Why does a clojure future block the main thread? -

-

i have trivial lein project -main contains future:

(def f (future 42))  (defn -main [& args]   (println @f))

when run lein run prints 42 not return.

i don't understand why not return ?

how lein run return ?

your question twofold:

  1. why lein not return?

lein hangs because thread pool backs clojure futures not use daemon threads have explicitly shut down. if change code following, should work:

(def f (future 42))  (defn -main [& args]   (println @f)   (shutdown-agents))
  1. futures block main thread

the line (println @f) can potentially block main thread when "derefing" f if future hasn't finished job yet.

this limitation of clojure futures can addressed using core.async or rxclojure. i've been working on alternative implementation of futures clojure plan open source , addresses these issues.


Comments

Post a Comment

Popular posts from this blog

java - Oracle EBS .ClassNotFoundException: oracle.apps.fnd.formsClient.FormsLauncher.class ERROR -

-
i need in configuring java on machine because, when try loading forms, loader goes in circles , gives error: java.lang.classnotfoundexception: oracle.apps.fnd.formsclient.formslauncher.class @ sun.plugin2.applet.applet2classloader.findclass(unknown source) @ sun.plugin2.applet.plugin2classloader.loadclass0(unknown source) @ sun.plugin2.applet.plugin2classloader.loadclass(unknown source) @ sun.plugin2.applet.plugin2classloader.loadclass(unknown source) @ java.lang.classloader.loadclass(unknown source) @ sun.plugin2.applet.plugin2classloader.loadcode(unknown source) @ sun.plugin2.applet.plugin2manager.createapplet(unknown source) @ sun.plugin2.applet.plugin2manager$appletexecutionrunnable.run (unknown source) @ java.lang.thread.run(unknown source) i have tried re-installing firefox, older versions of java runtime environments, disabling proxy. what missing? application working on other machines. i spent around 100 hours finding s
Read more

c# - how to use buttonedit in devexpress gridcontrol -

-
Image
i trying create gridcontrol buttonedit in 1 of columns. when user clicks button edit, popups form select product. when selection done on popup, returns datarow selection main grid below. but when column loses focus, value wrote column disappear. here code creates gridcontrol's data , buttonedit's click event. private void frmsiparisnew_load(object sender, eventargs e) { dt = new datatable(); dt.columns.add("malzeme_kodu",typeof(string)); dt.columns.add("malzeme_aciklama", typeof(string)); dt.columns.add("adet", typeof(decimal)); dt.columns.add("birim", typeof(string)); dt.columns.add("fiyat", typeof(decimal)); dt.columns.add("kur", typeof(string)); dt.columns.add("tutar", typeof(decimal)); datarow dr = dt.newrow(); dt.rows.add(dr); gc.datasource = dt; } private void repositoryitembuttoneditmal
Read more

nvd3.js - angularjs-nvd3-directives setting color in legend as well as in chart elements -

-
good morning i using angularjs-nvd3-directives, great, having difficulties when setting color of multi bar chart ( http://cmaurer.github.io/angularjs-nvd3-directives/multi.bar.chart.html ). the show legend works well: <div ng-controller="examplectrl"> <nvd3-multi-bar-chart data="exampledata" id="showlegendexample" width="550" height="300" showxaxis="true" showyaxis="true" xaxistickformat="xaxistickformatfunction()" showlegend="true"> <svg></svg> </nvd3-multi-bar-chart> </div> but when add option in conjunction color="colorfunction()" where, var colorarray = ['#ff0000', '#0000ff', '#ffff00', '#00ffff']; $scope.colorfunction = function() { return function(d, i) { return colorarray[i]; }; } the color of cha
Read more