diff --git a/AUTHORS.adoc b/AUTHORS.adoc
index f2be0ad2..007ed5ce 100644
--- a/AUTHORS.adoc
+++ b/AUTHORS.adoc
@@ -17,3 +17,4 @@
 - Geoff Gole (@gsg)
 - Roma Sokolov (@little-arhat)
 - Malcolm Matalka (`orbitz`)
+- David Sheets (@dsheets)
diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index 506ae9df..85ecba8e 100644
--- a/CHANGELOG.adoc
+++ b/CHANGELOG.adoc
@@ -1,5 +1,27 @@
 = Changelog
 
+== 0.22
+
+- threads/CCLock: add `try_with_lock` to wrap `Mutex.try_lock`
+- Add `CCMultiSet.remove_all`
+- document errors in `CCIO` (close #86)
+- use the new qtest/qcheck
+
+== 0.21
+
+- (breaking) make default `start`/`stop` arguments empty in printers (#82)
+
+- add `CCFormat.{with_color_sf,fprintf_dyn_color,sprintf_dyn_color}`
+- add `CCFormat.Dump` for easy debugging (see #82)
+- add `CCArray.Sub.to_list`
+- add `CCArray.{sorted,sort_indices,sort_ranking}` (closes #81)
+
+- handle '\r` in CCSexpM (fixes #83)
+- add alias `Containers.IO`
+- bugfixes in `CCArray.Sub`
+- bugfix + tests for `CCArray.Sub.sub`
+- disable parallel build to support cygwin
+
 == 0.20
 
 - bugfix in `CCArray.equal`
diff --git a/README.adoc b/README.adoc
index 0bb2bf97..62877090 100644
--- a/README.adoc
+++ b/README.adoc
@@ -180,7 +180,6 @@ Iterators:
 - `CCKList`, a persistent iterator structure (akin to a lazy list, without memoization)
 - `CCKTree`, an abstract lazy tree structure
 
-
 === Thread
 
 In the library `containers.thread`, for preemptive system threads:
diff --git a/_oasis b/_oasis
index 646621b2..60512027 100644
--- a/_oasis
+++ b/_oasis
@@ -1,6 +1,6 @@
 OASISFormat: 0.4
 Name:        containers
-Version:     0.20
+Version:     0.22
 Homepage:    https://github.com/c-cube/ocaml-containers
 Authors:     Simon Cruanes
 License:     BSD-2-clause
diff --git a/opam b/opam
index a2874818..066583a7 100644
--- a/opam
+++ b/opam
@@ -38,8 +38,6 @@ depopts: [
 ]
 conflicts: [
   "sequence" { < "0.5" }
-  "qtest" { < "2.2" }
-  "qcheck"
 ]
 tags: [ "stdlib" "containers" "iterators" "list" "heap" "queue" ]
 homepage: "https://github.com/c-cube/ocaml-containers/"
diff --git a/src/core/CCFormat.mli b/src/core/CCFormat.mli
index 6a826b15..187577dd 100644
--- a/src/core/CCFormat.mli
+++ b/src/core/CCFormat.mli
@@ -173,7 +173,7 @@ val with_color_sf : string -> ('a, t, unit, string) format4 -> 'a
       CCFormat.with_color_sf "red" "%a" CCFormat.Dump.(list int) [1;2;3] |> print_endline;;
     ]}
     {b status: experimental}
-    @since NEXT_RELEASE *)
+    @since 0.21 *)
 
 (** {2 IO} *)
 
@@ -207,7 +207,7 @@ val sprintf_dyn_color : colors:bool -> ('a, t, unit, string) format4 -> 'a
       CCFormat.sprintf_dyn_color ~colors:false "@{<Red>%a@}"
         CCFormat.Dump.(list int) [1;2;3] |> print_endline;;
     ]}
-    @since NEXT_RELEASE *)
+    @since 0.21 *)
 
 val fprintf : t -> ('a, t, unit ) format -> 'a
 (** Alias to {!Format.fprintf}
@@ -215,7 +215,7 @@ val fprintf : t -> ('a, t, unit ) format -> 'a
 
 val fprintf_dyn_color : colors:bool -> t -> ('a, t, unit ) format -> 'a
 (** Similar to {!fprintf} but enable/disable colors depending on [colors]
-    @since NEXT_RELEASE *)
+    @since 0.21 *)
 
 val ksprintf :
   f:(string -> 'b) ->
@@ -246,7 +246,7 @@ val to_file : string -> ('a, t, unit, unit) format4 -> 'a
         [| [1, true; 2, false]; []; [42, false] |];;
     ]}
 
-    @since NEXT_RELEASE *)
+    @since 0.21 *)
 
 module Dump : sig
   type 'a t = 'a printer
diff --git a/src/core/CCIO.mli b/src/core/CCIO.mli
index 6ce18d4b..6319fb25 100644
--- a/src/core/CCIO.mli
+++ b/src/core/CCIO.mli
@@ -46,6 +46,7 @@ val with_in : ?mode:int -> ?flags:open_flag list ->
 (** Open an input file with the given optional flag list, calls the function
     on the input channel. When the function raises or returns, the
     channel is closed.
+    @raise Sys_error in case of error (same as {!open_in} and {!close_in})
     @param flags opening flags (default [[Open_text]]). [Open_rdonly] is used in any cases *)
 
 val read_chunks : ?size:int -> in_channel -> string gen
@@ -77,12 +78,14 @@ val with_out : ?mode:int -> ?flags:open_flag list ->
   string -> (out_channel -> 'a) -> 'a
 (** Same as {!with_in} but for an output channel
     @param flags opening flags (default [[Open_creat; Open_trunc; Open_text]]).
+    @raise Sys_error in case of error (same as {!open_out} and {!close_out})
     [Open_wronly] is used in any cases *)
 
 val with_out_a : ?mode:int -> ?flags:open_flag list ->
   string -> (out_channel -> 'a) -> 'a
 (** Similar to {!with_out} but with the [[Open_append; Open_creat; Open_wronly]]
-    flags activated, to append to the file *)
+    flags activated, to append to the file.
+    @raise Sys_error in case of error (same as {!open_out} and {!close_out}) *)
 
 val write_line : out_channel -> string -> unit
 (** Write the given string on the channel, followed by "\n" *)
@@ -102,6 +105,7 @@ val with_in_out : ?mode:int -> ?flags:open_flag list ->
   string -> (in_channel -> out_channel -> 'a) -> 'a
 (** Combines {!with_in} and {!with_out}.
     @param flags opening flags (default [[Open_creat]])
+    @raise Sys_error in case of error
     @since 0.12 *)
 
 (** {2 Misc for Generators} *)
@@ -144,7 +148,7 @@ module File : sig
   (** [remove_exn path] tries to remove the file at [path] from the
       file system.
 
-      {b Raises} [Sys_error] if there is no file at [path].
+      @raise Sys_error if there is no file at [path] or access rights are wrong.
       @since 0.8 *)
 
   val remove : t -> unit or_error
@@ -158,11 +162,13 @@ module File : sig
   val read_dir : ?recurse:bool -> t -> t gen
   (** [read_dir d] returns a sequence of files and directory contained
       in the directory [d] (or an empty stream if [d] is not a directory)
+      @raise Sys_error in case of error (e.g. permission denied)
       @param recurse if true (default [false]), sub-directories are also
         explored *)
 
   val read_exn : t -> string
   (** Read the content of the given file, or raises some exception
+      @raise Sys_error in case of error
       @since 0.16 *)
 
   val read : t -> string or_error
@@ -171,6 +177,7 @@ module File : sig
 
   val append_exn : t -> string -> unit
   (** Append the given string into the given file, possibly raising
+      @raise Sys_error in case of error
       @since 0.16 *)
 
   val append : t -> string -> unit or_error
@@ -179,6 +186,7 @@ module File : sig
 
   val write_exn : t -> string -> unit
   (** Write the given string into the given file, possibly raising
+      @raise Sys_error in case of error
       @since 0.16 *)
 
   val write : t -> string -> unit or_error
@@ -191,7 +199,8 @@ module File : sig
   (** Similar to {!read_dir} (with [recurse=true]), this function walks
       a directory recursively and yields either files or directories.
       Is a file anything that doesn't satisfy {!is_directory} (including
-      symlinks, etc.) *)
+      symlinks, etc.)
+      @raise Sys_error in case of error (e.g. permission denied) during iteration *)
 
   val show_walk_item : walk_item -> string
 
diff --git a/src/core/containers.ml b/src/core/containers.ml
index bb89ba14..79bdf24a 100644
--- a/src/core/containers.ml
+++ b/src/core/containers.ml
@@ -83,4 +83,3 @@ module String = struct
   include CCString
 end
 module Vector = CCVector
-
diff --git a/src/data/CCMultiSet.ml b/src/data/CCMultiSet.ml
index 8f33b3f8..39d13019 100644
--- a/src/data/CCMultiSet.ml
+++ b/src/data/CCMultiSet.ml
@@ -33,6 +33,10 @@ module type S = sig
       @raise Invalid_argument if [n < 0]
       @since 0.6 *)
 
+  val remove_all : t -> elt -> t
+  (** [remove_all set x] removes all occurrences of [x] from [set]
+      @since 0.22 *)
+
   val update : t -> elt -> (int -> int) -> t
   (** [update set x f] calls [f n] where [n] is the current multiplicity
       of [x] in [set] ([0] to indicate its absence); the result of [f n]
@@ -136,6 +140,8 @@ module Make(O : Set.OrderedType) = struct
 
   let remove ms x = remove_mult ms x 1
 
+  let remove_all ms x = M.remove x ms
+
   let update ms x f =
     let n = count ms x in
     match f n with
diff --git a/src/data/CCMultiSet.mli b/src/data/CCMultiSet.mli
index 8dcb6b9a..2f060dc2 100644
--- a/src/data/CCMultiSet.mli
+++ b/src/data/CCMultiSet.mli
@@ -33,6 +33,10 @@ module type S = sig
       @raise Invalid_argument if [n < 0]
       @since 0.6 *)
 
+  val remove_all : t -> elt -> t
+  (** [remove_all set x] removes all occurrences of [x] from [set]
+      @since 0.22 *)
+
   val update : t -> elt -> (int -> int) -> t
   (** [update set x f] calls [f n] where [n] is the current multiplicity
       of [x] in [set] ([0] to indicate its absence); the result of [f n]
diff --git a/src/threads/CCLock.ml b/src/threads/CCLock.ml
index cd9aa456..c1f0bf14 100644
--- a/src/threads/CCLock.ml
+++ b/src/threads/CCLock.ml
@@ -35,6 +35,18 @@ let with_lock l f =
   assert_equal 10 (get l)
 *)
 
+let try_with_lock l f =
+  if Mutex.try_lock l.mutex
+  then
+    try
+      let x = f l.content in
+      Mutex.unlock l.mutex;
+      Some x
+    with e ->
+      Mutex.unlock l.mutex;
+      raise e
+  else None
+
 module LockRef = struct
   type 'a t = 'a lock
   let get t = t.content
diff --git a/src/threads/CCLock.mli b/src/threads/CCLock.mli
index 75e4b07c..354e47c0 100644
--- a/src/threads/CCLock.mli
+++ b/src/threads/CCLock.mli
@@ -18,6 +18,12 @@ val with_lock : 'a t -> ('a -> 'b) -> 'b
     the lock [l], in a critical section. If [f x] fails, [with_lock l f]
     fails too but the lock is released *)
 
+val try_with_lock : 'a t -> ('a -> 'b) -> 'b option
+(** [try_with_lock l f] runs [f x] in a critical section if [l] is not
+    locked. [x] is the value protected by the lock [l]. If [f x]
+    fails, [try_with_lock l f] fails too but the lock is released
+    @since 0.22 *)
+
 (** Type allowing to manipulate the lock as a reference
     @since 0.13 *)
 module LockRef : sig
@@ -48,7 +54,8 @@ val mutex : _ t -> Mutex.t
 (** Underlying mutex *)
 
 val get : 'a t -> 'a
-(** Get the value in the lock. The value that is returned isn't protected! *)
+(** Atomically get the value in the lock. The value that is returned
+    isn't protected! *)
 
 val set : 'a t -> 'a -> unit
 (** Atomically set the value