Make reaper workloads modifiable

It is convenient to be able to modify reaper workloads outside of the
`reaperAction` in scenarios where we don't want to wait for `reaperDelay` for
the jobs to be updated. This PR adds an atomic `reaperModify` function to the
reaper API which enables this.

Since this changes the visible `Reaper` constructor, I did a major version bump
(`auto-update` 0.1.6 -> 0.2.0) and added a changelog entry. I also bumped the
`warp` dependency on `auto-update`.

auto-update/ChangeLog.md

@@ -1,5 +1,11 @@
 # ChangeLog for auto-update
 
+## 0.2.0
+
+* Add `reaperModify` to the `Reaper` API, allowing workload modification outside
+  of the main `reaperAction` loop.
+  [#985](https://github.com/yesodweb/wai/pull/985)
+
 ## 0.1.6
 
 * Add control of activation on leading vs. trailing edges for Control.Debounce

auto-update/Control/Reaper.hs

@@ -109,6 +109,20 @@ data Reaper workload item = Reaper
     -- ^ Adding an item to the workload
     , reaperRead :: IO workload
     -- ^ Reading workload.
+    , reaperModify :: (workload -> workload) -> IO workload
+    -- ^ Modify the workload. The resulting workload is returned.
+    --
+    --   If there is no reaper thread, the modifier will not be applied and
+    --   'reaperEmpty' will be returned.
+    --
+    --   If the reaper is currently executing jobs, those jobs will not be in
+    --   the given workload and the workload might appear empty.
+    --
+    --   If all jobs are removed by the modifier, the reaper thread will not be
+    --   killed. The reaper thread will only terminate if 'reaperKill' is called
+    --   or the result of 'reaperAction' satisfies 'reaperNull'.
+    --
+    --  @since 0.2.0
     , reaperStop :: IO workload
     -- ^ Stopping the reaper thread if exists.
     --   The current workload is returned.
@@ -136,6 +150,7 @@ mkReaper settings@ReaperSettings{..} = do
         Reaper
             { reaperAdd = add settings stateRef tidRef
             , reaperRead = readRef stateRef
+            , reaperModify = modifyRef stateRef
             , reaperStop = stop stateRef
             , reaperKill = kill tidRef
             }
@@ -145,6 +160,13 @@ mkReaper settings@ReaperSettings{..} = do
         case mx of
             NoReaper -> return reaperEmpty
             Workload wl -> return wl
+    modifyRef stateRef modifier = atomicModifyIORef' stateRef $ \mx ->
+        case mx of
+            NoReaper ->
+              (NoReaper, reaperEmpty)
+            Workload wl ->
+              let !wl' = modifier wl
+               in (Workload wl', wl')
     stop stateRef = atomicModifyIORef' stateRef $ \mx ->
         case mx of
             NoReaper -> (NoReaper, reaperEmpty)

auto-update/auto-update.cabal

@@ -1,5 +1,5 @@
 name:                auto-update
-version:             0.1.6
+version:             0.2.0
 synopsis:            Efficiently run periodic, on-demand actions
 description:         API docs and the README are available at <http://www.stackage.org/package/auto-update>.
 homepage:            https://github.com/yesodweb/wai

warp/warp.cabal

@@ -39,7 +39,7 @@ Flag x509
 Library
   Build-Depends:     base                      >= 4.12       && < 5
                    , array
-                   , auto-update               >= 0.1.3    && < 0.2
+                   , auto-update               >= 0.2      && < 0.3
                    , bsb-http-chunked                         < 0.1
                    , bytestring                >= 0.9.1.4
                    , case-insensitive          >= 0.2