diff options
Diffstat (limited to 'LOCKS')
| -rw-r--r-- | LOCKS | 81 |
1 files changed, 0 insertions, 81 deletions
@@ -1,81 +0,0 @@ -Some notes about locking in dnbd3 - -The order of aquiring multiple locks is -VERY IMPORTANT, as you'll produce a possible deadlock -if you do it in the wrong order. -Take very good care of locking order if you have lots -of functions that call each other. You might lose -track of what's going on. ;) - -===== FUSE ===== -mutexInit -newAltLock -altLock -connection.sendMutex -requests.lock - -===== SERVER ===== -This is a list of used locks, in the order they -have to be aquired if you must hold multiple locks: -remoteCloneLock | reloadLock -_clients_lock -_clients[].lock -integrityQueueLock -_images_lock -_images[].lock -pendingLockConsume -pendingLockProduce -uplink.queueLock -altServersLock -client.sendMutex -client.statsLock -statisticsSentLock -statisticsReceivedLock -uplink.rttLock -uplink.sendMutex - -If you need to lock multiple clients/images/... at once, -lock the client with the lowest array index first. - -If the program logic would require to aquire the -locks in a different order, you HAVE TO rework the -code. -For example, if you hold the lock for client 10 and -you need to look up some other client. You MUST NOT -simply fetch the _clients_lock now and then iterate -over the clients until you find the one you need, -as it violates the above order to first lock on the -clients array and then the clients lock. -Instead, you need to release client 10's lock, -then lock on _clients_lock and iterate over the -clients. Now you check if you either encounter -the client you originally held the lock on, or -the client you are looking for. You immediately -lock on those two. You can then release the -_clients_lock and work with both clients. -pseudo code: - -// client10 is assumed to be a pointer to -// a client, which happens to be at index 10 -lock (client10->lock); -.... -// oh, i need another client -unlock(client10->lock); -lock(_clients_lock); -client clientA = NULL, clientB = NULL; -for (i = 0; i < _num_clients; ++i) { - if (client[i] == client10) { - clientA = client[i]; - lock(clientA.lock); - } else if (client[i].something == <whatever>) { - clientB = client[i]; - lock(clientB.lock); - } -} -unlock(_clients_lock); -if (clientA && clientB) { // Make sure we actually found both! - // DO something important with both clients -} -if (clientA) unlock(clientA.lock); -if (clientB) unlock(clientB.lock); - |