diff --git a/AsimpleCacheDemo/ASimpleCache/org/afinal/simplecache/ACache.java b/AsimpleCacheDemo/ASimpleCache/org/afinal/simplecache/ACache.java
index 94a5ae6..caa6f1d 100644
--- a/AsimpleCacheDemo/ASimpleCache/org/afinal/simplecache/ACache.java
+++ b/AsimpleCacheDemo/ASimpleCache/org/afinal/simplecache/ACache.java
@@ -83,8 +83,12 @@ public static ACache get(Context ctx, long max_zise, int max_count) {
 	public static ACache get(File cacheDir, long max_zise, int max_count) {
 		ACache manager = mInstanceMap.get(cacheDir.getAbsoluteFile() + myPid());
 		if (manager == null) {
-			manager = new ACache(cacheDir, max_zise, max_count);
-			mInstanceMap.put(cacheDir.getAbsolutePath() + myPid(), manager);
+			synchronized(this){
+				if(manager == null){
+					manager = new ACache(cacheDir, max_zise, max_count);
+					mInstanceMap.put(cacheDir.getAbsolutePath() + myPid(), manager);
+				}
+			}
 		}
 		return manager;
 	}