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diff --git a/getdown/src/getdown/core/src/main/java/com/threerings/getdown/cache/ResourceCache.java b/getdown/src/getdown/core/src/main/java/com/threerings/getdown/cache/ResourceCache.java
new file mode 100644
index 0000000..0210e9a
--- /dev/null
+++ b/getdown/src/getdown/core/src/main/java/com/threerings/getdown/cache/ResourceCache.java
@@ -0,0 +1,80 @@
+//
+// Getdown - application installer, patcher and launcher
+// Copyright (C) 2004-2018 Getdown authors
+// https://github.com/threerings/getdown/blob/master/LICENSE
+
+package com.threerings.getdown.cache;
+
+import java.io.File;
+import java.io.IOException;
+
+import com.threerings.getdown.util.FileUtil;
+
+/**
+ * Maintains a cache of code resources. The cache allows multiple application instances of different
+ * versions to open at the same time.
+ */
+public class ResourceCache
+{
+    public ResourceCache (File _cacheDir) throws IOException
+    {
+        this._cacheDir = _cacheDir;
+        createDirectoryIfNecessary(_cacheDir);
+    }
+
+    private void createDirectoryIfNecessary (File dir) throws IOException
+    {
+        if (!dir.exists() && !dir.mkdirs()) {
+            throw new IOException("unable to create directory: " + dir.getAbsolutePath());
+        }
+    }
+
+    /**
+     * Caches the given file under its {@code digest}.
+     * @param fileToCache file to cache.
+     * @param cacheSubdir the subdirectory of the cache directory in which to store the cached
+     * file. Usually either {@code digest} or a prefix of {@code digest}.
+     * @param digest a crypto digest of the cached files contents.
+     * @return the cached file.
+     */
+    public File cacheFile (File fileToCache, String cacheSubdir, String digest) throws IOException
+    {
+        File cacheLocation = new File(_cacheDir, cacheSubdir);
+        createDirectoryIfNecessary(cacheLocation);
+
+        File cachedFile = new File(cacheLocation, digest + getFileSuffix(fileToCache));
+        File lastAccessedFile = new File(
+                cacheLocation, cachedFile.getName() + LAST_ACCESSED_FILE_SUFFIX);
+
+        if (!cachedFile.exists()) {
+            createNewFile(cachedFile);
+            FileUtil.copy(fileToCache, cachedFile);
+        }
+
+        if (lastAccessedFile.exists()) {
+            lastAccessedFile.setLastModified(System.currentTimeMillis());
+        } else {
+            createNewFile(lastAccessedFile);
+        }
+
+        return cachedFile;
+    }
+
+    private void createNewFile (File fileToCreate) throws IOException
+    {
+        if (!fileToCreate.exists() && !fileToCreate.createNewFile()) {
+            throw new IOException("unable to create new file: " + fileToCreate.getAbsolutePath());
+        }
+    }
+
+    private String getFileSuffix (File fileToCache) {
+        String fileName = fileToCache.getName();
+        int index = fileName.lastIndexOf(".");
+
+        return index > -1 ? fileName.substring(index) : "";
+    }
+
+    private final File _cacheDir;
+
+    static final String LAST_ACCESSED_FILE_SUFFIX = ".lastAccessed";
+}