Advanced Android Heap Analysis

public class HProfExceptionHandler implements Thread.UncaughtExceptionHandler {

    private final Context appContext;
    private final Thread.UncaughtExceptionHandler parentExceptionHandler;

    public HProfExceptionHandler(Context context, Thread.UncaughtExceptionHandler parentHandler) {
        // If this exception handler is installed into a VM with an existing exception handler,
        // we want to be sure that we call through to the already-registered handler so that any
        // other crash reporters still work.
        this.appContext = context.getApplicationContext();
        this.parentExceptionHandler = parentHandler;
    }

    @Override
    public void uncaughtException(Thread t, Throwable e) {
        // Check if this error is an out of memory error
        if (OutOfMemoryError.class.isAssignableFrom(e.getClass())) {
            // If it is, then try and dump it to the filesystem
            dumpHeapToFile();
        }

        // Propagate the error to the parent exception handler, if present
        if (this.parentExceptionHandler != null) {
            parentExceptionHandler.uncaughtException(t, e);
        }
    }

    private void dumpHeapToFile() {
        // First, ensure our dump location exists
        File dumpDir = getDumpDirectory();
        if (!dumpDir.exists()) {
            if (!dumpDir.mkdirs()) {
                Log.w(TAG, "Failed to create dump directory " + dumpDir.getAbsolutePath());
                return;
            }
        }

        // Create a new filename for this dump
        File dumpPath = new File(dumpDir, String.format(Locale.US, "%s.hprof", UUID.randomUUID().toString()));

        // Attempt to write out the heap
        try {
            Debug.dumpHprofData(dumpPath.getAbsolutePath());
            Log.d(TAG, "Successfully wrote heap dump " + dumpPath.getName());
        } catch (IOException e1) {
            Log.e(TAG, e1.getMessage(), e1);
        }
    }
}

% Now, let's open up that heap dump
{ok, Parser} = hprof_parser:parse_file('my_heap.dump').

% Since we're going in blind here, the first thing I'd check is the largest
% objects we might expect to allocate - bitmaps.
% So first, let's get all the instances in this dump that are of the type
% android.graphics.Bitmap
{ok, BmpRef} = hprof_parser:get_instances_for_class(Parser, <<"android.graphics.Bitmap">>).
{ok, Bitmaps} = hprof:await_acc(BmpRef, [], fun(A, I) -> [I|A] end).

% Now, each bitmap stores its actual image data in a byte array, called
% 'mBuffer', so let's read the mBuffer value for each of these bitmaps
% To make this easy, first read in the record definitions
rr("include/records.hrl").
BufferVars = [maps:get(<<"mBuffer">>, Vars) || #hprof_heap_instance{instance_values=Vars} <- Bitmaps].

% Now we have a list of #hprof_instance_field{}, each of which has the ID of
% the relevant native array, so let's fetch those
ByteArrayIds = [V || #hprof_instance_field{value=V} <- BufferVars].

% Now that we know which byte arrays are bitmaps, let's fetch all the
% primitive arrays and filter them down.
ByteArrayIdSet = sets:from_list(ByteArrayIds).
{ok, ByteArrayRef} = hprof_parser:get_primitive_arrays_of_type(Parser, byte).
{ok, BitmapByteArrays} = hprof:await_acc(
    ByteArrayRef,
    [],
    fun(Acc, Array) ->
        case sets:is_element(Array#hprof_primitive_array.object_id, ByteArrayIdSet) of
            true -> [Array|Acc];
            false -> Acc
        end
    end
).

% At this point, we can do some quick maths to see how much of the heap is
% taken up by bitmap data:
ImageSizesBytes = [byte_size(E) || #hprof_primitive_array{elements=E} <- BitmapByteArrays].
TotalImageSize = lists:foldl(fun(A, B) -> A + B end, 0, ImageSizesBytes).

% Odds are that if we see the images, as the developer we'll know what they're
% from. So let's convert all those bitmaps we fetched earlier to PNGs and save
% them somewhere
lists:foreach(
    fun(Bitmap) ->
        case hprof_bitmap:make_png(Parser, Bitmap) of
            {ok, PngData} ->
                file:write_file(
                    integer_to_list(Bitmap#hprof_heap_instance.object_id) ++ ".png",
                    PngData
                );
            _ -> ok
        end
    end,
    Bitmaps
).

ReferenceMap = ets:new(objects, [bag]).
{ok, InstancesRef} = hprof_parser:get_all_instances(Parser).
ok = hprof_await(
    InstancesRef,
    fun(I=#hprof_heap_instance{object_id=Oid, instance_values=Values}) ->
        % For each instance, we want to check if it has any fields that point
        % to other objects. If it does, for each of these fields we store a
        % tuple of {referent object id, this object id}
        % Note that you may also want to exclude certain instance types, such
        % as WeakReference and FinalizerReference, from analysis
        maps:fold(
            fun(_VariableName, #hprof_instance_field{type=T, value=V}, _Acc) ->
                % If this variable is of type object, and isn't null, then
                % track this reference in the ETS table
                case (T =:= object) and (V =/= 0) of
                    true -> ets:insert(ReferenceMap, {V, Oid});
                    false -> ok
                end
            end,
            ok,
            Values
        )
    end
).

StaticallyReferenced = ets:new(statics, [bag]).
{ok, ClassDumpRef} = hprof_parser:get_class_dumps(Parser).
ok = hprof:await(
    ClassDumpRef,
    fun(#hprof_class_dump{class_id=ClsId, static_fields=Statics}) ->
        lists:foreach(
            fun(#hprof_static_field{type=T, data=D}) ->
                case (T =:= ?HPROF_BASIC_OBJECT) and (D =/= 0) of
                    true ->
                        % So if this class has a static reference to this
                        % object D, then we both update the reference map from
                        % before and tag that object as statically referenced
                        % by inserting it into the second table.
                        ets:insert(ReferenceMap, {D, ClsId}),
                        ets:insert(StaticallyReferenced, {D});
                    false -> ok
                end
            end,
            Statics
        )
    end
).

detect_reference_chain(ReferenceMappings, StaticallyHeld, TargetId, PreviousRoots, RefChain) ->
    % At each step of our search, we want to first find all of the objects that
    % reference our 'target' object.
    % We can look this up using the first table we created:
    Referers = [Referrer || {_, Referrer} <- ets:lookup(ReferenceMappings, TargetId)],

    % Now, we want to iterate over all of the referers:
    % - If the referer is already in the PreviousRoots set, then we've already
    % traversed it while trying to detect a reference chain - this means there's
    % a circular reference, so don't recurse in this case or we'd be here forever
    % - If the referer is not statically referenced, then recurse with the referer
    % as the new target, and the current target added to the previous root set
    % and RefChain, which is the reference stack so far.
    % - If the referer *is* statically referenced, then we've found a potential
    % memory leak! In the full implementation, this would be passed to the
    % pretty-printer worker to resolve the names and numbers of the objects involved.
    lists:foreach(
        fun(Referer) ->
            % This is where we check if we've already seen it (reference loop)
            case sets:is_element(Referer, PreviousRoots) of
                true -> ok; % Return back up the stack
                false ->
                    % Check if this object has a static root
                    case ets_contains(StaticallyHeld, Referer) of
                        false ->
                            % Recurse
                            detect_reference_chain(
                                ReferenceMappings, StaticallyHeld,
                                Referer, % Takes the place of target
                                % Add the target here to prevent any future loops
                                sets:add_element(TargetId, PreviousRoots),
                                [TargetId|RefChain]
                            );
                        true ->
                            % The RefChain stack contains the list of object
                            % pointers that got us here, so add the referer to
                            % it and fob it off on the pretty printer
                            spawn(?MODULE, pretty_print, [[Referer|RefChain]])
                    end
            end
        end,
        Referers
    ).