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-rw-r--r--Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Ping & KeepAlive.m21
1 files changed, 19 insertions, 2 deletions
diff --git a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Ping & KeepAlive.m b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Ping & KeepAlive.m
index d46b5552..8728bf3f 100644
--- a/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Ping & KeepAlive.m
+++ b/Frameworks/SPMySQLFramework/Source/SPMySQLConnection Categories/Ping & KeepAlive.m
@@ -85,9 +85,9 @@
if(keepAliveThread) {
NSLog(@"warning: overwriting existing keepAliveThread: %@, results may be unpredictable!",keepAliveThread);
}
+ keepAliveThread = [NSThread currentThread];
}
- keepAliveThread = [NSThread currentThread];
[keepAliveThread setName:[NSString stringWithFormat:@"SPMySQL connection keepalive monitor thread (id=%p)", self]];
// If the maximum number of ping failures has been reached, determine whether to reconnect.
@@ -282,7 +282,24 @@ void _pingThreadCleanup(void *pingDetails)
if (keepAliveThread) {
// Mark the thread as cancelled
- [keepAliveThread cancel];
+ @synchronized(self) {
+ // the synchronized is neccesary here, because we don't retain keepAliveThread.
+ // If it were ommitted, for example this could happen:
+ //
+ // this thread keepalive thread
+ // -------------- -----------------
+ // 1 fetch value of keepAliveThread to register
+ // 2 keepAliveThread = nil
+ // 3 [[NSThread currentThread] release]
+ // 4 objc_msgSend() <-- invalid memory accessed
+ //
+ // With synchronized we are guaranteed to either message nil or block the keepAliveThread from exiting
+ // (and thus releasing the NSThread object) until this call finishes.
+ //
+ // We can omit it in the other 2 cases, since keepAliveThread is already volatile and we are only
+ // checking for NULL, not dereferencing it.
+ [keepAliveThread cancel];
+ }
// Wait inside a time limit of ten seconds for it to exit
uint64_t threadCancelStartTime_t = mach_absolute_time();