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Commit 8f83a355 authored by Mark Salyzyn's avatar Mark Salyzyn
Browse files

logd: correct duplicate message state machine 

Inspection turned up that for the case of three identical messages,
the result would be a stutter of the first message only.  Added
comments to describe the state machine, incoming variables, outcoming
and false condition outputs, for proper maintenance in the future.

Test: gTest liblog-benchmarks BM_log_maximum* and manually check
      for correct midstream chatty messages,
Bug: 33535908
Change-Id: I852260d18a484e6207b80063159f1a74eaa83b55
parent 152b003b

logd/LogBuffer.cpp

+70 −6
Original line number Diff line number Diff line
@@ -206,6 +206,68 @@ int LogBuffer::log(log_id_t log_id, log_time realtime, 
    if (currentLast) {

        LogBufferElement *dropped = droppedElements[log_id];

        unsigned short count = dropped ? dropped->getDropped() : 0;

        //

        // State Init

        //     incoming:

        //         dropped = NULL

        //         currentLast = NULL;

        //         elem = incoming message

        //     outgoing:

        //         dropped = NULL -> State 0

        //         currentLast = copy of elem

        //         log elem

        // State 0

        //     incoming:

        //         count = 0

        //         dropped = NULL

        //         currentLast = copy of last message

        //         elem = incoming message

        //     outgoing: (if *elem == *currentLast)

        //         dropped = copy of first identical message -> State 1

        //         currentLast = reference to elem

        //     break: (if *elem != *currentLast)

        //         dropped = NULL -> State 0

        //         delete copy of last message (incoming currentLast)

        //         currentLast = copy of elem

        //         log elem

        // State 1

        //     incoming:

        //         count = 0

        //         dropped = copy of first identical message

        //         currentLast = reference to last held-back incoming

        //                       message

        //         elem = incoming message

        //     outgoing: (if *elem == *currentLast)

        //         delete copy of first identical message (dropped)

        //         dropped = reference to last held-back incoming

        //                   message set to chatty count of 1 -> State 2

        //         currentLast = reference to elem

        //     break:

        //         delete dropped

        //         dropped = NULL -> State 0

        //         log reference to last held-back (currentLast)

        //         currentLast = copy of elem

        //         log elem

        // State 2

        //     incoming:

        //         count = chatty count

        //         dropped = chatty message holding count

        //         currentLast = reference to last held-back incoming

        //                       message.

        //         dropped = chatty message holding count

        //         elem = incoming message

        //     outgoing: (if *elem == *currentLast)

        //         delete chatty message holding count

        //         dropped = reference to last held-back incoming

        //                   message, set to chatty count + 1

        //         currentLast = reference to elem

        //     break:

        //         log dropped (chatty message)

        //         dropped = NULL -> State 0

        //         log reference to last held-back (currentLast)

        //         currentLast = copy of elem

        //         log elem

        //

        if (identical(elem, currentLast)) {

            if (dropped) {

                if (count == USHRT_MAX) {
@@ -226,13 +288,15 @@ int LogBuffer::log(log_id_t log_id, log_time realtime, 
            pthread_mutex_unlock(&mLogElementsLock);

            return len;

        }

        if (dropped) {

            log(dropped);

            droppedElements[log_id] = NULL;

        if (dropped) { // State 1 or 2

            if (count) { // State 2

               log(dropped); // report chatty

            } else { // State 1

               delete dropped;

            }

        if (count) {

            log(currentLast);

        } else {

            droppedElements[log_id] = NULL;

            log(currentLast); // report last message in the series

        } else { // State 0

            delete currentLast;

        }

    }