diff --git a/packages/DocumentsUI/src/com/android/documentsui/ClipStorage.java b/packages/DocumentsUI/src/com/android/documentsui/ClipStorage.java
index 5102718..3f0427f 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/ClipStorage.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/ClipStorage.java
@@ -16,9 +16,12 @@
 
 package com.android.documentsui;
 
+import android.content.SharedPreferences;
 import android.net.Uri;
 import android.os.AsyncTask;
 import android.support.annotation.VisibleForTesting;
+import android.system.ErrnoException;
+import android.system.Os;
 import android.util.Log;
 
 import java.io.Closeable;
@@ -27,62 +30,157 @@
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.nio.channels.FileLock;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Scanner;
+import java.util.concurrent.TimeUnit;
 
 /**
  * Provides support for storing lists of documents identified by Uri.
  *
- * <li>Access to this object *must* be synchronized externally.
- * <li>All calls to this class are I/O intensive and must be wrapped in an AsyncTask.
+ * This class uses a ring buffer to recycle clip file slots, to mitigate the issue of clip file
+ * deletions.
  */
 public final class ClipStorage {
 
+    public static final int NO_SELECTION_TAG = -1;
+
+    static final String PREF_NAME = "ClipStoragePref";
+
+    @VisibleForTesting
+    static final int NUM_OF_SLOTS = 20;
+
     private static final String TAG = "ClipStorage";
 
+    private static final long STALENESS_THRESHOLD = TimeUnit.DAYS.toMillis(2);
+
+    private static final String NEXT_POS_TAG = "NextPosTag";
+    private static final String PRIMARY_DATA_FILE_NAME = "primary";
+
     private static final byte[] LINE_SEPARATOR = System.lineSeparator().getBytes();
-    public static final long NO_SELECTION_TAG = -1;
 
     private final File mOutDir;
+    private final SharedPreferences mPref;
+
+    private final File[] mSlots = new File[NUM_OF_SLOTS];
+    private int mNextPos;
 
     /**
      * @param outDir see {@link #prepareStorage(File)}.
      */
-    public ClipStorage(File outDir) {
+    public ClipStorage(File outDir, SharedPreferences pref) {
         assert(outDir.isDirectory());
         mOutDir = outDir;
+        mPref = pref;
+
+        mNextPos = mPref.getInt(NEXT_POS_TAG, 0);
     }
 
     /**
-     * Creates a clip tag.
+     * Tries to get the next available clip slot. It's guaranteed to return one. If none of
+     * slots is available, it returns the next slot of the most recently returned slot by this
+     * method.
      *
-     * NOTE: this tag doesn't guarantee perfect uniqueness, but should work well unless user creates
-     * clips more than hundreds of times per second.
+     * <p>This is not a perfect solution, but should be enough for most regular use. There are
+     * several situations this method may not work:
+     * <ul>
+     *     <li>Making {@link #NUM_OF_SLOTS} - 1 times of large drag and drop or moveTo/copyTo/delete
+     *     operations after cutting a primary clip, then the primary clip is overwritten.</li>
+     *     <li>Having more than {@link #NUM_OF_SLOTS} queued jumbo file operations, one or more clip
+     *     file may be overwritten.</li>
+     * </ul>
      */
-    public long createTag() {
-        return System.currentTimeMillis();
+    public synchronized int claimStorageSlot() {
+        int curPos = mNextPos;
+        for (int i = 0; i < NUM_OF_SLOTS; ++i, curPos = (curPos + 1) % NUM_OF_SLOTS) {
+            createSlotFile(curPos);
+
+            if (!mSlots[curPos].exists()) {
+                break;
+            }
+
+            // No file or only primary file exists, we deem it available.
+            if (mSlots[curPos].list().length <= 1) {
+                break;
+            }
+            // This slot doesn't seem available, but still need to check if it's a legacy of
+            // service being killed or a service crash etc. If it's stale, it's available.
+            else if(checkStaleFiles(curPos)) {
+                break;
+            }
+        }
+
+        prepareSlot(curPos);
+
+        mNextPos = (curPos + 1) % NUM_OF_SLOTS;
+        mPref.edit().putInt(NEXT_POS_TAG, mNextPos).commit();
+        return curPos;
+    }
+
+    private boolean checkStaleFiles(int pos) {
+        File slotData = toSlotDataFile(pos);
+
+        // No need to check if the file exists. File.lastModified() returns 0L if the file doesn't
+        // exist.
+        return slotData.lastModified() + STALENESS_THRESHOLD <= System.currentTimeMillis();
+    }
+
+    private void prepareSlot(int pos) {
+        assert(mSlots[pos] != null);
+
+        Files.deleteRecursively(mSlots[pos]);
+        mSlots[pos].mkdir();
+        assert(mSlots[pos].isDirectory());
     }
 
     /**
      * Returns a writer. Callers must close the writer when finished.
      */
-    public Writer createWriter(long tag) throws IOException {
-        File file = toTagFile(tag);
+    private Writer createWriter(int tag) throws IOException {
+        File file = toSlotDataFile(tag);
         return new Writer(file);
     }
 
-    @VisibleForTesting
-    public Reader createReader(long tag) throws IOException {
-        File file = toTagFile(tag);
+    /**
+     * Gets a {@link File} instance given a tag.
+     *
+     * This method creates a symbolic link in the slot folder to the data file as a reference
+     * counting method. When someone is done using this symlink, it's responsible to delete it.
+     * Therefore we can have a neat way to track how many things are still using this slot.
+     */
+    public File getFile(int tag) throws IOException {
+        createSlotFile(tag);
+
+        File primary = toSlotDataFile(tag);
+
+        String linkFileName = Integer.toString(mSlots[tag].list().length);
+        File link = new File(mSlots[tag], linkFileName);
+
+        try {
+            Os.symlink(primary.getAbsolutePath(), link.getAbsolutePath());
+        } catch (ErrnoException e) {
+            e.rethrowAsIOException();
+        }
+        return link;
+    }
+
+    /**
+     * Returns a Reader. Callers must close the reader when finished.
+     */
+    public Reader createReader(File file) throws IOException {
+        assert(file.getParentFile().getParentFile().equals(mOutDir));
         return new Reader(file);
     }
 
-    @VisibleForTesting
-    public void delete(long tag) throws IOException {
-        toTagFile(tag).delete();
+    private File toSlotDataFile(int pos) {
+        assert(mSlots[pos] != null);
+        return new File(mSlots[pos], PRIMARY_DATA_FILE_NAME);
     }
 
-    private File toTagFile(long tag) {
-        return new File(mOutDir, String.valueOf(tag));
+    private void createSlotFile(int pos) {
+        if (mSlots[pos] == null) {
+            mSlots[pos] = new File(mOutDir, Integer.toString(pos));
+        }
     }
 
     /**
@@ -96,27 +194,39 @@
         return clipDir;
     }
 
-    public static boolean hasDocList(long tag) {
-        return tag != NO_SELECTION_TAG;
-    }
-
     private static File getClipDir(File cacheDir) {
         return new File(cacheDir, "clippings");
     }
 
     static final class Reader implements Iterable<Uri>, Closeable {
 
+        /**
+         * FileLock can't be held multiple times in a single JVM, but it's possible to have multiple
+         * readers reading the same clip file. Share the FileLock here so that it can be released
+         * when it's not needed.
+         */
+        private static final Map<String, FileLockEntry> sLocks = new HashMap<>();
+
+        private final String mCanonicalPath;
         private final Scanner mScanner;
-        private final FileLock mLock;
 
         private Reader(File file) throws IOException {
             FileInputStream inStream = new FileInputStream(file);
-
-            // Lock the file here so it won't pass this line until the corresponding writer is done
-            // writing.
-            mLock = inStream.getChannel().lock(0L, Long.MAX_VALUE, true);
-
             mScanner = new Scanner(inStream);
+
+            mCanonicalPath = file.getCanonicalPath(); // Resolve symlink
+            synchronized (sLocks) {
+                if (sLocks.containsKey(mCanonicalPath)) {
+                    // Read lock is already held by someone in this JVM, just increment the ref
+                    // count.
+                    sLocks.get(mCanonicalPath).mCount++;
+                } else {
+                    // No map entry, need to lock the file so it won't pass this line until the
+                    // corresponding writer is done writing.
+                    FileLock lock = inStream.getChannel().lock(0L, Long.MAX_VALUE, true);
+                    sLocks.put(mCanonicalPath, new FileLockEntry(1, lock, mScanner));
+                }
+            }
         }
 
         @Override
@@ -126,12 +236,21 @@
 
         @Override
         public void close() throws IOException {
-            if (mLock != null) {
-                mLock.release();
-            }
+            synchronized (sLocks) {
+                FileLockEntry ref = sLocks.get(mCanonicalPath);
 
-            if (mScanner != null) {
-                mScanner.close();
+                assert(ref.mCount > 0);
+                if (--ref.mCount == 0) {
+                    // If ref count is 0 now, then there is no one who needs to hold the read lock.
+                    // Release the lock, and remove the entry.
+                    ref.mLock.release();
+                    ref.mScanner.close();
+                    sLocks.remove(mCanonicalPath);
+                }
+
+                if (mScanner != ref.mScanner) {
+                    mScanner.close();
+                }
             }
         }
     }
@@ -155,12 +274,28 @@
         }
     }
 
+    private static final class FileLockEntry {
+        private int mCount;
+        private FileLock mLock;
+        // We need to keep this scanner here because if the scanner is closed, the file lock is
+        // closed too.
+        private Scanner mScanner;
+
+        private FileLockEntry(int count, FileLock lock, Scanner scanner) {
+            mCount = count;
+            mLock = lock;
+            mScanner = scanner;
+        }
+    }
+
     private static final class Writer implements Closeable {
 
         private final FileOutputStream mOut;
         private final FileLock mLock;
 
         private Writer(File file) throws IOException {
+            assert(!file.exists());
+
             mOut = new FileOutputStream(file);
 
             // Lock the file here so copy tasks would wait until everything is flushed to disk
@@ -192,9 +327,9 @@
 
         private final ClipStorage mClipStorage;
         private final Iterable<Uri> mUris;
-        private final long mTag;
+        private final int mTag;
 
-        PersistTask(ClipStorage clipStorage, Iterable<Uri> uris, long tag) {
+        PersistTask(ClipStorage clipStorage, Iterable<Uri> uris, int tag) {
             mClipStorage = clipStorage;
             mUris = uris;
             mTag = tag;
@@ -202,7 +337,7 @@
 
         @Override
         protected Void doInBackground(Void... params) {
-            try (ClipStorage.Writer writer = mClipStorage.createWriter(mTag)) {
+            try(Writer writer = mClipStorage.createWriter(mTag)){
                 for (Uri uri: mUris) {
                     assert(uri != null);
                     writer.write(uri);
diff --git a/packages/DocumentsUI/src/com/android/documentsui/DocumentClipper.java b/packages/DocumentsUI/src/com/android/documentsui/DocumentClipper.java
index 72413bd..c95ffd1 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/DocumentClipper.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/DocumentClipper.java
@@ -21,9 +21,7 @@
 import android.content.ClipboardManager;
 import android.content.ContentResolver;
 import android.content.Context;
-import android.content.SharedPreferences;
 import android.net.Uri;
-import android.os.BaseBundle;
 import android.os.PersistableBundle;
 import android.provider.DocumentsContract;
 import android.support.annotation.Nullable;
@@ -48,7 +46,7 @@
  * ClipboardManager wrapper class providing higher level logical
  * support for dealing with Documents.
  */
-public final class DocumentClipper implements ClipboardManager.OnPrimaryClipChangedListener {
+public final class DocumentClipper {
 
     private static final String TAG = "DocumentClipper";
 
@@ -57,34 +55,14 @@
     static final String OP_JUMBO_SELECTION_SIZE = "jumboSelection-size";
     static final String OP_JUMBO_SELECTION_TAG = "jumboSelection-tag";
 
-    // Use shared preference to store last seen primary clip tag, so that we can delete the file
-    // when we realize primary clip has been changed when we're not running.
-    private static final String PREF_NAME = "DocumentClipperPref";
-    private static final String LAST_PRIMARY_CLIP_TAG = "lastPrimaryClipTag";
-
     private final Context mContext;
     private final ClipStorage mClipStorage;
     private final ClipboardManager mClipboard;
 
-    // Here we're tracking the last clipped tag ids so we can delete them later.
-    private long mLastDragClipTag = ClipStorage.NO_SELECTION_TAG;
-    private long mLastUnusedPrimaryClipTag = ClipStorage.NO_SELECTION_TAG;
-
-    private final SharedPreferences mPref;
-
     DocumentClipper(Context context, ClipStorage storage) {
         mContext = context;
         mClipStorage = storage;
         mClipboard = context.getSystemService(ClipboardManager.class);
-
-        mClipboard.addPrimaryClipChangedListener(this);
-
-        // Primary clips may be changed when we're not running, now it's time to clean up the
-        // remnant.
-        mPref = context.getSharedPreferences(PREF_NAME, 0);
-        mLastUnusedPrimaryClipTag =
-                mPref.getLong(LAST_PRIMARY_CLIP_TAG, ClipStorage.NO_SELECTION_TAG);
-        deleteLastUnusedPrimaryClip();
     }
 
     public boolean hasItemsToPaste() {
@@ -112,24 +90,8 @@
     /**
      * Returns {@link ClipData} representing the selection, or null if selection is empty,
      * or cannot be converted.
-     *
-     * This is specialized for drag and drop so that we know which file to delete if nobody accepts
-     * the drop.
      */
-    public @Nullable ClipData getClipDataForDrag(
-            Function<String, Uri> uriBuilder, Selection selection, @OpType int opType) {
-        ClipData data = getClipDataForDocuments(uriBuilder, selection, opType);
-
-        mLastDragClipTag = getTag(data);
-
-        return data;
-    }
-
-    /**
-     * Returns {@link ClipData} representing the selection, or null if selection is empty,
-     * or cannot be converted.
-     */
-    private @Nullable ClipData getClipDataForDocuments(
+    public ClipData getClipDataForDocuments(
         Function<String, Uri> uriBuilder, Selection selection, @OpType int opType) {
 
         assert(selection != null);
@@ -147,7 +109,7 @@
     /**
      * Returns ClipData representing the selection.
      */
-    private @Nullable ClipData createStandardClipData(
+    private ClipData createStandardClipData(
             Function<String, Uri> uriBuilder, Selection selection, @OpType int opType) {
 
         assert(!selection.isEmpty());
@@ -178,7 +140,7 @@
     /**
      * Returns ClipData representing the list of docs
      */
-    private @Nullable ClipData createJumboClipData(
+    private ClipData createJumboClipData(
             Function<String, Uri> uriBuilder, Selection selection, @OpType int opType) {
 
         assert(!selection.isEmpty());
@@ -210,8 +172,8 @@
         bundle.putInt(OP_JUMBO_SELECTION_SIZE, selection.size());
 
         // Creates a clip tag
-        long tag = mClipStorage.createTag();
-        bundle.putLong(OP_JUMBO_SELECTION_TAG, tag);
+        int tag = mClipStorage.claimStorageSlot();
+        bundle.putInt(OP_JUMBO_SELECTION_TAG, tag);
 
         ClipDescription description = new ClipDescription(
                 "", // Currently "label" is not displayed anywhere in the UI.
@@ -232,7 +194,7 @@
                 getClipDataForDocuments(uriBuilder, selection, FileOperationService.OPERATION_COPY);
         assert(data != null);
 
-        setPrimaryClip(data);
+        mClipboard.setPrimaryClip(data);
     }
 
     /**
@@ -250,68 +212,10 @@
         PersistableBundle bundle = data.getDescription().getExtras();
         bundle.putString(SRC_PARENT_KEY, parent.derivedUri.toString());
 
-        setPrimaryClip(data);
-    }
-
-    private void setPrimaryClip(ClipData data) {
-        deleteLastPrimaryClip();
-
-        long tag = getTag(data);
-        setLastUnusedPrimaryClipTag(tag);
-
         mClipboard.setPrimaryClip(data);
     }
 
     /**
-     * Sets this primary tag to both class variable and shared preference.
-     */
-    private void setLastUnusedPrimaryClipTag(long tag) {
-        mLastUnusedPrimaryClipTag = tag;
-        mPref.edit().putLong(LAST_PRIMARY_CLIP_TAG, tag).commit();
-    }
-
-    /**
-     * This is a good chance for us to remove previous clip file for cut/copy because we know a new
-     * primary clip is set.
-     */
-    @Override
-    public void onPrimaryClipChanged() {
-        deleteLastUnusedPrimaryClip();
-    }
-
-    private void deleteLastUnusedPrimaryClip() {
-        ClipData primary = mClipboard.getPrimaryClip();
-        long primaryTag = getTag(primary);
-
-        // onPrimaryClipChanged is also called after we call setPrimaryClip(), so make sure we don't
-        // delete the clip file we just created.
-        if (mLastUnusedPrimaryClipTag != primaryTag) {
-            deleteLastPrimaryClip();
-        }
-    }
-
-    private void deleteLastPrimaryClip() {
-        deleteClip(mLastUnusedPrimaryClipTag);
-        setLastUnusedPrimaryClipTag(ClipStorage.NO_SELECTION_TAG);
-    }
-
-    /**
-     * Deletes the last seen drag clip file.
-     */
-    public void deleteDragClip() {
-        deleteClip(mLastDragClipTag);
-        mLastDragClipTag = ClipStorage.NO_SELECTION_TAG;
-    }
-
-    private void deleteClip(long tag) {
-        try {
-            mClipStorage.delete(tag);
-        } catch (IOException e) {
-            Log.w(TAG, "Error deleting clip file with tag: " + tag, e);
-        }
-    }
-
-    /**
      * Copies documents from clipboard. It's the same as {@link #copyFromClipData} with clipData
      * returned from {@link ClipboardManager#getPrimaryClip()}.
      *
@@ -324,10 +228,6 @@
             DocumentStack docStack,
             FileOperations.Callback callback) {
 
-        // The primary clip has been claimed by a file operation. It's now the operation's duty
-        // to make sure the clip file is deleted after use.
-        setLastUnusedPrimaryClipTag(ClipStorage.NO_SELECTION_TAG);
-
         copyFromClipData(destination, docStack, mClipboard.getPrimaryClip(), callback);
     }
 
@@ -352,33 +252,38 @@
 
         PersistableBundle bundle = clipData.getDescription().getExtras();
         @OpType int opType = getOpType(bundle);
-        UrisSupplier uris = UrisSupplier.create(clipData);
+        try {
+            UrisSupplier uris = UrisSupplier.create(clipData, mContext);
+            if (!canCopy(destination)) {
+                callback.onOperationResult(
+                        FileOperations.Callback.STATUS_REJECTED, opType, 0);
+                return;
+            }
 
-        if (!canCopy(destination)) {
-            callback.onOperationResult(
-                    FileOperations.Callback.STATUS_REJECTED, opType, 0);
+            if (uris.getItemCount() == 0) {
+                callback.onOperationResult(
+                        FileOperations.Callback.STATUS_ACCEPTED, opType, 0);
+                return;
+            }
+
+            DocumentStack dstStack = new DocumentStack(docStack, destination);
+
+            String srcParentString = bundle.getString(SRC_PARENT_KEY);
+            Uri srcParent = srcParentString == null ? null : Uri.parse(srcParentString);
+
+            FileOperation operation = new FileOperation.Builder()
+                    .withOpType(opType)
+                    .withSrcParent(srcParent)
+                    .withDestination(dstStack)
+                    .withSrcs(uris)
+                    .build();
+
+            FileOperations.start(mContext, operation, callback);
+        } catch(IOException e) {
+            Log.e(TAG, "Cannot create uris supplier.", e);
+            callback.onOperationResult(FileOperations.Callback.STATUS_REJECTED, opType, 0);
             return;
         }
-
-        if (uris.getItemCount() == 0) {
-            callback.onOperationResult(
-                    FileOperations.Callback.STATUS_ACCEPTED, opType, 0);
-            return;
-        }
-
-        DocumentStack dstStack = new DocumentStack(docStack, destination);
-
-        String srcParentString = bundle.getString(SRC_PARENT_KEY);
-        Uri srcParent = srcParentString == null ? null : Uri.parse(srcParentString);
-
-        FileOperation operation = new FileOperation.Builder()
-                .withOpType(opType)
-                .withSrcParent(srcParent)
-                .withDestination(dstStack)
-                .withSrcs(uris)
-                .build();
-
-        FileOperations.start(mContext, operation, callback);
     }
 
     /**
@@ -397,28 +302,6 @@
         return true;
     }
 
-    /**
-     * Obtains tag from {@link ClipData}. Returns {@link ClipStorage#NO_SELECTION_TAG}
-     * if it's not a jumbo clip.
-     */
-    private static long getTag(@Nullable ClipData data) {
-        if (data == null) {
-            return ClipStorage.NO_SELECTION_TAG;
-        }
-
-        ClipDescription description = data.getDescription();
-        if (description == null) {
-            return ClipStorage.NO_SELECTION_TAG;
-        }
-
-        BaseBundle bundle = description.getExtras();
-        if (bundle == null) {
-            return ClipStorage.NO_SELECTION_TAG;
-        }
-
-        return bundle.getLong(OP_JUMBO_SELECTION_TAG, ClipStorage.NO_SELECTION_TAG);
-    }
-
     public static @OpType int getOpType(ClipData data) {
         PersistableBundle bundle = data.getDescription().getExtras();
         return getOpType(bundle);
diff --git a/packages/DocumentsUI/src/com/android/documentsui/DocumentsApplication.java b/packages/DocumentsUI/src/com/android/documentsui/DocumentsApplication.java
index 3d3902d..93eb527 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/DocumentsApplication.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/DocumentsApplication.java
@@ -77,7 +77,9 @@
 
         mThumbnailCache = new ThumbnailCache(memoryClassBytes / 4);
 
-        mClipStorage = new ClipStorage(ClipStorage.prepareStorage(getCacheDir()));
+        mClipStorage = new ClipStorage(
+                ClipStorage.prepareStorage(getCacheDir()),
+                getSharedPreferences(ClipStorage.PREF_NAME, 0));
         mClipper = new DocumentClipper(this, mClipStorage);
 
         final IntentFilter packageFilter = new IntentFilter();
diff --git a/packages/DocumentsUI/src/com/android/documentsui/Files.java b/packages/DocumentsUI/src/com/android/documentsui/Files.java
index 38f98be..009fecb4 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/Files.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/Files.java
@@ -26,13 +26,11 @@
     private Files() {}  // no initialization for utility classes.
 
     public static void deleteRecursively(File file) {
-        if (file.exists()) {
-            if (file.isDirectory()) {
-                for (File child : file.listFiles()) {
-                    deleteRecursively(child);
-                }
+        if (file.isDirectory()) {
+            for (File child : file.listFiles()) {
+                deleteRecursively(child);
             }
-            file.delete();
         }
+        file.delete();
     }
 }
diff --git a/packages/DocumentsUI/src/com/android/documentsui/UrisSupplier.java b/packages/DocumentsUI/src/com/android/documentsui/UrisSupplier.java
index c5d30aa..e4a11ef 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/UrisSupplier.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/UrisSupplier.java
@@ -31,6 +31,7 @@
 import com.android.documentsui.dirlist.MultiSelectManager.Selection;
 import com.android.documentsui.services.FileOperation;
 
+import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -54,31 +55,25 @@
      *
      * @param context We need context to obtain {@link ClipStorage}. It can't be sent in a parcel.
      */
-    public Iterable<Uri> getDocs(Context context) throws IOException {
-        return getDocs(DocumentsApplication.getClipStorage(context));
+    public Iterable<Uri> getUris(Context context) throws IOException {
+        return getUris(DocumentsApplication.getClipStorage(context));
     }
 
     @VisibleForTesting
-    abstract Iterable<Uri> getDocs(ClipStorage storage) throws IOException;
+    abstract Iterable<Uri> getUris(ClipStorage storage) throws IOException;
 
-    public void dispose(Context context) {
-        ClipStorage storage = DocumentsApplication.getClipStorage(context);
-        dispose(storage);
-    }
-
-    @VisibleForTesting
-    void dispose(ClipStorage storage) {}
+    public void dispose() {}
 
     @Override
     public int describeContents() {
         return 0;
     }
 
-    public static UrisSupplier create(ClipData clipData) {
+    public static UrisSupplier create(ClipData clipData, Context context) throws IOException {
         UrisSupplier uris;
         PersistableBundle bundle = clipData.getDescription().getExtras();
         if (bundle.containsKey(OP_JUMBO_SELECTION_TAG)) {
-            uris = new JumboUrisSupplier(clipData);
+            uris = new JumboUrisSupplier(clipData, context);
         } else {
             uris = new StandardUrisSupplier(clipData);
         }
@@ -87,7 +82,9 @@
     }
 
     public static UrisSupplier create(
-            Selection selection, Function<String, Uri> uriBuilder, Context context) {
+            Selection selection, Function<String, Uri> uriBuilder, Context context)
+            throws IOException {
+
         ClipStorage storage = DocumentsApplication.getClipStorage(context);
 
         List<Uri> uris = new ArrayList<>(selection.size());
@@ -99,7 +96,7 @@
     }
 
     @VisibleForTesting
-    static UrisSupplier create(List<Uri> uris, ClipStorage storage) {
+    static UrisSupplier create(List<Uri> uris, ClipStorage storage) throws IOException {
         UrisSupplier urisSupplier = (uris.size() > Shared.MAX_DOCS_IN_INTENT)
                 ? new JumboUrisSupplier(uris, storage)
                 : new StandardUrisSupplier(uris);
@@ -110,24 +107,32 @@
     private static class JumboUrisSupplier extends UrisSupplier {
         private static final String TAG = "JumboUrisSupplier";
 
-        private final long mSelectionTag;
+        private final File mFile;
         private final int mSelectionSize;
 
         private final transient AtomicReference<ClipStorage.Reader> mReader =
                 new AtomicReference<>();
 
-        private JumboUrisSupplier(ClipData clipData) {
+        private JumboUrisSupplier(ClipData clipData, Context context) throws IOException {
             PersistableBundle bundle = clipData.getDescription().getExtras();
-            mSelectionTag = bundle.getLong(OP_JUMBO_SELECTION_TAG, ClipStorage.NO_SELECTION_TAG);
-            assert(mSelectionTag != ClipStorage.NO_SELECTION_TAG);
+            final int tag = bundle.getInt(OP_JUMBO_SELECTION_TAG, ClipStorage.NO_SELECTION_TAG);
+            assert(tag != ClipStorage.NO_SELECTION_TAG);
+            mFile = DocumentsApplication.getClipStorage(context).getFile(tag);
+            assert(mFile.exists());
 
             mSelectionSize = bundle.getInt(OP_JUMBO_SELECTION_SIZE);
             assert(mSelectionSize > Shared.MAX_DOCS_IN_INTENT);
         }
 
-        private JumboUrisSupplier(Collection<Uri> uris, ClipStorage storage) {
-            mSelectionTag = storage.createTag();
-            new ClipStorage.PersistTask(storage, uris, mSelectionTag).execute();
+        private JumboUrisSupplier(Collection<Uri> uris, ClipStorage storage) throws IOException {
+            final int tag = storage.claimStorageSlot();
+            new ClipStorage.PersistTask(storage, uris, tag).execute();
+
+            // There is a tiny race condition here. A job may starts to read before persist task
+            // starts to write, but it has to beat an IPC and background task schedule, which is
+            // pretty rare. Creating a symlink doesn't need that file to exist, but we can't assert
+            // on its existence.
+            mFile = storage.getFile(tag);
             mSelectionSize = uris.size();
         }
 
@@ -137,8 +142,8 @@
         }
 
         @Override
-        Iterable<Uri> getDocs(ClipStorage storage) throws IOException {
-            ClipStorage.Reader reader = mReader.getAndSet(storage.createReader(mSelectionTag));
+        Iterable<Uri> getUris(ClipStorage storage) throws IOException {
+            ClipStorage.Reader reader = mReader.getAndSet(storage.createReader(mFile));
             if (reader != null) {
                 reader.close();
                 mReader.get().close();
@@ -149,7 +154,7 @@
         }
 
         @Override
-        void dispose(ClipStorage storage) {
+        public void dispose() {
             try {
                 ClipStorage.Reader reader = mReader.get();
                 if (reader != null) {
@@ -158,18 +163,18 @@
             } catch (IOException e) {
                 Log.w(TAG, "Failed to close the reader.", e);
             }
-            try {
-                storage.delete(mSelectionTag);
-            } catch(IOException e) {
-                Log.w(TAG, "Failed to delete clip with tag: " + mSelectionTag + ".", e);
-            }
+
+            // mFile is a symlink to the actual data file. Delete the symlink here so that we know
+            // there is one fewer referrer that needs the data file. The actual data file will be
+            // cleaned up during file slot rotation. See ClipStorage for more details.
+            mFile.delete();
         }
 
         @Override
         public String toString() {
             StringBuilder builder = new StringBuilder();
             builder.append("JumboUrisSupplier{");
-            builder.append("selectionTag=").append(mSelectionTag);
+            builder.append("file=").append(mFile.getAbsolutePath());
             builder.append(", selectionSize=").append(mSelectionSize);
             builder.append("}");
             return builder.toString();
@@ -177,12 +182,12 @@
 
         @Override
         public void writeToParcel(Parcel dest, int flags) {
-            dest.writeLong(mSelectionTag);
+            dest.writeString(mFile.getAbsolutePath());
             dest.writeInt(mSelectionSize);
         }
 
         private JumboUrisSupplier(Parcel in) {
-            mSelectionTag = in.readLong();
+            mFile = new File(in.readString());
             mSelectionSize = in.readInt();
         }
 
@@ -236,7 +241,7 @@
         }
 
         @Override
-        Iterable<Uri> getDocs(ClipStorage storage) {
+        Iterable<Uri> getUris(ClipStorage storage) {
             return mDocs;
         }
 
diff --git a/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java b/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java
index 21f772e..ce4e993 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java
@@ -99,6 +99,7 @@
 import com.android.documentsui.services.FileOperationService.OpType;
 import com.android.documentsui.services.FileOperations;
 
+import java.io.IOException;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.util.ArrayList;
@@ -409,7 +410,7 @@
         if (resultCode == Activity.RESULT_CANCELED || data == null) {
             // User pressed the back button or otherwise cancelled the destination pick. Don't
             // proceed with the copy.
-            operation.dispose(getContext());
+            operation.dispose();
             return;
         }
 
@@ -494,26 +495,6 @@
         state.dirState.put(mStateKey, container);
     }
 
-    void dragStarted() {
-        // When files are selected for dragging, ActionMode is started. This obscures the breadcrumb
-        // with an ActionBar. In order to make drag and drop to the breadcrumb possible, we first
-        // end ActionMode so the breadcrumb is visible to the user.
-        if (mActionMode != null) {
-            mActionMode.finish();
-        }
-    }
-
-    void dragStopped(boolean result) {
-        if (result) {
-            clearSelection();
-        } else {
-            // When drag starts we might write a new clip file to disk.
-            // No drop event happens, remove clip file here. This may be called multiple times,
-            // but it should be OK because deletion is idempotent and cheap.
-            deleteDragClipFile();
-        }
-    }
-
     public void onDisplayStateChanged() {
         updateDisplayState();
     }
@@ -1005,10 +986,15 @@
                                     Log.w(TAG, "Action mode is null before deleting documents.");
                                 }
 
-                                UrisSupplier srcs = UrisSupplier.create(
-                                        selected,
-                                        mModel::getItemUri,
-                                        getContext());
+                                UrisSupplier srcs;
+                                try {
+                                    srcs = UrisSupplier.create(
+                                            selected,
+                                            mModel::getItemUri,
+                                            getContext());
+                                } catch(IOException e) {
+                                    throw new RuntimeException("Failed to create uri supplier.", e);
+                                }
 
                                 FileOperation operation = new FileOperation.Builder()
                                         .withOpType(FileOperationService.OPERATION_DELETE)
@@ -1041,8 +1027,12 @@
                 getActivity(),
                 DocumentsActivity.class);
 
-        UrisSupplier srcs =
-                UrisSupplier.create(selected, mModel::getItemUri, getContext());
+        UrisSupplier srcs;
+        try {
+            srcs = UrisSupplier.create(selected, mModel::getItemUri, getContext());
+        } catch(IOException e) {
+            throw new RuntimeException("Failed to create uri supplier.", e);
+        }
 
         Uri srcParent = getDisplayState().stack.peek().derivedUri;
         mPendingOperation = new FileOperation.Builder()
@@ -1276,8 +1266,19 @@
         }
     }
 
-    public void clearSelection() {
-        mSelectionManager.clearSelection();
+    void dragStarted() {
+        // When files are selected for dragging, ActionMode is started. This obscures the breadcrumb
+        // with an ActionBar. In order to make drag and drop to the breadcrumb possible, we first
+        // end ActionMode so the breadcrumb is visible to the user.
+        if (mActionMode != null) {
+            mActionMode.finish();
+        }
+    }
+
+    void dragStopped(boolean result) {
+        if (result) {
+            mSelectionManager.clearSelection();
+        }
     }
 
     @Override
@@ -1300,10 +1301,6 @@
         activity.setRootsDrawerOpen(false);
     }
 
-    private void deleteDragClipFile() {
-        mClipper.deleteDragClip();
-    }
-
     boolean handleDropEvent(View v, DragEvent event) {
         BaseActivity activity = (BaseActivity) getActivity();
         activity.setRootsDrawerOpen(false);
@@ -1508,7 +1505,7 @@
                     // the current code layout and framework assumptions don't support
                     // this. So for now, we could end up doing a bunch of i/o on main thread.
                     v.startDragAndDrop(
-                            mClipper.getClipDataForDrag(
+                            mClipper.getClipDataForDocuments(
                                     mModel::getItemUri,
                                     selection,
                                     FileOperationService.OPERATION_COPY),
diff --git a/packages/DocumentsUI/src/com/android/documentsui/services/CopyJob.java b/packages/DocumentsUI/src/com/android/documentsui/services/CopyJob.java
index 54ccc2a..7497a83 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/services/CopyJob.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/services/CopyJob.java
@@ -272,7 +272,7 @@
     private void buildDocumentList() throws ResourceException {
         try {
             final ContentResolver resolver = appContext.getContentResolver();
-            final Iterable<Uri> uris = srcs.getDocs(appContext);
+            final Iterable<Uri> uris = srcs.getUris(appContext);
             for (Uri uri : uris) {
                 DocumentInfo doc = DocumentInfo.fromUri(resolver, uri);
                 if (canCopy(doc, stack.root)) {
diff --git a/packages/DocumentsUI/src/com/android/documentsui/services/DeleteJob.java b/packages/DocumentsUI/src/com/android/documentsui/services/DeleteJob.java
index f6202c5..92440a2 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/services/DeleteJob.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/services/DeleteJob.java
@@ -97,7 +97,7 @@
         try {
             final List<DocumentInfo> srcs = new ArrayList<>(this.srcs.getItemCount());
 
-            final Iterable<Uri> uris = this.srcs.getDocs(appContext);
+            final Iterable<Uri> uris = this.srcs.getUris(appContext);
 
             final ContentResolver resolver = appContext.getContentResolver();
             final DocumentInfo srcParent = DocumentInfo.fromUri(resolver, mSrcParent);
diff --git a/packages/DocumentsUI/src/com/android/documentsui/services/FileOperation.java b/packages/DocumentsUI/src/com/android/documentsui/services/FileOperation.java
index ce63864..c905a35 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/services/FileOperation.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/services/FileOperation.java
@@ -71,8 +71,8 @@
         mDestination = destination;
     }
 
-    public void dispose(Context context) {
-        mSrcs.dispose(context);
+    public void dispose() {
+        mSrcs.dispose();
     }
 
     abstract Job createJob(Context service, Job.Listener listener, String id);
diff --git a/packages/DocumentsUI/src/com/android/documentsui/services/Job.java b/packages/DocumentsUI/src/com/android/documentsui/services/Job.java
index 29e0210..f9f49ca 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/services/Job.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/services/Job.java
@@ -151,7 +151,7 @@
 
             // NOTE: If this details is a JumboClipDetails, and it's still referred in primary clip
             // at this point, user won't be able to paste it to anywhere else because the underlying
-            srcs.dispose(appContext);
+            srcs.dispose();
         }
     }
 
diff --git a/packages/DocumentsUI/tests/src/com/android/documentsui/ClipStorageTest.java b/packages/DocumentsUI/tests/src/com/android/documentsui/ClipStorageTest.java
index 851000b..788a5b3 100644
--- a/packages/DocumentsUI/tests/src/com/android/documentsui/ClipStorageTest.java
+++ b/packages/DocumentsUI/tests/src/com/android/documentsui/ClipStorageTest.java
@@ -16,17 +16,20 @@
 
 package com.android.documentsui;
 
+import static com.android.documentsui.ClipStorage.NUM_OF_SLOTS;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
+import android.content.SharedPreferences;
 import android.net.Uri;
 import android.os.AsyncTask;
+import android.support.test.InstrumentationRegistry;
 import android.support.test.filters.SmallTest;
 import android.support.test.runner.AndroidJUnit4;
 
 import com.android.documentsui.ClipStorage.Reader;
-import com.android.documentsui.dirlist.TestModel;
 import com.android.documentsui.testing.TestScheduledExecutorService;
 
 import org.junit.AfterClass;
@@ -37,13 +40,14 @@
 import org.junit.runner.RunWith;
 
 import java.io.File;
-import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 
 @RunWith(AndroidJUnit4.class)
 @SmallTest
 public class ClipStorageTest {
+    private static final String PREF_NAME = "pref";
     private static final List<Uri> TEST_URIS = createList(
             "content://ham/fancy",
             "content://poodle/monkey/giraffe");
@@ -51,22 +55,22 @@
     @Rule
     public TemporaryFolder folder = new TemporaryFolder();
 
+    private SharedPreferences mPref;
     private TestScheduledExecutorService mExecutor;
-
     private ClipStorage mStorage;
-    private TestModel mModel;
 
-    private long mTag;
+    private int mTag;
 
     @Before
     public void setUp() {
+        mPref = InstrumentationRegistry.getContext().getSharedPreferences(PREF_NAME, 0);
         File clipDir = ClipStorage.prepareStorage(folder.getRoot());
-        mStorage = new ClipStorage(clipDir);
+        mStorage = new ClipStorage(clipDir, mPref);
 
         mExecutor = new TestScheduledExecutorService();
         AsyncTask.setDefaultExecutor(mExecutor);
 
-        mTag = mStorage.createTag();
+        mTag = mStorage.claimStorageSlot();
     }
 
     @AfterClass
@@ -83,7 +87,9 @@
     public void testRead() throws Exception {
         writeAll(mTag, TEST_URIS);
         List<Uri> uris = new ArrayList<>();
-        try(Reader provider = mStorage.createReader(mTag)) {
+
+        File copy = mStorage.getFile(mTag);
+        try(Reader provider = mStorage.createReader(copy)) {
             for (Uri uri : provider) {
                 uris.add(uri);
             }
@@ -92,12 +98,43 @@
     }
 
     @Test
-    public void testDelete() throws Exception {
+    public void testGetTag_NoAvailableSlot() throws Exception {
+        int firstTag = mStorage.claimStorageSlot();
+        writeAll(firstTag, TEST_URIS);
+        mStorage.getFile(firstTag);
+        for (int i = 0; i < NUM_OF_SLOTS - 1; ++i) {
+            int tag = mStorage.claimStorageSlot();
+            writeAll(tag, TEST_URIS);
+            mStorage.getFile(tag);
+        }
+
+        assertEquals(firstTag, mStorage.claimStorageSlot());
+    }
+
+    @Test
+    public void testReadConcurrently() throws Exception {
         writeAll(mTag, TEST_URIS);
-        mStorage.delete(mTag);
-        try {
-            mStorage.createReader(mTag);
-        } catch (IOException expected) {}
+        List<Uri> uris = new ArrayList<>();
+        List<Uri> uris2 = new ArrayList<>();
+
+        File copy = mStorage.getFile(mTag);
+        File copy2 = mStorage.getFile(mTag);
+        try(Reader reader = mStorage.createReader(copy)) {
+            try(Reader reader2 = mStorage.createReader(copy2)){
+                Iterator<Uri> iter = reader.iterator();
+                Iterator<Uri> iter2 = reader2.iterator();
+
+                while (iter.hasNext() && iter2.hasNext()) {
+                    uris.add(iter.next());
+                    uris2.add(iter2.next());
+                }
+
+                assertFalse(iter.hasNext());
+                assertFalse(iter2.hasNext());
+            }
+        }
+        assertEquals(TEST_URIS, uris);
+        assertEquals(TEST_URIS, uris2);
     }
 
     @Test
@@ -108,7 +145,7 @@
         assertFalse(clipDir.equals(folder.getRoot()));
     }
 
-    private void writeAll(long tag, List<Uri> uris) {
+    private void writeAll(int tag, List<Uri> uris) {
         new ClipStorage.PersistTask(mStorage, uris, tag).execute();
         mExecutor.runAll();
     }
diff --git a/packages/DocumentsUI/tests/src/com/android/documentsui/UrisSupplierTest.java b/packages/DocumentsUI/tests/src/com/android/documentsui/UrisSupplierTest.java
index 719f0e2..2622322 100644
--- a/packages/DocumentsUI/tests/src/com/android/documentsui/UrisSupplierTest.java
+++ b/packages/DocumentsUI/tests/src/com/android/documentsui/UrisSupplierTest.java
@@ -19,9 +19,11 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 
+import android.content.SharedPreferences;
 import android.net.Uri;
 import android.os.AsyncTask;
 import android.provider.DocumentsContract;
+import android.support.test.InstrumentationRegistry;
 import android.support.test.filters.MediumTest;
 import android.support.test.runner.AndroidJUnit4;
 
@@ -42,6 +44,7 @@
 @MediumTest
 public class UrisSupplierTest {
 
+    private static final String PREF_NAME = "pref";
     private static final String AUTHORITY = "foo";
     private static final List<Uri> SHORT_URI_LIST = createList(3);
     private static final List<Uri> LONG_URI_LIST = createList(Shared.MAX_DOCS_IN_INTENT + 5);
@@ -49,6 +52,7 @@
     @Rule
     public TemporaryFolder folder = new TemporaryFolder();
 
+    private SharedPreferences mPref;
     private TestScheduledExecutorService mExecutor;
     private ClipStorage mStorage;
 
@@ -57,7 +61,8 @@
         mExecutor = new TestScheduledExecutorService();
         AsyncTask.setDefaultExecutor(mExecutor);
 
-        mStorage = new ClipStorage(folder.getRoot());
+        mPref = InstrumentationRegistry.getContext().getSharedPreferences(PREF_NAME, 0);
+        mStorage = new ClipStorage(folder.getRoot(), mPref);
     }
 
     @AfterClass
@@ -66,14 +71,14 @@
     }
 
     @Test
-    public void testItemCountEquals_shortList() {
+    public void testItemCountEquals_shortList() throws Exception {
         UrisSupplier uris = createWithShortList();
 
         assertEquals(SHORT_URI_LIST.size(), uris.getItemCount());
     }
 
     @Test
-    public void testItemCountEquals_longList() {
+    public void testItemCountEquals_longList() throws Exception {
         UrisSupplier uris = createWithLongList();
 
         assertEquals(LONG_URI_LIST.size(), uris.getItemCount());
@@ -83,35 +88,35 @@
     public void testGetDocsEquals_shortList() throws Exception {
         UrisSupplier uris = createWithShortList();
 
-        assertIterableEquals(SHORT_URI_LIST, uris.getDocs(mStorage));
+        assertIterableEquals(SHORT_URI_LIST, uris.getUris(mStorage));
     }
 
     @Test
     public void testGetDocsEquals_longList() throws Exception {
         UrisSupplier uris = createWithLongList();
 
-        assertIterableEquals(LONG_URI_LIST, uris.getDocs(mStorage));
+        assertIterableEquals(LONG_URI_LIST, uris.getUris(mStorage));
     }
 
     @Test
     public void testDispose_shortList() throws Exception {
         UrisSupplier uris = createWithShortList();
 
-        uris.dispose(mStorage);
+        uris.dispose();
     }
 
     @Test
     public void testDispose_longList() throws Exception {
         UrisSupplier uris = createWithLongList();
 
-        uris.dispose(mStorage);
+        uris.dispose();
     }
 
-    private UrisSupplier createWithShortList() {
+    private UrisSupplier createWithShortList() throws Exception {
         return UrisSupplier.create(SHORT_URI_LIST, mStorage);
     }
 
-    private UrisSupplier createWithLongList() {
+    private UrisSupplier createWithLongList() throws Exception {
         UrisSupplier uris =
                 UrisSupplier.create(LONG_URI_LIST, mStorage);