automatic stall detection

annex.stalldetection can now be set to "true" to make git-annex do
automatic stall detection when it detects a remote is updating its transfer
progress consistently enough.

This commit was sponsored by Luke Shumaker on Patreon.

Annex/StallDetection.hs

@@ -0,0 +1,78 @@
+{- Stall detection for transfers.
+ -
+ - Copyright 2020-2021 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Annex.StallDetection (detectStalls, StallDetection) where
+
+import Annex.Common
+import Types.StallDetection
+import Utility.Metered
+import Utility.HumanTime
+import Utility.DataUnits
+import Utility.ThreadScheduler
+
+import Control.Concurrent.STM
+
+detectStalls :: Maybe StallDetection -> TVar (Maybe BytesProcessed) -> IO () -> IO ()
+detectStalls Nothing _ _ = noop
+detectStalls (Just (StallDetection minsz duration)) metervar onstall =
+	detectStalls' minsz duration metervar onstall Nothing
+detectStalls (Just ProbeStallDetection) metervar onstall = do
+	-- Only do stall detection once the progress is confirmed to be
+	-- consistently updating. After the first update, it needs to
+	-- advance twice within 30 seconds. With that established,
+	-- if no data at all is sent for a 60 second period, it's
+	-- assumed to be a stall.
+	v <- getval >>= waitforfirstupdate
+	ontimelyadvance v $ \v' -> ontimelyadvance v' $
+		detectStalls' 1 duration metervar onstall
+  where
+	getval = atomically $ fmap fromBytesProcessed
+		<$> readTVar metervar
+	
+	duration = Duration 60
+
+	delay = Seconds (fromIntegral (durationSeconds duration) `div` 2)
+	
+	waitforfirstupdate startval = do
+		threadDelaySeconds delay
+		v <- getval
+		if v > startval
+			then return v
+			else waitforfirstupdate startval
+
+	ontimelyadvance v cont = do
+		threadDelaySeconds delay
+		v' <- getval
+		when (v' > v) $
+			cont v'
+
+detectStalls'
+	:: ByteSize
+	-> Duration
+	-> TVar (Maybe BytesProcessed)
+	-> IO ()
+	-> Maybe ByteSize
+	-> IO ()
+detectStalls' minsz duration metervar onstall st = do
+	threadDelaySeconds delay
+	-- Get whatever progress value was reported most recently, if any.
+	v <- atomically $ fmap fromBytesProcessed
+		<$> readTVar metervar
+	let cont = detectStalls' minsz duration metervar onstall v
+	case (st, v) of
+		(Nothing, _) -> cont
+		(_, Nothing) -> cont
+		(Just prev, Just sofar)
+			-- Just in case a progress meter somehow runs
+			-- backwards, or a second progress meter was
+			-- started and is at a smaller value than
+			-- the previous one.
+			| prev > sofar -> cont
+			| sofar - prev < minsz -> onstall
+			| otherwise -> cont
+  where
+	delay = Seconds (fromIntegral (durationSeconds duration))

Annex/TransferrerPool.hs

@@ -1,6 +1,6 @@
 {- A pool of "git-annex transferrer" processes
  -
- - Copyright 2013-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2013-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -16,15 +16,13 @@ import Types.TransferrerPool
 import Types.Transferrer
 import Types.Transfer
 import qualified Types.Remote as Remote
-import Types.StallDetection
 import Types.Messages
 import Types.CleanupActions
 import Messages.Serialized
 import Annex.Path
+import Annex.StallDetection
 import Utility.Batch
 import Utility.Metered
-import Utility.HumanTime
-import Utility.ThreadScheduler
 import qualified Utility.SimpleProtocol as Proto
 
 import Control.Concurrent
@@ -177,28 +175,6 @@ performTransfer stalldetection level runannex r t info transferrer = do
 	updatemeter _bpv metervar Nothing = liftIO $
 		atomically $ writeTVar metervar Nothing
 
-detectStalls :: Maybe StallDetection -> TVar (Maybe BytesProcessed) -> IO () -> IO ()
-detectStalls Nothing _ _ = noop
-detectStalls (Just (StallDetection minsz duration)) metervar onstall = go Nothing
-  where
-	go st = do
-		threadDelaySeconds (Seconds (fromIntegral (durationSeconds duration)))
-		-- Get whatever progress value was reported last, if any.
-		v <- atomically $ fmap fromBytesProcessed
-			<$> readTVar metervar
-		let cont = go v
-		case (st, v) of
-			(Nothing, _) -> cont
-			(_, Nothing) -> cont
-			(Just prev, Just sofar)
-				-- Just in case a progress meter somehow runs
-				-- backwards, or a second progress meter was
-				-- started and is at a smaller value than
-				-- the previous one.
-				| prev > sofar -> cont
-				| sofar - prev < minsz -> onstall
-				| otherwise -> cont
-
 {- Starts a new git-annex transfer process, setting up handles
  - that will be used to communicate with it. -}
 mkTransferrer :: SignalActionsVar -> RunTransferrer -> IO Transferrer

CHANGELOG

@@ -15,6 +15,9 @@ git-annex (8.20210128) UNRELEASED; urgency=medium
   * Fix build on openbsd.
     Thanks, James Cook for the patch.
   * Include libkqueue.h file needed to build the assistant on BSDs.
+  * annex.stalldetection can now be set to "true" to make git-annex
+    do automatic stall detection when it detects a remote is updating its
+    transfer progress consistently enough.
 
  -- Joey Hess <id@joeyh.name>  Thu, 28 Jan 2021 12:34:32 -0400
 

Types/GitConfig.hs

@@ -205,7 +205,7 @@ extractGitConfig configsource r = GitConfig
 	, annexRetryDelay = Seconds
 		<$> getmayberead (annexConfig "retrydelay")
 	, annexStallDetection =
-		either (const Nothing) Just . parseStallDetection
+		either (const Nothing) id . parseStallDetection
 			=<< getmaybe (annexConfig "stalldetection")
 	, annexAllowedUrlSchemes = S.fromList $ map mkScheme $
 		maybe ["http", "https", "ftp"] words $
@@ -377,7 +377,7 @@ extractRemoteGitConfig r remotename = do
 		, remoteAnnexRetryDelay = Seconds
 			<$> getmayberead "retrydelay"
 		, remoteAnnexStallDetection =
-			either (const Nothing) Just . parseStallDetection
+			either (const Nothing) id . parseStallDetection
 				=<< getmaybe "stalldetection"
 		, remoteAnnexAllowUnverifiedDownloads = (== Just "ACKTHPPT") $
 			getmaybe ("security-allow-unverified-downloads")

Types/StallDetection.hs

@@ -1,6 +1,6 @@
 {- types for stall detection
  -
- - Copyright 2020 Joey Hess <id@joeyh.name>
+ - Copyright 2020-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -10,20 +10,32 @@ module Types.StallDetection where
 import Utility.DataUnits
 import Utility.HumanTime
 import Utility.Misc
+import Git.Config
 
--- Unless the given number of bytes have been sent over the given
--- amount of time, there's a stall.
-data StallDetection = StallDetection ByteSize Duration
+data StallDetection
+	= StallDetection ByteSize Duration
+	-- ^ Unless the given number of bytes have been sent over the given
+	-- amount of time, there's a stall.
+	| ProbeStallDetection
+	-- ^ Used when unsure how frequently transfer progress is updated,
+	-- or how fast data can be sent.
 	deriving (Show)
 
 -- Parse eg, "0KiB/60s"
-parseStallDetection :: String -> Either String StallDetection
-parseStallDetection s = 
+--
+-- Also, it can be set to "true" (or other git config equivilants)
+-- to enable ProbeStallDetection. 
+-- And "false" (and other git config equivilants) explicitly
+-- disable stall detection.
+parseStallDetection :: String -> Either String (Maybe StallDetection)
+parseStallDetection s = case isTrueFalse s of
+	Nothing -> do
 		let (bs, ds) = separate (== '/') s
-	in do
 		b <- maybe 
 			(Left $ "Unable to parse stall detection amount " ++ bs)
 			Right
 			(readSize dataUnits bs)
 		d <- parseDuration ds
-		return (StallDetection b d)
+		return (Just (StallDetection b d))
+	Just True -> Right (Just ProbeStallDetection)
+	Just False -> Right Nothing

doc/git-annex.mdwn

@@ -1427,12 +1427,18 @@ Remotes are configured using these settings in `.git/config`.
   When this happens, the transfer will be considered to have failed, so
   settings like annex.retry will control what it does next.
 
-  The value specifies how much data git-annex should expect to see
-  flowing, minimum, when it's not stalled, over a given period of time.
-  The format is "$amount/$timeperiod". 
+  Set to "true" to enable automatic stall detection. With this setting,
+  if a remote does not update its progress consistently, no stall detection
+  will be done. And it may take a while for git-annex to decide a remote
+  is really stalled when using automatic stall detection, since it needs
+  to be conservative about what looks like a stall.
+
+  For more fine control over what constitutes a stall, set to a value in
+  the form "$amount/$timeperiod" to specify how much data git-annex should
+  expect to see flowing, minimum, over a given period of time.
 
   For example, to detect outright stalls where no data has been transferred
-  after 30 seconds: `git config annex.stalldetection "0/30s"`
+  after 30 seconds: `git config annex.stalldetection "1KB/30s"`
 
   Or, if you have a remote on a USB drive that is normally capable of
   several megabytes per second, but has bad sectors where it gets

doc/todo/dynamic_stall_detection.mdwn

@@ -3,14 +3,15 @@ to detect and retry stalls. But most users are not going to configure this.
 Could something be done to dynamically detect a stall, without configuration?
 
 Eg, wait until data starts to flow, and then check if there's at least some
-data being sent each minute. If so, the progress display is being updated
-at least every minute. So then if 2 minutes go by without more data
+data being sent each half minute. If so, the progress display is being updated
+at least every minute. So then if 1 minute goes by without more data
 flowing, it's almost certainly stalled. And if the progress display is
 updated less frequently, see if it's updated every 2 minutes, etc. Although
 realistically, progress displays are updated every chunk, and there's
 typically more than 1 chunk per minute. So longer durations than 1 minute
-may be an unncessary complication. And a couple of minutes to detect a
-stall is fine.
+may be an unncessary complication. And a minute to detect a stall is fine.
+
+> Implemented this, annex.stalldetection = true enables automatic.
 
 It may still need a config to turn it on, because running
 transfers in separate processes can lead to more resource use, or even

git-annex.cabal

@@ -662,6 +662,7 @@ Executable git-annex
     Annex.SpecialRemote
     Annex.SpecialRemote.Config
     Annex.Ssh
+    Annex.StallDetection
     Annex.TaggedPush
     Annex.Tmp
     Annex.Transfer