ping, and if the connection is found to be down attempts
* to quickly restore it, including the previous state.
+ *
+ * WARNING: This method may return NO if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
*/
- (BOOL)checkConnection
{
-
// If the connection is not seen as active, don't proceed
if (state != SPMySQLConnected) return NO;
@@ -607,6 +612,9 @@ const char *SPMySQLSSLPermissibleCiphers = "DHE-RSA-AES256-SHA:AES256-SHA:DHE-RS
* the connection and document have been closed.
* Runs its own autorelease pool as sometimes called in a thread following proxy changes
* (where the return code doesn't matter).
+ *
+ * WARNING: This method may exit early returning NO if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
*/
- (BOOL)_reconnectAllowingRetries:(BOOL)canRetry
{
@@ -996,6 +1004,9 @@ const char *SPMySQLSSLPermissibleCiphers = "DHE-RSA-AES256-SHA:AES256-SHA:DHE-RS
* each of which requires a round trip to the server - but handles most
* network issues.
* Returns whether the connection is considered still valid.
+ *
+ * WARNING: This method may return NO if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
*/
- (BOOL)_checkConnectionIfNecessary
{
diff --git a/Source/SPDatabaseStructure.h b/Source/SPDatabaseStructure.h
index b40dd449..03833ec3 100644
--- a/Source/SPDatabaseStructure.h
+++ b/Source/SPDatabaseStructure.h
@@ -51,7 +51,6 @@
// Setup and teardown
- (id)initWithDelegate:(SPDatabaseDocument *)theDelegate;
- (void)setConnectionToClone:(SPMySQLConnection *)aConnection;
-- (void)destroy:(NSNotification *)notification;
// Information
- (SPMySQLConnection *)connection;
diff --git a/Source/SPDatabaseStructure.m b/Source/SPDatabaseStructure.m
index 2eab3562..934a57fa 100644
--- a/Source/SPDatabaseStructure.m
+++ b/Source/SPDatabaseStructure.m
@@ -39,9 +39,16 @@
@interface SPDatabaseStructure (Private_API)
+- (void)_destroy:(NSNotification *)notification;
+
- (void)_updateGlobalVariablesWithStructure:(NSDictionary *)aStructure keys:(NSArray *)theKeys;
- (void)_cloneConnectionFromConnection:(SPMySQLConnection *)aConnection;
-- (BOOL)_ensureConnection;
+- (BOOL)_ensureConnectionUnsafe; // Use _checkConnection instead, where possible
+
+- (void)_addToListAndWaitForFrontCancellingOtherThreads:(BOOL)killOthers;
+- (void)_removeThreadFromList;
+- (void)_cancelAllThreadsAndWait;
+- (BOOL)_checkConnection;
@end
@@ -81,9 +88,9 @@
allKeysofDbStructure = [[NSMutableArray alloc] initWithCapacity:20];
[[NSNotificationCenter defaultCenter] addObserver:self
- selector:@selector(destroy:)
- name:SPDocumentWillCloseNotification
- object:delegate];
+ selector:@selector(_destroy:)
+ name:SPDocumentWillCloseNotification
+ object:delegate];
// Set up the connection, thread management and data locks
pthread_mutex_init(&threadManagementLock, NULL);
@@ -108,40 +115,16 @@
object:aConnection];
}
-/**
- * Ensure that processing is completed.
- */
-- (void)destroy:(NSNotification *)notification
-{
- delegate = nil;
-
- // 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);
-
-}
-
#pragma mark -
#pragma mark Information
- (SPMySQLConnection *)connection
{
- return mySQLConnection;
+ // this much is needed to make the accessor atomic and thread-safe
+ pthread_mutex_lock(&connectionCheckLock);
+ SPMySQLConnection *c = [mySQLConnection retain];
+ pthread_mutex_unlock(&connectionCheckLock);
+ return [c autorelease];
}
#pragma mark -
@@ -157,43 +140,14 @@
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);
+ [self _addToListAndWaitForFrontCancellingOtherThreads:[[userInfo objectForKey:@"cancelQuerying"] boolValue]];
+ if([[NSThread currentThread] isCancelled]) goto cleanup_thread_and_pool;
// This thread is now first on the stack, and about to process the structure.
+#warning Should not set delegate as the notification source object
[[NSNotificationCenter defaultCenter] postNotificationName:@"SPDBStructureIsUpdating" object:delegate];
- NSString *connectionID;
- if([delegate respondsToSelector:@selector(connectionID)])
- connectionID = [NSString stringWithString:[delegate connectionID]];
- else
- connectionID = @"_";
+ NSString *connectionID = ([delegate respondsToSelector:@selector(connectionID)])? [NSString stringWithString:[delegate connectionID]] : @"_";
// Re-init with already cached data from navigator controller
NSMutableDictionary *queriedStructure = [NSMutableDictionary dictionary];
@@ -234,33 +188,31 @@
}
}
- NSString *currentDatabase = nil;
- if ([delegate respondsToSelector:@selector(database)])
- currentDatabase = [delegate database];
+ NSString *currentDatabase = ([delegate respondsToSelector:@selector(database)])? [delegate database] : nil;
// 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])) {
+ if(![currentDatabase length]) {
shouldQueryStructure = NO;
-
+ }
// Otherwise, build up the schema key for the database to be retrieved.
- } else {
+ 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]]) {
+ if ([[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]) {
+ else if (![[userInfo objectForKey:@"forceUpdate"] boolValue]) {
shouldQueryStructure = NO;
}
}
@@ -268,20 +220,7 @@
// 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;
+ goto update_globals_and_cleanup;
}
// Retrieve the tables and views for this database from SPTablesList
@@ -305,19 +244,14 @@
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;
+ goto cleanup_thread_and_pool;
}
// 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"]) {
+ if([userInfo objectForKey:@"affectedItem"]) {
affectedItem = [userInfo objectForKey:@"affectedItem"];
if([userInfo objectForKey:@"affectedItemType"])
affectedItemType = [[userInfo objectForKey:@"affectedItemType"] intValue];
@@ -334,8 +268,6 @@
[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;
@@ -345,48 +277,16 @@
// 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(![aTableName isKindOfClass:[NSString class]] || ![aTableName length]) continue;
- // 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;
+ // check the connection.
+ // also NO if thread is cancelled which is fine, too (same consequence).
+ if(![self _checkConnection]) {
+ goto cleanup_thread_and_pool;
}
- pthread_mutex_unlock(&connectionCheckLock);
// Retrieve the column details
- theResult = [mySQLConnection queryString:[NSString stringWithFormat:@"SHOW FULL COLUMNS FROM `%@` FROM `%@`", [aTableName stringByReplacingOccurrencesOfString:@"`" withString:@"``"], currentDatabaseEscaped]];
+ theResult = [mySQLConnection queryString:[NSString stringWithFormat:@"SHOW FULL COLUMNS FROM %@ FROM %@", [aTableName backtickQuotedString], [currentDatabase backtickQuotedString]]];
if (!theResult) {
continue;
}
@@ -398,8 +298,8 @@
[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];
+ NSMutableDictionary *tableStructure = [NSMutableDictionary dictionary];
+ [databaseStructure setObject:tableStructure forKey:table_id];
// Loop through the fields, extracting details for each
for (NSArray *row in theResult) {
@@ -437,34 +337,10 @@
// 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;
+ // check the connection.
+ // also NO if thread is cancelled which is fine, too (same consequence).
+ if(![self _checkConnection]) {
+ goto cleanup_thread_and_pool;
}
// Retrieve the column details (only those we need so we don't fetch the whole function body which might be huge)
@@ -499,17 +375,19 @@
}
}
+update_globals_and_cleanup:
// Update the global variables
[self _updateGlobalVariablesWithStructure:queriedStructure keys:queriedStructureKeys];
- // Notify that the structure querying has been performed
- [[NSNotificationCenter defaultCenter] postNotificationName:@"SPDBStructureWasUpdated" object:delegate];
+ if(structureWasUpdated) {
+ // Notify that the structure querying has been performed
+#warning Should not set delegate as the notification source object
+ [[NSNotificationCenter defaultCenter] postNotificationName:@"SPDBStructureWasUpdated" object:delegate];
+ }
+cleanup_thread_and_pool:
// Remove this thread from the processing stack
- pthread_mutex_lock(&threadManagementLock);
- [structureRetrievalThreads removeObject:[NSThread currentThread]];
- pthread_mutex_unlock(&threadManagementLock);
-
+ [self _removeThreadFromList];
[queryPool release];
}
@@ -566,7 +444,7 @@
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
- [self destroy:nil];
+ [self _destroy:nil];
SPClear(structureRetrievalThreads);
pthread_mutex_destroy(&threadManagementLock);
@@ -588,6 +466,17 @@
@implementation SPDatabaseStructure (Private_API)
/**
+ * Ensure that processing is completed.
+ */
+- (void)_destroy:(NSNotification *)notification
+{
+ delegate = nil;
+
+ // Ensure all the retrieval threads have ended
+ [self _cancelAllThreadsAndWait];
+}
+
+/**
* Update the global variables, using the data lock for multithreading safety.
*/
- (void)_updateGlobalVariablesWithStructure:(NSDictionary *)aStructure keys:(NSArray *)theKeys
@@ -617,20 +506,9 @@
// 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);
+ [self _cancelAllThreadsAndWait];
- SPClear(mySQLConnection);
+ [mySQLConnection autorelease], mySQLConnection = nil; // note: aConnection could be == mySQLConnection
}
// Create a copy of the supplied connection
@@ -640,19 +518,31 @@
[mySQLConnection setDelegate:self];
// Trigger the connection
- [self _ensureConnection];
+ [self _ensureConnectionUnsafe];
pthread_mutex_unlock(&connectionCheckLock);
[connectionPool drain];
}
-- (BOOL)_ensureConnection
+/**
+ * Check if the MySQL connection is still available (reconnecting if possible)
+ *
+ * **Unsafe** means this function holds no lock on connectionCheckLock.
+ * You MUST obtain that lock before calling this method!
+ *
+ * WARNING: This method may return NO if the current thread is cancelled!
+ * You MUST check the isCancelled flag before using the result!
+ */
+- (BOOL)_ensureConnectionUnsafe
{
if (!mySQLConnection || !delegate) return NO;
// Check the connection state
if ([mySQLConnection isConnected] && [mySQLConnection checkConnection]) return YES;
+
+ // the result of checkConnection may be meaningless if the thread was cancelled during execution. (issue #2353)
+ if([[NSThread currentThread] isCancelled]) return NO;
// The connection isn't connected. Check the parent connection state, and if that
// also isn't connected, return.
@@ -671,4 +561,112 @@
return YES;
}
+/**
+ * Wait until either
+ * * there are no other threads of this object doing structure retrievals
+ * * or the current thread was cancelled
+ *
+ * @param killOthers Whether to cancel all other running threads first
+ */
+- (void)_addToListAndWaitForFrontCancellingOtherThreads:(BOOL)killOthers
+{
+ // Lock the management lock
+ pthread_mutex_lock(&threadManagementLock);
+
+ // If 'cancelQuerying' is set try to interrupt any current querying
+ if (killOthers) {
+ 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]) {
+ pthread_mutex_unlock(&threadManagementLock);
+
+ if ([[NSThread currentThread] isCancelled]) return;
+
+ usleep(1000000);
+
+ pthread_mutex_lock(&threadManagementLock);
+ }
+ pthread_mutex_unlock(&threadManagementLock);
+}
+
+/**
+ * Remove the current thread from the list of running threads
+ */
+- (void)_removeThreadFromList
+{
+ pthread_mutex_lock(&threadManagementLock);
+ [structureRetrievalThreads removeObject:[NSThread currentThread]];
+ pthread_mutex_unlock(&threadManagementLock);
+}
+
+/**
+ * Cancel all running threads and wait until they have exited
+ */
+- (void)_cancelAllThreadsAndWait
+{
+ pthread_mutex_lock(&threadManagementLock);
+
+ for (NSThread *eachThread in structureRetrievalThreads) {
+ [eachThread cancel];
+ }
+
+ while ([structureRetrievalThreads count]) {
+ pthread_mutex_unlock(&threadManagementLock);
+ usleep(100000);
+ pthread_mutex_lock(&threadManagementLock);
+ }
+
+ pthread_mutex_unlock(&threadManagementLock);
+}
+
+/**
+ * @return YES if the connection is available
+ * NO if either the connection failed, or this thread was cancelled
+ *
+ * You MUST check the thread's isCancelled flag before doing other stuff on negative return!
+ */
+- (BOOL)_checkConnection
+{
+ while (1) {
+ // we can fail to get the lock for two reasons
+ // 1. another thread is running this code
+ // => a regular pthread_mutex_lock() would be fine, it would succeed once the other thread is done
+ // 2. another thread is running _cloneConnectionFromConnection
+ // => that method will not let go of the lock until all other threads have exited.
+ // Since we are an "other thread", calling pthread_mutex_lock() would result in a deadlock!
+ // That is why we try to get the lock and if that fails check if we are cancelled (indicating the 2. case).
+ if(pthread_mutex_trylock(&connectionCheckLock) == 0 /* ESUCCESS */) {
+ break;
+ }
+
+ // If this thread has been cancelled, abort
+ if([[NSThread currentThread] isCancelled]) {
+ return NO;
+ }
+
+ usleep(100000);
+ }
+ // we now hold the connectionCheckLock!
+
+ BOOL cancelThread = ([[NSThread currentThread] isCancelled]);
+ BOOL connected = NO;
+
+ if (!cancelThread) {
+ // Check connection state before use
+ connected = [self _ensureConnectionUnsafe]; // also does a thread canellation check
+ }
+
+ pthread_mutex_unlock(&connectionCheckLock);
+
+ return connected; // cancelThread → ¬connected
+}
+
@end