aaudio: refactor references to shared FIFO

Reduce passing of raw pointers.
Use shared_ptrs and unique_ptrs.
Simplify memory management.

Refactor FifoBuffer into two subclasses so that
the internal memory management is simpler.

Bug: 151650670
Test: OboeTester "TEST OUTPUT"
Test: disable EXCLUSIVE mode
Test: OboeTester "ECHO INPUT TO OUTPUT"
Test: disable INPUT EXCLUSIVE mode
Change-Id: I10981767f8719f3cc3525df211285c53219a7979
diff --git a/services/oboeservice/SharedRingBuffer.h b/services/oboeservice/SharedRingBuffer.h
index 79169bc..c3a9bb7 100644
--- a/services/oboeservice/SharedRingBuffer.h
+++ b/services/oboeservice/SharedRingBuffer.h
@@ -18,8 +18,9 @@
 #define AAUDIO_SHARED_RINGBUFFER_H
 
 #include <android-base/unique_fd.h>
-#include <stdint.h>
 #include <cutils/ashmem.h>
+#include <stdint.h>
+#include <string>
 #include <sys/mman.h>
 
 #include "fifo/FifoBuffer.h"
@@ -47,15 +48,25 @@
     void fillParcelable(AudioEndpointParcelable &endpointParcelable,
                         RingBufferParcelable &ringBufferParcelable);
 
-    android::FifoBuffer * getFifoBuffer() {
+    /**
+     * Return available frames as a fraction of the capacity.
+     * @return fullness between 0.0 and 1.0
+     */
+    double getFractionalFullness() const;
+
+    // dump: write# read# available
+    std::string dump() const;
+
+    std::shared_ptr<android::FifoBuffer> getFifoBuffer() {
         return mFifoBuffer;
     }
 
 private:
     android::base::unique_fd  mFileDescriptor;
-    android::FifoBuffer      *mFifoBuffer = nullptr;
-    uint8_t                  *mSharedMemory = nullptr;
+    std::shared_ptr<android::FifoBufferIndirect>  mFifoBuffer;
+    uint8_t                  *mSharedMemory = nullptr; // mmap
     int32_t                   mSharedMemorySizeInBytes = 0;
+    // size of memory used for data vs counters
     int32_t                   mDataMemorySizeInBytes = 0;
     android::fifo_frames_t    mCapacityInFrames = 0;
 };