| /* |
| * Copyright (C) 2014 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package android.hardware.camera2.utils; |
| |
| import android.util.Log; |
| |
| import java.util.concurrent.locks.Condition; |
| import java.util.concurrent.locks.ReentrantLock; |
| |
| /** |
| * Implement a shared/exclusive lock that can be closed. |
| * |
| * <p>A shared lock can be acquired if any other shared locks are also acquired. An |
| * exclusive lock acquire will block until all shared locks have been released.</p> |
| * |
| * <p>Locks are re-entrant; trying to acquire another lock (of the same type) |
| * while a lock is already held will immediately succeed.</p> |
| * |
| * <p>Acquiring to acquire a shared lock while holding an exclusive lock or vice versa is not |
| * supported; attempting it will throw an {@link IllegalStateException}.</p> |
| * |
| * <p>If the lock is closed, all future and current acquires will immediately return {@code null}. |
| * </p> |
| */ |
| public class CloseableLock implements AutoCloseable { |
| |
| private static final boolean VERBOSE = false; |
| |
| private final String TAG = "CloseableLock"; |
| private final String mName; |
| |
| private volatile boolean mClosed = false; |
| |
| /** If an exclusive lock is acquired by some thread. */ |
| private boolean mExclusive = false; |
| /** |
| * How many shared locks are acquired by any thread: |
| * |
| * <p>Reentrant locking increments this. If an exclusive lock is held, |
| * this value will stay at 0.</p> |
| */ |
| private int mSharedLocks = 0; |
| |
| private final ReentrantLock mLock = new ReentrantLock(); |
| /** This condition automatically releases mLock when waiting; re-acquiring it after notify */ |
| private final Condition mCondition = mLock.newCondition(); |
| |
| /** How many times the current thread is holding the lock */ |
| private final ThreadLocal<Integer> mLockCount = |
| new ThreadLocal<Integer>() { |
| @Override protected Integer initialValue() { |
| return 0; |
| } |
| }; |
| |
| /** |
| * Helper class to release a lock at the end of a try-with-resources statement. |
| */ |
| public class ScopedLock implements AutoCloseable { |
| private ScopedLock() {} |
| |
| /** Release the lock with {@link CloseableLock#releaseLock}. */ |
| @Override |
| public void close() { |
| releaseLock(); |
| } |
| } |
| |
| /** |
| * Create a new instance; starts out with 0 locks acquired. |
| */ |
| public CloseableLock() { |
| mName = ""; |
| } |
| |
| /** |
| * Create a new instance; starts out with 0 locks acquired. |
| * |
| * @param name set an optional name for logging functionality |
| */ |
| public CloseableLock(String name) { |
| mName = name; |
| } |
| |
| /** |
| * Acquires the lock exclusively (blocking), marks it as closed, then releases the lock. |
| * |
| * <p>Marking a lock as closed will fail all further acquisition attempts; |
| * it will also immediately unblock all other threads currently trying to acquire a lock.</p> |
| * |
| * <p>This operation is idempotent; calling it more than once has no effect.</p> |
| * |
| * @throws IllegalStateException |
| * if an attempt is made to {@code close} while this thread has a lock acquired |
| */ |
| @Override |
| public void close() { |
| if (mClosed) { |
| if (VERBOSE) { |
| log("close - already closed; ignoring"); |
| } |
| return; |
| } |
| |
| ScopedLock scoper = acquireExclusiveLock(); |
| // Already closed by another thread? |
| if (scoper == null) { |
| return; |
| } else if (mLockCount.get() != 1) { |
| // Future: may want to add a #releaseAndClose to allow this. |
| throw new IllegalStateException( |
| "Cannot close while one or more acquired locks are being held by this " + |
| "thread; release all other locks first"); |
| } |
| |
| try { |
| mLock.lock(); |
| |
| mClosed = true; |
| mExclusive = false; |
| mSharedLocks = 0; |
| mLockCount.remove(); |
| |
| // Notify all threads that are waiting to unblock and return immediately |
| mCondition.signalAll(); |
| } finally { |
| mLock.unlock(); |
| } |
| |
| if (VERBOSE) { |
| log("close - completed"); |
| } |
| } |
| |
| /** |
| * Try to acquire the lock non-exclusively, blocking until the operation completes. |
| * |
| * <p>If the lock has already been closed, or being closed before this operation returns, |
| * the call will immediately return {@code false}.</p> |
| * |
| * <p>If other threads hold a non-exclusive lock (and the lock is not yet closed), |
| * this operation will return immediately. If another thread holds an exclusive lock, |
| * this thread will block until the exclusive lock has been released.</p> |
| * |
| * <p>This lock is re-entrant; acquiring more than one non-exclusive lock per thread is |
| * supported, and must be matched by an equal number of {@link #releaseLock} calls.</p> |
| * |
| * @return {@code ScopedLock} instance if the lock was acquired, or {@code null} if the lock |
| * was already closed. |
| * |
| * @throws IllegalStateException if this thread is already holding an exclusive lock |
| */ |
| public ScopedLock acquireLock() { |
| |
| int ownedLocks; |
| |
| try { |
| mLock.lock(); |
| |
| // Lock is already closed, all further acquisitions will fail |
| if (mClosed) { |
| if (VERBOSE) { |
| log("acquire lock early aborted (already closed)"); |
| } |
| return null; |
| } |
| |
| ownedLocks = mLockCount.get(); |
| |
| // This thread is already holding an exclusive lock |
| if (mExclusive && ownedLocks > 0) { |
| throw new IllegalStateException( |
| "Cannot acquire shared lock while holding exclusive lock"); |
| } |
| |
| // Is another thread holding the exclusive lock? Block until we can get in. |
| while (mExclusive) { |
| mCondition.awaitUninterruptibly(); |
| |
| // Did another thread #close while we were waiting? Unblock immediately. |
| if (mClosed) { |
| if (VERBOSE) { |
| log("acquire lock unblocked aborted (already closed)"); |
| } |
| return null; |
| } |
| } |
| |
| mSharedLocks++; |
| |
| ownedLocks = mLockCount.get() + 1; |
| mLockCount.set(ownedLocks); |
| } finally { |
| mLock.unlock(); |
| } |
| |
| if (VERBOSE) { |
| log("acquired lock (local own count = " + ownedLocks + ")"); |
| } |
| return new ScopedLock(); |
| } |
| |
| /** |
| * Try to acquire the lock exclusively, blocking until all other threads release their locks. |
| * |
| * <p>If the lock has already been closed, or being closed before this operation returns, |
| * the call will immediately return {@code false}.</p> |
| * |
| * <p>If any other threads are holding a lock, this thread will block until all |
| * other locks are released.</p> |
| * |
| * <p>This lock is re-entrant; acquiring more than one exclusive lock per thread is supported, |
| * and must be matched by an equal number of {@link #releaseLock} calls.</p> |
| * |
| * @return {@code ScopedLock} instance if the lock was acquired, or {@code null} if the lock |
| * was already closed. |
| * |
| * @throws IllegalStateException |
| * if an attempt is made to acquire an exclusive lock while already holding a lock |
| */ |
| public ScopedLock acquireExclusiveLock() { |
| |
| int ownedLocks; |
| |
| try { |
| mLock.lock(); |
| |
| // Lock is already closed, all further acquisitions will fail |
| if (mClosed) { |
| if (VERBOSE) { |
| log("acquire exclusive lock early aborted (already closed)"); |
| } |
| return null; |
| } |
| |
| ownedLocks = mLockCount.get(); |
| |
| // This thread is already holding a shared lock |
| if (!mExclusive && ownedLocks > 0) { |
| throw new IllegalStateException( |
| "Cannot acquire exclusive lock while holding shared lock"); |
| } |
| |
| /* |
| * Is another thread holding the lock? Block until we can get in. |
| * |
| * If we are already holding the lock, always let it through since |
| * we are just reentering the exclusive lock. |
| */ |
| while (ownedLocks == 0 && (mExclusive || mSharedLocks > 0)) { |
| mCondition.awaitUninterruptibly(); |
| |
| // Did another thread #close while we were waiting? Unblock immediately. |
| if (mClosed) { |
| if (VERBOSE) { |
| log("acquire exclusive lock unblocked aborted (already closed)"); |
| } |
| return null; |
| } |
| } |
| |
| mExclusive = true; |
| |
| ownedLocks = mLockCount.get() + 1; |
| mLockCount.set(ownedLocks); |
| } finally { |
| mLock.unlock(); |
| } |
| |
| if (VERBOSE) { |
| log("acquired exclusive lock (local own count = " + ownedLocks + ")"); |
| } |
| return new ScopedLock(); |
| } |
| |
| /** |
| * Release a single lock that was acquired. |
| * |
| * <p>Any other other that is blocked and trying to acquire a lock will get a chance |
| * to acquire the lock.</p> |
| * |
| * @throws IllegalStateException if no locks were acquired, or if the lock was already closed |
| */ |
| public void releaseLock() { |
| if (mLockCount.get() <= 0) { |
| throw new IllegalStateException( |
| "Cannot release lock that was not acquired by this thread"); |
| } |
| |
| int ownedLocks; |
| |
| try { |
| mLock.lock(); |
| |
| // Lock is already closed, it couldn't have been acquired in the first place |
| if (mClosed) { |
| throw new IllegalStateException("Do not release after the lock has been closed"); |
| } |
| |
| if (!mExclusive) { |
| mSharedLocks--; |
| } else { |
| if (mSharedLocks != 0) { |
| throw new AssertionError("Too many shared locks " + mSharedLocks); |
| } |
| } |
| |
| ownedLocks = mLockCount.get() - 1; |
| mLockCount.set(ownedLocks); |
| |
| if (ownedLocks == 0 && mExclusive) { |
| // Wake up any threads that might be waiting for the exclusive lock to be released |
| mExclusive = false; |
| mCondition.signalAll(); |
| } else if (ownedLocks == 0 && mSharedLocks == 0) { |
| // Wake up any threads that might be trying to get the exclusive lock |
| mCondition.signalAll(); |
| } |
| } finally { |
| mLock.unlock(); |
| } |
| |
| if (VERBOSE) { |
| log("released lock (local lock count " + ownedLocks + ")"); |
| } |
| } |
| |
| private void log(String what) { |
| Log.v(TAG + "[" + mName + "]", what); |
| } |
| |
| } |