When a transfer is already being run by another process, proceed on to the next file, rather than dying.

Logs/Transfer.hs

@@ -103,11 +103,13 @@ download u key = runTransfer (Transfer Download u key)
 
 {- Runs a transfer action. Creates and locks the lock file while the
  - action is running, and stores info in the transfer information
- - file. Will throw an error if the transfer is already in progress.
+ - file.
  -
  - If the transfer action returns False, the transfer info is 
  - left in the failedTransferDir.
  -
+ - If the transfer is already in progress, returns False.
+ -
  - An upload can be run from a read-only filesystem, and in this case
  - no transfer information or lock file is used.
  -}
@@ -116,11 +118,14 @@ runTransfer t file shouldretry a = do
 	info <- liftIO $ startTransferInfo file
 	(meter, tfile, metervar) <- mkProgressUpdater t info
 	mode <- annexFileMode
-	fd <- liftIO $ prep tfile mode info
-	ok <- retry info metervar $
-		bracketIO (return fd) (cleanup tfile) (const $ a meter)
-	unless ok $ recordFailedTransfer t info
-	return ok
+	(fd, cantransfer) <- liftIO $ prep tfile mode info
+	if cantransfer
+		then do
+			ok <- retry info metervar $
+		 		bracketIO (return fd) (cleanup tfile) (const $ a meter)
+			unless ok $ recordFailedTransfer t info
+			return ok
+		else return False
   where
 	prep tfile mode info = do
 #ifndef __WINDOWS__
@@ -128,18 +133,22 @@ runTransfer t file shouldretry a = do
 			openFd (transferLockFile tfile) ReadWrite (Just mode)
 				defaultFileFlags { trunc = True }
 		case mfd of
-			Nothing -> return mfd
+			Nothing -> return (mfd, True)
 			Just fd -> do
 				locked <- catchMaybeIO $
 					setLock fd (WriteLock, AbsoluteSeek, 0, 0)
-				when (isNothing locked) $
-					error "transfer already in progress"
-				void $ tryIO $ writeTransferInfoFile info tfile
-				return mfd
+				if isNothing locked
+					then do
+						hPutStrLn stderr "transfer already in progress"
+						return (Nothing, False)
+					else do
+						void $ tryIO $ writeTransferInfoFile info tfile
+						return (mfd, True)
 #else
-		catchMaybeIO $ do
+		mfd <- catchMaybeIO $ do
 			writeFile (transferLockFile tfile) ""
 			writeTransferInfoFile info tfile
+		return (mfd, True)
 #endif
 	cleanup _ Nothing = noop
 	cleanup tfile (Just fd) = do

debian/changelog

@@ -9,6 +9,8 @@ git-annex (4.20130710) UNRELEASED; urgency=low
   * uninit: Preserve .git/annex/objects at the end, if it still
     has content, so that old versions of files and deleted files
     are not deleted. Print a message with some suggested actions.
+  * When a transfer is already being run by another process,
+    proceed on to the next file, rather than dying.
 
  -- Joey Hess <joeyh@debian.org>  Tue, 09 Jul 2013 19:17:13 -0400