RESTRICT AUTOMERGE: Add a "cork" mechanism to prevent cache invalidation flooding am: 264abafff0 (3001ecce) · Commits · e / os / android_frameworks_base

core/java/android/app/PropertyInvalidatedCache.java

+93 −0

Original line number	Original line	Diff line number	Diff line
	@@ -22,6 +22,7 @@ import android.util.Log;

	import com.android.internal.annotations.GuardedBy;		import com.android.internal.annotations.GuardedBy;

			import java.util.HashMap;
	import java.util.LinkedHashMap;		import java.util.LinkedHashMap;
	import java.util.Map;		import java.util.Map;
	import java.util.Objects;		import java.util.Objects;
	@@ -168,6 +169,17 @@ public abstract class PropertyInvalidatedCache<Query, Result> {
	private static final boolean ENABLE = true;		private static final boolean ENABLE = true;
	private static final boolean VERIFY = false;		private static final boolean VERIFY = false;

			private static final Object sCorkLock = new Object();

			/**
			* A map of cache keys that we've "corked". (The values are counts.) When a cache key is
			* corked, we skip the cache invalidate when the cache key is in the unset state --- that
			* is, when a cache key is corked, an invalidation does not enable the cache if somebody
			* else hasn't disabled it.
			*/
			@GuardedBy("sCorkLock")
			private static final HashMap<String, Integer> sCorks = new HashMap<>();

	private final Object mLock = new Object();		private final Object mLock = new Object();

	/**		/**
	@@ -421,6 +433,25 @@ public abstract class PropertyInvalidatedCache<Query, Result> {
	* @param name Name of the cache-key property to invalidate		* @param name Name of the cache-key property to invalidate
	*/		*/
	public static void invalidateCache(@NonNull String name) {		public static void invalidateCache(@NonNull String name) {
			// Take the cork lock so invalidateCache() racing against corkInvalidations() doesn't
			// clobber a cork-written NONCE_UNSET with a cache key we compute before the cork.
			// The property service is single-threaded anyway, so we don't lose any concurrency by
			// taking the cork lock around cache invalidations. If we see contention on this lock,
			// we're invalidating too often.
			synchronized (sCorkLock) {
			Integer numberCorks = sCorks.get(name);
			if (numberCorks != null && numberCorks > 0) {
			if (DEBUG) {
			Log.d(TAG, "ignoring invalidation due to cork: " + name);
			}
			return;
			}
			invalidateCacheLocked(name);
			}
			}

			@GuardedBy("sCorkLock")
			private static void invalidateCacheLocked(@NonNull String name) {
	// There's no race here: we don't require that values strictly increase, but instead		// There's no race here: we don't require that values strictly increase, but instead
	// only that each is unique in a single runtime-restart session.		// only that each is unique in a single runtime-restart session.
	final long nonce = SystemProperties.getLong(name, NONCE_UNSET);		final long nonce = SystemProperties.getLong(name, NONCE_UNSET);
	@@ -430,6 +461,7 @@ public abstract class PropertyInvalidatedCache<Query, Result> {
	}		}
	return;		return;
	}		}

	long newValue;		long newValue;
	do {		do {
	newValue = NoPreloadHolder.next();		newValue = NoPreloadHolder.next();
	@@ -445,6 +477,67 @@ public abstract class PropertyInvalidatedCache<Query, Result> {
	SystemProperties.set(name, newValueString);		SystemProperties.set(name, newValueString);
	}		}

			/**
			* Temporarily put the cache in the uninitialized state and prevent invalidations from
			* moving it out of that state: useful in cases where we want to avoid the overhead of a
			* large number of cache invalidations in a short time. While the cache is corked, clients
			* bypass the cache and talk to backing services directly. This property makes corking
			* correctness-preserving even if corked outside the lock that controls access to the
			* cache's backing service.
			*
			* corkInvalidations() and uncorkInvalidations() must be called in pairs.
			*
			* @param name Name of the cache-key property to cork
			*/
			public static void corkInvalidations(@NonNull String name) {
			synchronized (sCorkLock) {
			int numberCorks = sCorks.getOrDefault(name, 0);
			// If we're the first ones to cork this cache, set the cache to the unset state so
			// existing caches talk directly to their services while we've corked updates.
			// Make sure we don't clobber a disabled cache value.

			// TODO(dancol): we can skip this property write and leave the cache enabled if the
			// caller promises not to make observable changes to the cache backing state before
			// uncorking the cache, e.g., by holding a read lock across the cork-uncork pair.
			// Implement this more dangerous mode of operation if necessary.
			if (numberCorks == 0) {
			final long nonce = SystemProperties.getLong(name, NONCE_UNSET);
			if (nonce != NONCE_UNSET && nonce != NONCE_DISABLED) {
			SystemProperties.set(name, Long.toString(NONCE_UNSET));
			}
			}
			sCorks.put(name, numberCorks + 1);
			if (DEBUG) {
			Log.d(TAG, "corked: " + name);
			}
			}
			}

			/**
			* Undo the effect of a cork, allowing cache invalidations to proceed normally.
			* Removing the last cork on a cache name invalidates the cache by side effect,
			* transitioning it to normal operation (unless explicitly disabled system-wide).
			*
			* @param name Name of the cache-key property to uncork
			*/
			public static void uncorkInvalidations(@NonNull String name) {
			synchronized (sCorkLock) {
			int numberCorks = sCorks.getOrDefault(name, 0);
			if (numberCorks < 1) {
			throw new AssertionError("cork underflow: " + name);
			}
			if (numberCorks == 1) {
			sCorks.remove(name);
			invalidateCacheLocked(name);
			if (DEBUG) {
			Log.d(TAG, "uncorked: " + name);
			}
			} else {
			sCorks.put(name, numberCorks - 1);
			}
			}
			}

	protected Result maybeCheckConsistency(Query query, Result proposedResult) {		protected Result maybeCheckConsistency(Query query, Result proposedResult) {
	if (VERIFY) {		if (VERIFY) {
	Result resultToCompare = recompute(query);		Result resultToCompare = recompute(query);