Additions

• Lwt_mvar.take_available, Lwt_mvar.is_empty (#459, Hezekiah Carty).
• Lwt_io.open_temp_file, Lwt_io.with_temp_file (#467, Joe Thomas).
• New reference documentation for module Lwt (#469).
• Lwt_pool.clear and ?dispose argument for Lwt_pool.create (#483, Hezekiah Carty).
• Lwt_pool.wait_queue_length (#493, Jerome Vouillon).

Bugs fixed

• Lwt.npick never worked (#447, Zack Coker).
• Lwt_pool.use now always calls ?validate on elements (#461, Joe Thomas).
• Better locations generated by the PPX (#470, Fabian Hemmer).
• Keep worker thread count accurate in Lwt_unix when pthread_create fails (#493, @koen-struyve).
• Leaked exceptions in Lwt_list (#499).
• Memory leak in Lwt_unix.getnameinfo (#503, Hannes Mehnert).

Planned to break in 4.0.0

See #453 for details and instructions about planned breakage in Lwt 4.0.0.

• The semantics of Lwt will be adjusted for better exception and stack safety (#500).
• The PPX will be factored out into its own opam package, lwt_ppx. This package is installable from opam now, as of Lwt 3.2.0 (#338).
• Similarly, the deprecated Camlp4 syntax will be factored out into lwt_camlp4, which is installable from opam now (#370).
• Modules Lwt_log, Lwt_log_core, Lwt_log_rules, and Lwt_daemon are being deprecated and factored out into opam package lwt_log, also installable from opam now. Use the logs library for logging, in particular module Logs_lwt. Direct daemonization is deprecated on most platforms (#484, Hannes Mehnert).
• The >> construct from the PPX will be deleted (#471, Raphaël Proust).
• Package lwt.preemptive is being merged into lwt.unix. In 3.2.0, lwt.preemptive becomes an alias for lwt.unix, and the package name lwt.preemptive will be deleted in 4.0.0 (#487).

Deprecations

• Lwt.waiter_of_wakener should not be used, as it can lead to soundness bugs in future (but not current) Lwt (#458).
• Lwt_sequence was deprecated in Lwt 2.6.0, but it now has a warning attached, as do Lwt.add_task_r and Lwt.add_task_l, which use it (#361).
• Use of the following functions is discouraged, but they have not yet received deprecation warnings: Lwt.with_value, Lwt.cancel, Lwt.state, Lwt.ignore_result (#359, #469).

Miscellaneous

• Replace references to Camlp4 in the manual with the PPX (#457, Bobby Priambodo).
• More tests for Lwt_pool (#464, Joe Thomas).
• Expect tests for the PPX (#474, Fabian Hemmer).