package lwt
Install
Dune Dependency
Authors
Maintainers
Sources
sha256=fc1654bb06fdd48180f093f6e05e7264936626a11fef23cc8cf2ca4b5e3d7d44
md5=6c45ce0035f627d0de0d3d185f2a1a7f
Description
A promise is a value that may become determined in the future.
Lwt provides typed, composable promises. Promises that are resolved by I/O are resolved by Lwt in parallel.
Meanwhile, OCaml code, including code creating and waiting on promises, runs in a single thread by default. This reduces the need for locks or other synchronization primitives. Code can be run in parallel on an opt-in basis.
Published: 19 Apr 2017
README
Lwt
Lwt is OCaml's concurrent programming library. It provides a single data type: the promise, which is a value that will become determined in the future. Creating a promise spawns a computation. When that computation is I/O, Lwt runs it in parallel with your OCaml code.
OCaml code, including creating and waiting on promises, is run in a single thread by default, so you don't have to worry about locking or preemption. You can detach code to be run in separate threads on an opt-in basis.
Here is a simplistic Lwt program which requests the Google front page, and fails if the request is not completed in five seconds:
let () =
let request =
let%lwt addresses = Lwt_unix.getaddrinfo "google.com" "80" [] in
let google = (List.hd addresses).Lwt_unix.ai_addr in
Lwt_io.(with_connection google (fun (incoming, outgoing) ->
let%lwt () = write outgoing "GET / HTTP/1.1\r\n" in
let%lwt () = write outgoing "Connection: close\r\n\r\n" in
let%lwt response = read incoming in
Lwt.return (Some response)))
in
let timeout =
let%lwt () = Lwt_unix.sleep 5. in
Lwt.return None
in
match Lwt_main.run (Lwt.pick [request; timeout]) with
| Some response -> print_string response
| None -> prerr_endline "Request timed out"; exit 1
(* ocamlfind opt -package lwt.unix -package lwt.ppx -linkpkg -o request example.ml
./request *)
In the program, functions such as Lwt_io.write
create promises. The let%lwt ... in
construct is used to wait for a promise to become determined; the code after in
is scheduled to run in a "callback." Lwt.pick
races promises against each other, and behaves as the first one to complete. Lwt_main.run
forces the whole promise-computation network to be executed. All the visible OCaml code is run in a single thread, but Lwt internally uses a combination of worker threads and non-blocking file descriptors to resolve in parallel the promises that do I/O.
Installing
opam install lwt
Documentation
The manual can be found here. There are also some examples available in doc/examples
.
Note: much of the manual still refers to 'a Lwt.t
as "lightweight threads" or just "threads." This will be fixed in the new manual. 'a Lwt.t
is a promise, and has nothing to do with system or preemptive threads.
Contact
Open an issue, visit Gitter chat, email the maintainer, or ask in #ocaml. If you think enough people will be interested in the answer, it is also possible to ask on Stack Overflow.
Subscribe to the announcements issue to get news about Lwt releases. It is less noisy than watching the whole repository. Announcements are also made in /r/ocaml and on the OCaml mailing list.
Contributing
Lwt is a very mature library, but there is considerable room for improvement. Contributions are welcome. To clone the source and install a development version,
opam source --dev-repo --pin lwt
This will also install the development dependency OASIS.
A list of project suggestions and a roadmap can be found on the wiki.
License
Lwt is released under the LGPL, with the OpenSSL linking exception. See COPYING
.
Dependencies (8)
-
ppx_tools
build
- base-no-ppx
-
cppo_ocamlbuild
build
-
cppo
build & >= "1.1.0"
- result
-
ocamlbuild
build
-
ocamlfind
build & >= "1.5.0"
-
ocaml
>= "4.02.0" & < "4.08.0"
Dev Dependencies
None
-
0install
>= "2.14"
- albatross
- alcotest-lwt
- alcotest-mirage
- ambient-context-lwt
-
amqp-client
>= "0.9.0" & < "1.0.2" | >= "1.1.0"
- amqp-client-lwt
- angstrom-lwt-unix
- anthill
- anycache-lwt
-
arakoon
< "1.8.6" | >= "1.8.8"
- archi-lwt
-
arp
>= "2.3.1"
- arp-mirage
- awa-lwt
-
awa-mirage
< "0.2.0"
-
aws
< "1.0.0"
- aws-s3-lwt
- awsm-lwt
- azure-cosmos-db
- baardskeerder
- balancer
-
bap
< "1.0.0"
-
bap-server
< "0.3.0"
- bimage-lwt
-
biocaml
= "0.4.0"
-
bistro
< "0.5.0"
-
brotli
< "1.2.0"
- brozip
- builder
-
bun
>= "0.3.3"
- c3
- calculon
-
camltc
< "0.9.5"
- canary
-
capnp-rpc-lwt
< "1.2.3"
-
capnp-rpc-unix
>= "0.9.0" & < "1.2.3"
-
caqti-lwt
< "0.11.0"
-
carton-git
< "0.7.2"
- carton-lwt
- channel
-
charrua-client-lwt
< "1.2.0"
-
charrua-client-mirage
< "1.2.0"
-
charrua-core
< "0.3"
-
charrua-unix
>= "0.3" & < "0.11.0" | >= "0.11.2"
- cmdtui-lambda-term
- coclobas
-
cohttp-lwt
< "6.0.0~alpha2"
- cohttp-lwt-jsoo
- cohttp-lwt-unix
- cohttp-lwt-unix-nossl
- cohttp-lwt-unix-ssl
- cohttp-mirage
- comby
- comby-semantic
- conan-lwt
-
conduit-lwt
< "7.0.0"
-
conduit-lwt-unix
< "7.0.0"
-
cowabloga
>= "0.2.2"
-
crunch
>= "2.0.0"
- cstruct-lwt
- csv-lwt
- csvprovider
-
ctypes
>= "0.6.0" & < "0.15.0"
-
ctypes-foreign
>= "0.21.1"
-
curly
< "0.2.0"
-
current_docker
< "0.6.4"
-
current_examples
< "0.6.4"
-
current_git
< "0.6.4"
-
current_github
< "0.6.4"
-
current_gitlab
< "0.6.4"
-
current_ocluster
< "0.2"
-
current_slack
< "0.6.4"
-
current_web
< "0.6.4"
- DkSDKFFIOCaml_Std
- dap
-
data-encoding
< "0.1.1"
- datakit
- datakit-bridge-github
- datakit-bridge-local-git
- datakit-ci
-
datakit-client
>= "0.11.0"
- datakit-github
- datakit-server
- devkit
-
dht
< "0.2.0"
-
distributed
= "0.4.0"
- dkim-mirage
-
dns
>= "0.19.1" & < "1.0.0"
-
dns-forward
>= "0.9.0"
- dns-forward-lwt-unix
- dns-lwt
- dnssd
- docker_hub
- dream
- dream-httpaf
- dream-pure
- dropbox
- dune_watch
-
earlybird
< "1.0.0"
-
elasticsearch-cli
< "0.4"
-
eliom
= "6.3.0"
- eris-lwt
- ethernet
- ezcurl-lwt
- ezirmin
-
ezjsonm
>= "0.4.2" & < "0.5.0"
- ezjsonm-lwt
- ezresto
- ezresto-directory
- faraday-lwt
- faraday-lwt-unix
-
fat-filesystem
>= "0.12.0"
- fiber-lwt
-
flowtype
>= "0.62.0" & < "0.72.0"
-
frenetic
< "2.0.0"
- fswatch_lwt
- fuseau-lwt
- gamepad
- gdb
-
gdbprofiler
< "0.3"
-
git
!= "1.4.3" & != "1.7.2"
- git-paf
-
git-unix
= "1.11.1" | >= "3.0.0" & < "3.10.0"
- github
- github-hooks
-
github-unix
>= "4.4.0"
- gitlab-unix
-
gluten-lwt
< "0.4.0"
-
gluten-lwt-unix
< "0.4.0"
-
gluten-mirage
< "0.4.0"
- graphql-lwt
- gufo
- h1
- h1-lwt-unix
-
h2-lwt
< "0.10.0"
-
h2-lwt-unix
< "0.10.0"
- h2-mirage
- happy-eyeballs-lwt
- happy-eyeballs-mirage
-
hardcaml
< "1.1.0"
-
hardcaml-examples
>= "0.3.0"
- hardcaml-framework
- hardcaml-waveterm
-
hiredis
< "0.6"
- hl_yaml
- http-lwt-client
-
http-multipart-formdata
>= "2.0.0" & < "3.0.0"
- http2https
- httpaf-lwt-unix
- httpun-lwt
- httpun-mirage
- httpun-ws-lwt
-
hvsock
< "1.0.2"
- i3ipc
- imaplet-lwt
- influxdb-lwt
-
inotify
>= "2.4"
-
inquire
< "0.3.0"
-
iocaml
< "0.4.6"
-
iocaml-kernel
>= "0.4.3"
- iocamljs-kernel
- ip2location
- ip2locationio
- ip2whois
-
ipv6-multicast
< "0.9"
- irc-client-lwt
- irc-client-lwt-ssl
- irc-client-tls
-
irmin
< "0.9.6" | = "0.9.10" | >= "0.11.0" & < "2.7.0"
-
irmin-bench
< "2.7.0"
-
irmin-chunk
< "2.7.0"
-
irmin-containers
< "2.7.0"
-
irmin-fs
>= "2.3.0" & < "2.7.0"
-
irmin-git
>= "2.3.0" & < "2.7.0"
-
irmin-graphql
>= "2.3.0" & < "2.7.0"
-
irmin-http
>= "2.3.0" & < "2.7.0"
- irmin-indexeddb
-
irmin-layers
< "2.7.0"
-
irmin-mem
>= "2.3.0"
-
irmin-mirage-git
>= "2.3.0" & < "2.7.0"
-
irmin-mirage-graphql
>= "2.3.0" & < "2.7.0"
-
irmin-pack
< "2.7.0"
-
irmin-test
>= "2.3.0" & < "2.7.0"
-
irmin-unix
>= "2.3.0" & < "2.7.0"
- irmin-watcher
- jitsu
- joolog
-
jose
< "0.9.0"
-
js_of_ocaml
< "3.0"
- js_of_ocaml-lwt
- jsoo_broadcastchannel
- jsoo_router
- jsoo_storage
-
jupyter
< "2.3.0"
-
jupyter-archimedes
< "2.3.2"
- jupyter-kernel
-
KaSim
>= "4.0.0"
-
kafka
>= "0.3" & < "0.5"
- kafka_lwt
-
ke
>= "0.5"
-
ketrew
>= "3.2.0"
-
kinetic-client
< "0.0.9"
-
lablqml
< "0.6"
- lambda-runtime
-
lambda-term
>= "1.11" & < "1.13"
- launchd
- letsencrypt
- letsencrypt-app
- letsencrypt-dns
- libres3
-
links
< "0.7.3"
-
lru_cache
< "v0.16.0"
- lwt-binio
- lwt-canceler
- lwt-dllist
- lwt-exit
-
lwt-parallel
>= "0.1.2"
- lwt-pipe
- lwt-pipeline
- lwt-watcher
- lwt-zmq
- lwt_camlp4
-
lwt_domain
< "0.3.0"
-
lwt_eio
< "0.4"
-
lwt_glib
>= "1.0.1"
-
lwt_log
< "1.1.0"
- lwt_named_threads
- lwt_ppx
- lwt_ppx_let
-
lwt_react
>= "1.0.1"
-
lwt_ssl
>= "1.0.1"
- macaque_lwt
- maki
-
mariadb
< "0.5.1"
-
markup
= "0.7.6"
- markup-lwt
- mdx
- mechaml
- metrics-influx
- metrics-lwt
- metrics-mirage
- metrics-unix
- mindstorm-lwt
-
mirage
< "0.9.1" | >= "0.10.0" & < "2.7.0"
-
mirage-block
< "1.0.0"
- mirage-block-ccm
- mirage-block-lwt
- mirage-block-ramdisk
- mirage-block-solo5
-
mirage-block-unix
< "2.8.3"
- mirage-block-xen
-
mirage-bootvar-solo5
>= "0.2.0"
- mirage-bootvar-unix
-
mirage-bootvar-xen
>= "0.4.0"
- mirage-channel-lwt
-
mirage-clock-freestanding
< "3.0.0"
- mirage-clock-lwt
-
mirage-clock-unix
>= "1.2.0" & < "3.0.0"
-
mirage-console
>= "2.1.1" & < "2.2.0"
- mirage-console-lwt
-
mirage-console-solo5
>= "0.2.0"
-
mirage-console-unix
>= "2.2.0" & < "3.0.0"
-
mirage-console-xen
>= "5.0.0"
-
mirage-console-xen-backend
< "3.0.1"
- mirage-console-xen-cli
-
mirage-dns
< "3.0.0"
-
mirage-entropy
< "0.5.0"
- mirage-entropy-unix
-
mirage-entropy-xen
!= "0.2.0"
-
mirage-flow
>= "1.0.3" & < "1.2.0"
- mirage-flow-lwt
- mirage-flow-rawlink
-
mirage-flow-unix
< "2.0.0"
- mirage-fs-lwt
-
mirage-fs-unix
!= "1.2.1"
- mirage-http
- mirage-http-unix
- mirage-http-xen
- mirage-kv-lwt
-
mirage-kv-unix
< "3.0.0"
- mirage-logs
-
mirage-nat
< "3.0.0"
- mirage-net-fd
- mirage-net-lwt
- mirage-net-macosx
- mirage-net-solo5
- mirage-net-unix
- mirage-net-xen
-
mirage-os-shim
>= "3.0.0"
- mirage-profile
- mirage-protocols-lwt
-
mirage-qubes
< "0.9.4"
-
mirage-qubes-ipv4
< "0.9.4"
-
mirage-random-stdlib
>= "0.1.0"
- mirage-solo5
- mirage-stack-lwt
- mirage-time-lwt
-
mirage-time-unix
< "2.0.0"
-
mirage-types-lwt
< "3.7.1"
- mirage-unix
- mirage-vnetif
- mirage-vnetif-stack
-
mirage-www
>= "1.1.0"
- mirage-xen
- mirror
- moonpool-lwt
-
mpris
= "0.1.1"
-
mqtt
= "0.0.2"
-
mrmime
>= "0.5.0"
- multipart-form-data
-
multipart_form
>= "0.2.0" & < "0.4.0"
-
multipart_form-lwt
< "0.6.0"
- mwt
- named-pipe
- nanomsg
-
nbd
= "2.1.1" | >= "3.0.0"
- nbd-tool
- nbd-unix
- netchannel
-
nocrypto
>= "0.5.4"
- noise
- nottui-lwt
- nproc
-
nsq
< "0.2.4"
- obrowser
-
obuilder
< "0.4"
-
obus
>= "1.1.8" & < "1.2.1"
-
ocaml-variants
>= "4.00.1+mirage-unix" & < "4.00.1+open-types"
-
ocluster
< "0.2"
-
ocluster-api
< "0.2"
- ocplib-concur
- ocplib-resto
-
ocsigen-start
= "1.1.0" | >= "4.1.0" & < "4.7.0"
-
ocsigen-toolkit
= "1.1.0"
-
ocsigenserver
>= "2.10"
-
odoc
>= "2.0.0" & < "2.1.0"
- ojquery
-
ojs-base
< "0.6.0"
-
opam-compiler
< "0.2.0"
-
opam-publish
= "0.3.5"
- opam-sync-github-prs
-
openflow
< "0.2.0"
-
opium
>= "0.11.0" & < "0.19.0"
- opium_kernel
- order-i3-xfce
- ordma
- osc-lwt
-
oskel
>= "0.3.0"
-
ounit-lwt
< "2.2.0"
- ounit2-lwt
-
ox
< "1.1.0"
- paf
- paf-cohttp
- passage
-
pcap-format
>= "0.3.3" & < "0.5.0"
- pgx_lwt
- pgx_lwt_mirage
-
pgx_lwt_unix
< "2.0"
-
plotkicadsch
< "0.2.0" | >= "0.4.0"
-
ppx_defer
>= "0.4.0"
- ppx_deriving_rpc
- ppx_json_types
- ppx_netblob
- ppx_rapper_lwt
- ppx_sqlexpr
- prof_spacetime
- prometheus
- prometheus-app
- promise_jsoo_lwt
-
protocol-9p
>= "0.10.0"
- protocol-9p-unix
-
pvem_lwt_unix
>= "0.0.2"
-
qcow
< "0.11.0"
- qcow-format
- qcow-tool
-
qfs
>= "0.5" & < "0.7"
- quests
- rashell
-
rawlink
< "2.1"
- rawlink-lwt
- redis-lwt
- resource-pooling
-
resp
>= "0.10.0"
-
resp-mirage
>= "0.10.0"
-
resp-unix
>= "0.10.0"
- resto
- resto-cohttp-client
- resto-cohttp-self-serving-client
- resto-cohttp-server
- resto-directory
- riak
- ringo-lwt
- river
-
rpc
>= "1.5.1" & < "7.1.0"
- rpclib-js
- rpclib-lwt
-
sanddb
>= "0.3.0"
- scgi
- sendmail-lwt
- session-cohttp-lwt
- session-cookie-lwt
-
session-postgresql-lwt
< "0.4.1"
- sessions
- shared-block-ring
-
shared-memory-ring
< "2.0.0"
- shared-memory-ring-lwt
- skkserv-lite
-
slacko
< "0.14.1"
- slipshow
- socket-daemon
- speed
-
spin
< "0.6.0"
-
spotify-web-api
< "0.2.1"
- sqlexpr
- statsd-client
-
stog
>= "0.16.0" & < "0.19.0"
-
syndic
>= "1.4" & < "1.6.0"
-
tar-format
>= "0.4.1"
-
tar-mirage
< "2.2.0"
-
tar-unix
< "3.0.0"
-
tcpip
>= "3.1.1" & < "4.0.0"
- telegraml
- testrunner
-
tezos-p2p
>= "11.0" & < "13.0"
-
tezos-stdlib
< "9.0"
-
tezos-stdlib-unix
< "9.0"
- tftp
- themoviedb
- timmy-lwt
-
tls
>= "0.10.1" & < "0.16.0"
-
tls-lwt
< "0.17.4"
- tls-mirage
-
tlstunnel
>= "0.2.0"
- transmission-rpc
- tube
-
tuntap
>= "1.0.0" & < "2.0.0"
- twirp_cohttp_lwt_unix
- typerex-lldb
- u2f
- usb
- uspf
- uspf-lwt
-
utop
>= "1.4.0"
- utp
-
uwt
>= "0.0.2"
-
vchan
>= "0.9.6" & < "2.0.0" | >= "2.0.3"
- vchan-unix
- vchan-xen
- vercel
-
vhd-format
>= "0.6.0" & < "0.9.1"
-
vhd-format-lwt
< "0.12.0"
-
vhd-tool
< "0.12.0"
- vmnet
-
vpnkit
>= "0.1.1"
-
vue-jsoo
< "0.3"
- webauthn
-
websocket
< "2.3"
-
websocket-lwt
= "2.11"
- xe-unikernel-upload
-
xen-api-client
< "0.9.14"
- xen-block-driver
- xen-evtchn
- xen-evtchn-unix
- xen-gnt
-
xen-gnt-unix
>= "4.0.2"
- xenctrl
- xenstore
- xenstore_transport
- xentropyd
-
yurt
!= "0.3" & < "0.5"
- zarr-lwt
- zbar
- zmq-lwt
Conflicts (3)
-
ocamlbuild
= "0.9.0"
-
ppx_tools
< "1.0.0"
-
ocaml-variants
= "4.02.1+BER"