Use a thread pool to optimize resource usage instead of always firing up new threads (less garbage collection).

Note: this is not a complete revert of r2153 since the pool is now automatically expanded as needed (different implementation).

src/com/fsck/k9/controller/MessagingController.java

@@ -18,6 +18,8 @@ import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArraySet;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.PriorityBlockingQueue;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -140,6 +142,8 @@ public class MessagingController implements Runnable
 
     ConcurrentHashMap<Account, Pusher> pushers = new ConcurrentHashMap<Account, Pusher>();
 
+    private final ExecutorService threadPool = Executors.newCachedThreadPool();
+
     public enum SORT_TYPE
     {
         SORT_DATE(R.string.sort_earliest_first, R.string.sort_latest_first, false),
@@ -401,7 +405,7 @@ public class MessagingController implements Runnable
      */
     public void listFolders(final Account account, final boolean refreshRemote, final MessagingListener listener)
     {
-        new Thread(new Runnable()
+        threadPool.execute(new Runnable()
         {
             public void run()
             {
@@ -457,7 +461,7 @@ public class MessagingController implements Runnable
                     l.listFoldersFinished(account);
                 }
             }
-        }).start();
+        });
     }
 
     private void doRefreshRemote(final Account account, MessagingListener listener)
@@ -557,13 +561,13 @@ public class MessagingController implements Runnable
      */
     public void listLocalMessages(final Account account, final String folder, final MessagingListener listener)
     {
-        new Thread(new Runnable()
+        threadPool.execute(new Runnable()
         {
             public void run()
             {
                 listLocalMessagesSynchronous(account, folder, listener);
             }
-        }).start();
+        });
     }
 
 
@@ -699,7 +703,7 @@ public class MessagingController implements Runnable
                   + ")");
         }
 
-        new Thread(new Runnable()
+        threadPool.execute(new Runnable()
         {
             public void run()
             {
@@ -891,7 +895,7 @@ public class MessagingController implements Runnable
                     listener.searchStats(stats);
                 }
             }
-        }).start();
+        });
     }
 
     public void loadMoreMessages(Account account, String folder, MessagingListener listener)
@@ -3101,7 +3105,7 @@ public class MessagingController implements Runnable
         {
             l.loadMessageForViewStarted(account, folder, uid);
         }
-        new Thread(new Runnable()
+        threadPool.execute(new Runnable()
         {
             public void run()
             {
@@ -3159,7 +3163,7 @@ public class MessagingController implements Runnable
 
                 }
             }
-        }).start();
+        });
     }
 
     /**