Additions

• Port to Jbuilder (#374, Andrew Ray).
• Lwt_io.establish_server_with_client_address (#346, Rudi Grinberg).
• Lwt_unix.getcwd (#403, Raphaël Proust).

Planned to break in 4.0.0

• Delete lwt.simple-top (#371).
• Delete Lwt_chan (#441).

Fixes

• Make Lwt_log functions tail-recursive (#348, Jan Doms).
• Make more of Lwt_list tail-recursive (#347, Jan Doms).
• Improve string messages in exceptions (#368, #382, Jan Doms, Raphaël Proust).
• Don't call Unix.set_nonblock or Unix.clear_nonblock unnecessarily on some fds (#356, David Sheets).
• Lwt_unix.sleep and Lwt_unix.timeout returning too early when using libev (#433, Stijn Devriendt).
• Lwt_sequence.fold_r iterating the wrong way in some cases (#405, Stijn Devriendt).
• Build conflicts in some cases due to duplicate cst_to_constr function (#362, Jérémie Dimino).
• Don't use deprecated readdir_r system call (#430, Raphaël Proust).

Miscellaneous

• The Lwt core, lwt.ml, has been thoroughly refactored and commented (#354, reviewed Gabriel Radanne, Edwin Török, Raphaël Proust, Jan Doms, Fabian Hemmer, Sebastien Mondet, Simon Cruanes, Anil Madhavapeddy, Pierre Chambart, and many others).
• Lots of tests for most of the Lwt core (#339, #389, #392, #440, #448, #450, Joseph Thomas, Ryan Slade).
• Documentation fixes (including by Joseph Thomas, Raphaël Proust, Richard Degenne, Stavros Polymenis).
• Contributing documentation (#379).
• Massively adjust whitespace for legibility (#400, #409, #416, Richard Degenne).
• Improvements to CI (Etienne Millon, Raphael Rafatpanah, Zack Coker, Yotam Barnoy).
• The additional packages lwt_ssl, lwt_react, lwt_glib get new minor releases, the change being new Jbuilder build systems (#374, Andrew Ray).

Breaking

• These changes were originally announced in release 2.7.0 (#308).
• Lwt_engine.libev now has an optional argument for selecting the libev back end (#269, #294, Jeremy Yallop).
• Lwt_io.establish_server has been changed to make it more difficult to leak file descriptors (#258, #260).
• Lwt_io.shutdown_server now evaluates to a promise, which completes when the listening socket's close(2) operation completes (#259).
• Lwt_unix.bind now evaluates to a promise, because the bind(2) system call can block for Unix domain sockets (#296, requested David Sheets).
• ocamlfind packages lwt.react, lwt.ssl, lwt.glib are replaced by lwt_react, lwt_ssl, lwt_glib. These have been separate OPAM packages, under those names, since 2.7.0 (#301).

Fixes

• OCaml 4.05 compatibility (Mauricio Fernandez, #322).
• Give Lwt_unix.file_exists the same semantics as Sys.file_exists, with respect to not raising Unix.Unix_error (Mauricio Fernandez, #316).
• Improve diagnostics from build scripts (Tim Cuthbertson, #313, #314).

Additions

• Announce Lwt_result, which was originally released as an experimental module in release 2.6.0 (Simon Cruanes, #320, #247).

General

• Values of types 'a Lwt.t are now referred to as promises rather than threads (#300). The manual has not yet been updated.

Breaking

• After this release, Lwt will switch to semantic versioning. Future breaking changes will first require deprecation, then a major version number increase (#293).
• Lwt no longer supports OCaml 4.01 (#272).
• Lwt_unix.fdatasync is no longer available on macOS. It was calling an undocumented system call on that system (#285, Jeremy Yallop).

Planned to break in 3.0.0

• APIs in this category have deprecation messages attached. The messages will be displayed if you recompile your code, and can also be seen in #308.
• Lwt_engine.libev will have an argument for selecting the libev back end (#269, #294, Jeremy Yallop).
• Lwt_io.establish_server will be replaced by a version that makes it difficult to leak file descriptors (#258, #260).
• Lwt_io.shutdown_server will evaluate to a promise, which indicates when the close operation completes (#259).
• Lwt_unix.bind will evaluate to a promise, since bind can block for Unix domain sockets (#296, requested David Sheets).
• ocamlfind packages lwt.react, lwt.ssl, and lwt.glib will be replaced by the new lwt_react, lwt_ssl, and lwt_glib. These are now distributed in new OPAM packages with the same names, separately from OPAM package lwt (#301).

Additions

• Lwt_unix.readv and Lwt_unix.writev – zero-copy scatter/gather I/O (#291, #299).
• ?fail_on_error argument for Lwt_log.load_rules (#306, Daniil Baturin).
• Lwt_log.level_of_string (#306, Daniil Baturin).

Changes

• Lwt_stream.of_list, Lwt_stream.of_array, Lwt_stream.of_string now immediately push all elements into the created streams (#239, Spiros Eliopoulos).

Deprecations

• Lwt_stream.map_exn in favor of Lwt_stream.wrap_exn, which uses OCaml's standard result type (#295).

Bugs fixed

• Ungraceful failure if directory handle used after Lwt_unix.closedir (#292).
• Buffer overflow in Lwt_unix.readdir and Lwt_unix.readdir_n (#292).
• Unnecessary allocations in Lwt_unix.readdir_n (#292, found Jeremly Yallop).

Miscellaneous

• Annotate existing deprecations with [@@ocaml.deprecated ...] (5737f5b).
• Improvements to the examples (#288, Rich Neswold).
• Documentation fixes, including by Rich Neswold.
• New tests and various minor internal improvements.
• Run tests in CI with all OCaml warnings enabled (dadb926).
• Much cleaner build output.
• Add scratch/ directory for local use by developers.

Additions

• Lwt_stream.closed and Lwt_stream.is_closed (#223, Spiros Eliopoulos).
• Lwt_switch.with_switch (#256, Thomas Leonard).
• Define 'a Lwt.result as ('a, exn) result (#247, Simon Cruanes).
• Lwt_condition.broadcast_exn (#241, Nicolas Ojeda Bar).
• Lwt_unix.utimes (#193).

Bugs fixed

• Memory leak in Lwt_unix.readdir_n (#229, diagnosed Thomas Leonard).
• Memory leak in Lwt.protected (#56, #181, reported @ygrek, Mauricio Fernandez).
• Lwt_switch.turn_off hook exception handling (995b704).
• Handling of ENOTCONN when channels passed to handler of Lwt_io.establish_server are closed (95fb431).
• Duplicate exceptions on implicit close in Lwt_io.with_connection (b1afe45).
• Deadlock in Lwt_main.at_exit (#48, #114, reported Jérôme Vouillon, Vincent Bernardoff).
• Performance of Lwt_preemptive.detach (#218, #219, Mauricio Fernandez).
• Bad hash functions for libev loops (#146, reported Mark Christiaens).
• Hash of uninitialized data in Lwt_io (#217, reported Jeremy Yallop).
• Update log sections after Lwt_log.load_rules (#188, reported @rand00).
• Print three digits for milliseconds in Lwt_log (#264, Fabian Hemmer).
• Do not truncate Unix job notification ids in C (#277, diagnosed @stijn-devriendt).

Deprecations

• Lwt_stream.on_termination: bind on Lwt_stream.closed instead.
• Lwt.make_value, Lwt.make_error: use result's Ok and Error constructors.
• Lwt_pqueue, Lwt_sequence: use min-heaps and linked lists from another library (#135).
• Pa_lwt, Pa_lwt_log: use Ppx_lwt.

Miscellaneous

• Update examples to use PPX syntax instead of Camlp4 (#108, Peter Zotov).
• Set up Travis, AppVeyor for testing on Linux, OS X, Cygwin, and MinGW. MSVC also planned.
• Large amount of local documentation fixes (including by Hezekiah Carty, Etienne Millon, Leo Wzukw, Sebastien Mondet).
• A bunch of new tests.

• Fix compatibility for 4.03 (#227)
• Various documentation fixes (#199,#200,#210)
• Improve wildcard detection in the ppx (#198)
• Fix Lwt_stream: bounded_push#close wake the reader (#201)
• Fix infinite loop with Lwt_stream.choose (#214)
• Fix lazyness failure with Lwt_io.common#close (#207)

• Lwt_stream.on_terminate -> Lwt_stream.on_termination
• Lwt_unix: handle O_CLOEXEC
• Lwt_log: add OSX syslog path
• Ppx: Improve lwt%match, improve catchall detection
• Add Lwt_unix.file_exists and Lwt_unix.Large_file.file_exists
• Build fixes

• API CHANGE: Functions in Lwt_io that were previously using a
  ~buffer_size argument now takes a ~buffer argument.
• Accept ?buffer argument in Lwt_ssl.{in,out}_channel_of_descr.
• Use newer Ssl bigarray read/write functionality to avoid
  allocation in Lwt_ssl.
• Fix non-reentrant function calls (#136)
• IPv4 multicast support.
• Add support for if%lwt in ppx extension.
• Add Lwt.return_some.
• Disable log syntax extension by default in ppx.
  Give [-log] as ppx argument to enable it.
• Nanosecond precision for Lwt_unix.stat.
• Minor fixes + documentation improvements.

Bug fix release:

• fix compilation under Windows;
• fix Lwt_engine.on_timer.

• Fix Lwt_ssl.{in,out}_channel_of_descr: shutdown and close the socket when the channel is closed.