| 1 | /* |
| 2 | * Copyright (C) 2011 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package android.support.v2.content; |
| 18 | |
| 19 | import android.content.Context; |
| 20 | import android.os.AsyncTask; |
| 21 | import android.os.Handler; |
| 22 | import android.os.SystemClock; |
| 23 | import android.support.v2.util.TimeUtils; |
| 24 | import android.util.Log; |
| 25 | |
| 26 | import java.io.FileDescriptor; |
| 27 | import java.io.PrintWriter; |
| 28 | import java.util.concurrent.CountDownLatch; |
| 29 | |
| 30 | /** |
| 31 | * Static library support version of the framework's {@link android.content.AsyncTaskLoader}. |
| 32 | * Used to write apps that run on platforms prior to Android 3.0. When running |
| 33 | * on Android 3.0 or above, this implementation is still used; it does not try |
| 34 | * to switch to the framework's implementation. See the framework SDK |
| 35 | * documentation for a class overview. |
| 36 | */ |
| 37 | public abstract class AsyncTaskLoader<D> extends Loader<D> { |
| 38 | static final String TAG = "AsyncTaskLoader"; |
| 39 | static final boolean DEBUG = false; |
| 40 | |
| 41 | final class LoadTask extends AsyncTask<Void, Void, D> implements Runnable { |
| 42 | |
| 43 | D result; |
| 44 | boolean waiting; |
| 45 | |
| 46 | private CountDownLatch done = new CountDownLatch(1); |
| 47 | |
| 48 | /* Runs on a worker thread */ |
| 49 | @Override |
| 50 | protected D doInBackground(Void... params) { |
| 51 | if (DEBUG) Log.v(TAG, this + " >>> doInBackground"); |
| 52 | result = AsyncTaskLoader.this.onLoadInBackground(); |
| 53 | if (DEBUG) Log.v(TAG, this + " <<< doInBackground"); |
| 54 | return result; |
| 55 | } |
| 56 | |
| 57 | /* Runs on the UI thread */ |
| 58 | @Override |
| 59 | protected void onPostExecute(D data) { |
| 60 | if (DEBUG) Log.v(TAG, this + " onPostExecute"); |
| 61 | try { |
| 62 | AsyncTaskLoader.this.dispatchOnLoadComplete(this, data); |
| 63 | } finally { |
| 64 | done.countDown(); |
| 65 | } |
| 66 | } |
| 67 | |
| 68 | @Override |
| 69 | protected void onCancelled() { |
| 70 | if (DEBUG) Log.v(TAG, this + " onCancelled"); |
| 71 | try { |
| 72 | AsyncTaskLoader.this.dispatchOnCancelled(this, result); |
| 73 | } finally { |
| 74 | done.countDown(); |
| 75 | } |
| 76 | } |
| 77 | |
| 78 | @Override |
| 79 | public void run() { |
| 80 | waiting = false; |
| 81 | AsyncTaskLoader.this.executePendingTask(); |
| 82 | } |
| 83 | } |
| 84 | |
| 85 | volatile LoadTask mTask; |
| 86 | volatile LoadTask mCancellingTask; |
| 87 | |
| 88 | long mUpdateThrottle; |
| 89 | long mLastLoadCompleteTime = -10000; |
| 90 | Handler mHandler; |
| 91 | |
| 92 | public AsyncTaskLoader(Context context) { |
| 93 | super(context); |
| 94 | } |
| 95 | |
| 96 | /** |
| 97 | * Set amount to throttle updates by. This is the minimum time from |
| 98 | * when the last {@link #onLoadInBackground()} call has completed until |
| 99 | * a new load is scheduled. |
| 100 | * |
| 101 | * @param delayMS Amount of delay, in milliseconds. |
| 102 | */ |
| 103 | public void setUpdateThrottle(long delayMS) { |
| 104 | mUpdateThrottle = delayMS; |
| 105 | if (delayMS != 0) { |
| 106 | mHandler = new Handler(); |
| 107 | } |
| 108 | } |
| 109 | |
| 110 | @Override |
| 111 | protected void onForceLoad() { |
| 112 | super.onForceLoad(); |
| 113 | cancelLoad(); |
| 114 | mTask = new LoadTask(); |
| 115 | if (DEBUG) Log.v(TAG, "Preparing load: mTask=" + mTask); |
| 116 | executePendingTask(); |
| 117 | } |
| 118 | |
| 119 | /** |
| 120 | * Attempt to cancel the current load task. See {@link AsyncTask#cancel(boolean)} |
| 121 | * for more info. Must be called on the main thread of the process. |
| 122 | * |
| 123 | * <p>Cancelling is not an immediate operation, since the load is performed |
| 124 | * in a background thread. If there is currently a load in progress, this |
| 125 | * method requests that the load be cancelled, and notes this is the case; |
| 126 | * once the background thread has completed its work its remaining state |
| 127 | * will be cleared. If another load request comes in during this time, |
| 128 | * it will be held until the cancelled load is complete. |
| 129 | * |
| 130 | * @return Returns <tt>false</tt> if the task could not be cancelled, |
| 131 | * typically because it has already completed normally, or |
| 132 | * because {@link #startLoading()} hasn't been called; returns |
| 133 | * <tt>true</tt> otherwise. |
| 134 | */ |
| 135 | public boolean cancelLoad() { |
| 136 | if (DEBUG) Log.v(TAG, "cancelLoad: mTask=" + mTask); |
| 137 | if (mTask != null) { |
| 138 | if (mCancellingTask != null) { |
| 139 | // There was a pending task already waiting for a previous |
| 140 | // one being canceled; just drop it. |
| 141 | if (DEBUG) Log.v(TAG, |
| 142 | "cancelLoad: still waiting for cancelled task; dropping next"); |
| 143 | if (mTask.waiting) { |
| 144 | mTask.waiting = false; |
| 145 | mHandler.removeCallbacks(mTask); |
| 146 | } |
| 147 | mTask = null; |
| 148 | return false; |
| 149 | } else if (mTask.waiting) { |
| 150 | // There is a task, but it is waiting for the time it should |
| 151 | // execute. We can just toss it. |
| 152 | if (DEBUG) Log.v(TAG, "cancelLoad: task is waiting, dropping it"); |
| 153 | mTask.waiting = false; |
| 154 | mHandler.removeCallbacks(mTask); |
| 155 | mTask = null; |
| 156 | return false; |
| 157 | } else { |
| 158 | boolean cancelled = mTask.cancel(false); |
| 159 | if (DEBUG) Log.v(TAG, "cancelLoad: cancelled=" + cancelled); |
| 160 | if (cancelled) { |
| 161 | mCancellingTask = mTask; |
| 162 | } |
| 163 | mTask = null; |
| 164 | return cancelled; |
| 165 | } |
| 166 | } |
| 167 | return false; |
| 168 | } |
| 169 | |
| 170 | /** |
| 171 | * Called if the task was canceled before it was completed. Gives the class a chance |
| 172 | * to properly dispose of the result. |
| 173 | */ |
| 174 | public void onCanceled(D data) { |
| 175 | } |
| 176 | |
| 177 | void executePendingTask() { |
| 178 | if (mCancellingTask == null && mTask != null) { |
| 179 | if (mTask.waiting) { |
| 180 | mTask.waiting = false; |
| 181 | mHandler.removeCallbacks(mTask); |
| 182 | } |
| 183 | if (mUpdateThrottle > 0) { |
| 184 | long now = SystemClock.uptimeMillis(); |
| 185 | if (now < (mLastLoadCompleteTime+mUpdateThrottle)) { |
| 186 | // Not yet time to do another load. |
| 187 | if (DEBUG) Log.v(TAG, "Waiting until " |
| 188 | + (mLastLoadCompleteTime+mUpdateThrottle) |
| 189 | + " to execute: " + mTask); |
| 190 | mTask.waiting = true; |
| 191 | mHandler.postAtTime(mTask, mLastLoadCompleteTime+mUpdateThrottle); |
| 192 | return; |
| 193 | } |
| 194 | } |
| 195 | if (DEBUG) Log.v(TAG, "Executing: " + mTask); |
| 196 | mTask.execute((Void[]) null); |
| 197 | // XXX TO DO: use reflection to call this version. |
| 198 | //mTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, (Void[]) null); |
| 199 | } |
| 200 | } |
| 201 | |
| 202 | void dispatchOnCancelled(LoadTask task, D data) { |
| 203 | onCanceled(data); |
| 204 | if (mCancellingTask == task) { |
| 205 | if (DEBUG) Log.v(TAG, "Cancelled task is now canceled!"); |
| 206 | mLastLoadCompleteTime = SystemClock.uptimeMillis(); |
| 207 | mCancellingTask = null; |
| 208 | executePendingTask(); |
| 209 | } |
| 210 | } |
| 211 | |
| 212 | void dispatchOnLoadComplete(LoadTask task, D data) { |
| 213 | if (mTask != task) { |
| 214 | if (DEBUG) Log.v(TAG, "Load complete of old task, trying to cancel"); |
| 215 | dispatchOnCancelled(task, data); |
| 216 | } else { |
| 217 | if (isAbandoned()) { |
| 218 | // This cursor has been abandoned; just cancel the new data. |
| 219 | onCanceled(data); |
| 220 | } else { |
| 221 | mLastLoadCompleteTime = SystemClock.uptimeMillis(); |
| 222 | mTask = null; |
| 223 | if (DEBUG) Log.v(TAG, "Delivering result"); |
| 224 | deliverResult(data); |
| 225 | } |
| 226 | } |
| 227 | } |
| 228 | |
| 229 | /** |
| 230 | */ |
| 231 | public abstract D loadInBackground(); |
| 232 | |
| 233 | /** |
| 234 | * Called on a worker thread to perform the actual load. Implementations should not deliver the |
| 235 | * result directly, but should return them from this method, which will eventually end up |
| 236 | * calling {@link #deliverResult} on the UI thread. If implementations need to process |
| 237 | * the results on the UI thread they may override {@link #deliverResult} and do so |
| 238 | * there. |
| 239 | * |
| 240 | * @return Implementations must return the result of their load operation. |
| 241 | */ |
| 242 | protected D onLoadInBackground() { |
| 243 | return loadInBackground(); |
| 244 | } |
| 245 | |
| 246 | /** |
| 247 | * Locks the current thread until the loader completes the current load |
| 248 | * operation. Returns immediately if there is no load operation running. |
| 249 | * Should not be called from the UI thread: calling it from the UI |
| 250 | * thread would cause a deadlock. |
| 251 | * <p> |
| 252 | * Use for testing only. <b>Never</b> call this from a UI thread. |
| 253 | * |
| 254 | * @hide |
| 255 | */ |
| 256 | public void waitForLoader() { |
| 257 | LoadTask task = mTask; |
| 258 | if (task != null) { |
| 259 | try { |
| 260 | task.done.await(); |
| 261 | } catch (InterruptedException e) { |
| 262 | // Ignore |
| 263 | } |
| 264 | } |
| 265 | } |
| 266 | |
| 267 | @Override |
| 268 | public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) { |
| 269 | super.dump(prefix, fd, writer, args); |
| 270 | if (mTask != null) { |
| 271 | writer.print(prefix); writer.print("mTask="); writer.print(mTask); |
| 272 | writer.print(" waiting="); writer.println(mTask.waiting); |
| 273 | } |
| 274 | if (mCancellingTask != null) { |
| 275 | writer.print(prefix); writer.print("mCancellingTask="); writer.print(mCancellingTask); |
| 276 | writer.print(" waiting="); writer.println(mCancellingTask.waiting); |
| 277 | } |
| 278 | if (mUpdateThrottle != 0) { |
| 279 | writer.print(prefix); writer.print("mUpdateThrottle="); |
| 280 | TimeUtils.formatDuration(mUpdateThrottle, writer); |
| 281 | writer.print(" mLastLoadCompleteTime="); |
| 282 | TimeUtils.formatDuration(mLastLoadCompleteTime, |
| 283 | SystemClock.uptimeMillis(), writer); |
| 284 | writer.println(); |
| 285 | } |
| 286 | } |
| 287 | } |