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
diff --git a/include/media/SingleStateQueue.h b/include/media/SingleStateQueue.h
index e2e58c5..d423962 100644
--- a/include/media/SingleStateQueue.h
+++ b/include/media/SingleStateQueue.h
@@ -32,6 +32,12 @@
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 @@
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 @@
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 @@
}
}
+ // (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