Bug 514708 - Performance improvement indexer by caching Strings.

Change-Id: If07961701bd568f674918c484cad16699bfa1cdf
Signed-off-by: Patrick Koenemann <patrick.koenemann@itemis.de>

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/db/Database.java

@@ -18,11 +18,16 @@ import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.RandomAccessFile;
+import java.lang.ref.Reference;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
 import java.nio.ByteBuffer;
 import java.nio.channels.ClosedByInterruptException;
 import java.nio.channels.ClosedChannelException;
 import java.nio.channels.FileChannel;
 import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Map;
 
 import org.eclipse.cdt.core.CCorePlugin;
 import org.eclipse.core.runtime.CoreException;
@@ -110,6 +115,22 @@ public class Database {
 	private long cacheHits;
 	private long cacheMisses;
 
+	/** Soft reference wrapper to keep track of the record for disposed strings. */
+	private static class SoftStringRef extends SoftReference<IString> {
+		private final long record;
+		public SoftStringRef(IString referent, ReferenceQueue<? super IString> q) {
+			super(referent, q);
+			record = referent.getRecord();
+		}
+		public long getRecord() {
+			return record;
+		}
+	}
+
+	// a cache for strings which is used for btree lookups; soft refs ensure garbage collection
+	private final Map<Long, Reference<IString>> stringCache = new HashMap<>();
+	private final ReferenceQueue<IString> stringDisposal = new ReferenceQueue<>();
+
 	/**
 	 * Construct a new Database object, creating a backing file if necessary.
 	 * @param location the local file path for the database
@@ -243,6 +264,8 @@ public class Database {
 			createNewChunks((int) setasideChunks);
 			flush();
 		}
+		// clear cache for strings which are used for btree searches
+		clearStringCache();
 	}
 
 	private void removeChunksFromCache() {
@@ -463,6 +486,7 @@ public class Database {
 		}
 		addBlock(chunk, blocksize, block);
 		freed += blocksize;
+		stringCache.remove(offset); // also remove record from string cache (if it exists)
 	}
 
 	public void putByte(long offset, byte value) throws CoreException {
@@ -564,9 +588,9 @@ public class Database {
 		}
 
 		if (bytelen > ShortString.MAX_BYTE_LENGTH) {
-			return new LongString(this, chars, useBytes);
+			return addStringToCache(new LongString(this, chars, useBytes));
 		} else {
-			return new ShortString(this, chars, useBytes);
+			return addStringToCache(new ShortString(this, chars, useBytes));
 		}
 	}
 
@@ -579,12 +603,33 @@ public class Database {
 	}
 
 	public IString getString(long offset) throws CoreException {
+		final Reference<IString> cachedStringReference = stringCache.get(offset);
+		if (cachedStringReference != null) {
+			final IString cachedString = cachedStringReference.get();
+			if (cachedString != null) {
+				return cachedString; // string already cached, no need to re-retrieve it :-)
+			}
+		}
 		final int l = getInt(offset);
 		int bytelen= l < 0 ? -l : 2 * l;
 		if (bytelen > ShortString.MAX_BYTE_LENGTH) {
-			return new LongString(this, offset);
+			return addStringToCache(new LongString(this, offset));
 		}
-		return new ShortString(this, offset);
+		return addStringToCache(new ShortString(this, offset));
+	}
+
+	private IString addStringToCache(IString string) {
+		// add string to cache
+		stringCache.put(string.getRecord(), new SoftStringRef(string, stringDisposal));
+		// also remove keys from cache list upon garbage collection
+		if (stringDisposal != null) {
+			Reference<? extends IString> disposedRef = stringDisposal.poll();
+			while (disposedRef instanceof SoftStringRef) {
+				stringCache.remove(((SoftStringRef) disposedRef).getRecord());
+				disposedRef = stringDisposal.poll();
+			}
+		}
+		return string;
 	}
 
 	/**
@@ -629,6 +674,7 @@ public class Database {
 		} catch (IOException e) {
 			throw new CoreException(new DBStatus(e));
 		}
+		clearStringCache();
 	}
 
 	/**
@@ -731,6 +777,15 @@ public class Database {
 
 		// Also handles header chunk.
 		flushAndUnlockChunks(dirtyChunks, true);
+
+		// And clear string cache
+		clearStringCache();
+	}
+
+	private void clearStringCache() {
+		stringCache.clear();
+		while (stringDisposal.poll() != null) {
+		}
 	}
 
 	private void flushAndUnlockChunks(final ArrayList<Chunk> dirtyChunks, boolean isComplete) throws CoreException {

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/db/LongString.java

@@ -27,6 +27,9 @@ public class LongString implements IString {
 	private final long record;
 	private int hash;
 
+	// this string is immutable, so we can cache the actual char array
+	private char[] cachedChars;
+
 	// Additional fields of first record.
 	private static final int LENGTH = 0; // Must be first to match ShortString.
 	private static final int NEXT1 = 4;
@@ -89,6 +92,9 @@ public class LongString implements IString {
 		} else {
 			chunk.putChars(nextRecord + CHARSN, chars, start, remaining);
 		}
+
+		// There is currently no need to store char[] in cachedChars because all
+		// callers are currently only interested in the record.
 	}
 	
 	@Override
@@ -98,6 +104,9 @@ public class LongString implements IString {
 
 	@Override
 	public char[] getChars() throws CoreException {
+		if (cachedChars != null) {
+			return cachedChars; // no need to re-retrieve array if it is already cached
+		}
 		int length = db.getInt(record + LENGTH);
 		final boolean useBytes = length < 0;
 		int numChars1 = NUM_CHARS1;
@@ -135,6 +144,7 @@ public class LongString implements IString {
 			start += partLen;
 			p= p + NEXTN;
 		}
+		cachedChars = chars; // cache the array
 		return chars;
 	}
 

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/db/ShortString.java

@@ -25,7 +25,10 @@ public class ShortString implements IString {
 	private final Database db;
 	private final long record;
 	private int hash;
-	
+
+	// this string is immutable, so we can cache the actual char array
+	private char[] cachedChars;
+
 	private static final int LENGTH = 0;
 	private static final int CHARS = 4;
 	
@@ -49,6 +52,9 @@ public class ShortString implements IString {
 		} else {
 			chunk.putChars(p, chars, 0, n);
 		}
+
+		// There is currently no need to store char[] in cachedChars because all
+		// callers are currently only interested in the record.
 	}
 	
 	@Override
@@ -63,6 +69,9 @@ public class ShortString implements IString {
 	
 	@Override
 	public char[] getChars() throws CoreException {
+		if (cachedChars != null) {
+			return cachedChars; // no need to re-retrieve array if it is already cached
+		}
 		final Chunk chunk = db.getChunk(record);
 		final int l = chunk.getInt(record + LENGTH);
 		final int length = Math.abs(l);
@@ -72,6 +81,7 @@ public class ShortString implements IString {
 		} else {
 			chunk.getChars(record + CHARS, chars, 0, length);
 		}
+		cachedChars = chars; // cache the array
 		return chars;
 	}