Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2014 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.hardware.camera2.utils; |
| 18 | |
| 19 | import android.util.Log; |
| 20 | |
| 21 | import java.util.concurrent.locks.Condition; |
| 22 | import java.util.concurrent.locks.ReentrantLock; |
| 23 | |
| 24 | /** |
| 25 | * Implement a shared/exclusive lock that can be closed. |
| 26 | * |
| 27 | * <p>A shared lock can be acquired if any other shared locks are also acquired. An |
| 28 | * exclusive lock acquire will block until all shared locks have been released.</p> |
| 29 | * |
| 30 | * <p>Locks are re-entrant; trying to acquire another lock (of the same type) |
| 31 | * while a lock is already held will immediately succeed.</p> |
| 32 | * |
| 33 | * <p>Acquiring to acquire a shared lock while holding an exclusive lock or vice versa is not |
| 34 | * supported; attempting it will throw an {@link IllegalStateException}.</p> |
| 35 | * |
| 36 | * <p>If the lock is closed, all future and current acquires will immediately return {@code null}. |
| 37 | * </p> |
| 38 | */ |
| 39 | public class CloseableLock implements AutoCloseable { |
| 40 | |
| 41 | private static final boolean VERBOSE = false; |
| 42 | |
| 43 | private final String TAG = "CloseableLock"; |
| 44 | private final String mName; |
| 45 | |
| 46 | private volatile boolean mClosed = false; |
| 47 | |
| 48 | /** If an exclusive lock is acquired by some thread. */ |
| 49 | private boolean mExclusive = false; |
| 50 | /** |
| 51 | * How many shared locks are acquired by any thread: |
| 52 | * |
| 53 | * <p>Reentrant locking increments this. If an exclusive lock is held, |
| 54 | * this value will stay at 0.</p> |
| 55 | */ |
| 56 | private int mSharedLocks = 0; |
| 57 | |
| 58 | private final ReentrantLock mLock = new ReentrantLock(); |
| 59 | /** This condition automatically releases mLock when waiting; re-acquiring it after notify */ |
| 60 | private final Condition mCondition = mLock.newCondition(); |
| 61 | |
| 62 | /** How many times the current thread is holding the lock */ |
| 63 | private final ThreadLocal<Integer> mLockCount = |
| 64 | new ThreadLocal<Integer>() { |
| 65 | @Override protected Integer initialValue() { |
| 66 | return 0; |
| 67 | } |
| 68 | }; |
| 69 | |
| 70 | /** |
| 71 | * Helper class to release a lock at the end of a try-with-resources statement. |
| 72 | */ |
| 73 | public class ScopedLock implements AutoCloseable { |
| 74 | private ScopedLock() {} |
| 75 | |
| 76 | /** Release the lock with {@link CloseableLock#releaseLock}. */ |
| 77 | @Override |
| 78 | public void close() { |
| 79 | releaseLock(); |
| 80 | } |
| 81 | } |
| 82 | |
| 83 | /** |
| 84 | * Create a new instance; starts out with 0 locks acquired. |
| 85 | */ |
| 86 | public CloseableLock() { |
| 87 | mName = ""; |
| 88 | } |
| 89 | |
| 90 | /** |
| 91 | * Create a new instance; starts out with 0 locks acquired. |
| 92 | * |
| 93 | * @param name set an optional name for logging functionality |
| 94 | */ |
| 95 | public CloseableLock(String name) { |
| 96 | mName = name; |
| 97 | } |
| 98 | |
| 99 | /** |
| 100 | * Acquires the lock exclusively (blocking), marks it as closed, then releases the lock. |
| 101 | * |
| 102 | * <p>Marking a lock as closed will fail all further acquisition attempts; |
| 103 | * it will also immediately unblock all other threads currently trying to acquire a lock.</p> |
| 104 | * |
| 105 | * <p>This operation is idempotent; calling it more than once has no effect.</p> |
| 106 | * |
| 107 | * @throws IllegalStateException |
| 108 | * if an attempt is made to {@code close} while this thread has a lock acquired |
| 109 | */ |
| 110 | @Override |
| 111 | public void close() { |
| 112 | if (mClosed) { |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 113 | if (VERBOSE) { |
| 114 | log("close - already closed; ignoring"); |
| 115 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 116 | return; |
| 117 | } |
| 118 | |
| 119 | ScopedLock scoper = acquireExclusiveLock(); |
| 120 | // Already closed by another thread? |
| 121 | if (scoper == null) { |
| 122 | return; |
| 123 | } else if (mLockCount.get() != 1) { |
| 124 | // Future: may want to add a #releaseAndClose to allow this. |
| 125 | throw new IllegalStateException( |
| 126 | "Cannot close while one or more acquired locks are being held by this " + |
| 127 | "thread; release all other locks first"); |
| 128 | } |
| 129 | |
| 130 | try { |
| 131 | mLock.lock(); |
| 132 | |
| 133 | mClosed = true; |
| 134 | mExclusive = false; |
| 135 | mSharedLocks = 0; |
| 136 | mLockCount.remove(); |
| 137 | |
| 138 | // Notify all threads that are waiting to unblock and return immediately |
| 139 | mCondition.signalAll(); |
| 140 | } finally { |
| 141 | mLock.unlock(); |
| 142 | } |
| 143 | |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 144 | if (VERBOSE) { |
| 145 | log("close - completed"); |
| 146 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 147 | } |
| 148 | |
| 149 | /** |
| 150 | * Try to acquire the lock non-exclusively, blocking until the operation completes. |
| 151 | * |
| 152 | * <p>If the lock has already been closed, or being closed before this operation returns, |
| 153 | * the call will immediately return {@code false}.</p> |
| 154 | * |
| 155 | * <p>If other threads hold a non-exclusive lock (and the lock is not yet closed), |
| 156 | * this operation will return immediately. If another thread holds an exclusive lock, |
| 157 | * this thread will block until the exclusive lock has been released.</p> |
| 158 | * |
| 159 | * <p>This lock is re-entrant; acquiring more than one non-exclusive lock per thread is |
| 160 | * supported, and must be matched by an equal number of {@link #releaseLock} calls.</p> |
| 161 | * |
| 162 | * @return {@code ScopedLock} instance if the lock was acquired, or {@code null} if the lock |
| 163 | * was already closed. |
| 164 | * |
| 165 | * @throws IllegalStateException if this thread is already holding an exclusive lock |
| 166 | */ |
| 167 | public ScopedLock acquireLock() { |
| 168 | |
| 169 | int ownedLocks; |
| 170 | |
| 171 | try { |
| 172 | mLock.lock(); |
| 173 | |
| 174 | // Lock is already closed, all further acquisitions will fail |
| 175 | if (mClosed) { |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 176 | if (VERBOSE) { |
| 177 | log("acquire lock early aborted (already closed)"); |
| 178 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 179 | return null; |
| 180 | } |
| 181 | |
| 182 | ownedLocks = mLockCount.get(); |
| 183 | |
| 184 | // This thread is already holding an exclusive lock |
| 185 | if (mExclusive && ownedLocks > 0) { |
| 186 | throw new IllegalStateException( |
| 187 | "Cannot acquire shared lock while holding exclusive lock"); |
| 188 | } |
| 189 | |
| 190 | // Is another thread holding the exclusive lock? Block until we can get in. |
| 191 | while (mExclusive) { |
| 192 | mCondition.awaitUninterruptibly(); |
| 193 | |
| 194 | // Did another thread #close while we were waiting? Unblock immediately. |
| 195 | if (mClosed) { |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 196 | if (VERBOSE) { |
| 197 | log("acquire lock unblocked aborted (already closed)"); |
| 198 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 199 | return null; |
| 200 | } |
| 201 | } |
| 202 | |
| 203 | mSharedLocks++; |
| 204 | |
| 205 | ownedLocks = mLockCount.get() + 1; |
| 206 | mLockCount.set(ownedLocks); |
| 207 | } finally { |
| 208 | mLock.unlock(); |
| 209 | } |
| 210 | |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 211 | if (VERBOSE) { |
| 212 | log("acquired lock (local own count = " + ownedLocks + ")"); |
| 213 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 214 | return new ScopedLock(); |
| 215 | } |
| 216 | |
| 217 | /** |
| 218 | * Try to acquire the lock exclusively, blocking until all other threads release their locks. |
| 219 | * |
| 220 | * <p>If the lock has already been closed, or being closed before this operation returns, |
| 221 | * the call will immediately return {@code false}.</p> |
| 222 | * |
| 223 | * <p>If any other threads are holding a lock, this thread will block until all |
| 224 | * other locks are released.</p> |
| 225 | * |
| 226 | * <p>This lock is re-entrant; acquiring more than one exclusive lock per thread is supported, |
| 227 | * and must be matched by an equal number of {@link #releaseLock} calls.</p> |
| 228 | * |
| 229 | * @return {@code ScopedLock} instance if the lock was acquired, or {@code null} if the lock |
| 230 | * was already closed. |
| 231 | * |
| 232 | * @throws IllegalStateException |
| 233 | * if an attempt is made to acquire an exclusive lock while already holding a lock |
| 234 | */ |
| 235 | public ScopedLock acquireExclusiveLock() { |
| 236 | |
| 237 | int ownedLocks; |
| 238 | |
| 239 | try { |
| 240 | mLock.lock(); |
| 241 | |
| 242 | // Lock is already closed, all further acquisitions will fail |
| 243 | if (mClosed) { |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 244 | if (VERBOSE) { |
| 245 | log("acquire exclusive lock early aborted (already closed)"); |
| 246 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 247 | return null; |
| 248 | } |
| 249 | |
| 250 | ownedLocks = mLockCount.get(); |
| 251 | |
| 252 | // This thread is already holding a shared lock |
| 253 | if (!mExclusive && ownedLocks > 0) { |
| 254 | throw new IllegalStateException( |
| 255 | "Cannot acquire exclusive lock while holding shared lock"); |
| 256 | } |
| 257 | |
| 258 | /* |
| 259 | * Is another thread holding the lock? Block until we can get in. |
| 260 | * |
| 261 | * If we are already holding the lock, always let it through since |
| 262 | * we are just reentering the exclusive lock. |
| 263 | */ |
| 264 | while (ownedLocks == 0 && (mExclusive || mSharedLocks > 0)) { |
| 265 | mCondition.awaitUninterruptibly(); |
| 266 | |
| 267 | // Did another thread #close while we were waiting? Unblock immediately. |
| 268 | if (mClosed) { |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 269 | if (VERBOSE) { |
| 270 | log("acquire exclusive lock unblocked aborted (already closed)"); |
| 271 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 272 | return null; |
| 273 | } |
| 274 | } |
| 275 | |
| 276 | mExclusive = true; |
| 277 | |
| 278 | ownedLocks = mLockCount.get() + 1; |
| 279 | mLockCount.set(ownedLocks); |
| 280 | } finally { |
| 281 | mLock.unlock(); |
| 282 | } |
| 283 | |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 284 | if (VERBOSE) { |
| 285 | log("acquired exclusive lock (local own count = " + ownedLocks + ")"); |
| 286 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 287 | return new ScopedLock(); |
| 288 | } |
| 289 | |
| 290 | /** |
| 291 | * Release a single lock that was acquired. |
| 292 | * |
| 293 | * <p>Any other other that is blocked and trying to acquire a lock will get a chance |
| 294 | * to acquire the lock.</p> |
| 295 | * |
| 296 | * @throws IllegalStateException if no locks were acquired, or if the lock was already closed |
| 297 | */ |
| 298 | public void releaseLock() { |
| 299 | if (mLockCount.get() <= 0) { |
| 300 | throw new IllegalStateException( |
| 301 | "Cannot release lock that was not acquired by this thread"); |
| 302 | } |
| 303 | |
| 304 | int ownedLocks; |
| 305 | |
| 306 | try { |
| 307 | mLock.lock(); |
| 308 | |
| 309 | // Lock is already closed, it couldn't have been acquired in the first place |
| 310 | if (mClosed) { |
| 311 | throw new IllegalStateException("Do not release after the lock has been closed"); |
| 312 | } |
| 313 | |
| 314 | if (!mExclusive) { |
| 315 | mSharedLocks--; |
| 316 | } else { |
| 317 | if (mSharedLocks != 0) { |
| 318 | throw new AssertionError("Too many shared locks " + mSharedLocks); |
| 319 | } |
| 320 | } |
| 321 | |
| 322 | ownedLocks = mLockCount.get() - 1; |
| 323 | mLockCount.set(ownedLocks); |
| 324 | |
| 325 | if (ownedLocks == 0 && mExclusive) { |
| 326 | // Wake up any threads that might be waiting for the exclusive lock to be released |
| 327 | mExclusive = false; |
| 328 | mCondition.signalAll(); |
| 329 | } else if (ownedLocks == 0 && mSharedLocks == 0) { |
| 330 | // Wake up any threads that might be trying to get the exclusive lock |
| 331 | mCondition.signalAll(); |
| 332 | } |
| 333 | } finally { |
| 334 | mLock.unlock(); |
| 335 | } |
| 336 | |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 337 | if (VERBOSE) { |
| 338 | log("released lock (local lock count " + ownedLocks + ")"); |
| 339 | } |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 340 | } |
| 341 | |
| 342 | private void log(String what) { |
Ruben Brunk | 2cdfa26 | 2014-07-11 11:46:20 -0700 | [diff] [blame] | 343 | Log.v(TAG + "[" + mName + "]", what); |
Igor Murashkin | 49b2b13 | 2014-06-18 19:03:00 -0700 | [diff] [blame] | 344 | } |
| 345 | |
| 346 | } |