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Commit 774acea9 authored by Andy Hung's avatar Andy Hung
Browse files

Add done() to SingleStateQueue 

This allows the SSQ sender to detect whether the SSQ receiver
has completed processing of the last queued item.

Change-Id: I4b962c9aec5f0d34b28b01e29b5af42e3dc9893a
parent 9b82924c

include/media/SingleStateQueue.h

+28 −4
Original line number Diff line number Diff line
@@ -32,6 +32,12 @@ public: 
    class Mutator;

    class Observer;



    enum SSQ_STATUS {

        SSQ_PENDING, /* = 0 */

        SSQ_READ,

        SSQ_DONE,

    };



    struct Shared {

        // needs to be part of a union so don't define constructor or destructor
@@ -71,10 +77,19 @@ private: 
            return sequence;

        }



        // return true if most recent push has been observed

        bool ack() const

        // returns the status of the last state push.  This may be a stale value.

        //

        // SSQ_PENDING, or 0, means it has not been observed

        // SSQ_READ means it has been read

        // SSQ_DONE means it has been acted upon, after Observer::done() is called

        enum SSQ_STATUS ack() const

        {

            return mShared->mAck - mSequence == 0;

            // in the case of SSQ_DONE, prevent any subtle data-races of subsequent reads

            // being performed (out-of-order) before the ack read, should the caller be

            // depending on sequentiality of reads.

            const int32_t ack = android_atomic_acquire_load(&mShared->mAck);

            return ack - mSequence & ~1 ? SSQ_PENDING /* seq differ */ :

                    ack & 1 ? SSQ_DONE : SSQ_READ;

        }



        // return true if a push with specified sequence number or later has been observed
@@ -120,7 +135,7 @@ private: 
                    if (after == before) {

                        value = temp;

                        shared->mAck = before;

                        mSequence = before;

                        mSequence = before; // mSequence is even after poll success

                        return true;

                    }

                    if (++tries >= MAX_TRIES) {
@@ -131,6 +146,15 @@ private: 
            }

        }



        // (optional) used to indicate to the Mutator that the state that has been polled

        // has also been acted upon.

        void done()

        {

            const int32_t ack = mShared->mAck + 1;

            // ensure all previous writes have been performed.

            android_atomic_release_store(ack, &mShared->mAck); // mSequence is odd after "done"

        }



    private:

        int32_t     mSequence;

        int         mSeed;  // for PRNG