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antirez authored
Sending a command like: BLPOP foo foo foo foo 0 Resulted into a crash before this commit since the client ended being inserted in the waiting list for this key multiple times. This resulted into the function handleClientsBlockedOnLists() to fail because we have code like that: if (de) { list *clients = dictGetVal(de); int numclients = listLength(clients); while(numclients--) { listNode *clientnode = listFirst(clients); /* server clients here... */ } } The code to serve clients used to remove the served client from the waiting list, so if a client is blocking multiple times, eventually the call to listFirst() will return NULL or worse will access random memory since the list may no longer exist as it is removed by the function unblockClientWaitingData() if there are no more clients waiting for this list. To avoid making the rest of the implementation more complex, this commit modifies blockForKeys() so that a client will be put just a single time into the waiting list for a given key. Since it is Saturday, I hope this fixes issue #801.
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